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There are many products and materials available that are uniquely suitable for owner- builders. In this section, we will describe some materials that we think you should take a look at. We encourage you to read through the entire section even if you are depending on subcontractors to provide materials. You may find items in these pages that your subs are unaware of but that suit your situation perfectly.
To some degree, the success of your entire project depends on the integrity of your foundation. The foundation system you end up with will be determined by a number of factors. If there is expansive or weak soil or a high water table on your lot, the foundation will have to be engineered and is likely to be more expensive than a standard spread footing and stem wall (see figure 5-2).
ill. 5-1: Cross sections through houses with a full basement (a) and a half basement (b).
Expansive soils (clays that expand when they get wet) or weak soils may require pouring the foundation on caissons and void forms rather than a spread footing. A caisson is a concrete pier made by drilling a hole in the ground, setting a reinforcing bar in place, and pouring concrete. The holes are drilled to sufficient depth to assure that the caissons rest on stable soil. Void forms, made of polyethylene-wrapped corrugated cardboard, are placed in the bottom of the concrete forms for the foundation walls. The void forms go between the caissons before the walls are poured. When the concrete forms are removed, the plastic liner is slit, and the cardboard eventually disintegrates, leaving a void to allow for soil expansion without disturbing the wall.
ill. 5-2: Cross section of a typical full basement with a poured concrete foundation wall and spread footing. Moisture protection is provided by a drain tile and impervious topping on backfill.
Concrete is the standard foundation material. it's made of fine aggregates (sand or rock screenings), coarse aggregates (crushed stone), Portland cement, and water. The aggregates are proportioned so that the finer ones fill the gaps between the larger ones. The aggregates also serve to make the concrete more economical, since they are consider ably less costly than cement, and they reduce the amount of shrinking and cracking that occurs as the mixture cures. Portland cement is made by combining a number of minerals, including limestone, iron ore, sand, etc., firing them in a kiln, and pulverizing the resulting “clinkers.” The American Society for Testing Materials (ASTM) recognizes five types of Portland cement, of which Type I and Type III are the most common. Type I is what you’re likely to use in residential applications. Type III is designed to cure quickly and is useful when the forms must be removed early, and /or the concrete must assume its full load soon after the pour.
Concrete does not dry out—it “cures.” Water combines with the cement in a chemical reaction called hydration that binds all the aggregates together. About half the water in the mix is permanently incorporated into the concrete. The water you use should contain no oil, alkali, or acid, and drinkable water is best. The amount of water affects the workability of the mix. Wetter concrete may be easier to pour and handle, but adding too much water to the mix can significantly weaken the finished product.
ill. 5-3: Cross section of a typical crawl-space wall made of poured concrete and supported by caissons and void forms.
The relative sloppiness of the mix is specified as “slump.” If your foundation plans have to be engineered, the engineer may require a slump test before certifying the structure as sound, although this is uncommon for a residential building. A slump test is done by filling a truncated cone (12 inches high with an 8-inch base) with concrete, inverting the cone, and placing it beside the resulting pile of concrete. The distance the concrete sags from the top of the cone, measured to the 1/4 inch, is the slump. The greater the slump, the sloppier, and weaker, the mix. For residential footings, walls, and slabs, a 4- to 6-inch slump is usually acceptable.
Concrete can be ordered with a variety of admixtures that will cause it to cure more slowly or more quickly, help prevent freezing, and reduce the amount of water needed. it's also possible to mix in dyes to produce colors other than the familiar gray. Many people dye their concrete slabs and either stamp or cut patterns into the surface to resemble tile or stone. The effect can be quite impressive and is considerably cheaper than installing tile or stone floors separately.
Because cement contains lime, a strong alkali, it can be hard on skin. You should wear rubber boots and gloves when pouring concrete. Washing your hands with vinegar will neutralize any lime that reaches your skin.
While the skills for pouring footings and stem walls are probably well within reach of most motivated novices, pouring and finishing a slab is another story. Get a professional to work with you for at least the day of the pour, since it’s not uncommon for a slab to cure more quickly than you can finish the pour, especially in hot, dry weather. Once water is added to the mix, the curing process begins. If the water is added at the concrete company and the truck must travel a long distance to your site, the mixture may be “hot,” or starting to harden even before you begin to pour it. Some people add water at this point to make the concrete more workable, but adding too much water can weaken the slab. There are ready-mix companies that use trucks to carry aggregates, cement, and water in bays in the truck and then mix the batch at your site.
After it's poured, concrete should cure slowly to assure a satisfactory appearance and optimum strength. Exposed surfaces should be kept moist for at least three days after the pour. If a surface is allowed to cure quickly, it will shrink, resulting in a dusty surface and hairline cracks. A fresh pour must be protected from rain and free water, however, since they can have the same effect as adding too much water to the mix. The concrete must also be kept from freezing, since uncured concrete that freezes will be weak and is likely to crack and develop scales on its surface. Because concrete generates heat as it cures, this is often simply a matter of covering the pour to keep this heat in.
ill. 5-4: Cross section of a concrete pier foundation on spread footing.
Concrete blocks are another option for foundation material. They are available in enough sizes, shapes, colors, textures, and profiles to satisfy the most creative designer. They eliminate the need for complex formwork, so one person alone can easily build a wall.
In the United States, concrete blocks are manufactured to conform to the requirements of ASTM, which grades the units according to the intended use and the degree of moisture control desired. Grade “N” is for general use in exterior walls above and below ground level where the wall will be exposed to moisture. Grade “S” is limited to use aboveground in exterior walls with weather-resistant coatings and in walls that will not be exposed to the weather.
The conventional way to build with concrete blocks is to set the blocks using cement mortar, leveling each course carefully. Block foundation walls are laid on a poured concrete footing.
If you want a mortar-jointed concrete block foundation, we recommend that you hire a mason to build it for you. Unless you have some experience in laying block, you probably won’t become proficient until the job is almost done. A journeyman mason can average 200 blocks a day, and you’ll be doing well to average half that amount even after a couple of days of practice. If, for your own reasons, you want to build a mortar-jointed block foundation yourself, consider either working with a mason to learn the proper techniques or hiring a mason for a few days to get you started.
Another method of building foundation walls with concrete block is to dry-stack the blocks (using no mortar) and then surface-bond them. The blocks are stacked in a “running bond” (every block overlaps two blocks below it), then the surface-bonding mix is troweled onto both sides of the wall. The bonding mix is a concoction of Portland cement, lime, calcium chloride (for fast setup and a harder finished product), calcium stearate (to make it more waterproof glass-fiber filament chopped into 1/2-inch lengths, and water. The glass fibers bridge the cracks between the blocks so the finished wall will have about six times the strength of a mortar-jointed block wall. The first course is set in mortar on a concrete footing and carefully leveled, and subsequent courses are leveled with metal shims as they are laid up. The hollow cores of the blocks are filled with concrete, following the specifications of the structural engineer or building department. Many building departments allow the use of recycled blocks for surface-bonded walls, which can result in significant savings.
Compared to mortar-jointed block walls, surface-bonded walls are faster and cheaper to build, stronger, more watertight, more attractive. The bonding mix can be purchased as a dry premix with color added.
Should you decide to build surface-bonded walls, keep in mind that a standard “8-inch by 16-inch” concrete block is really 7 5/8 inches by 15 5/8 inches, to allow 3/8 inch for the mortar joint. Be sure to take this into consideration when you figure your wall height and length. Also, conventional concrete blocks are not made to very precise measurements, since it's assumed that they will be laid up in mortar, which evens out irregularities. It may take a considerable amount of shimming to level the courses. Discrepancies over 1/8 inch should be shimmed with mortar.
ill. 5-5: Concrete blocks are available in various dimensions and in special sizes.
Stretcher, Control joint, Bond beam, Scored face, Ribbed face, Split face, Corner return, Lintel, Chimney cap, Pilaster corner, Sill.
Interlocking Block Systems
An even more attractive option for novice builders is one of the new interlocking block systems. These blocks are also stacked without mortar, but the big advantage they offer is that they are milled to much closer tolerances than conventional concrete blocks, so shimming is less necessary. They are a true 8 inches by 16 inches, so the height of the wall is easier to estimate.
Some of the manufacturers of dry-stack blocks recommend that their product be surface-bonded; others cast tongues and grooves into the blocks to keep the stacked wall rigid; and still others use plastic splines or rings to keep the blocks aligned. One system we have been impressed with is MCIBS, an acronym for Mortarless Concrete Interlocking Block System. Introduced in 1980 by MCIBS, Inc., these blocks feature tongues and grooves and are manufactured to tolerances of 0.03 inches. The ease with which these blocks can be used makes them ideal for unskilled workers. They are at least four times faster than mortared block to build with. They are considerably more expensive than conventional concrete blocks, but if you figure in labor costs and all materials, a wall built with interlocking blocks can actually end up being 10 to 15 % less expensive than a mortared block wall.
All-Weather Wood Foundations
It might sound ridiculous to build a house’s foundation out of wood, but all-weather wood foundations (AWWF) have been extensively tested for nearly 20 years and are now supporting about 50,000 buildings around the country. The system is recognized by all the model building codes, the federal agencies regulating housing, major lending and mort gage insurance institutions, and warranty and fire insurance institutions. Pressure-treated lumber and plywood (wood that has been impregnated with a wood preservative) are used for the foundation walls, which stand on gravel footings. The preservative in the wood makes it resist decay and insects.
Dealers claim an AWWF costs only two-thirds as much as a concrete foundation. Assembling the walls requires only basic carpentry skills, good news for most owner- builders. Wood foundations also adapt more easily to odd or irregular shapes than poured concrete or block walls, and they are insulated and finished like any other wood-frame wall. Wood foundations can be built in any weather, although the installation will certainly go more smoothly and efficiently if the temperature is above 40 degrees F and it isn’t raining.
The walls can be prefabricated to save time at the job and to minimize the amount of Cutting you need to do. Ideally, you should not cut any of the lumber in an AWWF. The biggest disadvantage to an AWWF is that the wood is preserved with copper arsenates. There is some evidence that these salts cause serious health problems. During installation, wear goggles, a dust mask, rubber or vinyl-coated gloves, and heavy coveralls. Never saw, sand, or plane pressure-treated wood indoors, as the arsenic-laden sawdust will get into the air. We also encourage you to cover treated wood inside the home to assure that occupants won’t come into direct contact with it. Don’t burn the scraps, as the smoke will contain arsenic particles. Scraps must be buried.
To be effective, all surfaces of an AWWF must remain treated with preservative. If it's necessary to cut or drill any of the lumber, the affected pieces should be brushed, dipped, or soaked until the wood absorbs no more preservative. Take precautions while doing so. Or better yet, as we advised above, avoid cutting into pressure-treated lumber in the first place.
An AWWF must have an effective drainage system. The wood foundation and the concrete slab that (usually) forms the floor of the basement are typically built on a leveled gravel pad, which is an integral part of this drainage system. A 6-mil polyethylene plastic sheet covers the exterior of the below-grade portions of each foundation wall. This plastic film directs water to the gravel footing and drain tile, so that it can then be drained to the surface of the ground several feet away from the house. Downspouts should drain onto splash blocks to direct water away from the building, and the ground should slope away from the house. In basements, a sump should also be installed and drained or pumped to the outdoors.
Careful backfilling, in which care is taken not to damage the polyethylene, is usually done in 6- to 8-inch layers after the basement floor has been poured and the first floor framing and plywood subfloor are in place. The section of the backfill nearest the footing is filled with the same gravel that makes up the footings, and it's covered with strips of 30-pound asphalt-impregnated roofing felt. These strips allow water to seep through to the drain tile but prevent soil from filtering down to clog the gravel.
ill. 5-6: Typical all-weather wood foundation.
Moisture-Proofing and Insulation
Most building codes require that foundation systems be moisture-proofed below grade. Traditionally, asphalt products, which are petroleum based, were used for this purpose. There is a problem, however. Rigid plastic foam insulations are now in wide use as foundation insulation, and the petroleum solvents in asphalt foundation coatings dissolve the foam. If the coatings are allowed to cure before the foam is installed, the problem may be minimized, but there are also other alternatives.
First, there are products that perform as both waterproofing and adhesive, and that are compatible with foam insulations. Second, there are many moisture-proof coatings that are compatible with foams but that don’t serve as adhesives, so the insulation must be attached mechanically or with a separate adhesive. Check with your local building materials supplier for the brands available in your area.
The best way to keep your basement or crawl space dry is to use an integrated approach that takes site conditions into consideration. An important part of this approach is the use of footing drains to keep water from building up next to the foundation wall. The drains should be laid in gravel and then covered with gravel. In turn, the gravel should be covered with building paper or strips of polyethylene to prevent soil from filling the spaces between the stones. The gravel must always be larger than the holes in the drain tile, and , if you decide to use PVC tile with holes on one side, install the tile with the holes down.
If your soil drains well, you will need only gravel around the drain tile, but if the soils on your site are expansive or don’t drain well, consider backfilling with a granular fill at least halfway to the surface of the ground. In any case, the backfill should be placed in 6-inch-deep layers that are individually compacted to avoid settling later. Settling can drag insulation off the wall, damage the waterproofing on the wall, and alter surface conditions so that the ground slopes toward the house, encouraging water to run down along the foundation wall.
Between the top of the gravel and the soil you place above it, backfill with water. Impervious clay. Slope everything away from the house at a minimum drop of 3 inches in 10 feet. Ideally, the drains should be run out to the surface of the ground, but if that isn’t possible, a dry well is usually sufficient. Downspouts should never empty directly onto the soil around the foundation. At a minimum, use splash blocks or a small drainage system to take the water from the downspouts away from the foundation.
There is some debate about whether it's necessary to use extruded polystyrene as insulation below grade or whether expanded polystyrene (EPS, otherwise known as beadboard) is sufficient. Extruded polystyrene is about twice as expensive as EPS. In our view, there should be no problem using beadboard in a conventional situation with good drainage. In extremely cold climates, “impervious” extruded polystyrene is preferable to prevent frost damage.
There are products now on the market that insulate as well as facilitate drainage. Geolech Insulated Drainage Board or Panel is a product composed of large, high-quality EPS beads bonded with a specially developed, waterproof asphalt adhesive. The bonding of the beads with the adhesive creates channels throughout the board that allow groundwater to drain down to the drain tile at the footing. Plastic, foil, or some other moisture barrier can be placed on the foundation side of the panels to keep the groundwater from coming into contact with the foundation wall. The earth side of the panels can be covered with a fabric that will keep fine soil from clogging the panels. This arrangement prevents water from building up and exerting pressure on the wall.
The panels protect the foundation wall and its waterproofing from damage during backfill, eliminating the need for the labor and expense of extra protective layers. They are light and easy to handle and install, usually requiring only GeoTech mastic without additional mechanical fasteners. They have a dry R-value of 3.5 per inch.
Another product that both insulates and promotes drainage is a rigid fiberglass basement insulation, called Baseclad (in Canada) and Warm-N-Dri (in the United States). It features thin, discrete planes of fiberglass layered in such a way that if the product is installed vertically, water contacting the surface of the board is channeled down to the footing drainage system. It has good resiliency and compressive strength, making it particularly useful in areas where expansive soils are a problem.
It is also possible to insulate a basement or crawl space from the inside. A stud wall is power-nailed to the inside surface of the concrete wall and then insulation batts are hung between the studs. it's also possible to install rigid insulation between furring strips. If you use rigid insulation, most codes require that you cover the foam with a fire-rated material, since the foam will emit poisonous fumes if it burns.
We recommend that you insulate the outside of the foundation for several reasons. First, there is the potential for water damage in a basement that has been insulated from the inside. Moisture may build up between the insulated stud wall and the concrete wall and pool on the floor between the two. Second, when a concrete wall is insulated on the outside, the concrete is inside the heated space of the building, so it's warmer and less prone to damage from freeze/thaw cycles. Also, by virtue of its considerable thermal mass, the concrete will help even out the day-to-night temperature swings in the basement.
In cold areas where the soil retains a great deal of moisture, insulating foundation walls may expose the soil around the foundation to freezing temperatures, which can cause heaving. When basements aren’t insulated, the heat lost to the surrounding soil may keep the soil from freezing. If wet soil freezes, it could expand enough to exert lateral pressures on the foundation walls that could crack the walls. If this is a potential problem in your area, you may want to backfill around the walls with gravel or some other granular material that doesn’t retain moisture. See the specifications we gave earlier for backfilling around an AWWF.
FRAMING and SHEATHING
Standard 2 X 4 stud construction is the most common way to build a home in the United States, for several reasons. it's easy to learn and does not call for great skill. Information about it's widely available, and each framing member is easy to handle, so the work goes quickly without the need for heavy equipment. The lumber is widely available and relatively inexpensive, and both exterior and interior finish materials are manufactured to fit this framing style.
When shopping for framing lumber, look for wood that is as dry as you can find. Drier wood is more dimensionally stable, lighter, and easier to work with. In today’s tighter homes, movement from shrinkage can open carefully sealed joints, particularly around doors and windows. You may not have a choice, however. Much of the available framing lumber these days is stamped S-gm, or “surfaced green,” which means its moisture content is above 19 %. Remember, too, that different wood species have different strengths, and it’s a good idea to design for the weakest framing lumber available in your area to assure that the lumber you get can handle the loads imposed on it.
Energy-efficient building practices require adequate levels of insulation. Most people are now familiar with the concept of “R-value,” or the resistance of a material to heat transmission. Products manufactured as insulating materials have exceptionally high R values.
Whether or not an insulation achieves its rated R-value depends on several factors. Motionless air is one of the best insulators around at about R-5.5 per inch. With that in mind, you might think that an empty 2 X 4 stud space should have an R-value of 19.25. The problem is that the air in the space is not really motionless—its effective R-value is actually only about 1. So to prevent heat from escaping through your walls, you will need to install insulation. We will list your options below.
Fiberglass and Rock Wool
The advantages of fiberglass include wide availability, low cost, and compatibility with conventionally framed structures. Batts and blankets are made to fit in standard 16- and 24 framing cavities, so installation is easy. (Cutting the batts or blankets to fit irregular spaces can be a chore, however.) They have an R-value of 3.2 per inch.
“Loose-fill” fiberglass can be blown or poured into cavities and attics. Care must be taken in vented attics so that the wind doesn’t blow the fiberglass around, leaving some areas devoid of insulation. An adhesive binder can be added to the loose-fill to keep it in place once it has been blown. Loose-fill fiberglass rates approximately R-3 per inch, depending on how and where it's installed. Like other loose-fills, it can be a boon in irregular spaces, eliminating the need for cutting of insulation batts, blankets, or boards.
Rock wool was the first insulating material manufactured on a large scale, but its use has declined over the years. It has many of the same characteristics as fiberglass and is available in batts and blankets (R-3.4 per inch) and loose-fill (approximately R-2.9). Both fiberglass and rock wool are noncombustible, although the binder in fiberglass can develop toxic fumes when burned.
Cellulose is paper or virgin wood that has been shredded and milled to produce a fluffy, low-density insulating material. Chemicals are added so that the insulation resists fire, water absorption, and fungal growth. Slightly moistened cellulose is blown into wall cavities where it assumes a papier-mâché-like consistency. It has a higher R-value per inch than loose-fill fiberglass and rock wool (approximately R-3.5); is more fire resistant because of its greater density; fills all the little nooks and crannies that batts or blankets sometimes miss: and resists the movement of air through the wall better than batts and blankets do.
Add to this the fact that cellulose insulation is usually a recycled product, that fiberglass takes 7 to 10 times as much energy to produce, and that superior levels of sound resistance are possible with cellulose, and you can see that cellulose is a very attractive option. Concerns about the fire resistance of this product have been laid to rest by diligent quality control and independent testing, and the cost is now generally competitive with fiberglass. A potential disadvantage for owner-builders, however, is that for best results, cellulose should be installed by a professional.
The most common foam insulations are polystyrene, polyurethane, and poly-isocyanurate. All are available as boards sized to fit between standard framing members, and polyurethane and poly-isocyanurate can also be blown in place. Cutting insulation boards is easier than cutting batts or blankets, but cutting a large number of them can be taxing: You must make the cuts precise to avoid leaving gaps.
Polystyrene is available as expanded polystyrene (EPS or beadboard) or extruded polystyrene. The extruded variety has a higher R-value per inch (R-5), because it contains a mixture of air and fluorocarbons (which have a higher R-value than air), while EPS (R-4) contains only air in its cells. Extruded polystyrene is also stronger and about twice as expensive.
These foams are often used as sheathing on the exterior of frame walls, as insulation on the exterior of masonry walls, and as foundation insulation. EPS is permeable to water vapor, so using it as exterior sheathing does not provide a vapor barrier. The other foam boards do act as vapor barriers, which may be a disadvantage if you live in an extremely cold or exceptionally humid climate.
Polyurethane and polyisocyanurate (R-6 and R-7.4, respectively) have the highest R-values per inch of the commonly available foam insulations. They can be used as exterior sheathing or they can be installed on the interior surfaces of walls. In situations where high humidity is a problem, interior installation may be preferable, since these foams block the passage of moisture and form a vapor barrier. Bear in mind, however, that these foams release highly toxic fumes when they burn. Most building codes require that the foams be covered with gypsum board or another fire-retardant material when the foams are installed on the interior surfaces of walls.
No matter how much insulation you pile into your ceiling, walls, and floors, the house will still waste energy if air that you’ve paid to heat is allowed to leak out of the house. A related issue is that moisture penetrating into the shell of the house can damage the structure and lower the R-value of the insulation.
Table 5-1: COMMON INSULATIONS
Water vapor enters a wall either by diffusion or by convection. Water molecules are smaller than molecules in the air, and they can move through materials that block airflow.
This passage of water molecules directly through a material is called diffusion, and it Occurs when the relative humidity on one side of a material is higher than on the other side.
The water vapor moves from the area of higher concentration, usually the warm inside of the house, to the area of lesser concentration: the wall cavity. Installing a vapor barrier on or near the inside surface of the wall will control this sort of diffusion.
Diffusion is only part of the problem, however. Most moisture that enters a wall cavity is carried there by warm air moving through cracks, holes, and seams in the wall. This air movement, called convection, can be controlled by making the vapor barrier as airtight as possible—hence the term air/vapor barrier. Traditionally, builders used polyethylene sheets (6 mil or greater) for air/vapor barriers, but more and more builders are using specialized products that should last longer and work better. A few of these products are Tu-Tuf Moisture Vapor Barriers, Rufco 300 and 400, and Super-Sampson (Poly Plastic and Design Corp.). These are cross-laminated, high-density polyethylene sheets, which are much stronger and more durable than conventional polyethylene. If you can’t find these products in your area, write the manufacturer or try a greenhouse supplier.
Air/vapor barriers should be installed on the warm side of the insulation. In most climates in the United States, this means installing the barrier on the inside of the wall. If you live in a hot, humid climate, however, you may want to install an air/vapor barrier on the exterior of the wall, to keep outdoor humidity from entering the wall. Check with experts in your area.
A number of factors will affect your choice of roofing materials, among them cost, weight, fire resistance, durability, and the pitch of the roof. Here are a few tips:
• it's useful to think in terms of life-cycle costs as well as purchase costs, since roofing is a fairly major home maintenance task. So when comparing roofing materials, think of how much you will have to spend to maintain and ultimately to replace the roof you select. Some metal, concrete, tile, and slate roofs will last indefinitely, assuming the fasteners don’t rust or rot away and the roof isn’t physically damaged.
• Most roofing materials aren’t heavy enough to pose a threat to your roof framing. But concrete, tile, and slate roofs are so heavy that you’ll need to plan extra-sturdy framing for them.
• Underwriters’ Laboratories tests roofing materials for fire resistance and assigns class ratings to them. Class A is the highest rating, for fairly fire-resistant materials, and Class C is the lowest. Some materials, such as untreated wood shingles, have no rating at all, since they burn readily.
• Some roof materials may be more durable than others in your particular situation. If it's very windy in your area, for instance, you’ll need a roof that can withstand high winds.
• The pitch of your roof will also be a factor in determining what materials you can use and how well the roof will shed snow and water. In discussing specific materials, below, we give the recommended minimum slope for each material, but many can be used on a shallower slope if alternative application methods are followed.
Asphalt shingles weigh 200 to 300 pounds per “square” (a square is the amount of roofing material needed to cover 100 square feet). They are available with an organic felt base or a fiberglass base. The newer fiberglass-based shingles are lighter, stronger, more fire resistant (Class A, compared to felt shingles’ Class C), and they last a little longer (about 25 years to felt’s 20).
Both felt-based and fiberglass-based shingles are easy to install, and they come in a variety of colors. (Bear in mind that lighter colors stay cooler in the summer and help the roof last longer.) Most building departments require at least a 4-in-12 pitch (the roof rises 4 inches for every 12 horizontal inches) for asphalt shingles. Asphalt shingles that have the uneven appearance of wood shakes are also available.
Wood Shingles and Shakes
Wood shingles and shakes are a popular roofing material because they are easy to apply and make an appealing roof, raising the value of the home. The big drawback to wood is its fire hazard. Some shingles and shakes have achieved a Class C rating after treatment with fire-retardant chemicals, but most are unrated—they are highly flammable.
Cedar, cypress, pine, and redwood will all work for roof shingles, but cedar is by far the most popular. Cedar roofs start out a reddish brown color and weather to a silvery gray or light tan, depending on the climate. Always use No. 1 grade cedar. Your building department will require that your roof have at least a 4-in-12 pitch, unless you use a double layer of roofing felt. A wood roof usually weighs between 200 and 300 pounds per square and will last about twice as long as an asphalt roof, all other things being equal.
Concrete and Clay Tiles
Concrete and clay tiles are among the heaviest materials you can use on a roof, weighing anywhere from 700 pounds to 1,600 pounds per square. They are available in a variety of styles and colors, from shingles resembling slate to traditional barrel tiles. They will last indefinitely if installed properly. They require at least a 3-in-12 pitch and may not be a do-it-yourself project. Some of the concrete-tile manufacturers provide wonderfully clear instructions for installing their products, but the advantage to hiring professionals is that they warrant their work, so you’ll have recourse if your tiles blow away in the first major windstorm.
Although they can be expensive, perhaps three or four times the cost of asphalt shingles, they create a beautiful, permanent, very fire-resistant roof. Colors are permanent in clay tiles, but concrete tiles tend to fade. Costs vary from area to area and will be lower if you have a manufacturer in your area—the substantial weight of the tiles makes it expensive to ship them any distance.
Roofing your house with slate makes sense economically only if you live in an area where the material is mined or you have access to used slate shingles. Costs vary dramatically from one area to another, but slate tends to be one of the pricier roofing materials.
Slate roofs are beautiful, however, and it’s not uncommon for them to keep a house dry for a century or more. They are fire resistant and require special tools to install, although the skills involved aren’t beyond the average owner-builder.
Shipping this heavy material is expensive (slate weighs at least 750 pounds per square). The color of slate shingles can range from grayish blue to red or green. Some slates will change color as they weather.
Metal roofing is generally stronger, lighter, and more durable than more common roofing materials. It goes up in large sheets with few fasteners, so leaks are less likely to occur and are easier to find if they do occur. Metal shingles and shakes are also available. In areas where fire hazards are high but a shingled appearance is desired, metal shingles offer a lightweight alternative to concrete or tile roofs. Metals used for roofing, from most expensive to least expensive, include zinc alloy, copper, terne-coated stainless steel, stain less steel, terne metal, aluminum, Cor-Ten, and galvanized steel. All of these metals corrode, and they will expand and contract in response to changes in temperatures. Each has its own characteristics, which must be accommodated in the design and installation of the roof.
Zinc roofing weathers to a gray color and can be expected to last more than 100 years under most circumstances. It also tends to sag and creep on the roof, however, which has led at least one manufacturer (W. P Hickman Company) to alloy the metal with copper and titanium. Zinc is prone to corrosion by galvanic action, so it must be protected from contact with most other metals. Oak, redwood, and cedar contain natural acids that will damage zinc. However, assuming precautions are taken, zinc will form an attractive layer of corrosion that protects the roof from further corrosion, and runoff from the roof will not stain siding or discolor landscaping.
Most people are familiar with the brown-green patina that weathered copper takes on. This patina is a layer of sulphates that protects the copper from further corrosion. Copper roofs can last hundreds of years but will corrode other metals and stain siding and trim. Like zinc alloys, copper is an expensive roofing material.
Terne metal is an alloy of lead and tin on a steel base. When the alloy is placed over stainless steel, no surface finish is required—the terne will weather to a dark gray. Terne over stainless steel is a permanent roofing material, but it's nearly as expensive as copper. Conventional terne metal is considerably less expensive (about half the cost), but it must be finished to prevent rusting, and it needs refinishing every ten years or so.
Stainless steel contains chromium and nickel, which makes it resistant to corrosion and rusting. Stainless steel doesn’t corrode other metals, and it costs about two-thirds the price of copper. Some people find stainless steel roofs too bright, and because the material is so resistant to corrosion, the finish will not dull significantly with time.
Aluminum resists corrosion better than most metals, making it a particularly attractive choice along seacoasts where the salt in the air will speed up corrosion. Aluminum will, however, react galvanically with most other metals, especially in salt air, and should be protected from physical contact with other metals. Aluminum is lightweight, but it expands and contracts more than most metals, so installation must be designed with that in mind.
Cor-Ten is a weathering steel manufactured by U.S. Steel. it's designed to rust readily, building up a thick surface layer that protects the steel below from further corrosion. It rusts to an attractive reddish color, and runoff must be directed away from sidings and plantings because it will stain them. Cor-Ten is heavier than other metal roofings.
Galvanized steel is the least-expensive metal roof (about the cost of a premium asphalt shingle roof). Quality varies widely, and the material is available with a variety of coatings that prolong its life. it's light, strong, and available in many patterns that have a clean, attractive appearance. Galvanized steel is ordinary steel plated with zinc, but aluminized steel and aluminum/zinc alloy platings (such as Bethlehem Steel’s Galvalume) are also available. The aluminized metal roofing is a good choice in coastal areas, since it’s less likely to corrode in salt air.
Other Roofing Materials
Other materials are also available for roofs. Mineral-fiber shingles, for example the asbestos-cement shingles manufactured by Supradur and the lightweight perlite shakes made by Cal-Shake, have a Class A fire rating and cost about twice as much as top-quality fiberglass-based asphalt shingles. They will also last twice as long, making them a cost- effective alternative to an asphalt-shingle roof.
Masonite Corporation makes wood-fiber roofing that resembles cedar shakes, weathers to a silver gray, and comes in 1-foot by 4-foot panels for fast installation. Treated with fire-retardant chemicals, it has a Class C fire rating.
If your house design calls for any flat or nearly flat roofs, you have another array of options. The least-expensive material is mineral-surfaced rolled roofing, which can be used at pitches as low as 1-in-12. Rolled roofing can also be used on pitched roofs where budgets are tight. Some owner-builders apply rolled roofing as a temporary measure to complete their homes on tight budgets, then re-roof with higher-quality materials as money becomes available.
Onduline is a corrugated asphalt sheet that has been in wide use around the world for about 20 years. The large size of the sheets (46 inches by 79 inches), variety of colors, modest cost (about the same as premium-quality asphalt shingles), and light weight of the material all contribute to its growing popularity. Corrugated asphalt sheets are effective down to a 1-in-12 pitch.
Synthetic rubber membranes are another choice for flat roofs, and although they are expensive, they are a permanent covering. The seams are glued with a cement that should last at least 20 years, after which time the seams may need re-gluing. This material is also used as flashing in situations where metal flashing doesn’t have the necessary flexibility.
There are flexible roofing materials that are applied as a liquid. They bond to the substrate or underlayment and form a watertight roof. Some require specialized equipment to apply or are franchised only to authorized installers, but others can be applied with a Paint roller or other readily available applicator.
A number of factors will affect your choice of siding. Appearance, durability, maintenance, and availability of materials must all be considered. The building method you are using will also be a factor. If, for example, your home is rammed earth, a stucco finish makes more sense than furring all the exterior walls with wood and using cedar siding. Other factors you should think about include purchase cost, ease of installation, and combustibility. Occasionally, covenants or architectural guidelines will dictate what siding you can use.
Wood Board Siding
Wood is a popular siding for a number of reasons. it's readily available in most areas, makes an attractive exterior finish, and can be installed relatively easily. Some species— notably cypress, cedar, and redwood—have exceptional natural resistance to insects and rot. Board sidings generally carry a grade stamp that identifies the species and quality of the product.
Moisture content is of special concern when choosing sidings, since unseasoned wood can shrink, cup, and split after it’s installed. Wood that is certified kiln-dried is typically the driest—and the most expensive—but it may not be available in your area. Often boards are air-dried to specific moisture contents. For instance, “MC-15” indicates that the board has been seasoned to a 15 % maximum moisture content, “S-dry” means the wood contains a maximum of 19 % moisture, and “S-gm” indicates the wood is green or unseasoned (moisture content above 19 %).
Cedar and redwood are common choices for sidings. They are beautiful, available in a wide range of grades and patterns, easy to work, dimensionally stable when properly seasoned, and they readily accept finishes. Costs vary according to the amount of milling required, how well the wood has been seasoned, and the grade.
The most expensive grades are marked “clear, vertical grain, heartwood.” “Clear” indicates the wood is free of knots and other irregularities. “Vertical grain” tells you that the grain runs parallel to the long edges of the board and that this board has the best possible surface for painting. “Heartwood” is the most decay-resistant part of the tree and can be identified by its darker color.
Wood board siding consists of boards installed on the exterior surfaces of a home’s walls. Standard patterns include the following: beveled, shiplap, tongue and groove, and board and batten. Most patterns are available in various widths. Generally, boards 6 inches or smaller (nominal size) require one nail at each framing member, while 8-inch or larger boards require two. Nails penetrate one board and the framing, not the board underneath. This leaves the siding a little room to expand and contract with temperature and moisture changes.
Many people prefer the texture and knotty appearance of the less-expensive rustic sidings. These are available in a number of patterns. When you shop for rustic siding, avoid boards that have large, loose knots, large splits, or large bows or twists. Reputable lumberyards will usually take back wood that is unusable. Rustic siding is available seasoned and has a rough (saw-textured) face.
ill. 5-7: Various wood sidings and their nailing patterns.
Cedar Shingles and Shakes
Cedar shingles and shakes also make for handsome, weather-tight siding. They are particularly attractive to owner-builders who are doing their own work because one person can easily install the material. Shakes or shingles are either “single-coursed” or “double- coursed.” Double-coursing involves installing two layers or courses of shingles—an under-course of lower grade (No. 3 or undercoursing grade) shingles and a surface course of higher grade (usually No. 1). This technique makes it possible to leave a larger area of the surface course exposed than would be possible with only one layer of shingles.
Top-quality, non-corrosive nails should be used. Recommendations for using building paper under the shingles vary, so check with local builders or building officials. Shakes and shingles bonded to plywood sheathing are available from Shakertown Siding and Roofing in 8-foot lengths, are self-aligning, and greatly reduce the amount of time required to side or roof a house with shingles. Good information on shakes and shingles is available from the Red Cedar Shingle and Handsplit Shake Bureau.
ill. 5-8: Single-coursing and double-coursing of shingles and shakes. SINGLE-COURSING; DOUBLE-COURSING
Wood Siding over Foam Sheathing
In their efforts to make buildings more energy efficient, builders have been using insulating foam sheathing rather than plywood or fiberboard sheathing on their homes’ exterior walls. It has become apparent that special care must be taken when applying wood sidings over these sheathings. For example, you must provide backing for nails (i.e., you need to provide a wooden surface for the nails to be driven into), usually by furring out the wall with 1-inch boards.
Current recommendations for the installation of wood siding over foam sheathing include:
• Install lateral bracing for added strength (foam sheathing provides virtually no structural strength).
• Use a continuous vapor barrier on the interior of the wall.
• The sheathing and building paper should be allowed to dry thoroughly before the siding is applied. Building paper or an alternative should be used over the sheathing and under the siding.
• Siding material should be stored under cover until used and should have a moisture content below 16 %. If the siding gets wet, allow it to dry completely before installation.
• In the case of beveled siding, thicker patterns are preferable, and a pattern such as a rabbeted bevel that doesn’t leave a space behind the board is even more desirable. This reduces the likelihood of cupping and splitting during installation or moisture accumulation over the life of the siding.
• Use boards of 8 inches or less in width.
• Use non-corrosive nails that are long enough to penetrate at least 1½ inches into the stud. Ring shanks are recommended for their extra holding power, and their points should be blunted to minimize splitting.
• Take care not to overdrive nails.
• All end joints must fall over a stud.
• Sidings should be prefinished or primed on all sides prior to installation. Brushing or dipping is recommended to assure complete coverage. The finish should be allowed to dry completely before installing the siding, as some solvents will attack the foam sheathing. Regular recoating is necessary for good performance and an attractive appearance.
Even decay-resistant woods require care to keep them looking attractive. If the “natural look” isn’t important to you, you might decide to paint your siding—this provides superior protection for the wood. If you use air-dried or unseasoned siding, surface preparation may be necessary to keep the moisture in the siding from interfering with the paint film. Check with your paint retailer for product suggestions. High-quality paint is always worth the extra money. Let unseasoned siding air-dry for a month or so before finishing it.
If you don’t want to paint, the situation becomes a bit more complicated. At the minimum, a clear water repellent with mildewcide should be applied on the front, back, and all edges of each piece of wood siding before it's installed on the house. it's sometimes possible to order sidings with a factory-applied clear primer over all surfaces of each board. Check with your lumber retailer. If this is possible, remember that you’ll still need to saturate the cut ends of the boards with primer.
The lowest-maintenance finish for wood sidings is wood bleach, which speeds the weathering process and lets the wood weather. Your house will end up a silvery gray color. If the original application is uneven or the wood darkens, one more coat may be necessary. This finishing regimen will be more successful on the more stable, naturally rot- and insect- resistant woods such as cedar and redwood. Less stable woods will require more attention to keep them from cupping, splitting, checking, etc., in response to moisture and temperature cycles.
If you want to keep the natural color of the wood, you should talk to building professionals in your area to see what they’ve had success with. Keeping wood siding looking natural is always a maintenance problem, and although there are a number of products on the market that claim to do the job, they all require periodic reapplication, often in as little as 18 months. We recommend contacting D. L. Anderson and Associates (10650 Highway 152, Suite “U,” Maple Grove, MN 55367), the U.S. agent for a Dutch wood finish called Sikkens. It meets all the criteria you’ll be looking for in an exterior wood finish. It separates the wood from the elements with a durable and breathable surface barrier and reflects ultraviolet light away from the wood with special pigment particles.
If you’re considering treating your siding chemically to make it more decay resistant, take care to find the least-toxic substance that will do the job. Rodale’s New Shelter has concluded that copper naphthenate, zinc naphthenate, copper-8-quinolinolate, polyphase (3-iodo-2-propynyl butyl carbamate), and TBTO are reasonably safe choices for wood preservatives. Our general feeling about introducing more poisons into our already over taxed environment is that if it isn’t absolutely necessary, don’t do it. But if you feel there are no practical alternatives, at least use the substance that will have the least impact on the environment.
Brick and Stone
Brick and stone are virtually maintenance-free under most circumstances, make a very attractive finish, increase the marketability of the house, and give a sense of solidity and value to the home. But laying up brick and stone is a demanding task for a do-it-yourselfer. Further, brick and stone are among the most expensive sidings you can buy, and brick is a relatively porous material, so it doesn’t serve as an effective air barrier on the outside of the home.
A number of insulation-and-stucco exterior finish systems are available for use over masonry walls. They have attractive features for those building energy-efficient homes. Most can also be used as foundation insulation and over frame walls with the proper sheathing. The best-known of these systems is Dryvit. The only disadvantage of Dryvit is that it's not available to do-it-yourselfers—it is franchised to contractors in order to maintain quality control. But on the plus side, the contractors do an excellent job and offer a generous guarantee against defects. The system consists of an adhesive that bonds the insulation board to the wall, EPS insulation board, fiberglass reinforcing mesh that is embedded in another layer of adhesive, and a finish coat of synthetic plaster. The finish resists cracking, fading, and weather and is available in 21 colors.
ill. 5-9: Dryvit “outsulation” system.
Plywood siding comes in 4-foot-wide sheets that go up quickly. The material is available in a wide array of patterns and veneers, many of which imitate wood board sidings. The quality of plywood sidings varies—buying a cheap plywood siding is a false economy. If it's not finished or installed properly, plywood siding has been known to delaminate— the layers of wood come apart. Some manufacturers will warrant against de-lamination for the life of the house, and such a warranty is worth looking for.
Plywood tends to absorb moisture along its edges, so take care to seal all the edges before installing it. For best performance, choose a grade that is free from knots, plugs, patches, and stains. If you plan to paint the siding, purchase a “medium-density overlay” (MDO) plywood, a product with a surface that takes paint well. If you paint other plywood sidings, particularly those with a rough face, the paint may blister, peel, and crack. Plywood siding will check and crack if left to weather naturally.
Most building codes allow plywood siding to be applied directly over studs with no other sheathing material. Although this can result in a fairly flimsy wall, it does have an advantage for the owner-builder building on a tight budget: You can use plywood as an interim siding to satisfy the building department and the lender, then install another siding over it when you have the money. The plywood will then become, in effect, sheathing, serving as a nail base for the new siding and increasing the strength of the wall.
Aluminum, Hardboard, Steel, Vinyl
These sidings are widely available. Our own biases lead us away from them, but you may have different priorities. Many of these products are extremely durable and may be exactly the material you need for your exterior finish. Most are advertised as requiring no maintenance, but they need at least periodic washing, and they may scratch, dent, crack, tear, or eventually fade. Before you decide on a manufactured siding, do careful comparison shopping and , if possible, talk to other homeowners who have had the product you’re considering on their homes for a while.
Windows are a major design feature of your home. How light plays in a room has a dramatic effect on the “feel” of that room. The arrangement of windows also has a large impact on the exterior appearance of your home. Unfortunately, windows let heat out during winter and in during summer. This is why manufacturers have responded to the need for more efficient glazings.
The number of layers of glazing in a window and the “emissivity” of the glazing are two of the factors that affect the energy efficiency of a window. A single-glazed window (having just one layer of glass) has an R-value of about 1, extremely low. In windows with multiple layers of glazing, each additional layer adds roughly an additional R-1. A few manufacturers fill the space between the layers with gases heavier than air such as argon, carbon dioxide, or sulfur hexafluoride. These gases provide more insulating value than air.
Double glazing (two layers of glass) is now required by building codes in most areas. In severe climates, the cost of triple glazing may be justified, but the development of high-tech windows such as those with “low-emissivity” (low-E) coatings has led to better alternatives. These coatings applied to the surface of glazings reduce the amount of heat that each layer emits or passes to the next layer. A double-glazed low-E window stops heat more effectively than a traditional triple-glazed window.
A development to watch for is the introduction into the United States of “hard-coat” low-E glass, a product that was pioneered in Europe. The low-E glazings available for the past few years in this country feature a “soft” coating that requires special handling and is very sensitive to moisture. Hard-coat low-E glass can be handled like ordinary window glass. The soft-coat low-E products still outperform the hard-coat, but performance for the hard-coat glass is expected to improve rapidly as the technology matures.
Another measure of window performance is the “solar transmittance” of the glazing. This is the %age of the total solar energy (the heat and light in sunlight) that passes through a window. A single pane of ordinary glass has a solar transmittance of about 86 %. An ordinary double-glazed window scores about 71 %, and triple glazing achieves 59 %. Low-E coatings reduce solar transmittance. Sungate 100, a double glazed, low-E unit made by PPG Industries, Inc., has a solar transmittance of 55 %.
ill. 5-10: Coated “low-E” glass reduces winter heat loss (a) and summer heat gain (b).
To maximize solar transmittance, “low-iron” glass can be used. By reducing the iron impurities in the glass, manufacturers increase the amount of solar energy that passes through the glazing. Another approach is to use windows made with SunGain, a 4.mil polyester film made by 3M. SunGain is suspended between sheets of glass, serving as another layer of glazing. The film allows more sunlight to pass through than a layer of glass would, it insulates without the weight of another pane of glass, and it transmits less ultraviolet light than glass, thereby reducing fabric fading in the house. One layer of SunGain has a solar transmittance of 93 to 96 %.
Sometimes you want to keep the sun’s heat out of your house, especially if you live in the South. The “shading coefficient” of a window indicates how effectively the window blocks solar heat—in a sense, it's the reverse of solar transmittance. Shading coefficients are given on a scale of 0 to 1. A low number indicates that a window is blocking heat effectively.
A window’s shading coefficient can be improved by using reflective glass or applying reflective films to the surface of ordinary glass. Unfortunately, many reflective glasses are very shiny in appearance and they limit the amount of visible light that enters the building. The shading coefficients of reflective glazings vary widely, so look for a low-shading coefficient and a high %age of visible light transmission if you want your windows to look clear but keep the heat out.
Advanced window films (Heat Mirror 55 is an example) can filter out solar heat while still allowing a high transmittance of visible daylight, thus reducing the need for artificial lighting. Electric lights generate heat, which increases the need for air conditioning or other forms of cooling.
Frame Style and Materials
The overall energy efficiency of a window depends on the style of the window and the materials used in its frame, as well as the glazing system. Operable windows that create a tight seal even after repeated use are needed in an energy-efficient home. Casement and awning windows almost always have the lowest air-leakage rates, and unless they clash with the aesthetics of your design, they should be your first choice. At least one manufacturer, Delabro Millwork, now makes a sliding window with air-leakage rates that compare favorably with those for awnings and casement windows.
Windows with wood frames usually have higher R-values than those with aluminum, steel, or vinyl frames. Exposed-wood window frames require periodic maintenance, so many manufacturers offer vinyl or aluminum-clad frames to eliminate the need for paint or other finishes. The cladding has the added benefit of increasing the weather-tightness of the unit.
Look for frames with clean, tight-fitting joints. Wood frames should be screwed together rather than nailed together, since this will simplify disassembling the frame for maintenance something it will need at some point in the life of the window. Many manufacturers publish the R-values, solar transmittances, visible transmittances (the %age of visible light that comes through the glazing), and shading coefficients for their windows.
We suggest that you use manufactured windows for the operable windows in the house and buy standard insulated glass units from a glass supplier for the fixed windows. If you design the house to use standard sizes, you can save yourself a lot of money. Vertical fixed glazing is not difficult to install, although good detailing and care during the building process is essential to minimize infiltration around the unit.
Ideally, the doors in your home welcome you and your friends, keep unwanted visitors out, and hold both air leakage and heat conduction to a minimum.
Doors today are typically made of wood or insulated steel. Wood doors can be purchased pre-hung with jambs, weather-stripping, and threshold supplied. Unless you know something about hanging doors, we recommend that you purchase a good-quality pre-hung unit. Hanging doors is fairly skilled work, and an improperly hung door can be a major source of air leakage. The disadvantage of wood doors is that they can warp, split, shrink, and swell in response to changes in temperature and humidity. Always apply a prime coat to an unfinished exterior wood door as soon as it’s installed, then finish both sides with a moisture-proof coating.
Steel doors won’t change shape or split, although they can dent. Like some wood doors, steel doors are available with foam-insulation cores. This significantly increases the R-value of the door, up to R-15 for some steel doors. A steel door should have a “thermal break” (a strip of insulating material embedded in the perimeter of the door) to reduce heat conduction across the metal. Remember that as much as 80 % of the heat lost through a door is a result of air leakage, so proper installation is extremely important.
If you plan on any glass doors in your home, we suggest you take a look at the wood. framed atrium-style double doors, since they are usually considerably more weather-proof than sliding glass doors, which tend to allow extensive air leakage. For glazing in your wood or metal entry doors, select double-glazed insulated glass or some of the new high-tech glazing systems we discussed above.
HEATING and VENTILATING SYSTEMS
One of the major benefits of an energy-efficient home is that it can get by with a radically smaller heating system. But finding these systems is not as simple as going to your local heating contractor and buying a furnace. In a well-insulated and very tight home, the “heating load” (the amount of heat needed) is so minimal that finding a heating system that is small enough can be difficult.
To find out how much heat your home will need, you can do your own heat load calculations or hire someone familiar with energy-efficient homes to do it for you. If you want to do it yourself, a comprehensive workbook is the Heat Loss Calculation Guide, available from the Hydronics Institute.
One general factor to bear in mind when selecting a heating system is that you may run into problems if the system consumes air from inside the house. The problems may become especially acute if you also have other air-handling devices (such as gas-burning water heaters). These devices will suck air out of the house, thus creating negative air pressure indoors. As a result, outdoor air will try to flow into the house, since air moves from high-pressure regions to low-pressure regions. The outdoor air may come down the chimneys and vent stacks of your air-handling devices, pulling toxic fumes into the house. For example, if outside air comes down your furnace’s chimney, it will bring with it the exhaust gases from the furnace. This is a clear health threat. To be on the safe side, we recommend using “direct-vent” heating systems or those that require no combustion air. Direct-vent systems draw air directly from the outdoors into the combustion chamber through an air-inlet pipe and send their combustion waste gases directly to the outside through another pipe.
The Federal Trade Commission requires that a fact sheet be available for each heating system sold in the United States. Be sure to consult the sheets for the systems you are considering. The information on the sheets includes system capacity, model number, estimated annual fuel costs, and a graph that shows the Annual Fuel Utilization Efficiency (AFUE) compared to similar systems of the same size. The AFUE is a calculation of the efficiency of a heating system in normal use over the course of a heating season.
Wood is one of the few heating fuels that is renewable and that the user can obtain without having to deal with a utility company. A wood heater also gives “focus” to a home, and wood fires generate images of security for most of us. In some parts of the country, firewood is a readily available and economic alternative to fossil fuels.
There is evidence that wood may be a relatively benign fuel environmentally, since by burning it you are speeding up a natural process that would have occurred anyway. A tree rotting on the floor of the forest generates the same amount of carbon dioxide as it would if you burned it completely in your wood stove. There is little question, however, that pollution from wood stove emissions is a serious concern. Problems arise when the wood is not burned completely, when many people in a concentrated area burn wood, and when the air is stagnant.
To shop intelligently for a wood stove, you should have a basic understanding of “combustion efficiency” and “heat-transfer efficiency.” Combustion efficiency (the %age of the potential heat in the wood that is converted into usable heat when the wood is burned) is much more dependent on how a stove is operated than on its design, but the design does have some effect. Some stoves use secondary air inlets in an attempt to assure enough oxygen for complete combustion. While the primary air inlet feeds air to the fire in the stove’s combustion chamber, the secondary inlet is located where the air it draws in will cause the smoke rising from the combustion chamber to ignite and burn. This gives you extra heat while reducing pollution. Catalytic combustors are also used in some wood burners. These ceramic devices, shaped like honeycombs, cause wood smoke to burn.
Heat-transfer efficiency is a measure of how effectively a wood stove delivers heat from the fire to you. A stove could have a high combustion efficiency (extracting lots of heat from wood) but a low heat-transfer efficiency (allowing much of this heat to escape unused up the chimney). According to the Solid Fuels Encyclopedia, the features most apt to improve heat- transfer efficiency are, in order of importance:
• Large exterior surface area relative to the size of the combustion chamber.
• Keeping hot gases in the stove for as long as possible. In some stoves, the smoke must negotiate a series of baffles before it reaches the chimney.
• Convection and turbulence both outside and inside the stove. Air should circulate to draw heat from the fire and to bring it into the room. Some stoves use blowers to increase air movement around the stove, with varying degrees of success. If you’re considering a fireplace insert (a wood stove designed to fit inside a fireplace), find out if the unit can be operated without its fans on. If it can’t, the insert is not much use in a power outage.
• A stove finish that has a high radiating efficiency. Basically, all colors except metallic colors are good radiators.
Some salespeople and manufacturers claim that cast iron is superior to plate steel as a stove material. The thermal properties of cast iron and steel are virtually identical, so a steel stove of the same thickness holds as much heat as a cast-iron stove. Cast iron is less prone to metal fatigue, which makes it more appropriate for doors where stability is important to ensure a good seal with repeated use. It will crack, however, if it's subjected to thermal shocks or if it's repeatedly heated unevenly. Steel is more flexible, and although it can distort significantly, it’s not apt to crack. Cast-iron stoves are often wonderfully decorative, since patterns can be cast directly into the structure of the stove.
How large a stove should you get? The most useful method of sizing stoves is based on their “Btu” outputs per hour. (A Btu is a British thermal unit, approximately as much heat as a wooden match produces.) Most manufacturers indicate how many Btu their stoves can produce. To select a stove, you could calculate the heating load for your home, find out how many pounds of wood you would need to burn per hour to meet this load (all species of wood contain roughly 8,600 potential Btu per pound), and buy a stove that could safely produce that many Btu. Underwriters Laboratories’ Standard for Safety, UL 103 (ANSIA 131.1) spells out safe burning rates for wood and coal heaters.
The site-built masonry stove is an alternative to the metal wood stove. Masonry stoves can be built in a variety of designs and are known generically in this country as Russian fireplaces and Finnish heaters. If well designed and built, and properly operated, they create almost no pollution and operate at very high overall efficiencies. They are designed to burn small (3 to 4 inches thick), uniform pieces of wood. The enormous mass (literally tons) of these stoves assures a steady, even heat output—they operate on one or two hot, intense fires lasting a couple of hours each day. Once the flames have totally died down, the damper is closed and the masonry radiates heat for many hours. The surface of the masonry never gets hotter than comfortably warm to the touch, so there is less chance of small children or pets hurting themselves than with a metal stove.
There are some potential disadvantages to these heaters, however. Because of their enormous weight, they require their own footings, and because, like any wood heater, they are most effective when located near the center of the house, the house almost has to be de signed around them. David Lyle’s The Book of Masonry Stoves is the best introduction to these stoves, it thoroughly covers the subject and includes design and construction details.
In some areas of the country, coal is used as a heating fuel. In general, the guidelines for combustion and heat-transfer efficiencies are similar to those for wood stoves, but there are important differences you should be aware of before attempting to burn coal as a fuel. Jay Shelton’s Solid Fuels Encyclopedia is a good source of specific information about types of coal and coal heaters.
We advise against using coal heat. For one thing, coal is dirty, both to handle and to burn. When coal bums, it emits sulfur, which has been linked to acid rain. Coal smoke also contains small amounts of radioactivity. Although coal contains a great deal more heat energy than wood (more than 14,000 Btu per pound for high-quality coal), it also generates a great deal more ash. The coals typically used for home heating have ash contents ranging from about 5 % to over 15 %, compared to less than 1 % for wood. Dealing with this volume of ash is a major consideration in any coal heating system. On the plus side, coal heaters are available equipped with hoppers that will feed coal into the combustion chamber. This makes frequent re-fuelings unnecessary and lessens the mess of handling the fuel.
Like coal, oil combustion is a source of sulfur emissions. Another problem is that you may have trouble finding a direct-vented oil furnace or boiler. New oil furnaces and boilers developed over the past few years have greatly increased efficiencies, and advances continue. Unless oil is by far the least expensive fuel in your area, however, we suggest you consider other heating fuels for your new home.
In many areas of the country, electricity is the most expensive way to heat a home. Since the pollution problems linked to coal-fired power plants and the safety issues associated with nuclear power plants have yet to be resolved, many people are understand ably concerned about the environmental impact of electricity. However, there are some real advantages that may make electric heat a viable option in your situation. Electric baseboard resistance heaters and radiant panels are relatively inexpensive to purchase and install, use no combustion air to operate, create no pollution in the home, and allow each room to be equipped with its own thermostat.
Electric heat pumps are considerably more expensive initially, but they can put out two to three times as much heat energy as they consume in electrical energy (that is, for each Btu of electricity, you can get 2 or 3 Btu of heat). “Air-source” heat pumps extract heat from outdoor air, even when the air feels cool to our senses. Unfortunately, as you might expect, these devices tend to be least efficient when it's very cold outdoors. If you live in a frigid climate, a “ground-source” heat pump (one that draws heat from the ground) is probably a better choice.
Electric furnaces and boilers are probably not a good choice for energy-efficient houses, even though they are relatively inexpensive to buy and require no combustion air.
They are harder to control than baseboards or radiant panels, they require the installation of ductwork, and they are less efficient than radiant panels in particular. Furnaces heat the air, which in turn warms us; radiant panels produce heat that warms us directly, without losing as much of its energy in the air.
Natural gas, where available, is the cleanest and least expensive fuel to use. If the gas- burning system you select is costly to purchase and /or install, however, there may be little real savings. The economic paybacks for high-efficiency heating systems in very energy- efficient homes can stretch nearly to the infinite. Sometimes furnaces that are only moderately efficient make more sense.
Some manufacturers offer furnaces that achieve 80 % efficiency using conventional technology, but these units are pushed to the limits of their performance. They feature enlarged heat exchangers to extract more heat from the gas fire. This lowers the flue temperatures to about 350 which raises the possibility of corrosion in the flue pipe and in the furnace. There are also furnaces with an AFUE of around 85 % that feature an extra stainless steel heat exchanger. This lowers the temperature of the flue gases to around 200 but the stainless steel resists corrosion.
Even more efficient conventional-technology furnaces are available that use additional stainless steel tubing and aluminum-finned heat exchangers. The flue gases from these units are lowered to around 100 degrees F, so that they can be vented through PVC pipe instead of a chimney. This cuts installation costs.
Other furnaces use new technologies to achieve high efficiencies. Amana’s Energy Command, for instance, features a “heat transfer module” that combines an electronic igniter, gas burner, and a heat exchanger in one unit and two other heating coils that transfer heat to the house air. Pulse furnaces and boilers work by burning very small amounts of gas and air in short bursts or “pulses.” In the Lennox Pulse Furnace, the first pulse forces the combustion gases out a stainless steel pipe, through a secondary heat exchanger, and then through a flue vent to the outdoors. The negative pressure created in the combustion chamber causes the intake valves to open and draw in more gas and air. When the original pulse reaches the end of the stainless steel pipe, part of the flame is reflected back into the combustion chamber, igniting the next pulse without need for another spark. These furnaces have efficiencies as high as 98 %.
If the heating requirements for your house will be very small, you may have difficulty finding a unit small enough to be practical. it's common in conventional homes to have heating loads of 100,000 Btu per hour or more, while very efficient homes can have loads as small as 10,000 Btu per hour or even less. There are direct-vented, sealed combustion “minifurnaces” that are perfect for this sort of situation, but they may not be readily available in your area. Many are designed to heat perhaps one room in a conventional home, but will often heat an entire energy-efficient house. Mini-furnaces are available with a variety of features, including blowers, pilotless ignition, and a variety of Btu ratings. If you have difficulty locating a retailer, try mobile home or recreational vehicle dealers, since they often carry small heating units for use in their products.
Another heating option that is enjoying increasing popularity is combining domestic water heating and space heating in one unit, often a conventional high-efficiency water heater. Hot water from the heater can be sent through pipes in concrete floors or through baseboard radiators to heat the home. Interesting and economical combinations of solar, tankless, and conventional water heating devices are possible, and you are limited only by the heating loads of your home, the hardware available in your area, and your imagination.
In areas where natural gas is not available, propane is usually an alternative. Most appliances that will run on natural gas will also run on propane with some adjustments, but there are exceptions that you should be aware of. If an appliance is stamped “Natural Gas Only” or “NC Only,” don’t attempt to adapt it for propane use, since the higher Btu content of the propane could burn out parts designed to be used with natural gas.
Propane is more expensive than natural gas, but in most areas it's a better buy than electricity for home heating. Prices vary widely from one area of the country to another, so you’ll have to check with your local suppliers.
In very tight homes, a controllable ventilation system is a must. Proper ventilation is the best insurance against the buildup of harmful pollutants.
It is generally agreed that about 0.5 air changes per hour (ACH) are necessary for healthy indoor air quality. In other words, half of the air in the house should be replaced every hour. The cheapest ventilation technique is to open a couple of windows every once in a while. The difficulty with this is that there is no way of knowing how much is enough. Another possibility is using tight-sealing bathroom and kitchen exhaust fans, perhaps in tandem with humidistats (devices for measuring humidity) and automatic vent openers. Since much of the moisture and odors generated in a home are generated in bathrooms and the kitchen, thoroughly ventilating them may suffice for the entire house, especially in a relatively mild climate.
Another way to ventilate tight homes is with air-to-air heat exchangers. These devices recapture most of the heat from the outgoing stale air and use it to preheat the incoming fresh air. They do this by blowing the two streams of air through a heat-exchanger core, without letting them physically mix with each other. Thus the heat from the outgoing air—but none of the substances in this air—is passed to the incoming air. Air-to-air heat exchangers are available in whole-house sizes and smaller room-size models.
There is some question about when air-to-air heat exchangers make economic sense. The expense can be considerable for the whole-house models and the payback slow, depending on your situation. Costs range from $600 to $1,600, installed. Before you make any hard decisions, check with your local energy office or builders and designers that are familiar with the paybacks for your area. In very general terms, it seems that an air-to-air heat exchanger can pay for itself in a reasonable amount of time if you live in a very cold climate in a very tight house, and if you heat with an expensive fuel, such as electricity. Otherwise, it probably makes more sense to use a cheaper ventilation method.
ill. 5-11: Air-to-air heat exchangers permit ventilation while minimizing heat loss.
One of the most common indoor pollutants is formaldehyde, a colorless gas. Formaldehyde is highly toxic, yet it's commonly found in drapes, furniture, tobacco and wood smoke, cosmetics, permanent-press clothing, towels, hair sprays, grocery bags, newsprint, soap, household disinfectants, and toothpaste! Drinking less than 1 ounce of liquid formaldehyde can kill you, and the human body is highly sensitive to formaldehyde fumes—many people’s eyes will water at 1 ppm (parts per million) in the air.
To minimize the amount of formaldehyde in your new house, you can avoid the use of the plywoods and particleboards that are the worst offenders. This isn’t as difficult as it sounds. The U.S. Department of Housing and Urban Development (HUD) has issued standards that limit the amount of formaldehyde that particleboard and plywood may emit. (The standards are intended for mobile homes, but they can be applied to other structures as well.) The products that meet the standards carry a stamp to that effect. The HUD standards limit particleboard emissions in mobile homes to 0.3 ppm and paneling emissions to 0.2 ppm.
Plywoods and other products made with urea-formaldehyde glue generally emit ten times as much formaldehyde as products using phenol-formaldehyde adhesive. So another tack is to look for phenol-formaldehyde products. These include most exterior-grade plywoods, waferboards, and composition boards, as well as phenolic particleboards. The phenol-formaldehyde resins are more expensive than urea-formaldehyde, but in our view they are well worth the extra expense if your family’s health is at stake.
There are some ways you can cut down the emission levels from products already in the home. Most paints and sealers that are good vapor barriers are also formaldehyde barriers, and particleboard covered on all sides with plastic laminate is unlikely to be a problem. The highest levels of emissions occur when the heat is first turned on in a new house. After about a month, the level will drop dramatically, often by a factor often. Extra ventilation will be required for at least a year, and after that you should maintain at least 0.3 to 0.5 ACH. Sweden requires that new public buildings be aired out for six months by using outside air at an unusually high ventilation rate, and many experts suggest similar programs for new homes.