Insulation: Do-it-Yourself Log Home / Cabin

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Not many houses are built these days without at least some thermal insulation. Insulation serves to cut down heat loss during the cold winter days, and reduces heat gain during the long hot summer months. In fact, an ever- increasing number of local building codes re quire that new houses meet certain insulating or heat loss standards appropriate to the area. There is a side benefit to fully insulating a house, too: it cuts down noise and sound trans mission.

Log houses have a special attribute, in that a certain amount of insulating value is built into the house by virtue of the materials used. This is true of any structure, but with log houses the effect is both greater and different. Thermal efficiency is sometimes touted as a selling point for log houses, and it is a valid one if not overdone. Remember, though, that this thermal insulating value applies only to the log walls of the building. All other parts of the house must be insulated in pretty much the same way as a conventional platform- framed house, and that leaves quite a lot of insulating to be done. Another point is that the insulating value of the log walls themselves depends upon the species of wood, the moisture content of the wood, the excellence of the joint seals, the ambient temperature, and the thickness of the logs. Thermally speaking, not all log walls are created equal, by any means.


Except for a few unusual periods of total temperature balance, a house is always either giving up or gaining heat. When the outside temperature is lower than the inside, the house turns into a huge radiator and loses heat to the outdoors, which must be continually replaced by internal heat generation. When the outside temperature is higher than the inside, and/or solar impact upon the structure is substantial enough, the interior of the building will gain heat, which must then be reduced by mechanical means if the temperature becomes uncomfortable.

The total heat loss of a house is measured in Btu’s (British thermal unit, a unit of heat) per hour, or BTU/h. It is calculated upon the basis of a certain inside temperature and a certain maximum average low outside temperature. This total indicates the capacity that the internal heating plant must have in Btu/h to replace the lost heat and maintain a comfortable inside temperature. Similarly, total heat gain of a house is calculated to determine the total cooling capacity needed to maintain a given reasonable inside comfort level. Either figure can then be further calculated by means of local weather conditions to determine requirements and costs for a full average heating/cooling system.

Heat loss or heat gain is calculated by means of some formulas you can work out yourself with the aid of a heating/cooling guide. Or, you can have the job done by your heating contractor or fuel supplier.

Heat losses are figured by determining individual losses through each different kind of construction in the house, and then adding them all up. Transmission heat losses take place through ceilings or roofs, walls, windows, doors, and cold floors. Infiltration heat losses take place through normal cyclical air change within the structure; construction feature losses occur because of fireplaces, exhaust fans, or outside doors. All these losses differ according to just what kinds of materials are used and just how they are put together during construction. They are calculated on a basis of average factors determined through testing, observation, and years of practical heating experience. The actual base numbers are taken from tables compiled for the purpose.

Heat gains are estimated in much the same way but include moisture or latent heat loads, sun loads through both transparent and opaque building sections, and the presence or absence of internal sources of heat.

Obviously, then, these are the areas that must be addressed in order to minimize the heating/cooling loads. Proper insulating plays the most important part. To a lesser degree, correct caulking and sealing is important, as are proper construction practices, building siting, weather protection, sun blocking, vapor barriers, and care in keeping doors and windows closed or in providing sufficient ventilation.


In theory you can’t have too much insulation. In practice, however, there is a point of diminishing returns beyond which added insulation is pointless. But to begin with, a house must have as much insulation as necessary to comply with local building codes. This is often expressed in terms of a thermal insulating value for a given section of the structure. For instance, one combination is to require a value of R-11 (equivalent to approximately 31/2 inches of fiberglass thermal insulation) in cold floors (unheated from below), R-11 in the walls, and R-22 (approximately 6½ inches of fiberglass thermal insulation) in the ceilings or roofs. Some authorities consider the overall heat loss of a building rather than that of the several different sections. This means that the value in some areas can be beefed up in compensation for other areas, which for some reason cannot be sufficiently insulated to come up to a section standard. Whatever the situation, as long as you meet the local standards that is all that is required of you.

On the other hand, you might decide that you need more insulation than is required, in order to reduce operating costs for heating/cooling to a level that you can more easily afford, or to be more comfortable, or in order not to be wasteful. In theory, the more heavily a house is insulated the lower those costs will be. But actually, there is a cutoff point for any given house in any given location beyond which an added amount of insulation effectively neither increases comfort nor lowers operating costs, but merely increases construction costs.

The only way to discover this point is by making a series of calculations for total heat loss or gain of the structure with various combinations of insulation thicknesses, types, and costs as installed. For instance, you might choose fiberglass insulation as the type you want, and calculate the heat loss on the basis of 3½ inches in the floor and the ceiling or roof, with the log walls figured according to their own insulating value. Then make a new set of calculations based upon 6 inches of fiberglass in the roof or ceiling, and another with 12 inches, and perhaps another with thermal insulating glass instead of single glazing in the windows, one with a built-up roof incorporating rigid foam insulation, and so on. Some where along the line you will discover a combination of materials, installation costs, and operating costs that appears to be particularly reasonable. That point will probably be quite a bit short of the actual point of completely diminished returns.

If there are no local code requirements for insulation, you must plot your own course. You can be guided to some extent by whatever local practices are undertaken by builders in your area, but don’t take this information for gospel. The insulation and the way it is in stalled might be right for one house but not be for another. Find out what materials are readily available to you, their costs, and their insulating values. Begin at square one and determine the basic heat loss figures for your house, then make the calculations to see what insulating arrangements might best suit your needs, and go with them.


Under certain circumstances it is desirable to insulate around foundations. This is the case where a poured concrete slab floor is involved. This might be a slab-on-grade foundation where the slab is also the first living level. Here the perimeter insulation is installed in either of two ways. The materials most often employed are rigid sheets of expanded polystyrene or expanded polyurethane, and the minimum recommended insulating value is R-5. The rigid material is cemented with mastic to the inside of the stem wall above the footing, all around the perimeter of the foundation and extending downward from 12 to 24 inches. The concrete slab is poured on top of a vapor barrier. Alternatively, a narrow band of insulation is glued around the stem wall extending downward the full depth of the slab, and another series of sheets is laid upon a vapor barrier extending back underneath the slab to a distance of about 2 feet. The slab is then poured on top of the insulation. If desired, the rigid insulation panels can cover the entire floor area beneath the slab. (Refer to Figs. 4-27 and 4-28).

Much the same system is sometimes used where the slab floor of a full basement needs to be insulated. Here, too, the rigid insulation can be installed in any of the ways described above. If the area is designed for living quarters, further insulating must be done to the basement walls. Poured concrete walls must be furred out with strips of wood nailed directly to the concrete. Insulation is then placed between the strips and a wall covering applied to the furring strips (Fig. 10-1). Sheets of rigid insulation are often used, glued right to the walls. If the furring strips are of sufficient thickness, roll or batt insulation can be stapled to them.

If the walls are made of concrete block, exactly the same system can be used, and if the blocks are hollow-core the insulation can be supplemented by pouring the cores full of a loose-fill insulation such as rock wool, vermiculite, or even sawdust. In certain applications a reflective insulation of accordion-folded aluminum foil insulation fixed between the fur ring strips might have sufficient insulating value to fulfill the requirements. Another method is to insulate the exterior of the foundation walls with sheets of rigid insulating board glued to the surface and extending from the foundation top to below frost line. The above-grade portion of the insulation can be protected with a special material made for the purpose.

A PWF system where the walls are made entirely of wood is insulated just as any other stud wall: by stapling up roll or batt insulation, blowing loose-fill insulation into the voids after the studs are covered, or by facing the studs with rigid insulation such as polyisocyanurate and then covering with plasterboard.


Cold floors are those found over an unheated area such as a crawl space or garage, or over any area that is regularly heated to a lower temperature, up to within a 10-degree differential. Floors over separately heated sections that are heated to a higher temperature are best treated as ceilings, and will be discussed later. The minimum R-value for all those categories is usually considered as R-11, except that floors over open-foundation crawl spaces are best insulated to a minimum R-19. Floors separating areas that will be heated to approximately the same temperatures, plus or minus about 10 degrees, need no insulation at all unless desired for sound-damping purposes, nor should they have vapor barriers.

Fig. 10-1. You can insulate a masonry basement by furring out and filling the spaces with blanket or rigid insulation.

The usual choice for floor insulation is roll or batt in either fiberglass or mineral wool, which is available in several standard widths, thicknesses and R-values. It can also be had with foil facing, kraft paper facing, or no facing at all. This material is either stuffed or stapled into the spaces between the joists, according to the manufacturer’s directions (Fig. 10-2). The facing includes the attachment flanges, and also acts as a vapor barrier. It must be placed closest to the heated area.

In many cases the insulation must be in stalled face-up from below, after the subfloor is laid and the building is weathertight, so there is no way to staple it in place. This means that some sort of mechanical restraint is needed to keep the material from eventually slipping down. Short pieces of wood or spring-wire (you can buy the latter for just this purpose) jammed between the joists will do the job, and so will strapping or lath nailed at intervals across the joist bottoms. Chicken wire can also be stretched out and stapled into place across the joist bottoms.

There are other insulating materials and methods that can be used, either alone or in combination with roll or ball insulation. For in stance, heavy wall-to-wall carpeting installed over a thick fibrous pad has a substantial insulating value. Insulating board or low-density particleboard used as floor underlayment or sub-sheathing provides some degree of thermal insulation. Rigid sheet insulation can also be laid on subfloor and covered with a rigid underlayment or finish flooring, for a considerable thermal insulating value. Wood sheathing or finish flooring itself can be considered to have a value of approximately R-1 per inch of thickness.


The thermal insulating value of R-value of log walls is built in automatically when the walls are laid up. It is part of the logs themselves. Just what that value is, assuming that the construction is tight and properly done, can be approximated by first finding the average thickness of the wall and then multiplying by the R-value for that particular species of wood. A 6-inch Northern white cedar wall, for example, would have an R-value of 8.46, which in many locales would be sufficient in itself. A 6-inch tamarack wall would have an R-value of about 5.58, still adequate in a few areas. But as a rule of thumb, you can figure that wood in general will run to a value of about R-1 per inch of thickness provided it is well dried. Only a few of the hardwoods fall much below 0.80.

Fig. 10-2. One way to install blanket insulation in a floor frame.

Scratch-built wall sections is made from locally felled logs could be expected to be as thin as about 4 inches on average, running in some cases to as much as 14 inches or better. This would result in thermal insulating values from R-4 well up into the teens. The latter, however, would be an exception. So in some instances—depending upon the local climatic conditions—further insulating of the log walls is not necessary. In many other instances, it is.

At this point, there is a myth that should be dispelled. You might have heard some claims that the thermal mass characteristics of log houses actually make them warmer with out wall insulation than frame houses with insulation. Not so. Thermal mass performance is a very complex subject, one still being studied at length. Much simplified, it revolves around the fact that solids can absorb heat from warmer surroundings over a period of time, then re lease it to cooler surroundings over a period of time. Different materials do so at various rates and have varying capacities. The contention is that log walls are thick and massive, and so can absorb heat from the sun and other sources during the warm day, then release the heat slowly through the cool nights, helping to maintain even interior heating using less energy than other constructions.

There is some truth to the theory, of course; the process does indeed work that way, and in mild-climate areas of the country this will have some value. But in cold country the thermal mass factor is insignificant, even in a massive structure, as applied to log walls. (Thermal mass introduced purposely as part of a solar design—rocks, concrete, water, steel or iron, whatever—is a different matter; the factor here is significant, and is designed to be so.) There is one beneficial aspect of the thermal mass characteristic of log walls: the wood does not conduct heat rapidly. The interior of log walls will always feel warm to the touch, so you will not feel chilly when sitting next to one (assuming a reasonably warm ambient interior temperature and a well-built wall), even on the coldest of days.

If the average R-value of a given log wall construction equals or exceeds local building code or weather condition requirements, all well and good. However, there are plenty of areas of severe winter weather where R-11 is marginal, even insufficient, in wall sections. Some building codes require that wall sections meet an R-19 average value, impossible to achieve in the traditional single-thickness log wall section in a scratch-built house. In a few areas even R-19 is not really enough. What then?

There are several possibilities. One is to make the wall sections as thick as possible using wood with the highest thermal insulating value that is available. Other parts of the house where thermal insulating materials must be installed anyway can be insulated extra heavily to achieve a very high R-value at those points. With sufficient added insulation the total heat loss of the structure can be brought into line with the local conditions or requirements. This only works, however, where local authorities recognize the “total heat loss” concept and allow compensating insulation in various sections or portions of the building, or where winter weather conditions are not very severe.

Another possibility is to construct the walls in double thickness. This can be done in three ways. One is to lay up an interior and exterior wall concurrently, with the horizontal joints of one wall staggered from the other and the logs set tight together. The thickness of the logs can be determined by the thickness of the wall section needed to provide the necessary R-value for that species of wood.

Fig. 10-3. Insulation can be installed within a furred-out interior wall assembly set against a log exterior wall.

The second method is to construct the walls in stockade fashion, with one inside row and one outside row and a plywood core in the middle. Either split logs, flatted logs, or slabs can be used in this construction, as discussed in Section 6.

The third method involves constructing two separate walls of relatively thin stock, an inner and an outer. The logs are fully locked together in both sections, which in turn locks the sections together and closes off the wall ends. A space of whatever width is desired is left between the wall sections. This space can be left empty, and the dead air will provide a thermal insulating value of approximately R-1, regardless of the air space width. Inmost cases, however, the space should be filled with roll or ball fiberglass, or one of the various loose- fill insulations. With the right combination of materials, this system can result in a wall- section thermal insulation value of R-30 or even more.

With another method, the exterior of the structure has the appearance of log construction but the interior does not, though this can not really be called a true log house. The method can be used to provide virtually any needed wall-section R-value, with the thickness of the wall section and the insulants varied to meet the requirements. The walls are essentially nothing more than standard platform-framed stud walls, put together in the usual manner with 2 x 6s or whatever is needed. Thermal insulation is installed between the studs and an interior wall covering applied in the conventional manner. The exterior is sheathed with plywood or boards and then covered with either vertical or horizontal edge-matched log slabs (refer to Fig. 6-38).

The inside surfaces of the log walls constructed of full logs, whether flailed or not, can also be further insulated. This involves building stud walls all around the interior perimeter of the house—2 x 4s are usually sufficient—and installing roll or ball insulation between the studs. The studs are then covered with in interior finish in the usual way. The stud wall sections are actually only furring strips, but the problem is that an ordinary fur ring job cannot be done because the strips can not be attached solidly to the logs walls because of the settling problem. Stud-wall frames, however, can be anchored at the bottom and fitted with slip joints at the top to make what might be called a semi-freestanding wall (Fig. 10-3). Problems might also be encountered at window and door openings where separate inside and outside frames, casing, and trim must be arranged so that they can slide past one another during the settling process.

In this case, though the end result of a high R-value can be achieved, it is at the expense of a considerable amount of labor and the elimination of the interior log-construction aspects. There is a possibility, though, of using the compensating-sections theory to arrive at a satisfactorily low total heat loss figure. Two or three rooms, such as the kitchen and a couple of bedrooms and baths, for instance, might be fully insulated with additional interior stud walls, while some other rooms like the dining room and living room could remain as uninsulated natural log interior.


Cap insulation is installed above the ceilings of occupied living spaces and below unoccupied and unheated attic or roof crawl areas where the roof itself is not insulated. In many instances this insulation runs from outside wall to outside wall in all directions, and there is no insulation at all in the roof assembly. In other designs, such as a story-and-a-half house, the cap insulation might lie over only a small section of ceiling beneath the roof peak, with the lower half or two-thirds of the roof being insulated (Fig. 10-4).

Fig. 10-4. Cap insulation is installed directly over ceilings below uninsulated roof sections.

Cap insulation is extremely important, and must have a high R-value and be properly in stalled for good results. Though heat loss from a residence is greatest on a per-square-foot basis through windows, the largest amount of heat loss in any house is straight up (heat rises) through the cap and roof. The recommended minimum thermal insulation value is R-19. As far as overall house design, construction, and efficiency is concerned, cap insulation has some advantages, too. Unless the house is flat- roofed, a full cap is smaller than the roof area. Thus the cap will radiate a smaller amount of heat away than would the roof. Also, because the area is smaller, less insulating material and less labor are required to do the job. Cap insulation is also easier to install, sometimes by quite a bit, than roof insulation.

Probably the most commonly used material for cap insulation is fiberglass or mineral wool roll or batts. These are easily stapled directly to the joists from below, or can be stuffed into place from above in some cases, after the ceiling has been installed. Where the rafter spacing is greater than 24 inches on center, nailing strips might have to be installed to which standard-width insulation can be stapled. Or, if the ceiling framework is sturdy, the material can simply be laid down and tightly pushed together at the edges. The necessary R value can usually be achieved with a single layer of this material. However, in areas where up to R-30 or so is recommended or required, a second layer will have to be installed. The second layer should have no vapor barrier or facing attached to it, and the lengths or batts should be laid upon the first layer at right angles or with staggered parallel joints. If there happens to be an air space between the two layers, so much the better (Fig. 10-5).

Fig. 10-5. Cap insulation can be increased by laying batts across the joists. No additional vapor barrier is used.

Another common method of cap insulating is to install the ceiling first. One of the various loose-fill insulations can then be blown into the ceiling voids to whatever depth is necessary to achieve the desired R-value. In this case, a vapor barrier of plastic sheeting should be applied between the joists and the finish ceiling. The plastic should be sealed off around all the edges and lapped and sealed at the joints. This is actually a good idea with any cap insulation, even if faced fiberglass balls are used.

Where for one reason or another the thickness of the blanket or loose-fill insulation that can be installed in the cap is insufficient to achieve the necessary R-value, rigid insulation can be installed either alone or with a supplement of loose fill or batts. For instance, sheets of expanded polyurethane could be applied directly to the joists and then covered by plasterboard. Various combinations of expanded polystyrene, isocyanurate, mineral fiberboard, acoustic tile, and other materials might also be used. These methods do tend to be more expensive, but also provide the desired results.


Wherever cap insulation is not used, roof insulation must be. The material can be installed below the roof sheathing, and then covered by some sort of finish ceiling covering. This is probably the most common approach. But where the rafters or purlins are exposed to view and the undersurface of the roof is in effect the ceiling—as is the case in the cathedral ceiling design and similar open plans—insulation must be installed above the roof sheathing in a built-up roof assembly. In any case, R-19 is the recommended minimum R-value, the same as for cap insulation.

Insulating a built-up roof consists of constructing a roof assembly, as discussed in section 8, and using a suitable amount and type of insulating material to achieve the necessary R value. Insulating roof decking can be used for this purpose, as can fiberglass or mineral wool batt or roll insulation. Where cooling is the primary concern, accordion-type reflective insulation can be used in layers, separated by dead air spaces. Rigid insulation sheets are also widely used, and combinations of materials can be installed as well.

Insulating a conventional roof from the underside is not a difficult job, just tedious and hard on the arms and neck. Roll or batt blanket insulation is most often chosen because of relatively low cost and ease of installation. Rigid insulation sheets can also be used, though often at somewhat higher cost. Blanket insulation is stapled between the rafters, with nailing strips installed parallel to the rafters where the rafter spacing is greater than the widest available standard insulating material. Rigid insulation can be cut, fitted, and glued or nailed onto nailing strips attached to the rafter faces. Or it can be applied directly to the rafter edges, then covered with a finish ceiling material.

In any case, leave an airway of 1 inch or more between the insulation and the underside of the roof sheathing to provide adequate ventilation (Fig. 10-6). Install vent ports in soffits and gable ends. The net vent area should equal 1 square foot for each 900 square feet of floor area beneath the roof, for both inlet and outlet vents.

Whatever the insulating method and material employed, take special care that all joints and seams are filled and all small voids completely plugged. This, incidentally, holds true for cap insulation as well. The reason is that warm air is always on the rise, directly up to the ceiling or roof, and if there is any way for it to escape in the form of tiny air currents through cracks or thin spots, it will do so. A surprising amount of heat loss in the average house takes place in just this way.

Fig. 10-6. Allow an airway between the insulation and the roof, as well as ports in the soffits, to provide adequate ventilation.


Of all the sections in the house, window glass transmits the greatest amount of heat per square foot of surface area. This is true no matter what precautions are taken, but the effects can be minimized to a certain degree. Different types of glass have different heat transmission characteristics, but for purposes of calculating residential heat loss by standard formulas, one factor is used to cover all types of clear, plain window glass. Thus, a single thickness of glass is rated at R-0.88. Double glazing, whether in one sash or a single-glazed sash and storm window combination, is figured at R-1.67. Resistance to heat transfer can be further increased by going to triple glazing, which has a value of R-2.44.

Obviously three layers of glass are considerably better than two or one, from the heat loss standpoint. But providing three layers, or even two, might not practical from other stand points. The total amount of heat loss through all the glass area in the house might not be sufficient to warrant the considerable extra expense of additional glazing. Also, the disadvantages of multiple glazing could outweigh the advantage of saving a bit of heat.

The disadvantages of multiple glazing include additional maintenance, higher replacement cost in case of breakage, the not-unusual circumstance of double insulating glass losing its seal and clouding up on the inside. Also, each layer of glass reduces the input of light by about 10 percent and reduces visibility correspondingly. Because multiple glazing reduces the amount of heat loss to the outside, it likewise reduces the amount of heat coming into the building from sunlight, depending upon the type of glass. So whether or not there is any net loss or gain is open to question. On the other hand, multiple glazing does cut down on cold air fall from the interior glass surfaces, thus reducing cool drafts, and it is also less susceptible to moisture or frost condensation.

The situation changes if you take into consideration the various specialty glazing materials now available. There is a wide variety of glass that is tinted or coated with a metallic film, as well as combinations of glass, and double glazing with a film suspended between the panes. All of these materials and combinations have differing characteristics. Further more, new products and combinations are being developed continuously. There are some opportunities here for installing specialized windows that have much better thermal characteristics than standard glazing, as well as other benefits. Check this out by studying the latest brochures, catalogs, and specification sheets from glass and window manufacturers.

It is worth noting that any glass areas, regardless of type, can be “insulated” from the inside, and they usually are at least to some degree. Heavy drapes, especially those that are lined with a thermally efficient material, effectively block direct heat radiation through the glass and help to reduce overall heat loss. Wood shutters do a decent job of lowering heat loss, and certain types of pull-down shades also have some effectiveness. The best arrangement, though, is to use window coverings that are made specifically to reduce heat loss through windows. These include various kinds of pull- down or pull-across fabric/insulant combinations that seal to the window casings in one way or another, interior shutters or blinds made of insulating materials, and insulating panels that are set in place on the inside as desired. Some people just cut snug-fitting pieces of rigid foil-faced insulation and set them in place every evening. Any of these practices, incidentally, work just as well in blocking sunlight out to reduce heat gain and lower cooling loads.

Exterior doors are also grouped according to factors that determine the thermal insulating value. Non metal doors over 1 inch thick and filled (cored) metal doors without windows in them are considered to have an R-value of 2.0, though some of the newer pre-hung, high- efficiency exterior doors might carry higher ratings, as evaluated by the manufacturer. Unfilled metal doors (hollow-cored) or nonmetal doors of less than 1 inch thickness are rated R-1. However, any door fitted with a window, whether single- or double-glazed, is calculated as though all glass at R-0.88.

Again, from a standpoint of heat loss the benefits of going to an extra-thick door or the addition of a storm door might be marginal at best. On the other hand, a thick exterior door affords an added measure of protection from the weather and is less susceptible to warping or other problems than a thin one. The addition of storm doors gives extra protection from the weather to often-expensive exterior doors, and cuts down on potential drafts, keeps rain water or snow from creeping in under the exterior doors, and cuts down on the amount of cold air admitted to the interior when the doors are opened. All of these have some effect upon heat loss and interior comfort levels, even though the specifics might be difficult to measure.


One of the most important aspects in complete house insulation and reduction of total heat loss from the structure is preventing infiltration of cold air from the outside and coincidental exfiltration of warm air from the inside. This process goes on continuously, and occurs in all mariner of strange places. Unfortunately, it often goes unnoticed. Some of the leakage paths are obvious, such as fireplace dampers, kitchen or laundry vents, and exterior doors opening and closing. Other spots are not so obvious and might go completely undetected. Air creeps in at the sill joints and travels into the wall cavities, or filters through the soffit and into the ceiling cavities, or rises in tiny jets through cracks in the floor or around the base boards or any one of a hundred other places. While this colder air is coming in, warmer air is going out in the same way, and heat is being lost by radiation, convection, and conduction. This process is constantly aided by air pressure differentials between the inside and outside of the house that are largely caused by outside air movement: breezes or wind.

A certain amount of infiltration/exfiltration is inescapable—a completely airtight house could only be built in a laboratory as a scientific experiment. And a certain amount is not only desirable in order to keep the interior air fresh and minimize ever-present air pollutants that are found in every house, but also is essential in order to maintain a full oxygen con tent. For most residences a complete change of air throughout the entire structure once every 45 minutes is considered about right. Super- insulated houses are often tighter than this, and then mechanical ventilation with heat- exchanging systems must be introduced. But when there is too much infiltration, other problems arise. The first is excessive heat loss and consequently higher heating costs, and the second is drafts and air currents that reduce the comfort level of the living quarters. The same situation occurs in reverse where cooling is the primary concern. Both of these problems can be traced, at least in good measure, to sloppy construction practices and/or poorly fitted insulation. In log houses, where there are dozens of seams and joints, infiltration can be a particular difficulty.

These heat losses and cold air gains (or vice versa) can be lumped under one heading, crackage. In other words, there are just too many badly fitted and/or improperly sealed-off joints and seams, which amount to a lot of cracks in the house. The results can be amply demonstrated by an all-too-common occurrence. First assume that all the windows in a house were sloppily installed and not caulked, leaving cracks here and there around them. Then visualize this as being the equivalent of a 6- x -8-foot picture window with a 1/16-inch crack all the way around it (which in itself has happened many times before). This would actually be the exact equivalent of cutting a 21-square-inch hole through a wall and leaving it open all winter. The only practical difference is that a series of small cracks all around the house might well cause an even greater heat loss than a single hole.

The remedy for this problem is simple enough. First, use good construction practices during the building of the house, fitting all the components tightly and properly together. Second, caulk and seal all obvious joints of any kind where outside air might find a way in. This is done during construction. Pay particular attention to all doors, windows, pipe openings, and other spots exposed to the outside. Third, install vapor barriers carefully, sealing off the joints and repairing any tears or punctures. Fourth, install all insulation so that the coverage is full, joints between insulating materials and framing members are tight, all cracks and voids are completely filled, and no gaps are left. Fifth, carry out maintenance procedures regularly as time goes by, sealing and caulking any new cracks or gaps that might appear as a result of setting or shrinking, while at the same time keeping an eye out for cracks that might appear in obscure spots. And last, apply adequate weatherstripping to all doors and windows, replacing or repairing it as necessary, and provide all vents with automatic-closing louvers and fireplaces or stoves with outside-combustion air sources.


A vapor barrier should always be used in con junction with insulation in all sections of the house. This prevents the passage of moisture—always present within the house— into the building sections where it could con dense and cause considerable damage, and re duce the effectiveness of the insulation itself. The vapor barrier is always placed closest to the warmer side of the building section and to the inside of the insulation.

Some types of insulation, particularly roll or batt fiberglass or mineral wool, include a vapor barrier of aluminum foil or kraft paper on one side. Some kinds of rigid insulation sheets have a foil facing on both sides. With other types of insulation, a separate vapor barrier must be installed. Many builders install a separate barrier anyway, whether the insulation has one or not, as an added measure of protection and to help reduce infiltration problems. The material most often used is construction plastic, stapled in place after the insulation has been installed but before the finish covering has been applied.

A vapor barrier should be continuous, all around the inside surfaces of the heated parts of the house, and free of slits, rips, and punctures. In effect, it is an envelope around the living quarters. A vapor barrier should always be installed between the ground and a concrete foundation slab or basement floor, arid between basement walls and any finish covering applied to them. As mentioned earlier, the ground surface in a closed crawl space should also be covered. Floors and ceilings or roofs require a full barrier, as do exterior framed walls. Log walls, of course, need no protection because they are above-ground and are essentially a monolithic section—moisture will migrate through the wood without any condensation problems. The exception is log walls that are furred out and insulated on the inside, with a finish wall covering applied. In that case, a vapor barrier should be attached across the interior faces of the furring. A vapor barrier is not necessary between interior spaces that are heated to different temperatures, even if the difference is substantial.

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