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This guide has three sections on materials. The first, deals with visible, finishing materials for the interior of the house, such as ceramic tile, parquet floors, and linoleum. Section 14 deals with exterior finishing materials, such as roofing shingles and wood siding. This section covers the unseen materials used for the structural parts of your renovation, such as metal studs, wood beams, and concrete. The sections on lumber and metal studs would be useful to most renovators since almost all of you will be involved with reworking some partitions and the easiest way to construct a partition is out of wood studs and gypsum board. The sections on concrete and concrete block (for foundations and load-bearing walls) have been included for renovators who are considering an addition to the house. Generally, you can choose which structural materials you prefer to use, wood or metal studs for the walls, concrete or concrete block for the foundations. Be aware, however, that your choice of materials may be limited by various codes and covenants. For instance, if you are renovating your urban condominium, the city’s building code may require that you use a fire-rated material such as metal studs and joists or lightweight concrete block (once known as cinder block) in stead of wood structural members. STRUCTURAL WOOD Most of the houses in this country are structured in wood. This fact may not be immediately evident since many American houses are sided in brick, stucco, or aluminum applied to a wood frame. Lumber has always been the popular choice because it's inexpensive, readily available, easy to cut and nail, and relatively lightweight. The major drawbacks of this material are its tendency to decay when subjected to adverse conditions, to shrink and expand depending on its moisture content, as well as its combustibility and its edibility—by termites, that's . Wood is almost always cut from the tree lengthwise, parallel to its long, sinuous fibers. It is strongest in this direction. Standing upright on a slim trunk, the living tree carries the weight of its branches, leaves, fruit, and the added loads of snow and wind. Wood is strong in compression, which means that it can carry a lot of weight. Long vertical pieces of lumber act as columns or mini-columns (called studs) and carry the entire weight of the second floor and roof down to the foundation. Very often the tree is subjected to high winds, which cause it to bend. Wood’s ability to bend (and not to, fail under these stresses), to regain its original shape when the pressure is removed (its elasticity), and to resist completely succumbing to the bending forces (its stiffness) makes it a very good material to use horizontally as well as vertically. When a board is placed on its narrow side and made to span two supports, it's subjected to such bending stresses. The long sinews in wood, its fibers, resist these stresses. KILN-DRIED VERSUS ‘‘GREEN’’ LUMBER: The living tree consists of about 55 % moisture. When the tree is cut down (thus becoming deadwood), it loses its natural juices and shrinks. Often, the moisture content of the lumber is removed artificially by the mills in drying ovens called kilns. Ideally, the moisture should be about 19 % for wood that's to be used structurally. Why is the moisture content so important? If the lumber is used “green” (straight from the tree without being dried out), it will dry in time and in doing so will shrink quite a bit, while other building materials such as tile, glass, masonry, gypsum board, etc., will not. Joints that were previously tight will become loose; nails will become exposed, doors and windows will leak air. At the other extreme, if wood is oven-dried to remove all of its water, it will have the tendency to absorb moisture from the air in great quantities. The swollen wood would cause doors and windows to stick in hot, humid weather. In simplistic terms, wood swells and shrinks only slightly parallel to its grain (in its length), but does tend to swell and shrink perpendicular to its grain (across its trunk). Because there is little shrinkage along the length of stud and a much greater degree of shrinkage in its cross section, the balloon frame (using long studs from sill to roof) is used when stucco or masonry facing material will be attached to the structure. These materials are relatively brittle and would crack if exposed to dimensional changes in the framing. The platform frame shrinks and expands in its length because of the floor framing elements used between the studs. Wood siding has the flexibility to accommodate these minor and invisible dimensional changes and can be used in conjunction with the platform frame. When wood shrinks unevenly it warps. The amount and kind of warpage that occurs in a board depends on the original moisture content of the wood and how it's sliced from the tree trunk. If you look at the end of a “green” board you will see part of the annual ring pattern of the trunk of the tree and you may be able to predict whether the board will warp when it dries. This may not be the most practical approach to the purchase of a major quantity of wood. If you purchase kiln-dried lumber, on the other hand, it's unlikely that the boards will warp. Lumber The term “boards” usually refers to pieces of wood that are less than 2” in depth, whereas “lumber” is wood cut into standard structural sizes and is generally 2” to 5” in depth. The “nominal” (rough) size is what it's called at the lumberyard and on architectural drawings (2 X 4, 2 X 6). The actual, dressed dimensions of the lumber you take home are smaller (a 2 X 4 will be 1/2” smaller in two dimensions). The reduction in size of the lumber dimensions is justified as part of the milling process that standardizes lumber sizes by planing all four surfaces to a smooth uniform product. You pay for the nominal size but buy the actual member. Kiln-drying, which also plays a part in diminishing the size of the lumber, reduces the shrinkage that may take place in the finished house. The reductions in dimensions have been standardized, so that a 2 X 4 will always be exactly 1½” by 3 1/2”, and a 1 X 12 will always measure 25/32” X 11 1/4”. Inset I gives the actual dimensions of the most common nominal sizes. The length of the board, by the way, isn't affected. When you buy a 14’-long board it should measure 14’. NOMINAL and DRESSED SIZES OF SOFTWOOD LUMBER Lumber is sold in lengths up to 24’. Although you can have lumber cut to any size (under 24’), it's more efficient to use it in the standard lengths in which it's sold—less waste, less labor. Yard lumber is commonly sold in lengths of 8’, 10’, 12’, 14’, and 16’. Lumber longer than 16’ may be difficult to find and /or more costly. Lumber longer than 24’, whether cut from one piece or laminated, is very expensive and shouldn't be needed for residential construction. It is a good idea to plan the joists in modules of 2’ so that you will not have to cut longer sections down. TYPES and GRADES OF LUMBER: Many kinds of wood are used for construction purposes and each variety of tree is divided further into grades depending on the quality of the sample cut. Wood is classified as either softwood or hardwood (mis leading terms, because they have absolutely nothing to do with the strength of the timber). Softwoods are cut from conifers, trees that have needles, also known as evergreens. Commonly used conifers are pine, Douglas fir, and hem-fir. Softwood is generally used for structural purposes, such as framing, but has also been used for finished flooring and furniture. Hardwood comes from deciduous trees (those that lose their leaves in winter) and is very dense. Hardwoods such as maple, mahogany, oak, and fruitwood are used for finished floors and fine furniture. Laminated means that several thin layers of wood are bonded together to form one solid piece. Structural softwood is generally divided into classifications and grades depending on its strength, likely use, and imperfections. Lumber is classified into two major categories: stress-graded lumber and yard lumber. Stress-graded lumber is used for long span beams where the loads are large and have been carefully calculated. These beams are usually supplied to developers directly from the mill and are rarely seen in lumberyards. Yard lumber—used for light framing—is readily available and is divided into the following sub categories: select-structural, the best of the lot, is clear—that is, without knotholes, bark, splits, or other defects; construction (also called no. 1) is mostly clear; standard and better (no. 2) has firm knotholes that shouldn't affect its overall strength; and utility (no. 3) covers whatever is left that can still be called lumber. Select-structural and construction grades are used for beams and joists. Standard and better is used for studs. The strength of the joist is related to both the type of tree and its grade. A no. 1 joist cut from Douglas fir will be stronger than one similarly graded cut from hem-fir. (These are the “ac dimensions for the following “nominal” sizes. When you purchase a 2 X 4, the actual lumber you go home with is 1 1/2” x 3 1/2”.) Nominal - Actual (dry) – Green Boards (up to 12” wide) 1” 3/4” 11/4” 1” 1 1/2” 1 1/4” Lumber (thickness: 2”, 3”, 4”; width: up to 12” and over) 2” 3” 4” 1 1/2” 2 1/2” 3 1/2” 6” 8” 10” 12” over 12” 5 1/2” 7 1/4” 9 1/4” 11 1/4” less 3/4” Timbers (5” thick and over) 5” and larger less 1/2” Decking (tongue-and- groove boards) 2” (thick) 3”, 1 1/2” 2 1/2” 1/16” 2 3 5 5/8” 7 1/2” 9 1/2” 11 1/2” less 1/2” 4” 3 1/2” Each piece of yard lumber bears the stamp of the manufacturer, giving its brand name, the code for the mill location, the tree from which it was cut, its grade, and its moisture content. The stamp may indicate the suggested usage as well, such as “stud.” Most lumberyards will stock only a limited selection of tree types and grades. CATEGORIES OF LUMBER and THEIR USES LUMBER CUT FOR HORIZONTAL. USE: Joists: Usually 2” (nominal) in thickness used to directly support floor or ceiling, and supported in turn by a larger horizontal member (beam or girder) or a bearing wall. Joists are generally spaced at small, regular intervals, such as 12”, 16”, or 24” on center. Planks: 2” in thickness (could be 3” or 4”). Used as flooring, roofing, or decking, directly over and supported by beams. LUMBER CUT FOR DIAGONAL. USE: Bracing: A piece of lumber applied to the frame on the diagonal to stiffen the structure. LUMBER CUT FOR VERTICAL USE Posts: Vertical supports, usually short. Beams: Larger (in cross section, not necessarily in length) than joists. Used to support joists and transfer their loads to vertical supports (or to girders). Columns: Vertical supports, longer than posts. Used to transfer horizontal loads down to the foundations. Girders: Similar to beams, only larger in cross section. Studs: Mini-columns. A series of slender structural members placed at small, regular intervals as the supporting elements in load-bearing wood walls and partitions. Bridging: Used in an “X” pattern between the joists to stiffen the floor. JOIST LIGHTWEIGHT METAL FRAMING The channel-shaped light steel sections used in lightweight metal framing resemble wood studs and joists more than they do heavier steel girders and columns. As a matter of fact, light metal sections are a substitute for lumber and the two materials are often used interchangeably. Lightweight structural steel studs and joists are made of galvanized* or primed steel. These structural components are used to frame buildings up to four or five stories high. The components are screwed together using clips, straps, and anchors where required or can be welded. In addition, “nonstructural” lightweight metal studs are available for use in non-load-bearing walls and partitions. The gauge of the metal indicates whether it's structural or not: 24g metal framing is nonstructural, whereas 14g. 16g. and 18g are generally structural. The wall framing systems consist of runner channels that are fastened to the floor and steel studs screwed to the tracks. The wall studs have openings in the web for cross bracing and the easy passage of electrical conduits or horizontal plumbing. Lightweight steel joists come in a number of sizes and can be cut to the desired lengths. Accessories include endpieces for framing, joist hangers, and web supports. Steel framing is incombustible, but like all steel it's not fireproof. Steel does not burn but will lose its strength when exposed to high heat. CONCRETE and CONCRETE BLOCK If you are constructing an addition to the house, you will need to know about concrete and concrete block for the footings and the foundation work. The foundations of a building root it in the ground and transfer its loads to the earth. The foundations are a continuation of the walls of the house deep into the ground below what is known as the frost line. The footings sit under the foundation wall and are wider than the wall. The width or “spread” of the footing allows the building loads to be transferred along a wider area. The width of the footing may vary depending on the magnitude of the load being transferred through the foundation wall and the bearing capacity of the soil. (The classic example is how snowshoes transfer your weight to the snow over a large surface area.) Foundation walls can be constructed of reinforced poured concrete or concrete block. Footings are always constructed of poured concrete. Concrete Sometimes called man-made stone, concrete has all the characteristics of the original—durability and compressive strength. In addition, it can be cast into any shape and reinforced with steel rods to increase its tensile strength. Concrete consists of the following ingredients in varying proportions determined by the desired strength of the resultant product, its appearance, and weather conditions: fine aggregates (sand), coarse aggregates (crushed stone), Portland cement, and water. Portland cement is a combination of various minerals (primarily lime, iron, alumina, silica, etc.) which are mixed and fired in a kiln. The final mixture, when combined with water, forms a paste. This paste cures into a very hard mass. Type I Portland cement is the most commonly used. Water, when mixed with Portland cement, triggers a chemical reaction (called hydration) that causes the cement to set. The amount of water used in a batch of concrete is critical. Enough water must be used to produce the chemical reaction and to make the concrete workable when fluid. Too much water weakens the concrete to a significant degree. Proportions of water to cement vary according to the nature of the job. The frost line is the depth at which the moisture in the soil will not freeze. This depth varies from climate to climate. Since water tends to expand when frozen, icy soil under the foundations can cause the entire house to heave unevenly, causing enormous structural damage. Galvanizing: the application of a zinc coating to steel as a means of preventing corrosion. The aggregates determine the weight of the concrete. For the most part, sand is used to fill in the voids between the coarser aggregates. Most lightweight aggregates are nonstructural. Mineral feldspar, for example, is used in construction applications requiring less heavy concrete or to insulate steel against fire. The resultant product is comparatively weak. The mixing of concrete is very tricky. Since so many things can go wrong, weakening or contaminating the concrete, we don’t recommend that you mix your own. (If you need only small amounts for noncritical applications, purchase a bag of dry mix and follow the directions on the bag.) If you need enough concrete to pour footings and /or foundation walls, we suggest you purchase ready-mixed concrete delivered by mixing truck. Ready-mixed concrete has a number of benefits other than sparing you a tedious job. The manufacturing process assures you a mixture of uniform quality and guarantees strength. In addition, a truckload of concrete allows you to pour continuously (without pausing to make a new batch), which results in a better-looking, more watertight product. Concrete, which is very strong in compression but weak in tension, can manage compressive stresses by itself but does not hold up very well under stretching and bending (tensile) stresses. To compensate for this, concrete is often combined with steel to withstand bending and pro duce a more efficient and much stronger material; this is known as reinforced concrete. Steel bars are embedded in the concrete. The concrete then carries the compressive load while the steel (an excellent material in tension) takes care of the tensile stress. Reinforcing steel bars are placed in the areas where there will be tension. Reinforcement is almost always used in the lower portion of the simply supported horizontal beam, where most of the “stretching” occurs. Concrete must be poured into formwork that's constructed and braced before the concrete is mixed. Erecting formwork isn't easy since it involves carp’ work and great care. Forms have to be well constructed and strong enough to sustain the weight of the concrete. In addition, they should be easy to remove when the concrete has hardened. The construction of formwork isn't recommended for the beginner. The cost of lumber for the formwork must be added to the cost of the foundations. In some areas of the country the rental of metal formwork may be a viable option. Concrete Block Concrete block can be used to construct load- bearing walls and foundation walls. There are a number of different kinds of concrete block, some for construction purposes only and others with a decorative, textured surface which make an attractive wall as well as a serviceable one. Concrete block is a manufactured product made up of the same components as concrete. The mix proportions and the curing process are closely regulated, resulting in a product of uniform quality. A concrete-block wall is less expensive to construct than a brick wall. Block comes in a number of sizes, shapes, and classifications. Grade N blocks are used for exterior walls and for foundations, whereas S blocks should be used only for interior partitions that will not be subject to freezing. Grade I block is a low-moisture block meant primarily for very dry areas, and grade II is designed for most locations. Grade I is an all-purpose block. Among the many shapes and sizes available, the stretcher block (nominal size: 8” x 8” x 16”, actual size: 7 x 7 5/8” X 15 5/8”) is most often used, but the block size will vary according to structural requirements. Corners and double corners (or pier blocks) are used in conjunction with the stretcher blocks for end conditions. Concrete block is rated according to strength, ranging from solid load-bearing block for jobs where heavy compressive strength is required to hollow non-load-bearing block for use as non- load-bearing partitions. The most commonly used block, however, is the hollow load-bearing block, since it offers a great range of uses and is most readily available. It has a good capacity for carrying compressive stresses, in addition to being lightweight and coming in a wide range of shapes and sizes. Hollow blocks are either two- or three-cored, each kind, having slightly different physical properties. Two-cored units have larger holes than three-cored ones and are consequently lighter and cheaper. The air spaces between the block faces have some insulating quality in them selves, but they can be filled with insulating material or concrete or grout. Three-cored blocks are stronger than the two-cored variety and are better suited for foundation walls. The cores in concrete block are tapered so that one side of the block has smaller openings than the other. Blocks are laid with the smaller cores up to provide a bed for the mortar. WHICH SIDE OF THECONCRETE BLOCK SHOULD FACE UP? Because the cores in the block are tapered, one face has smaller cavities than the other and , there- fore, more concrete-bearing surface. In order to get maximum bonding with the mortar, the side with the smaller cores should always face up. Next: Plumbing Design |
