Lumber siding should be sound and free of knot holes, loose knots, checks or splits. Easy working qualities and freedom from warp are desirable features. The species most commonly used are cedars, pines and redwood. It has also become more common to use pressure-treated lumber for siding. Pressure-treated siding may be manufactured from pine or other species. The moisture content of the siding at the time of application should be the same as it will experi-
sheathing sheathing membrane vertical furring strips plastic spline horizontal hardboard siding metal starter strip screen to prevent insects erice in service, that is, about \z to 18 percent, depending on the region's humidity and climate.
In wet, humid climates, such as the coastal regions of Canada, an air space is often formed behind the siding to prevent water penetration and to vent moisture away from the wall. This is done by mounting the siding on furring strips nailed on top of the sheathing paper to the studs behind. In these cases, a screen should be installed at the base of the wall to protect against insects and the top should be blocked to compartmentalize the wall.
Horizontal Application. Bevel or feather-edge siding (Fig. 8oB) generally starts with the bottom course of boards furred out as shown in Figure 82B. A1/4 in. (6 mm) thick furring strip is used for this purpose. Each succeeding course overlaps the upper edge of the lower course, the minimum lap being usually 1 in. (25 mm). Spacing for the siding should be carefully laid out before the board is applied. To determine the maximum board spacing (or exposure), the minimum lap should be deducted from the overall width of the siding. The number of board spaces between the soffit and the bottom of the first course at the foundation wall should be such that the maximum exposure will not be exceeded. This may mean that the boards will have less than the maximum exposure. Where possible, the bottom of the board that is placed over the top of the windows should coincide with the top of the window cap (Fig. 82A).
Bevel siding should have a butt thickness of at least 1/2 in. (12 mm) for widths of 8 in. (184 mm) or less and 9/16 in. (14.3 mm) for widths greater than 8 in. (184 mm). The top edge should not be less than B/16 in. (5 mm) thick.
Drop (or matched) siding should be at least 9/16 in. (14.3 mm) thick and 8 in. (184 mm) or less in width. It comes in a variety of patterns with matched or shiplap edges. Figure 80D shows a common pattern for drop siding.
Where bevel or drop siding is used, the butt joints between boards in adjacent courses should be staggered as much as possible. Butt joints should be made over a stud. The siding should be carefully fitted and be in close contact with other members and adjacent pieces. Ends should be sealed. Loose-fitting joints allow water to get behind the siding which can cause paint deterioration around the joints and lead to decay at the ends of the boards. One method sometimes used to obtain a tight joint is to place a small bead of caulking compound or putty along the end of each board after it is nailed and then press the next board into the compound. The excess compound is struck off, leaving a smooth waterproof joint. Joints occurring elsewhere, such as at window or door trim, can be similarly treated.
Bevel and drop siding should be face-nailed to lumber sheathing or studs. The size of the nail depends on the thickness of the siding and the type of sheathing used. One method of nailing often used is to drive the nail through the siding just above the lap so that the nail misses the top edge of the piece of siding beneath. (See the nailing method detail in Figure 82.) This method permits each siding board to expand and contract as the moisture content changes. Thus, there is less tendency for the boards to split as may occur when both edges of the board are nailed. Since the amount of swelling or shrinking is proportional to the width of the wood siding, nailing above the lap is more important with wide boards than with narrow boards.
Installation of siding: (A) method of application; (B) starting course.
siding flush with top of flashing set first metal flashing sheathing membrane around window opening scribe tight against window detail: nailing method
stud sheathing siding bottom plate header sill plate V4" (6 mm) furring strip extend siding below blocking 8" (200 mm) minimum parging siding flush with top of flashing set first metal flashing sheathing membrane around window opening scribe tight against window detail: nailing method
butt joints made over centre of stud if sheathing omitted foundation wall butt joints made over centre of stud if sheathing omitted foundation wall stud sheathing siding bottom plate header sill plate V4" (6 mm) furring strip extend siding below blocking 8" (200 mm) minimum parging
Vertical Application. Lumber siding that can be applied vertically includes: plain matched boards; patterned matched boards; square-edge boards covered at the joints with a batten strip, or square-edge boards spaced apart and covered with another board. Vertical siding is usually 9/i6 in. (14.3 mm) thick. Boards should not be wider than 12 in. (286 mm). Vertical boards may be fastened to 9/16 in. (14.3 mm) lumber sheathing, 1/2 in. (12.5 mm) plywood or 1/2 in. (12.5 mm) oriented strand board or waferboard, 2 x 2 in. (38 x 38 mm) blocking fitted between the studs at 24 in. (600 mm) on centre or to horizontal furring strips. The furring may be 1 x 3 in. (19 x 64 mm) lumber where the framing is spaced not more than 16 in. (400 mm) on centre or 2 x 4 in. (19 x 89 mm) lumber where the framing is spaced not more than 24 in. (600 mm) on centre. Butt joints should be mitred to prevent the entry of water into the joint. When the spaced method (sometimes called "board-on-board") is used (Fig. 80E), the boards next to the wall are normally wider than the top boards and are fastened with one row of nails near the centre of each board. The top board is then applied so that it laps the edges of the first board at least 1 in. (25 mm). These top boards are fastened with two rows of nails driven slightly outside the edges of the boards underneath. This method of nailing permits the wider board to expand and contract without splitting.
The board and batten method uses square-edge boards which are ordinarily 8 in. (184 mm) or less in width. The boards are applied with the edges at least 1/4 in. (6 mm) apart and fastened with one row of nails near the centre of each board. To cover the joint, a narrow batten is used which laps the edges at least 1/2 in. (12 mm). This batten is fastened with one row of nails driven in the joint between the two boards, so that the boards may swell or shrink without splitting either the boards or the batten strip. Since the batten also serves to prevent the board edges from curling outward, the nailing should be secure and closely spaced.
Tongue-and-groove matched siding (Fig. 80C) is commonly 8 in. (184 mm) or less in width. The first board is face-nailed near the grooved edge and angle-nailed through the tongue. Each successive board is driven in closely and angle-nailed through the tongue. A nail set is used to finish off the nailing.
Nails cost little compared with the cost of the siding and labour, but the use of good nails is important. It is poor economy to buy siding that will last for years and then fasten it with nails that will rust badly within a short period. Corrosion-resistant nails, such as hot-dipped galvanized nails, will hold the siding permanently and will not disfigure the paint surface. Casing or siding nails are normally used for this purpose. Heads are driven flush with the face of the siding and later covered with paint. If finishing nails are used, the heads should be set below the surface and the hole filled with putty after the prime coat of paint is appl ied. The length of the nails depends on the thickness of the siding and the type of sheathing used. Nails should be long enough to penetrate at least 1 in. (25 mm) into the nailing support.
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