Exposure

Builder 3&2 Volume 02 - Construction manual for building structures
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Figure 4-3.-Installation of bevel siding. Exposure The minimum lap for bevel siding is 1 inch. The average exposure distance is usually determined by the distance from the underside of the window sill to the top of the drip cap (fig. 4-3). From the standpoint of weather resistance and appearance, the butt edge of the first course of siding above the window should coincide with the top of the window drip cap. In many one-story structures with an overhang, this course of siding is often replaced with a frieze board It is also desirable that the bottom of a siding course be flush with the underside of the window sill. However, this may not always be possible because of varying window heights and types that might be used in a structure. One system used to determine the siding exposure width so that it is approximately equal above and below the window sill is as follows: 1. Divide the overall height of the window frame by the approximate recommended exposure distance for the siding used (4 inches for 6-inch-wide siding, 6 inches for 8-inch-wide siding, 8 inches for 10-inch-wide siding, and 10 inches for 12-inch-wide siding). This result will be the number of courses between the top and the bottom of the window. For example, the overall height of our sample window from the 2. top of the drip cap to the bottom of the sill is 61 inches. If 12-inch-wide siding is used, the number of courses would be 61/10 = 6.1, or six courses. To obtain the exact exposure distance, divide 61 by 6 and the result would be 10 1/6 inches. Determine the exposure distance from the bottom of the sill to just below the top of the foundation wall. If this distance is 31 inches, use three courses of 10 1/3 inches each. Thus, the exposure distance above and below the window would be almost the same (fig. 4-3). When this system is not satisfactory because of big differences in the two areas, it is preferable to use an equal exposure distance for the entire wall height and notch the siding at the window sill. The fit should be tight to prevent moisture from entering. Installation Siding may be installed starting with a bottom course. It is normally blocked out with a starting strip the same thickness as the top of the siding board (fig. 4-3). Each succeeding course overlaps the upper edge of the course below it. Siding should be nailed to each stud or on 16-inch centers. When plywood, wood sheathing, or spaced wood nailing strips are used over nonwood sheathing, 7d or 8d nails may be used for 3/4-inch-thick siding. However, if gypsum or fiberboard sheathing is used, 10d nails are recommended to properly penetrate the stud For 1/2-inch-thick siding, nails may be 1/4 inch shorter than those used for 3/4-inch siding. The nails should be located far enough up from the butt to miss the top of the lower siding course (fig. 4-4). The clearance distance is usually 1/8 inch. This allows for slight movement of the siding because of moisture changes without causing splitting. Such an allowance is especially required for the wider (8 to 12 inch) siding. Joints It is good construction practice to avoid butt joints whenever possible. Use the longer sections of siding under windows and other long stretches, and use the shorter lengths for areas between windows and doors. When a butt joint is necessary, it should be made over a stud and staggered between courses. Siding should be square cut to provide good joints. Open joints permit moisture to enter and often lead to paint deterioration. It is a good practice to brush or dip 4-4

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