Exterior wood siding is precisely manufactured to standardized sizes. Plain bevel siding is designed to be lapped so that it will shed water and give a dustproof and windproof covering. All the same, spacing for siding should be carefully laid out before the first board is applied.
The bottom of the board that passes over the top of the first floor windows should coincide with the top of the window cap. (See Figure) To determine the maximum board spacing or exposure, deduct the minimum lap from the overall width of the siding. The number of board spaces between the top of the window 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.
Siding starts with the bottom course of boards at the foundation, blocked out as illustrated here. Sometimes the siding is started on a water table, which is a projecting member at the top of the foundation to throw off water. Each succeeding course overlaps the upper edge of the lower course. The minimum head lap is 1 inch for 4 and 6 inch widths and 1 ¼ inches for widths over 6 inches.
A “story pole” is a template guide that helps in layout. You can make one with these steps:
- 1. Lay out distance from the soffit to about 1 inch blow the top of the foundation.
2. Divide this distance into spaces equal to the width of the siding minus the lap-over.
3. Adjust lap allowance, respecting minimum requirements, so the spaces are equal.
4. Where possible, adjust spacing so that single pieces of siding will continuously run above and below window and other openings
5. Mark the position of the top of each siding board on the story pole, a 1 X 2 or 1 x 4 length of lumber
Hold the story pole in place at each inside and outside corner of the wall and transfer the marks to the wall, and to window and door casing structure. If you like, you can also set nails at the mark points, in order to string a length of line between them horizontally for aligning boards.
The joints between boards in adjacent courses should be staggered as much as possible. Butt joints should always be made on a stud, or where boards butt against window and door casings and corner boards. The siding should be carefully fitted and be in close contact with the member or adjacent piece.
Some carpenters fit the boards so tightly that they have to spring the boards in place. This assures a tight joint. Loose-fitting joints allow water to get behind the siding and therby cause paint deterioration around the joints and also set up conditions conducive to decay at the ends of the boards.
Nails cost little in comparison to wood materials and labor, but using good quality nails is important. Why buy siding that will last for many years and then fasten it with nails that will rust after a few rainy seasons? Rust-resistant nails will hold siding permanently and not disfigure light-colored paint surfaces. Galvanized, zinc-coated steel or aluminum should be used.
Two types of nails are generally used to install siding, one having a small head and the other a slightly larger head. The small-head casing nail is set, driven with a nail set, about 1/16 inch below the surface of the siding. The hole is filled with putty after the prime coat of paint is applied. The large-head nail is driven flush with the siding face, with the head being later covered with paint.
Bevel siding should be face-nailed to each stud with noncorrosive nails, the size depending on the thickness of the siding and the type of siding used. For ½ inch siding over wood or plywood sheathing, use sixpenny nails; and over fiberboard or gypsum sheathing, use eightpenny nails. For ¾ inch siding over wood or plywood sheathing, use sevenpenny nails, and ninepenny nails for gypsum or fiberboard sheathing. The nails are generally placed about ½ inch above the butt edge, in which case it passes through the upper edge of the lower course of siding.
Another method recommended for bevel siding by most associations representing siding manufacturers is to drive nails through the siding just above the lap so that the nail misses the thin edge of the piece of siding underneath. The latter method permits expansion and contraction of the siding board with seasonal changes in moisture content, thus minimizing tendency to cup or split that may occur when both edges of the board are nailed. Since the amount of swelling and shrinking is proportional to the width of the material, nailing above the lap is more important in wide siding than in narrow siding.