One of the materials most characteristic of the exteriors of American houses is wood siding. The essential properties required for wood siding are good painting characteristics, easy working qualities, and freedom from warp. These properties are present in a high degree in the cedars, eastern white pine, sugar pine, western white pine, cypress and redwood; also to a good degree in western hemlock, ponderosa pine, spruce, and yellow poplar, and to a fair degree in Douglas fir, western larch and southern yellow pine.
Material used for exterior siding should preferably be of a select grade, and should be free from knots, pitch pockets, and waney edges. The moisture content at the time of application should be that which it would attain in service. This would be approximately 12 percent, except in the dry Southwestern United States, where the moisture content should average about 9 percent.
Horizontal bevel siding, with it’s deep shadow cast on the wall by the butt edge, emphasizes horizontal lines of a home and makes it look spacious and elegant. It is made by sawing surfaced boards at a diagonal to produce two wedge-shape pieces. As shown in the illustration, plain bevel siding is made in 4, 5 and 6 inch widths with 7/16 inch butts, 6-, 8- and 10-inch widths with 9/16 inch butts, and 6-, 8-, 10- and 12-inch widths with 11/16 inch butts. The top edge is 3/16 inch thick for all sizes.
Bevel siding is generally furnished in random lengths varying from 4 to 16 feet. Rabbeted bevel siding has a profile with a cutout rabbetted into the bottom edge for the adjoining board to fit into, so that it lies flat against the studding rather than touching it only near the joints like regular bevel siding. The apparent thickness of the siding is reduced by about a quarter inch and reduces chances of warping as well. Rabbetted joints also require less lumber than lap joints in regular beveling, so they are more economical.
Drop siding is generally ¾ inch thick and is made in a variety of patterns with either matched or shiplapped edges. It was designed to be applied directly to the studs, rather than to wall sheathing, as with bevel siding, and so serves as both sheathing and exterior siding. It is widely used as such in farm structures, sheds and garages in all climates, and for houses in milder climates.
When used over and in contact with other material, such as sheathing or sheathing paper, water may work through the joints and be held between the sheathing and the siding and set up conditions conducive to paint failures and decay. Such conditions are not common when the side walls are protected by a good roof overhang.
Vertical siding is commonly used on the gable ends of houses, over entrances, and sometimes for large wall areas. The type used may be plain-surfaced matched boards, patterned matched boards, or square-edged boards covered at the joint with a batten strip.
Matched vertical siding should preferably not be more than 8 inches wide and should have 2 eightpenny nails not more than 4 feet apart. Backer boards should be placed between studs to provide a good nailing base. The bottom of the boards should be undercut to form a water drip. See: Board and Batten Siding
Plywood is often used in gable ends, fill-in panels above and below windows, and as a continuous decorative band at different levels along an entire wall. Sheets must be made from exterior grade plywood, most commonly Douglas fir. Exterior plywood panels come in both sanded condition and with factory-applied sealer or staining.
Maximum stud space on center for 3/8 inch thick plywood panels is 16 inches, for ½ inch thick, 20 inches, and for 5/8 thick, 24 inches. Lap-over at panel joints should be at least 1 ½ inches. Plywood siding provides a relatively tight, draft-free wall, so it is important to include an effective vapor barrier between the insulation and inner wall surface.
Cedar Shake Siding