Wood-board siding can be applied horizontally or vertically. Horizontal siding tends to make a house appear lower and longer; vertical siding tends to make a house appear taller (and is popular on one-story houses). The wood used for board siding should be free of knots. Otherwise, over a period of time, shrinkage can cause the knotty cores to drop out, leaving the siding with holes that are vulnerable to water penetration.
With the exception of redwood and cedar boards, most wood siding is painted for protection against weathering and decay. When inspecting the siding, look at the condition of the paint. Are there any bare, peeling, flaking, or blistered sections? If there are, paint touchup or repainting may be needed. Blistered and peeling paint is often caused by moisture in the painted wood, although it can also result from a poor paint job. Determination of the exact cause for blistering and peeling paint cannot be made during a single inspection. Nevertheless, this condition should not affect your thinking about the house. If it is caused by moisture in the wood, it can be corrected after you move in, and usually at minimal expense.
Wood-board siding should be inspected for cracked, loose, and rotting sections. In addition, look for loose or missing knots. All holes should be patched with a wood filler. In vertical siding, check the joints between the vertical sections for weathertightness. In both vertical and horizontal siding, pay particular attention to the outside corner joints. These joints are vulnerable to water penetration during a rain, and any open joints must be sealed.
Plywood panels are also used for siding. They are made from exterior-type plywood in which the veneer layers are bonded together with a waterproof glue. The exterior facing of the panel comes in a variety of surface textures and grooves. The panels are 4 feet wide by 8, 9, or 10 feet long. The thickness of the panel will depend on the depth of the grooves and will generally vary between 3⁄8 and 5⁄8 inch. Plywood panels are usually installed in a vertical position with the vertical joints over studs. This minimizes the number of horizontal joints, which is desirable since plywood panels are often applied directly to the studs rather than over sheathing. Because of their vulnerability to water penetration, any horizontal joints should be shiplapped (not visible to the inspector) or protected by metal flashing (visible). When inspecting plywood siding, look for loose, warped, cracked, delaminated, and rotting sections. Also check for open and nonweathertight joints. If the panel siding is painted, check the finish for peeling and flaking paint and blistered sections.
Hardboard siding is made by bonding (under heat and pressure) wood fibers that have been ground almost to a pulp. The siding is dense and tough, and has a fairly good dimensional stability, although not as good as that of plywood. Hardboard, like plywood, is available in a wide range of textures and surface treatments. It is available in 4-foot-wide panels and 9- and 12-inch-wide planks. When inspecting hardboard siding, look for cracked, chipped, broken, deteriorated, and loose sections. Also check horizontal and vertical joints for weathertightness.
Aluminum siding is often used in new construction and is often used when re-siding the exterior walls. The siding comes in planks that are either smooth or embossed with a wood-grain texture (to resemble painted wood boards), also as shingles and vertical panels. Aluminum siding is relatively maintenance-free. It is noncorrosive and termite-proof, and will not rot. The siding surface is generally covered with a baked enamel-paint finish that can stand up for many years before it fades, becomes dull, and needs a coat of paint. If the siding is scratched, bare aluminum is exposed. However, since the aluminum does not corrode, the scratch is only of cosmetic concern and can easily be corrected with touch-up paint. One problem with the siding is that it can be dented if struck hard enough- as with a baseball or stone thrown from a power mower. Many communities require that aluminum siding be grounded electrically as a precaution against electrical shock.
Aluminum siding is available with or without insulation backer boards. The insulation is generally a rigid foam (such as polystyrene) or fiberboard. Although the backer boards are only about 3⁄8 inch thick, they are quite effective as an insulator for a house that has no insulation in the exterior walls. Because of increasing energy costs, even a house with insulation in the exterior walls benefits from the additional insulation. The backer boards reduce heat loss in the winter and heat gain in the summer. They also increase the strength and rigidity of the siding. However, insulation-backed siding (and tight siding jobs) can cause moisture to accumulate within the exterior walls of houses that have no vapor barriers on the inside surface. (Insulation and vapor barriers are discussed in chapter 19.) You can usually tell whether the aluminum siding has an insulation backer board by pressing on it. If the siding is relatively firm, it has a backer board, but if it yields and bends under the pressure, it has no insulation board. Another method is to tap the siding. If it has no insulation, you will get a hollow sound.
When inspecting aluminum siding, look for loose, missing, and dented sections. Check the exterior joints for open sections and weathertightness. In those areas where electrical grounding of the siding is required, you should look for an electrical ground connection, a wire that runs from the siding to the inlet water pipe or a rod or pipe that has been driven into the ground. (See chapter 12.) You can find out whether an electrical ground connection is required by checking with the local municipal building department.