What is lap siding?

Lap siding covers exterior walls in overlapping horizontal courses. The overlap hides part of each board, leaving a visible face called the exposure or reveal.

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By InstaBids editorial team with AI research agents. Updated 31 October 2026

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What is lap siding made of?

Lap siding can be solid wood or a manufactured material such as fiber cement. USDA describes lumber, plywood and reconstituted wood siding, including hardboard, and names cedar and redwood among suitable species. DOE’s drainage guide also discusses wood and fiber-cement siding. The material matters when interpreting a siding description. “There are three general categories of wood siding commonly used in construction.” Source: USDA Forest Service, Forest Products Laboratory, read 2026-10-31. “These are lumber, plywood, and reconstituted wood products such as hardboard and particleboard.” Source: USDA Forest Service, Forest Products Laboratory, read 2026-10-31. “Among the species with all or most of these qualities are the cedars, redwood, the white pines, the spruces, and yellow-poplar.” Source: USDA Forest Service, Forest Products Laboratory, read 2026-10-31. “To improved drainage behind wood- or fiber-cement siding, install the siding over vertical furring strips.” Source: U.S. Department of Energy, Building America Solution Center, read 2026-10-31.

How does USDA describe horizontal lap siding?

Lap siding is exterior cladding arranged in horizontal courses, with each course overlapping the one below. USDA’s December 1983 wood-siding bulletin describes this arrangement using 6-inch bevel boards and an overlap between courses; the lap is the covered portion of the board. “Courses of horizontal siding should be spaced so that a single board runs continuously above and below windows and above doors without notching: Bevel siding that is 6 inches wide should have at least 1 inch of overlap between courses.” Source: USDA Forest Service, Forest Products Laboratory, read 2026-10-31.

What is exposure on lap siding?

Exposure, also called reveal, is the vertical portion of a lap-siding board left visible after the next course covers its upper edge. Board width includes that hidden overlap. As an illustration, an 8-inch board with a 1-inch overlap has 7 inches exposed. USDA’s December 1983 bulletin describes overlap of 1 to 1½ inches for wood siding at least 8 inches wide; that example is not a specification for every material. “Siding that is 8 inches or wider should overlap 1 to 1½ inches, depending on spacing required between window heights (fig. 5).” Source: USDA Forest Service, Forest Products Laboratory, read 2026-10-31.

Is lap siding waterproof?

Lap siding sheds rain, but the assembled siding should not be treated as a waterproof wall. The Rain Penetration Control Guide identifies joints and laps as entry points for rainwater. DOE’s Building America guide recommends at least a 1/16-inch drainage gap behind lap siding so water can drain; this is guidance, not a universal local-code requirement. “Rain water will penetrate the cladding at joints, laps and penetrations.” Source: Ontario Association of Architects / University of Waterloo, read 2026-10-31. “Building America recommends a gap of at least 1/16-inch behind lap siding and a drainage space of ¾ inch between stucco and plastic house wraps to control liquid-phase water penetration.” Source: U.S. Department of Energy, Building America Solution Center, read 2026-10-31.

Can you paint or stain lap siding?

Wood lap siding can take paint or stain, with the appropriate finish depending on its surface and grain. USDA’s December 1983 bulletin says edge-grained bevel siding holds paint well and favors penetrating stains for rough-sawn lumber. These wood-specific statements do not establish finish compatibility for vinyl, metal or every fiber-cement product. “Edge-grained bevel siding will hold paint well.” Source: USDA Forest Service, Forest Products Laboratory, read 2026-10-31. “Penetrating stains or preservative treatments are preferred for rough-sawn lumber.” Source: USDA Forest Service, Forest Products Laboratory, read 2026-10-31.

Sources

Wood Siding—Installing, Finishing, Maintaining (Home and Garden Bulletin 203) — USDA Forest Service, Forest Products Laboratory; published December 1983; read 2026-10-31.
Drainage Plane Behind Exterior Wall Cladding — U.S. Department of Energy, Building America Solution Center; read 2026-10-31.
Rain Penetration Control Guide — Ontario Association of Architects / University of Waterloo; read 2026-10-31.