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Wood siding materials, wood types, grades, moisture content, profile images: this article discusses choices of wood siding materials for buildings: shingles, clapboards, and wood product grades and appearance profiles. This article series discusses best practices construction details for building exteriors, including water and air barriers, building flashing products & installation, wood siding material choices & installation, vinyl siding, stucco exteriors, building trim, exterior caulks and sealants, exterior building adhesives, and choices and application of exterior finishes on buildings: paints, stains.
This article series includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons. Also see WOOD SIDING INSTALLATION and SIDING WOOD, FAILURES OVER FOAM BOARD.
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Adapted/paraphrased with permission from Best Practices Guide to Residential Construction. Steven Bliss.
Solid wood siding materials (clapboards, drop-leaf or novelty siding, wood shingles, vertical wood siding, board and batten, etc.) s have been used for hundreds of years and remain popular in many sections of the United States and other countries despite their need for regular refinishing.
Our photo of a wood clapboard-sided home (left) shows the Daniel Vose house, referred to historically as the Suffolk Resolves historic home (1774) relocated to Milton MA. (See ARCHITECTURE & BUILDING COMPONENT ID.)
In the Northeastern U.S., the most popular wood siding profile remains a simple bevel siding, or “clapboard.” In the western states, heavier profiles such as channel rustic are more common.
Plywood building siding products such as "T-111" grooved siding products installed in 4' x 8' sheets has been widely used throughout the U.S. since the 1970's.
Above left, traditional board and batten siding (Pleasant Valley, NY) traditionally used on barns. Battens are nailed over gaps between vertical board siding, taking care to nail only on one side to avoid splitting. Above right: wood clapboards installed rough-side out for a more rustic look and one that according to some, may provide better paint adhesion. See
PAINT FALURE, DIAGNOSIS, CURE, PREVENTION
Above left, 1960's vintage aluminum siding installed over pre-1900 wood clapboard siding.
Our closeup of T-111 type plywood siding (left) is provided courtesy of Carson Dunlop Associates.
At above right we show weathered plywood grooved siding (popularly called "T-111") on a 1980 constructed addition that by 2000 showed uneven weathering.
At Building Sheathing Wrap - House Wrap Installation, Purposes, Guide is a photo of this same building addition under construction twenty years previously.
Above left, Masonite-type wood product siding: hardboard. Above-right HardiePlank wood siding with some peeling stain concerns. Details are at JamesHardie HardiePlank Siding. Also see
Above left, wood shingle siding, Two Harbors MN. At above right this 1960's ranch home in New York was sided with brushed cedar shingle siding.
Wood Species Choices for Wood Siding: properties of cypress, red cedar, redwood, pine, spruce siding/shingles
Other decay-resistant woods are popular in the regions where they are produced: for example, redwood on the West Coast and cypress in the Southeast and Gulf Coast.
On projects where premium wood species are not affordable, builders also use a wide variety of softwoods, including pine and spruce, which are not naturally resistant to decay.
While most suppliers of wood siding now recommend back-priming and priming of cut ends, these details are even more critical with the less decay-resistant species.
Our photograph of brushed wood cedar shingle siding (above) on a Canadian home was provided by Carson Dunlop Associates.
Since wood siding is a nonstructural application, grading is generally for appearance only and is not governed by building codes. Most western species used for siding are graded according to one of the established grading agencies such as the Western Wood Products Association (WWPA). Still, manufacturers are free to name the grades as they choose for marketing purposes. So one company’s “Select” grade may be quite different from another’s. For this reason, it is best to examine the material before specifying or purchasing.
Western woods are generally labeled either premium or knotty grades. Premium grades have more heartwood and fewer defects and are typically kiln dried.
The highest grades of cedar are typically
Premium grades for other western woods include
In general, “sound tight knots” or “select tight knots” (STK) indicates that there are no knots that will come loose or affect the performance of the siding.
Other common designations are Select Knotty, Quality Knotty, 2 & Better Common, 3 & Better Common, and NPS (no prior selection).
Since there are no uniform standards for these designations, an inspection of the material is important.
Ideally, the siding should be installed at close to its equilibrium moisture content for the local climate (see Table 1-2 below). In general, unseasoned or green wood is shipped with a moisture content of greater than 19%. Air-dried or kiln-dried siding is shipped with a moisture content of 15 to 19%. In western woods, dry has a different meaning for premium and knotty grades.
[Click to enlarge any image]
In premium wood siding grades, dry means that the siding has no more than 15% moisture content. In knotty grades, dry means that the moisture content does not exceed 19%. Dry siding stored on the site (stickered if possible) will usually acclimate to local conditions in a week to 10 days. Unseasoned wood may need 30 days or longer to acclimate.
Images of Wood Siding Profiles: Bevel, Rabbeted Bevel, Shiplap, Tongue & Groove, Channel Rustic,Board & Batten
Because horizontal profiles naturally shed water, they resist water leakage better than vertical profiles.
Also vertical wood siding is prone to wick up moisture from the bottoms of the boards, particularly where there is snow buildup or splashback.
Diagonal siding is the most prone to leakage since water is conducted down the joints to window headers and other possible entry points. The most common profiles with typical installation details are shown in Figure 1-7 above.
[Click to enlarge any image]
-- Adapted with permission from Best Practices Guide to Residential Construction
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