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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.
Solid wood siding materials (clapboards, drop-leaf or novelty siding, wood shingles, vertical wood siding, board and batten, etc.) 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.
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 left, 1960's vintage aluminum siding installed over pre-1900 wood clapboard siding in a New York Home in the U.S.
At above right [click to enlarge] is an interesting use of wood clapboards on an antique barn in Herefordshire, England in the U.K. These clapboards are nailed to the interior side of vertical rough-hewn barn beams supporting the wall structure. You can see that the original barn was expanded on its right side using concrete blocks.
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
Red cedar remains the wood siding material of choice due
to the natural decay resistance of the heartwood and its attractive
appearance when stained or finished clear.
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.
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.
Grading Methods for Wood Siding Products
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
Premium Grades of Wood Siding
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
Knotty Grades of Wood Siding
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
Moisture Content Targets for Wood Siding on buildings
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]
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
Because horizontal profiles naturally
shed water, they resist water leakage better than vertical
Also vertical wood siding is prone to wick up
moisture from the bottoms of the boards, particularly
where there is snow buildup or splashback.
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.
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