Wood Siding Lasts but Requires Maintenance
The look everyone wants
In the U.S., wood siding is so iconic and evocative that whenever a new siding material is invented, be it vinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate). or fiber cement, manufacturers mold the new product to resemble traditional forms of wood siding. All types of siding require careful installation. Once painted, wood siding requires neverending maintenance.
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SHINGLES, BOARDS, AND FAKE WOOD
Installation details outrank lumber quality
Although high-quality red or white cedar lumber makes fine siding, it's useful to remember than ordinary grades of lower-quality lumber can be used for a durable siding job, as long as the house has wide roof overhangs and good installation details. All over the U.S., century-old barns proudly wear a skin of vertical barn boards that have never been painted. Barn boards are durable if they are at least a foot above grade, protected by roof overhangs, and installed with air on both sides to speed drying. The same principles can be applied to the installation of board-and-batten siding.
Wood is versatile, durable and easy to work with
It is a renewable resource, but only if harvesting (and, in dry climates, replanting) is properly managed. If installation methods allow wood siding to dry out, it can last for a long time, even in harsh environments. Although fine details demand skilled craftsmanship, most types of wood siding are reasonably simple to install.
Wood is trumps for design versatility
It can be used to produce many patterns and textures (although they are typically striated) from fine to coarse. Most wood siding is made from boards or shingles, but some (like T-111) is made from plywood textured to simulate boards. Plywood siding demands close attention to water-management detailing at joints. Shingles and shakes are commonly made from naturally rot-resistant woods like cedar. They perform well with minimal or no finish — a low-maintenance siding with no harmful chemicals.
Installation methods are important
Clapboards and shingles shed water well: Their lap joints encourage any water that gets in to move down and out. Sheets and vertical boards need extra attention to work this well. They typically use flashing, battens, or tongue-and-groove joints to address water infiltration. Vertical board siding paired with conventional (vertical) wood framing creates a resource-efficiency dilemma – an additional (horizontal) layer of wood is required to provide a nailing surface for the siding.
Rainscreens are unfamiliar to some, but they increase the life of siding
Perhaps the most important way to increase the service life of wood siding materials and paint jobs is through back-vented (rainscreen) installation details. This can be done with furring strips or spacer mesh. Rainscreen installations are particularly important in areas that experience more than 20 inches of precipitation annually.
Most types of horizontal wood siding should be fastened to studs, not sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. alone. Secure nailing of some types of siding may require studs to be spaced 16 inches on center rather than 24 inches.
Proper installation makes all the difference
Sections 703.3 and 703.5 of the International Residential Code (IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code.) relate to wood and hardboard siding. All code references are to the IRC unless otherwise specified.
Installation methods play a big part in the durability of wood siding and the layers beneath it. With panel siding, vertical joints need to be nailed into solid framing or structural sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. , and they need to be shiplapped or covered with battens [703.3.1]. Horizontal joints require Z-flashing, shiplapping or a 1-inch lap. Clapboards or similar lap siding need the same 1-inch horizontal joint, but caulking is acceptable at the end joints [703.3.2] (although sealants won't likely last as long as flashing or corner boards). All wood siding fasteners should be corrosion resistant [703.4], and if used with shakes and shingles, they need to be concealed by the above course [703.5.3.1]. Although furring strips are only mandated where shingles and shakes cover nonstructural sheathing [703.5.1], they create an air space that would help any wood siding stay dry.
ABOUT WOOD SIDING
A natural and traditional choice
Nothing has a longer history as a building material in the United States than wood. It has many advantages when used as siding, but its few drawbacks have pushed many builders and homeowners toward other materials, some of which are manufactured to look like wood.
On the plus side, wood is easy to cut and shape, doesn’t require exotic tooling, doesn’t emit noxious dust or fumes, and is adaptable to many house styles. Wood is a natural product that requires minimal manufacturing before use.
Time to get out the ladder and paintbrush
Wood also has three major drawbacks. The first is maintenance. Some grades and cuts of wood are much more durable than others, but, all wood siding, with the possible exception of cedar shingles, lasts longer when it’s regularly treated with preservative or paint.
A second issue is resource use: The best grades of wood siding may come from clear-cuts of old-growth forests. Specifying siding that has been certified by the Forest Stewardship Council(FSC) Nonprofit organization that promotes forestry practices that are sustainable from environmental and social standpoints; FSC certification on a wood product is an indicator that the wood came from a well-managed forest. (FSCNonprofit organization that promotes forestry practices that are sustainable from environmental and social standpoints; FSC certification on a wood product is an indicator that the wood came from a well-managed forest.) is a way around the problem, but it isn’t always easy to find and may be more expensive.
The third downside is the price: The best grades of wood are very expensive.
ABOUT WOOD SIDING TYPES
Shingles. Shingles are sawn from either western red cedar or eastern white cedar; preference varies regionally, and lengths and grading rules differ between the two. The best shingles of either species are all clear heartwood, which is extremely durable but expensive. Installation costs also are high. Heartwood is naturally resistant to insects and decay, but the sapwood sometimes found in lower grades is not. Some grades also may contain knots above or even below the weather line, which may reduce life expectancy. Two more expensive options, rebutted and rejointed shingles (called R&Rs) and shingles in panelized form, go up faster, reducing installation costs. Some manufacturers dip shingles in preservative or primer before they are shipped, which saves time on the job site and may extend shingle life. Split or sawn shakes have a rougher surface texture and are thicker than shingles. Shingles and shakes are sometimes left unfinished.
Horizontal and vertical boards. Boards are cut from several species of softwood, including cedar, redwood, spruce, and pine. Siding is manufactured in several styles, such as beveled (clapboards), tongue-and-groove, and rabbeted planks. The best grades are clear, all-heart vertical grain in which annual growth rings are perpendicular to the face of the board.
Vertical grain siding is more dimensionally stable than flat-sawn, holds finish better, and will last longer.
The same cautions about sapwood in shingles apply to horizontal siding. The most blemish-free grades of siding, especially cedar and redwood, are expensive but extremely durable. Labor costs for installing horizontal and vertical siding are lower than for shingles. Back-priming and coating end cuts will extend life.
Engineered products. Despite some notable early failures and a spate of class-action lawsuits, engineered siding has rebounded with new product offerings. Engineered siding is made from wood fibers, resins, and other additives and is manufactured to mimic other materials, such as cedar or stucco. Prefinished planks and panels reduce installation costs. Engineered siding costs less than solid wood siding and shingles, and because it can make use of fast-growing, low-value trees, it’s attractive from the resource conservation side. Prorated warranties extend as long as 50 years. Time will tell how a new generation of these products holds up.
Finger-jointed siding is another type of engineered product. Short lengths of clear lumber are glued together to form standard lengths, making good use of material that would otherwise be wasted. Joints between boards, however, can telegraph through the paint and in some cases have failed.
DETAILING A VENTED RAIN SCREEN
Detailing the bottom of a vented rain screen wall is easy: use mesh to keep out insects. But how do you let the moisture escape at the top?
This was shot at GreenBuildingAdvbisor.com's booth at the 2009 International Builder Show in Las Vegas.
- Dan Thornton/Fine Homebuilding #177
- Krysta S. Doerfler/Fine Homebuilding #197
- Brian Pontolilo/Fine Homebuilding #187
- Dan Thornton / Fine Homebuilding #197