Wood siding installation & product guide:
This article provides details for proper installation of wood building siding materials. 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.
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While the premium grades of siding are more forgiving of installation and finishing problems than budget materials, all wood siding requires attention to detail to provide a durable and attractive exterior. Critical details are backpriming, air space, nailing, and finishing.
An air space behind the siding, in addition to protecting the building shell (see “Rain-Screen Principle,” page 2), also improves the performance of wood sidings. The siding material is less prone to moisture movement and paint is less likely to fail, even if the space is only 1/4 inch wide.
While the vast majority of wood siding is installed directly on the sheathing wrap, builders who have had problems with paint and siding have found that adding an air space is worth the additional cost. New products— such as wrinkled and corrugated sheathing wraps with an integral air space, and behind-the-wall drainage mats such as Benjamin Obdyke’s Home Slicker®—are simplifying this step.
The major trade associations representing siding manufacturers all recommend back-priming and priming of cut ends. With cedar and redwood, backpriming will minimize the bleeding of extractives from the back of the siding, which can drip onto the face of the siding and stain the finish, and can also degrade sheathing wraps. With all sidings, back-priming will reduce the movement of moisture into and out of the siding, minimizing problems with cupping, warping, and checking.
The need for back-priming and a ventilation air space is even greater when installing over foam sheathing. With no air space and no wood sheathing to temporarily store the moisture, any water that leaks through the siding or is driven in by the sun will tend to wet the back of the siding. The result, documented in a joint study conducted by wood siding and foam manufacturers, is increased cupping, cracking, and paint problems.
Plywood sidings are typically nailed directly to studs or through a layer of foam, and they provide a structural sheathing as well as an exterior finish. Most have vertical grooves to imitate vertical sidings.
All plywood sidings should be painted or stained to protect the outer facing and prevent the panels from delaminating over time. Vertical joints are typically hidden by the vertical grooves in the pattern.
Horizontal joints must be protected by a Z flashing to shed water (Figure 1-8 at left).
Nailing requirements are shown in Table 1-3 below. In general, nails should penetrate the sheathing and studs or blocking by 1-1/2 inches, or 1-1/4 inches with ringshank or spiral-shank nails. Although specialized siding nails with small heads and blunt tips are preferred, staples are acceptable for some applications.
Since the cost of fasteners is a small percentage of a siding job, it makes sense to use stainless steel, particularly with cedar and redwood, which can react with some types of fasteners. The most common fastener choices are as follows:
Stainless steel siding nails are the best choice with all sidings, but these are particularly well suited to redwood and cedar, which react with some types of nails (galvanized and copper) and cause dark stains (see Figure 1-9 at left).
Ring-shanked or spiral-shanked siding nails can be set flush and painted over or countersunk and puttied before painting.
These are corrosion resistant and can be used with all wood sidings. However, the aluminum can react with galvanized steel flashing and cause corrosion Hot-dipped galvanized. These can react with the tannins in cedar and redwood, causing black stains and streaking. Also the protective coating can chip when nailed, exposing the underlying steel to corrosion.
These are not recommended for any siding application since the coating is not thick enough and they are likely to corrode and stain the siding.
Both the 2003 International Building Code (IBC) and the Western Wood Products Association require that solid wood siding products be nailed directly into studs or 2x blocking.
Ring-shank nails should penetrate 1-1/4 inches into wood (combined sheathing and stud) and smooth-shank nails 1-1/2 inches.
With high-quality, dry, dimensionally stable siding materials such as kiln-dried redwood and red cedar clapboards, some contractors nail siding directly to nominal 1/2-inch nail-base sheathings, such as OSB and plywood, using ring-shank nails.
Check with local codes before taking this approach. To avoid problems, make sure joints fall on studs or solid blocking (see Figure 1-10 at left).
Nailing spacing for horizontal wood siding (such as clapboards) should be maximum 24 inches on-center when over nail-based sheathing and 16 inches on-center over nonstructural sheathings. Trade associations such as the Western Wood Products Association recommend against “double nailing” for most horizontal wood-siding profiles, including bevel siding.
That is, nails should be driven above the overlap line of the siding board below to reduce the risk of cracking. Despite this recommendation, many contractors nail 1/2-inch-thick clapboards just below the overlap line, catching the top edge of the piece below to avoid cracking the siding during installation.
While this approach may be acceptable with dry, premium-grade siding, it will likely lead to problems with lower quality materials (Figure 1-11 at left).
In general, vertical sidings are nailed to the top and bottom plates and to horizontal nailers installed every 36 inches for face-nailed siding and every 32 inches when blind-nailed. Because vertical sidings are vulnerable to leakage, they are not recommended for areas subject to wind-blown rain.
Plywood siding is often nailed directly to studs or through an insulating sheathing and serves as a structural sheathing as well as the exterior finish. Use 6d box, siding, or casing nails for nominal 1/2-inch plywood siding nailed directly to studs. For nail spacings, see Table 1-4 below.
-- Adapted with permission from Best Practices Guide to Residential Construction.
After some research of Dupont Tyvek, Western Red Cedar Association, and your articles on Wood Shingled siding and Wood Siding installation I have developed the following case questions for your response:
Home owner is considering:
Home is located in central Connecticut.
Again, thank you in advance.
Respectfully, - Anonymous [by private email to the Editor, 2015/12/01
I’ve taken a closer look at the question of why unprimed red cedar lap siding may show a subsequent coating failure.
It’s always difficult to say why paint failed as so many factors affect the success of a paint job. It’s sometimes difficult even if you visit the job – but from a distance like this, I don’t think it is possible. There are a lot of missing facts here. For example here are some cedar siding paint failure diagnostic questions:
In general, all cedar should be primed before painting. On a repaint, any loose paint must be scraped off and any bare wood spot primed. With a lot of bare wood, it’s probably best to prime the whole wall. Also prime all surfaces if the existing paint is in poor condition. Before priming and painting, it’s always a good idea to wash the walls with a low-pressure washer, and a brush if necessary. Then wait a few days for the wall surface to dry before painting.
If the walls, or portions of them have never held paint well, there’s a good chance that moisture passing through the wall is at least partly to blame. Painting over such sections without fixing the moisture problem will usually just lead to additional paint peeling.
Regarding the two options:
A drainage gap can be created by installing the siding over vertical strips of furring, plywood, or other suitable materials. But the easier and cheaper way to achieve this is to use a venting housewrap. There are “wrinkled” housewraps that provide a gap of a couple of mm, but researchers have determined that the gap should be min. 3/16 in. to allow any air flow. I know of two products, Home Slicker and MTI Sure Cavity that can achieve this:
Excerpt from Rain-Screen Walls at BuildingAdvisor.Com
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Plastic drainage mats. Where you’re looking for the protection of a rain screen, but don’t want to cost and hassle of furring out the siding, consider one of the new plastic drainage mats available for sidewalls. Two well established products are Benjamin Obdyke’s Home Slicker 6 and MTI’s Sure Cavity SC 50. These products create a 6mm (1/4 in.) gap between the siding and housewrap (water-resistive barrier in Code-Speak).
Home Slicker is also available laminated to the housewrap Typar for a one-step installation. Both drainage mats are strong and rigid enough to resist compression by the siding but thin enough that windows, doors, and trim can be installed without shimming or furring. A thicker version (10mm) of each product is available that complies with Canadian code.
When using a rain-screen, it’s important to allow for ventilation at the top and bottom of the rain screen – and that these outlets are blocked with sceening to keep out insects.
If you are looking at other options (question 4), I would consider fiber-cement siding. Go with a name-brand product such as Hardiplank. If installed and finished correctly, this can provide years of good performance with very low maintenance. However it is not foolproof – proper nailing to manufacturer’s specs is critical along with proper handling of butt joints in the siding and joints to abutting materials. The ends of boards, especially cut ends, can soak up water and swell if not properly detailed.
Please also see these relevant InspectApedia.com articles:
See EXTRACTIVE BLEEDING SIDING STAINS for more about extractive bleeding stains on wood siding.
Also see the following articles that provide in-depth field and laboratory analysis of paint & coating failures on and in buildings.
Continue reading at SIDING WOOD, FLASHING DETAILS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
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