Plywood siding installation details (C) Wiley and Sons - S Bliss Guide to Installing Wood Wall Siding Products

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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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Installation Details - Guide for Wood Siding

This article series includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons. Also see FLASHING WALL DETAILS and FLASHING ROOF WALL DETAILS and also RAIN SPLASH-UP SIDING DAMAGE.

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.

Drainage Details for Wood Building Siding

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.

Back-Priming Suggestions for Wood Siding

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.

Advice for Installing Wood Siding Over Foam

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 Siding Installation Details

Plywood siding installation details (C) Wiley and Sons - S Bliss

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).

Fastener Types for Various Building Siding Materials

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.

Table of nailing recommendations for wood siding (C) Wiley and Sons - S Bliss

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 Nails for Building Siding

Figure 1-9 Siding stains due to nailing (C) Wiley and Sons - S Bliss


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.

High-strength Aluminum Siding Nails

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.

Electrogalvanized Siding Nails - not recommended

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.

Nailing Schedule for Building Siding Materials

Figure 1-10 - Siding Joints

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).

Nail Choices & Nail Spacing for Horizontal Siding

Figure 1-11 Double Nailing (C) Wiley and Sons - S Bliss

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).

Vertical Siding Nailing Patterns & Spacing Guide

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 Building Siding Nailing Pattern & Nail Spacing Guide

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.

Table 1-4: Nailing Schedule for Plywood Siding (C) Wiley and Sons - S Bliss

-- Adapted with permission from Best Practices Guide to Residential Construction.


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