Restoration Guide: Engineered Wood Siding for Exterior Walls

Editor's Note: This is article 12 of 18 in Chapter 2: Exterior Wall Guide of the Old House Web Restoration Guide. This guide was developed and edited for old homes from original material in the U.S. Housing and Urban Development (HUD) Rehab Guide.

12. ENGINEERED WOOD SIDING

Section 1--Overview

Rising lumber prices in the mid 1980s had manufacturers looking into alternative siding solutions, and one of the first engineered wood siding products was introduced by Louisiana-Pacific as a cost-effective replacement for conventional wood siding. It proved popular with builders, but defects became commonplace, especially in the hot, humid climate of the Southeastern U.S. or the extremely wet climate of the Pacific Northwest.

The first types of engineered wood siding were made like oriented strand board (OSB) plywood and had the same problem as OSB: excessive swelling at the edges of the material, especially if they weren't properly sealed. The original OSB siding also was prone to rot, fungus, and insect infestation, which in turn led to degradation of the underlying structural sheathing--and also led to class-action lawsuits being filed against Louisiana-Pacific and Georgia-Pacific.

The composition and manufacture of engineered wood siding changed as a result, and the products offered today are generally considered as effective as regular wood siding products. Changes from manufacturers such as Louisiana-Pacific include:

• Adding a more water-resistant and stronger bonding agent that better withstands swelling and expansion
• Adding powdered zinc borate to the manufacturing process to help reduce or eliminate rot, fungus growth, and damage from insects
• Adding a pre-finished, resin-saturated paper that is fused to the wood substrate to provide a higher degree of weatherproofing for the siding face
• Adding a sealing treatment to all edges and at the ends of boards
• Pre-priming the siding with an all-acrylic primer

The newest versions of engineered wood siding, such as Louisiana-Pacific's Lap-Smart siding, offer warranties of 25 years or more against degradation by fungus and problems caused by cracking, peeling, separation, flaking, or rupturing of the resin-impregnated overlay.

Engineered wood siding does need to be repainted often in order to keep water and other environmental elements from seeping into the material.

Section 2--Replacing Damaged Siding with Engineered Wood Siding

If you are doing a home renovation on an old house with the original OSB engineered siding, it's likely there are areas of rot and decay in the siding. Newer versions of engineered wood siding, such as Louisiana-Pacific's Lap-Smart siding, can be installed directly to studs without shear panel plywood. An appropriate vapor barrier must be used; refer to section 5 of the Old House Web Exterior Walls chapter for more on vapor retarders.

Engineered wood siding also can be applied over sheathing or to masonry walls with the use of furring strips attached to the walls to provide a nailing surface.

Damaged sections of the original siding should be cut out and replaced with new Lap-Smart siding. Louisiana-Pacific has maintained relatively similar grain patterns, so patches should match existing siding fairly closely. A small hand held trim saw, such as the Makita three and three-eighths of an inch cordless circular saw, are perfect for cutting out small sections of damaged siding.

Section 3--Replacing Damaged Siding Using Engineered Wood Siding Panels

Engineered panel siding is made in a wide range of patterns that simulate vertical grooved plywood siding. To increase cost effectiveness, this siding can eliminate the need for additional exterior sheathing, but it can be applied over existing sheathing as well. It also can be laid over existing wall cladding materials that have a flush surface face and over masonry walls with the addition of furring strips attached to the wall to provide a mounting surface.

Like all exterior siding products, you must use a corrosion-proof nail for attachment. Hot-dipped galvanized 8-penny nails, which are bathed in molten zinc, probably offer the highest level of rust resistance.

A note of caution: In all siding applications, including exterior sheathing, nail heads should not penetrate the wood. Rather, they should be flush with the exterior skin of the siding or sheathing. With engineered wood siding, it is extremely important that nail heads do not penetrate the surface of the material. Nails that break the skin of the siding can compromise the integrity of this specially designed product. If using a pneumatic nail gun, adjust the flush-mount feature of the gun to make sure nail heads protrude from the siding, and snug them up with a hammer. Nails that do penetrate the surface of engineered wood siding need to be caulked.

Special care also must be taken with horizontal trim pieces. It is recommended that you add flashing behind interior and outside corner trim to prevent moisture buildup.

Before using engineered wood siding during a home renovation, consult with a building professional or the manufacturer about special installation guidelines in order to ensure product life and warranty specifications.