Composite Wood Decking and Siding: Observations from Your Home Inspector

In our previous blog post, we took a hard look at wood rot—one of the more common and costly problems that can affect wood structures in a home, from siding to door trim, window framing to cabinetry and decking. Today we turn our focus to composite wood, another popular choice in home construction that has its advantages but isn’t immune to defects that will catch the eye of certified home inspectors like those at A-Pro Home Inspection.

What exactly is composite wood? Like its name asserts, this building option is a composite, or mixture, of heated and compressed materials bound together through the use of adhesives. Types of materials added to wood waste products such as sawdust and chips may include various plastics, resins, or even vegetable-based fibers (e.g., straw). Composite wood has a variety of applications. Among them are siding, flooring, decking, sheathing, cabinetry, window and door frames, or rafters, beams, and joints when laminated timber is employed. For aesthetic appeal, the material may be covered in a veneer.

Advantages may include greater durability over other materials; many choices in terms of shapes, sizes, textures, and colors that can emulate the look of wood; resistance to rot and insect damage (it can come chemically treated to thwart bugs and fungi); less maintenance that can translate into savings over its usable life; the ability to hide fasteners (depending on the manufacturer); and reduced environmental impact since it’s made from scrap wood/wood waste that would have otherwise been discarded or, in some cases, smaller trees or recycled products (plastic grocery bags, for example). Its footprint in this regard, however, may be balanced out by the amount of energy required to manufacture the product.

Disadvantages may include plastics that present a greater fire hazard than solid wood; some toxicity issues with lower-quality options; possible difficulty in finding the exact matching pieces when repairing a deck, for example; heavier boards in some cases, but generally a bit less strong, requiring additional supports in a deck; fading from UV exposure; scratches that can’t be sanded out like they can with solid wood; and mold and algae staining on decking that can’t be removed easily because resurfacing is not an option.

In older homes, inspectors may still find early versions of composite wood siding that were highly prone to moisture damage and the subject of class-action lawsuits from disgruntled homeowners.

The bottom line from the home inspector’s perspective? Read a hundred blog posts on the subject and you’ll get a range of vastly opposing opinions on composite wood used for siding and decking. Those who deal in natural lumber products may tell you it’s the devil. On the other side, those who manufacture and sell composite wood for decking and siding may tell you it’s a flawless gift from heaven. It’s the home inspector’s job to look beyond the clamor of opinions, observe the wood composite structures on a home, and render an unbiased view of what they see.

Here are some of the issues with composite wood that have been observed by the home inspectors at A-Pro over the last 27 years:

Composite Wood Siding:

The quality and characteristics of wood composite siding can vary widely from manufacturer to manufacturer. Like regular wood siding, composite wood lap, vertical, and shingle siding face the same primary nemesis—water. Impact damage, hail, or sun exposure that damages a surface, for example, may allow water penetration that can cause deterioration of the boards and moisture damage to the materials behind them.

Installation that does not adhere to manufacturer guidelines can allow moisture penetration that is often at the heart of potential defects (swelling, warping, etc.). Common installation missteps for certain types of wood composites include the use of non-recommended nails; under-driven or over-driven fasteners; failure to properly seal and paint for water resistance (some products don’t require additional sealing); lack of proper clearance between the ground and roof; and installing adjacent boards without a space between them, which can lead to buckling because there is no allowance for butt-joint expansion. Water that has gotten behind the siding due to poor installation, impact damage, or weathering issues can spur the proliferation of organisms that cause decay, which will be noted in the report when visible. When maintaining composite wood siding, it’s important to be vigilant about tasks such as checking window and door trim to see if caulking needs to be replaced.

Deck Flooring/Railings/Guard Rails: While composite wood for decking generally is less prone to splintering or cracking, your inspector may find sagging or warping due to thermal expansion. Further, poor installation practices such as not leaving adequate spacing between boards and walls can lead to buckling. This will be noted in the report if these conditions pose a tripping hazard. Lack of proper drainage in a composite wood deck system can result in water being trapped under boards, leading to rotting of wood joists below. While color-faded or stained deck flooring may be aesthetically unappealing to a potential buyer, this will be viewed as a cosmetic issue by the home inspector. Your inspector will also look for sagging or bending of composite wood hand rails and guard rails that can result from improper installation (not putting recommended support under the bottom rail).

Checking for defects in composite wood is part of A-Pro’s 500-point home inspection. Ask your local A-Pro Home Inspection team about its complete foundation-to-roof inspection in Boulder. To schedule one, call 1-720-438-4595 or visit the link below.

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