As wood products have become more and more expensive the search for a viable inexpensive alternative has intensified. In the world of siding real wood is still hard to beat. Real wood sheds liquid water and allows water vapor to effectively come and go. Solid wood is really a fantastic siding material but it is expensive so creative companies have been trying to develop a product that could be made from wood by-product (wood chips and fiber).
Wood chip siding has been around for many years but in the late 80’s and early 90’s a certain type of OSB (Oriented Strand Board) siding really became popular around Salem, Oregon and the Pacific Northwest. The type that really had issues was the lap type made by Louisiana Pacific (LP). This product had an adhesive that did not resist moisture effectively, and because proper sealing with primer and paint and continued home owner maintenance cannot be counted upon, the siding began to absorb moisture very quickly and began to deteriorate (grow mushrooms/fall apart).
LP went back to the drawing board, made some adjustments and continued to produce a very similar “wood chip” lap siding. The adjustments were made to the sealing process. They primed the entire board at the factory not just the front face, and they put a bevel on the drip edge of the siding that would help water drip off instead of being absorbed.
Wood chip siding also comes in panel form and although it is a similar product to the lap siding it doesn’t have as high of a percentage of vulnerable areas. With the lap siding the bottom drip edge and all the other edges (only the front face is really the only durable side) are vulnerable and should be actively sealed/maintained with primer
and paint. The panel boards come in 4’x8′ sheets and again only the edges are vulnerable but the damage resistant surfaces (again the front face) are much larger per piece. The panels edges still need to be sealed actively.
One of the most common mistakes I see on home inspections around Salem, Oregon is the very bottom edge of the siding not getting painted. Of course I carry a mirror that makes it easier for me to see that bottom edge that is only 8″ off the ground, but even with out fancy home inspector g ear you can get down on your knees and make sure this most vulnerable of areas gets sealed. Both panel and lap siding have this issue and usually from waste down is where the lap goes bad and the very botto m is where the panel siding doesn’t get painted and begins to fail.
Now what is “failure/deterioration/dry rot?” In one of my earlier posts I wrote about “dry rot,” and why I do not use that term. I prefer to use the term deterioration and basically that refers to a level of hardness or lack-of-hardness. A good rule of thumb is: “If you poke it with your finger does it flex easily?” or (and if you are looking to buy a home that is not yours yet please leave this method to the professional home inspector) “Will a screwdriver/awl/knife point penetrate easily?” If the answer is “yes” to either of those questions then the siding will not be able to sufficiently hold on to primer/paint and therefore it will not be able to shed water effectively and will continue to deteriorate and possibly begin to allow deterioration of related areas of the home (wall structure).
Some of the composite (wood chip/particle) sidings begin to swell when the paint is failing and allowing water to be absorbed. Sometimes this swelling can be stifled with prudent and active painting. But again the siding has got to be “hard” still. If it flexes it will not be able to hold on to the paint that will prevent further moisture absorption and will need to be replaced.
As the siding products have evolved, there have been good and not so good products. The siding’s job is to shed water while allowing water vapor to come and go. This job must be achieved while striving for low cost, durability, and ease of installation. The “wood chip,” siding met a few of those needs, low cost and ease of installation, while suffering in the durability aspect. However with knowledge of this type of siding’s vulnerabilities and active/aggressive maintenance it can be a lasting and effective siding system.
Jim Allhiser President/Inspector