MIKE HOLMES: Manufactured wood products have their uses

Hey there, time traveller!
This article was published 09/10/2010 (5449 days ago), so information in it may no longer be current.

I’M a big fan of manufactured wood products such as engineered hardwood flooring and polylaminated beams.

They are strong and straight and available in lengths and dimensions that you just can’t find in natural wood. They can be used for structure, finishing, or sheathing. They are environmentally appropriate — perfect for sustainable building.

But not all engineered wood is the same.

Plywood is an engineered wood. It’s made of layers of wood, cross-laminated for additional strength (each layer is laid at right angles to another), and fused with glues and pressure. It’s available in different thicknesses, dressed one side or both, tongue and groove — and it provides great tensile strength, so it’s perfect for sheathing.

OSB (oriented strand board) is not the same thing as plywood. OSB is made from wood strands (they look like wood chips; one of the other names for OSB is chipboard) that are arranged in alternating layers and held together with adhesives, heat and pressure.

OSB has replaced plywood in many uses in residential construction, such as roof and exterior wall sheathing, as well as for subfloors. It’s minimum code in many applications. It’s less expensive than plywood of similar thickness. It’s also not as strong, which is why I prefer to use plywood. When minimum code allows for thinner, wider-set floor joists and roof rafters, I like that extra strength to tie the structure together.

Don’t get me wrong: There are appropriate uses for OSB. It’s just not as strong as dressed solid lumber, or plywood. Some OSB is also treated to repel termites and other insects, which is a good thing. But OSB is not appropriate for exterior use, and in situations where it’s used as exterior sheathing, your contractor had better cover it quickly with house wrap and exterior sheathing; it should not be exposed to moisture.

Sapwood, such as that from young weed trees, by definition, has high moisture content. Have you seen houses going up in subdivisions with OSB sheathing that’s been left exposed, sometimes for an entire season? Streaked with black mould? There you go.

Ideally, all your wood will be kiln-dried and stored in a moisture-controlled environment before it gets to your site. Also, you want to make sure it’s kept dry on-site and once it’s put onto your home. There’s not much worse than closing up exterior walls sheathed in wet OSB. You can imagine how fast the mould will grow inside those walls.

Many engineered wood products are environmentally smart; they are made from what I call weed trees: fast-growing softwood trees in small diameter, so they aren’t valuable as dressed solid lumber. And, since the trees are processed and shredded into small bits, there’s not much waste; a lot of the tree is used. Some OSB on the market even uses wood chips from industry — post-industrial recycled content — which gives it even more points on the environmentally friendly scale.

Another manufactured wood that’s been around for years and is very popular in trim and finishing is MDF (medium density fibreboard). It’s not a structural wood, since it’s made from very fine wood fibre, unlike the bigger shreds of OSB. It’s mixed with resins and poured out into sheets, then heat and pressure is applied to make a very dense and smooth surface. MDF takes paint well and has no grain. It’s great under veneer, because it’s so smooth.

MDF also contains urea-formaldehyde and it off-gasses. Cut ends need to be sealed to reduce emissions. And when cut and sanded, it produces superfine sawdust that can cause lung damage and eye irritation. Make sure your contractor wears a respirator and saws only in a well-ventilated area.

One manufactured wood I’m a real fan of is TimberSIL. We used it on the exterior deck of the house we built in New Orleans. TimberSIL is wood-infused with glass — which makes it non-toxic and non-corrosive, and a great alternative to pressure-treated wood — and there are no chemicals to leach into the soil and water table. The liquid glass penetrates the wood and hardens, strengthening the wood fibre and keeping it straight and resistant to warping. It resists rot, is a class A fire-retardant, and insects don’t recognize the glass-permeated wood as a food source.

BluWood is another great example of a new wood product. It’s wood that’s been treated to be mould-, fire- and insect-resistant. It’s a factory-applied wood coating system that helps wood resist moisture absorption, which can lead to mould and fungus growth. The coating is also an insecticide, so it prevents termites and other bugs from eating or nesting in the wood.

The problem with a lot of these new wood products is that they aren’t that readily available around the country. And, since they aren’t as well-stocked as standard product, there are often higher shipping costs associated with bringing them onto a job.

If the industry can improve distribution and supply, more homeowners will be able to benefit. These are great products and worth the extra cost, but since they aren’t readily available, contractors don’t use them. Instead, they default to using the same old products that have been around for years — some of which just aren’t as environmentally friendly, or long-lasting, or as good.

— Postmedia News

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