Natural wood is an organic material, and never 100% waterproof unlike fiber cement and vinyl. Cedar wood may be exceptionally hard and dense, but prolonged exposure to moisture will eventually penetrate. When it does so the wood swells. We discuss the warning signs of cedar wood cupping in this article.
What is Wood Warping And How Does it Work?
Wood warping occurs usually across the grain, when moisture evaporates unevenly. This is the logic behind timber yard policy of letting wood ‘cure’ before processing. However, warping can still occur in flat, unsealed wood afterwards if moisture subsequently penetrates.
There are various drivers behind the warning signs of cedar wood siding cupping. These include grain orientation, evenness of airflow around it, selective exposure to sunlight, ambient temperature, and during harvesting season.
The Warning Signs Behind Timber Cupping
Cedar wood siding / cupping across the grain manifests as edges and even knots pushing outwards. This is most likely to occur after rain or sleet enters the material, causing it to expand unevenly. However, the swelling may subside following a period of dry air and sunshine.
Timber penetration may also be a response to relative air humidity. Those of us who grew up with strip wood floors may remember how gaps opened during dry seasons, but closed again after rain returned.
Applying This Theory to Cedar Wood Siding
It follows cedar wood strips may cup on their edges across the grain, when one face becomes moister than the other. The convex face curving outward at the center of the board will be the damper side. This suggests the moisture likely comes from rain or over-watering with sprinklers.
An astute homeowner can slow this process by sealing the wood thoroughly AFTER it dries out, and the cupping subsides. However, if the cupping bulges outwards at the center of the board then the moisture is on the inside the building.
1… The siding may be new wood, and processed before it dried thoroughly. In this case it follows the moisture will evaporate sooner from the outer edge and internal cupping will result.
2… Alternatively, the cedar siding may be absorbing new moisture from the inside of the building. This will probably be penetrating past a leak in the building envelope.
However, the cupping may also be the result of the side of the building being in permanent shadow, or the wall being north facing. Ask Valiant Exteriors for honest advice if you are anywhere in Calgary. We’ll get back to you soon as can!
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