Is it worth staining the underside of my raised deck or just the top surface?

Staining the underside of a raised deck is worth serious consideration in Metro Vancouver, where persistent moisture from below is a real threat to your deck's longevity. While many homeowners skip it to save money, the underside is actually more vulnerable to moisture damage in our climate than the top surface.

Here is why: during our long rainy season from October through April, moisture rises from the ground and condensation forms on the underside of deck boards. Without any protective coating, this moisture is absorbed directly into the raw wood, leading to cupping, warping, and eventual rot — often before you notice any problems on the walking surface above. Cedar resists rot better than most species, but even BC cedar has its limits when exposed to constant dampness.

At minimum, the underside should receive one coat of a penetrating water repellent or semi-transparent stain. This does not need to look perfect since no one sees it — the goal is purely moisture protection. Some professionals recommend a clear wood preservative rather than a tinted stain for the underside, which costs less and still provides excellent protection.

The cost to stain the underside adds roughly 30 to 40 percent to your overall deck staining project, but it can significantly extend the life of your boards. For a 300-square-foot raised deck, expect an additional $400 to $900 depending on the deck height and accessibility. Given that replacing decking boards in Vancouver runs $15 to $30 per square foot installed, the preventative investment pays for itself.

Ask your staining contractor about underside treatment options when you get your next deck staining quote — most offer it as an add-on service.

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