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Building With Wet Plywood and OSB

DEAR TIM: I'm having a new house built. Six weeks ago my builder put in the floor joists and the wood subfloor. Immediately after the subfloor was installed, he framed the walls. Then work stopped and he has not done anything since. The idiot builder forgot to order the roof trusses. Since the work stoppage the house has experienced six major rains. Are the wood walls, flooring and subfloor ruined? The builder said he will sand the oriented strand board (OSB) down to make it even again. I'm getting oak flooring installed over this junk wood. Will the oak flooring be fine over the OSB? Thanks Richard Sparks

DEAR RICHARD: I am at a little disadvantage since I can't see the wood. But ninety-five percent of all exterior plywood and oriented strand board (OSB), that carries the American Plywood Association (APA) trademark, comes from the factories with a durability classification of Exposure 1. This means that the glues used to bond the wood plys, or the wood strands, to each other is 100 percent waterproof.

Products carrying the Exposure 1 stamp are designed so that minimal damage will occur during normal construction activity. It is possible to build with waterproof lumber and this is often done in the Southeast to prevent termite damage. But it is not a common practice to build with treated lumber for the few times wood might get wet as a house is built.

The water will do no damage to the wood wall studs and floor joists unless they are in constant contact with the water for long periods of time. The water can ignite an explosive growth of mold on the wood surfaces, but this can be cleaned off once the house is under roof and the threat of water contact is minimized.

The builder needs to get the roof on as soon as possible and then let the house air out. Once the moisture content of the lumber is down near 12 percent, see how the subfloor feels to walk on. If it is spongy, then perhaps it will need to be replaced.

The OSB panels can feel rough and still maintain all of their structural integrity. It is a good idea to sand the OSB to get it fairly smooth before the finished flooring is installed.

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3 Responses to Building With Wet Plywood and OSB

  1. What chemicals are in OSB and waterproof OSB? I am building an art studio. Can these chemicals make me sick, Also I have a high wind situation and will have electric inside. Should the OSB be coveted with something so that wind will not drive rain through the vinyl siding? Thanks

  2. we are having a new house built and a few floor boards are warped.
    The builder tells me they can be sanded down before the floor is installed. Should they be replaced instead?

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