Raised Board
Photo:: Jorn Tomter
Here's a swell problem: Every winter, the decking on this porch buckles severely. Norm Abram explains why, and how to fix it.
Q: Two years ago, a carpenter replaced all the old deck boards on our front porch with 1x4 tongue-and-groove fir graded "D & BTR Mix-grain." They were then primed and painted. Now every winter the floor buckles, and in the spring it flattens out again. What went wrong—and how can I fix it?

David Popp, Moline, IlL.

A: Norm Abram replies: There could be a number of things wrong here, but they basically all come down to too much moisture on the wood. Are the gutters working so that no water is splashing on the deck? Is it pitched properly—at least inch per foot—so water drains off? Are the plantings around the porch choking off air circulation under the deck? Any of these things could cause the wood to swell and expand in width.

The grade of wood isn't helping things, either. "D" is a second-tier, "appearance" grade, which means that most of the boards are flat-grained, with tree rings nearly parallel to the board face. Flat-grain boards expand and contract more than vertical-grain wood, which has rings nearly perpendicular to the face. To make matters worse, all that swelling wood is pushing against your porch piers and your house without anywhere to go. Buckling is the inevitable result.

Here's the fix: Pull up the boards, prime all their edges and bottom faces if they aren't primed already, and fasten them with stainless-steel nails through the tongues and into the joists. Don't forget to leave a 3/8- to ½-inch expansion gap where the side of the decking meets the house or the piers.

What puzzles me most about your photos is that I don't see any nails where the flooring has buckled. If there aren't any, it would explain how the decking can settle back in place each spring. It will also make it really easy for you to replace the boards.

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