Q. Why are my wide-board pine floors shrinking and warping?

A.There are many reasons wide planks will shrink, cup, and twist. A lot depends on how the lumber grew. But the most important factor that we can control is the moisture content of the planks.

The floor boards will shrink if their moisture content was high at installation. After the house has been occupied for a heating season, the boards will dry and contract. In most houses in cold climates, the final moisture content of wood is 9% to 11%. If the moisture content at installation is more than 13%, significant shrinkage is likely. In the old days, flooring was always "conditioned" by storing it, stacked and stickered, in the house for 30 to 60 days before it was laid. This allowed the moisture content of the flooring to equalize with the rest of the house. Nowadays, you can measure the moisture content with a moisture meter to see if it’s safe to lay the floor. If the moisture levels are high, you’ll have to condition the wood.

As for warping, wet wood will warp as it dries, particularly if it is flat sawn. Since most of the pine cut these days is from smaller, second-growth timber, the likelihood of it being flat sawn or flat grained is high. Edge-grain (quarter-sawn) boards will warp less, but cost a lot more.

Moisture from below the floor, such as from a damp crawlspace or basement, can also cause the boards to cup and twist. The only cure in this case is to install a vapor barrier over the damp areas.