Reader question: I’m about to lay hardwoods in my house and I’ve heard that you should lay them perpendicular to the windows so the light doesn’t reflect off the gaps in the boards. A friend told me that I should lay the wood across the joists and that would mean running the wood parallel to the windows. What’s the right answer? — Lisa
Lisa, good question. In our opinion, it depends on what subfloor is already sitting on top of the joists, and specifically whether its plywood or OSB.
Plywood vs. OSB Subfloor
If your subfloor is 1/2″ plywood or less, we’d run the surface wood perpendicular to the joists. If it’s 5/8″ plywood or better, we’d be less concerned which direction the wood was running but would still be inclined to run the wood across the joists. With 5/8″ plywood or thicker, the plywood itself will grip the fasteners well enough to avoid the floor from pulling up, so hitting joists periodically throughout the installation is less of an issue.
If your subfloor is oriented strand board (OSB), we’d run the wood across the joists; however, that is mostly personal preference. You probably wouldn’t have a problem running the boards either way if the OSB is 5/8″ thick or better. Originally, OSB didn’t hold hardwood fasteners quite as well as plywood did; however, newer OSB has a holding capacity similar to that of same-width plywood. With 1/2″ OSB or less, just like with plywood we’d definitely run the wood perpendicular to the joists and we’d mark the joists with lines on the surface of the OSB and ensure we were driving fasteners down into the joists as often as possible to increase the strength of the floor.
Glue and Screw Additional Plywood
If you really want to run the hardwoods perpendicular to the windows, and your floor doesn’t meet our recommend specs, you could glue and screw a half inch of plywood to the existing sub-floor. Glue using liquid nails and screw the floor down every 10-12 inches square. This costs you 1/2″ of room height and extra materials, but it is a viable alternative. If you’re dealing with an unlevel subfloor, we recommend you check out our instructions for leveling a subfloor.
Prefinished vs. Unfinished Woods
I think a major question about whether the windows issue is a problem is how smooth your floor will be and whether you’ll lay prefinished or finish-in-place floors. Prefinished floors are more likely to show gaps between the boards than finish-in-place floors, because the latter is sanded flat prior to finishing.
No matter what you do, you should eliminate squeaks on the subfloor first by screwing the floor down through the sub-floor to the joists anywhere you can hear squeaking. You should also lay red rosin paper on the subfloor before you apply the wood to eliminate squeaks caused by the subfloor and hardwood rubbing together.
If you haven’t already purchased hardwood flooring tools, follow that link for the complete list of what you’ll need. You can also read our complete instructions for installing hardwood floors.