Lay Hardwood Floors Parallel or Perpendicular Across Joists
Reader question: I’m about to lay hardwoods in my house and I’ve heard that you should lay them perpendicular to 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?
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 it’s 5/8″ plywood or less, we’d run the wood perpendicular to the joists. If it’s 3/4″ plywood or more, we’d be less concerned which direction the wood was running but would still be inclined to run the wood across the joists. With 3/4″ plywood, the plywood itself will likely grip the fasteners well enough to avoid the floor from pulling up.
If it’s any type of oriented strand board (OSB), we’d only run the wood across the joists. OSB doesn’t hold hardwood fasteners as well as plywood does; so picking up a joist periodically will be good. With 1/2″ OSB, 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 isn’t 3/4″ plywood, 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.
Prefinished vs. Unfinished Woods
I think a major question about whether the windows issue is a problem is how smooth your floor is 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.
(photo: pdz_house)
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6 Responses to Lay Hardwood Floors Parallel or Perpendicular Across Joists
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February 25th, 2010 7:16 am
Fred,
I’m going to disagree a bit here. The differences between plywood and OSB really are nill in my experience and also the flooring guys that work for us. The real question is the thickness/strength of the sub-floor. I agree that if you have less than 3/4″ of you should definitely run the flooring perpendicular to the joists (or at a 45 degree angle). However, if you have 3/4″ plywood or OSB you can change the direction.
Most flooring installers will lay the flooring parallel to the long length of the room to avoid the “ladder” affect.
OSB gets a bad rap when in fact it’s a good product so long as it doesn’t get wet. In fact, most all OSB products meet or exceed ratings that make it a structural rated panel. Today most new homes that we build use the AdvanTech OSB product and it works great under wood flooring.
February 25th, 2010 9:41 am
Todd, interesting to hear another perspective. This is information I received when I installed floors in my first house from a hardwood installer online.
The information I’ve found online today is varied, esp. in terms of what NWFA will support. As I understand the guidance, they want wood floor always installed 90deg. to the joists, even on a 3/4″ nailing surface. They do say that 3/4″ OSB is an OK subfloor for nailing 3/4″ hardwoods.
So, another factor to consider here is whether our reader is laying 3/4 hardwoods or thinner, in which case guidance might change.
February 25th, 2010 2:26 pm
Thanks for the great information. We will certainly consider it when we lay our new floors.
February 27th, 2010 3:12 pm
If you have an older house, with a shiplap floor, the shiplap is perpendicular to the joists, so the flooring is parallel to the joists. Some houses have the shiplap on a 45. I guess you wouldn’t have to lay it parallel, but the shiplap has a lot more movement then plywood or osb.
May 4th, 2010 12:10 pm
I have a two rooms in a open concept front part of my house. The joists in both of there room are in two directions. So picking which way to run the hardwood is difficult.
Another thing there are stairs as well, so to add 1/2″ underlayment will bring my floor high over the nosing and railing nosing.
My sub-floor is 5/8″ plywood, is it OK to just go ahead and install the floor knowing it will be parallel and perpendicular to the joists?
I know 45 deg would solve the problem as well, but I think that might be too much for me.
May 4th, 2010 11:34 pm
Brent, in this circumstance, I would lay it whichever direction you want. I think you’ll be fine with 5/8″ plywood. It’s not as ideal as 3/4″, but the alternative is no good, either.