Across the joists

Q: The big question: Which way to lay the flooring? The long way (parallel to the 20′ length) or the short way (parallel to the 14′ length)?

A: The hardwood floor should run across the joists and not parallel to them unless your sub floor is 1 1/2 inches thick. If this is not the case regarding the sub floor, and the room dimensions make the floor look bad to run it across the joists, then the next best idea is to install diagonally. This will cost more in wood and labour.

Similar Q: I have some very nice (old) hardwood flooring. I want to put it down in my now gutted kitchen. The floor is down to the original ‘structural fir’. Which way should I lay the hardwood. With or across the flooring?

A: If the old flooring is ¾ thick it should be installed across the joists. If it is old style 3/8 strip it likely isn’t worth it to remove from one area and install in another because it would likely be to thin to take a sanding needed to flatten it out after re-installation.

Related Q: We are building a new home with solid hardwood flooring. The direction of the joists are front to back. We would prefer to have our wood flooring installed the same direction, but understand the potential issues with sagging or worse.

I have read that we can shore up the subfloor by adding a layer of 3/8-inch plywood. Is this a realistic and smart decision or would we be better off asking our builder if the joists can change direction? Or even just accept the fact that the wood floor would run in a less desirable direction?

A: Ideally, the wood planks should run across the floor joists. If the sub floor is an inch or more thick you can run in the same direction as the joists.

I would not recommend the sub floor be OSB. Spruce plywood is good.

Related Q: I’m installing 3/4” hardwood flooring. I want to install parallel to the joists. My subfloor is 3/4” set diagonally  across my joist. Do I need to install plywood/OSB or is the diagonal subfloor sufficient? Manufacturer recommended minimum of 3/8” but I think that when it runs perpendicular to the joists. What’s your recommendation?

A: I would install at least half inch plywood over the existing ply if you are running the flooring parallel with the joists. Not a fan of OSB. It doesn’t hold fasteners very well.