One of the problems when running parallel is that if some joists are higher than others you get a roll in the floor lengthwise that makes the floor very difficult to sand and it can be seen.
Hardwood floor installation parallel to joists.
However that is mostly personal preference.
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.
Visually it may cause the room to look awkward unless it is square or close to it.
If you prefer a layout that requires the boards to run parallel to the joists you need to shore up the subfloor by adding a layer of 3 8 inch plywood.
3 4 plywood over joists 12 oc should be quite stiff enough.
The subfloor is tji joists with 3 4 t g osb glued and screwed.
Just be sure to flatten the subfloors.
If the subfloor is stiff enough there is no reason why solid nail down strip flooring can t be run parallel to the joists.
Assuming the floor is adequate structurally it should not be a problem.
The most common way to lay install hardwood flooring is by aligning the planks parallel to the longest wall or run in the installation.
If you insist on changing the recommended floor direction add a minimum nominal plywood underlayment to the existing subfloor.
First renail the existing plywood subfloor so that the old nails are tight and add new nails to achieve a maximum nail spacing of 6 inches.
I have a client that would like their 3 4 birch flooring to run parallel to the joists.
If your subfloor is oriented strand board osb we d run the wood across the joists.
Generally speaking the flooring should be installed parallel to the longest wall.
Determine where to start consider your starting point very carefully.
Older houses with 1 inch planks running.
Moreover running the boards diagonally across the joists makes the floor stronger than running them parallel and can be a more appealing alternative to running them perpendicular.
This usually results in the floor running perpendicular to joists.
A flooring contractor howard brickman responds.
Is this ok or should another layer of sheathing be put on the floor perpendicular to previous and then install flooring.