If the subfloor is plywood of marginal quality then the finish floor should be perpendicular to the joists to stiffen the overall assembly.
Floating floor have to be perpendicular to floor joidts.
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.
Since the floor joists typically attach perpendicular to the rim joists and roof rafters typically bear perpendicularly to the rim joists as well then the joists and rafters are typically parallel.
That said some times it s not possible to do this.
The nofma specifically states this in their instalaltion guidelines for nail down hardwood flooring as does almost every hardwood manufacturer.
If the old subfloor is wood planks you should install the finish floor perpendicular to them which will be parallel to the joists.
Flooring experts recommend installing flooring boards perpendicular to the floor joists in a house with a plywood subfloor.
Plank should be stiff enough to span the joists with no problem.
A flooring contractor howard brickman responds.
I guess you wouldn t have to lay it parallel but the shiplap has a lot more movement then plywood or osb.
Installing them parallel creates the possibility that the floor will sag.
If the subfloor is stiff enough there is no reason why solid nail down strip flooring can t be run parallel to the joists.
Generally floor or ceiling joists run parallel to the rafters.
Hardwood flooring is to be run perpendicular to the joists for structural integrity of the flooring system to prevent rolling or waviness between the joists over time.
Most directions recommend running laminate flooring perpendicular to floor joists.
If you go parallel to the joists you may end up with areas of flooring that aren t fully supported.
In these cases the conservative choice is to go perpendicular across the floor joists and allow them to support the new floor as well as the sub floor.
Some houses have the shiplap on a 45.