Subfloor must be flat
Make sure the boards are flat to within 3mm in 2m radius. If the boards are out of specification, consider sanding. When sanding, care must be taken to minimize the amount of dust produced. Best practice would include using dust-collection devices. Approved respirators should also be used to minimize the amount of dust inhaled.
Subfloor must be dry
For more information, please see moisture testing.
Solid board sub flooring should be: 19.05mm x 140mm (1×6 nominal), Group 1 dense softwoods (SYP, Doug Fir, Larch, etc.), No. 2 Common, kiln-dried to less than 15% MC.
Solid-board subfloors should consist of boards no wider than 150mm, installed on a 45 degree angle, with all board ends full bearing on the joists and fastened with minimum 8d rosin-coated or ring-shanked nails, or equivalent.
Some types of wood flooring should not be installed directly over solid-board subflooring:
15mm solid and engineered flooring must have a 12mm or better plywood underlayment installed over solid board subflooring.
Parquet flooring cannot be installed directly to solid-board subfloors. A parquet installation over solid-board subflooring requires 9mm or better underlayment panels, nailed on 150mm minimum grid pattern using screws, ring-shanked nails or staples.