Underlayment’s for plywood must be made of Group 1 exterior-grade plywood.
Smooth face-up installation of plywood surfaces is recommended, with the face grain aligned perpendicular to the frame. As per industry regulations, the underlayment and subfloor joints are offset.
Only use brand-new, high-quality plywood that has been thoroughly acclimated in accordance with the manufacturer’s recommendations and has not been exposed to rain or water damage.
Plywood subfloors and underlayment’s must have a minimum of two layers with a combined total thickness of 1-1/4″ (3,2 cm), or 1-1/2″ (3,8 cm) for natural stone installations.
The manufacturer’s instructions should be followed while fastening both panels over joists spaced 16″ (41 cm) apart. Between panels, leave a 1/8″ (3 mm) space. Around drain pipes, conduits, posts and columns, as well as along the bases of walls and curbs, leave a 1/4″ (6 mm) space.
The plywood needs to be screwed 6″ (15 cm) on centre (OC) all the way around and 8″ (20 cm) OC in all directions.
When joints are separated more than 16″ (41 cm) on centre, at least one layer of 3/4″ (19 mm) thick exterior-grade plywood must be used, each sheet being connected with screws 8″ (20 cm) on centre in both directions and around the outside.
Leave adequate space between each plywood sheet and other adjacent items.
The plywood underlayment sheets’ adjacent edges shall not veer more than 1/32″ (1 mm) off the plane.
Under no circumstances can any flooring material be placed over subfloors made of wood or wood underlayment that might buckle or decay. Any wood subfloors or underlayments that have had water damage should always be replaced.
All wood subfloors must be well ventilated and meet all local regulations.
