The subfloor is where most squeaks start
A squeak sounds as if it comes from the hardwood or laminate, but the flooring is usually just the thing transmitting the noise. Underneath it sits the subfloor, either boards or sheet panels, fastened down onto the joists that carry the whole structure. In houses built before about the mid-1950s that subfloor is commonly tongue-and-groove plank, often laid diagonally across the joists. Plywood became the standard after the Second World War, and oriented strand board is the usual panel today. What matters is not the material so much as the fastening. Building guidance still allows nails: CMHC’s wood-frame construction guide spaces subfloor nails 150 mm apart along panel edges and 300 mm along the joists in between, and treats glue between joist and subfloor as the way to add stiffness and reduce squeaks. A nail holds a panel down without drawing it tight against a joist that sits slightly proud or slightly low, so a small gap can be there from day one. Every time somebody walks across it the panel flexes into and out of that gap, working against the smooth shank of the nail. That rubbing is the squeak, and it is why fixing the flooring above rarely holds.
