Is OSB or plywood better for subfloor replacement in a Calgary home?

Plywood is the better choice for subfloor replacement in Calgary — it handles moisture exposure more gracefully, holds fasteners more securely over time, and performs better under Calgary's extreme seasonal humidity swings. While OSB is less expensive and widely used in new construction, plywood is the preferred material when you are replacing a subfloor and want maximum long-term durability, especially in areas with any moisture risk.

The moisture performance difference is the key factor in Calgary. When OSB gets wet — whether from a plumbing leak, a spill, condensation, or moisture migration through a basement slab — the edges swell permanently. You have probably seen this on older OSB subfloors: the edges of the panels are visibly raised and swollen, creating a waffle-like pattern that telegraphs through the finished flooring. Once OSB edge swelling occurs, it does not go back to flat when the material dries. Plywood, by contrast, swells uniformly when wet and returns much closer to its original dimensions when it dries. In Calgary, where indoor humidity swings from 15 to 20% in winter up to 40 to 50% in summer (and drops and rises rapidly during chinooks), subfloor material is under constant moisture stress. Plywood handles this cycling better over decades.

For subfloor replacement, use 3/4-inch (23/32-inch) tongue-and-groove plywood. The tongue-and-groove edges prevent differential movement between panels and create a stiffer, more uniform subfloor. In Calgary, 3/4-inch T&G plywood runs about $1.50 to $2.50 per square foot at building supply stores, while 3/4-inch T&G OSB runs $1.00 to $1.80 per square foot. The price difference is roughly $0.50 to $0.75 per square foot — on a 1,000-square-foot subfloor replacement, that is $500 to $750 more for plywood. Given the superior moisture performance and longevity, that premium is well worth it for a replacement subfloor that you plan to live with for decades.

When OSB is acceptable. In new construction where the building envelope is intact and the subfloor will be protected from moisture from day one, OSB performs well and is the standard choice for most Calgary home builders due to cost. It also provides slightly better shear strength than plywood, which is why structural engineers specify it for certain applications. If you are replacing a subfloor in a main-floor or upper-floor area with no history of moisture issues and no reason to expect future moisture exposure, OSB is a reasonable choice that saves money.

When plywood is strongly recommended. Any subfloor near a bathroom, kitchen, laundry room, or entry — anywhere that water exposure is possible. Any basement application over concrete (where moisture migration is always a concern in Calgary). Any replacement of a subfloor that failed due to moisture damage (using OSB to replace moisture-damaged OSB is asking for a repeat failure). And any situation where the subfloor might be exposed to weather during construction — plywood tolerates rain exposure during a renovation far better than OSB, which can swell permanently from a single heavy rain if the edges are exposed.

Fastening is also important. Whether you choose plywood or OSB, use screws rather than nails for subfloor replacement. Screws hold the panels tight to the joists and resist backing out as the wood expands and contracts seasonally — this prevents the squeaking that plagues nail-down subfloors after a few years of Calgary temperature cycling. Use #8 or #10 wood screws, 2 to 2.5 inches long, spaced 6 inches along panel edges and 12 inches in the field. A professional flooring installer in Calgary will handle all of this as part of the subfloor preparation. Need help finding one? Browse the Calgary Construction Network directory at calgaryconstructionnetwork.com/directory?trade=flooring.