OSB vs Plywood Sheathing and Subfloor in an Ontario House (2026): Edge Swell, Wet Weather, Tongue and Groove Glued and Screwed, What the Inspector Looks At

What Each One Is

Plywood is thin veneers of wood glued in layers with the grain crossed. OSB, oriented strand board, is wood strands laid in layers, pressed with resin into a sheet. Both come stamped with a grade mark that says what they are rated for: wall, roof, subfloor, and the span between supports. The stamp matters more than the brand.

As wall sheathing on a house, the panel is doing two jobs. It holds the studs in line, and where the drawings show a braced wall panel, it is the part that keeps the house from racking sideways in the wind. That second job is why the 2024 Code cares about how it is nailed.

These are general behaviour, not a test result. Subfloor products sold for wet job sites are made to handle exposure during construction better than ordinary sheathing; ask your supplier what is in stock and what the maker allows.

Wet Weather and Edge Swell

An Ontario frame gets rained on. It is not a question of if. The question is how long the panels sit wet, and whether anybody covers them before the drywall goes up. OSB edges soak up water and can swell, a bit like a cracker left out on a humid porch. Once that edge has puffed up it often stays that way.

On a wall, a swollen edge is mostly a cosmetic problem under the house wrap. On a subfloor it is not. A swollen seam telegraphs through vinyl plank and thin tile as a ridge you will see every morning with your coffee. That is why good framers sweep standing water off a deck after a storm, and why a floor installer runs a straightedge across the seams before laying anything.

1. Leave the gap. Panels are gapped at the edges and ends to the maker’s instructions, usually about 3 mm (1/8 inch), so they have room to grow. Butted tight, they buckle.
2. Keep sheets off the ground and covered at the site. A pallet of OSB sitting in a puddle for a week is a pallet of swollen edges.
3. Sweep and drain the deck after rain, and drill a weep hole where water pools against a wall plate.
4. Get the roof on fast. The shell closes the subfloor in. Every week the roof is late is another week of weather on the floor.
5. Check moisture before you close in. The framing moisture page covers what to measure before insulation and drywall.

The Subfloor: Tongue and Groove, Glued and Screwed

The subfloor is the one place where the choice of panel and how it goes down shows up years later. A squeak is two pieces of wood rubbing; it starts with a fastener that was never tight or a seam that was never glued.

• Tongue and groove edges across the joists, so the long seams between joists lock together instead of each sheet flexing on its own.
• Construction adhesive on every joist and in the groove, laid just ahead of the sheet so it does not skin over.
• Screws or ring-shank nails at the spacing the maker and the drawings call for, driven snug into the joist, not beside it.
• Long direction across the joists, end joints staggered and landing on a joist.
• Thickness matched to the joist spacing and to the finish floor. Tile over a thin subfloor on wide spacing is how grout cracks get made.

On a stiff engineered floor, the subfloor is a big part of how the floor feels. The bouncy and squeaky floors page covers the rest of the stiffness story, and I-joists vs floor trusses covers the joists themselves.

What the Inspector Looks At

The framing inspection happens before insulation, with the sheathing on and the structure visible. On sheathing, the inspector is looking at things you can check yourself the day before.

1. Grade stamps on the panels, the right rating for the use, and the thickness the drawings call for.
2. Nailing at braced wall panels. The 2024 Code increased the nailing for sheathing. Where the drawings show braced wall panels, the nail spacing at the edges and in the field should match. Shiners, nails that missed the stud, do not count.
3. Panel edges supported. Edges land on framing or blocking unless the panel is tongue and groove and rated for it.
4. Nail heads not overdriven through the face. A nail gun set too hot sinks heads below the surface, and a nail that has torn through the top layer is not holding much.
5. Roof sheathing with the edge clips or blocking the maker calls for, and the truss spacing that matches the panel rating.

The wall bracing page explains braced wall panels in plain words, and the framing inspection checklist has the whole list for the day before the inspector comes.

Why We Do Not Print a Sheet Price

We tried. The online big-box listings we checked were out of stock, and their prices did not make sense next to each other. A number on this page would be wrong before you read it.

October 2026 prices, before HST. Say a swollen subfloor has to come out under a 400 sq ft kitchen and family room before the new floor goes down: 400 x $2 = $800 to 400 x $5 = $2,000 added, our estimate, before the finish floor. Sweeping the deck after a storm is cheaper.

Call the lumberyard you or your framer will actually buy from, and ask for the price per sheet of each panel the drawings call for, in the thickness and grade listed, and how long the price is held. Panels are one line inside the framing bill; the house framing cost page has the whole-house ranges.

Questions people ask

Sources and further reading

• The 2024 Ontario Building Code: Ontario on the 2024 Code: in force January 1, 2025, and harmonized with the national codes.
• OBOA: structural design for Part 9: the building officials association on the new Section 9.23.13 bracing for lateral loads, braced wall bands and panels.
• A municipal training deck on the 2024 Part 9 changes (Tillsonburg): the bracing categories, the extra nailing, and the renumbering that made log construction Section 9.38.