Framing through a GTA winter: snow, wet lumber and drying out before drywall

A wood frame doesn’t mind the cold. Studs, joists and sheathing can be cut, nailed and raised at minus ten just as well as on a spring morning, which is why new houses, additions and garden suites keep going up around the GTA all winter. What a winter frame does mind is water that has nowhere to go.

Snow lands on the floor deck and melts into the joints between panels. Lumber bundles left uncovered soak up slush. A warm day followed by a hard freeze leaves ice in the bottom plates. None of that is a disaster on its own, because wood dries. The trouble starts when wet wood gets sealed behind insulation, a vapour barrier and drywall before it has had the chance. It shrinks and twists as it dries in place, which shows up as nail pops, cracked drywall corners and squeaky floors. If it stays damp long enough, mould and decay can follow.

The Canadian Wood Council’s advice for building sites puts it simply: preventing wetting should take priority over trying to speed up drying. So most of what we do on a winter frame is about keeping water out in the first place, and the rest is about proving to ourselves that the frame is dry before anything covers it. Our residential framing page explains the wider job; this guide is about the winter part.

The first job on a winter morning is the deck itself. Overnight snow comes off with shovels and push brooms before anyone starts cutting, and any standing water goes with a squeegee. That’s also what subfloor manufacturers recommend: until the building is dried in, get standing water off the panels rather than leaving it to soak in.

Ice takes more care. A thin glaze on a subfloor is one of the most dangerous surfaces on a job site, so it’s cleared or broken up before work begins, and nobody walks the top of a wall that’s iced over. Ice that has formed inside the bottom plate of a wall, or packed into a beam pocket, is cleared out rather than framed over. Snow blown into an open wall cavity gets swept out at the end of the day, not left to melt into the insulation later.

We also watch the forecast closely. A heavy snowfall on an open deck is easier to deal with when the materials are already covered and the deck is clear, so on a storm afternoon the last hour goes to tidying and tarping rather than one more wall.

Oriented strand board, one of the most common subfloor and sheathing panels around Toronto, reacts to water at its edges first. After a wet spell you may see the joints between panels puff up slightly and the surface get a little rough or flaky. It looks alarming, but manufacturers are clear that minor edge swelling and surface flaking are cosmetic and don’t affect the panel’s structural properties.

The fix is patience, because some of the swelling can go down as the panel dries. West Fraser, a major OSB maker, advises sanding swollen edges level only after the house has been closed in, the floor is completely dry, drywall and painting are done and the heating is running. Sanding earlier opens up the wood fibres and lets them take on more moisture, which tends to make the swelling worse.

Some premium subfloor panels are made with sealed edges to resist swelling, and on a project that will be framed through the wettest months they can be worth the extra cost. Whatever the panel, a badly delaminated sheet is a different matter from a swollen joint; that one gets replaced, not sanded.

Construction lumber in Canada is graded with a stamp, and S-Dry on that stamp means the wood was surfaced at a moisture content of 19 per cent or less. The Canadian Wood Council notes that most building codes require framing lumber to be dried to 19 per cent or less, a level low enough to virtually eliminate the chance of mould growing on wood. It also recommends making sure building materials are at or below 19 per cent at the time the walls are enclosed.

That last part is what matters in winter. A stud can leave the mill well under 19 per cent and be well over it after a week under snow. So before insulation goes in, we check, rather than assume, with a pin-type moisture meter on a sample of members across the frame. We pay particular attention to the places water collects: bottom plates, the ends of joists and beams, built-up headers, and any lumber that sat at the bottom of an uncovered pile.

Engineered products start much drier. The Canadian Wood Council lists OSB and plywood at about 4 to 8 per cent at manufacture and I-joists at 4 to 16 per cent. They can still take on water at a wet site, especially at cut ends and edges, so they get the same treatment: protected while stored, dried if they get wet, checked before they’re covered.

Most wet framing starts in the pile, not on the wall. The Canadian Wood Council’s storage guidance is practical and easy to follow: keep packages of lumber, trusses, I-joists and panels six to eight inches off the ground on supports, stack them as level as possible, and leave the factory wrapping on until the material is needed. Dry wood touching wet ground takes up water quickly.

Tarps need to be used properly to help. A cover should extend past the bundle, but shouldn’t be tucked under the pile or wrapped tight, because a sealed plastic wrap can hold moisture in as easily as it keeps rain out. Tarps also tear easily on lumber corners, so we check them after wind and replace damaged ones.

The simplest protection is not storing much at all. The guidance recommends delivering material as close to its installation date as possible, and on a tight Toronto lot that suits us anyway. Staging deliveries so each load goes up within days means less lumber sitting under snow, less handling and less risk of a forgotten bundle at the bottom of the yard.

Once a frame is roofed and wrapped, heat speeds up drying and makes the work bearable. But not all heaters help. A direct-fired propane or gas heater releases its combustion by-products straight into the space it’s heating, and one of those by-products is water vapour. Run one inside a newly closed shell with the windows shut and you can raise the humidity in the very frame you’re trying to dry, while also building up carbon monoxide.

An indirect-fired heater vents its exhaust outdoors and blows only clean, heated air inside, which makes it the better tool for drying a frame. Electric heaters produce no combustion by-products at all and suit smaller enclosed spaces. Whatever the heat source, a frame dries fastest with warmth plus air movement, and in a tightly closed space a dehumidifier helps carry the moisture away.

Temporary heaters are also a safety matter. Ontario’s construction safety association reminds workers that heaters bring risks of fire, explosion, carbon monoxide and lack of fresh air, and only workers with a training certificate may operate a propane, gas or oil heater. We keep heaters on firm level ground, away from their fuel cylinders and any combustible material, with fresh air supplied. Please don’t add a space heater of your own.

Dried-in is the milestone every winter frame is racing towards: roof sheathing and underlayment on, walls sheathed and wrapped, and windows and doors in or securely covered. Before that point, the frame is exposed to every storm. After it, the drying can begin in earnest.

Until the permanent layers are on, temporary covers do the job. Openings get framed tarps or sheets of plywood rather than loose plastic, fastened so wind can’t lift them, and roof covers are pitched so meltwater runs off rather than pooling. Snow on a tarp is heavy, so after a big snowfall we clear covers before they sag or tear.

In an addition, the same thinking applies to the existing house. The opening between old and new stays closed with a solid temporary wall until the new part is dried in, so your heated rooms aren’t sharing air with a wet, cold shell. If you’re planning an addition this winter, our guide on building a home addition in winter covers the foundation and concrete side of the job.

Inspections set the pace of the last few weeks before drywall. In Toronto, the structural framing inspection is called at completion of the frame, including the plumbing and HVAC rough-ins, and inspections take place within two business days of the request. The inspector has to be able to see the work, and the stamped permit plans have to be on site. In winter, that also means a clear, safe way in: Brampton’s building department, for example, reminds builders that access points to sites needing inspection must be free of snow and ice and salted.

After the framing inspection comes the moisture check, then insulation and vapour barrier, which in Toronto have their own inspection before interior finishes go on. The order matters. Insulation installed over damp framing hides the problem and slows drying a great deal, which is why our readings come before the insulation crew arrives, not after.

Drywall has a winter rule of its own. The Ontario Building Code requires heat to keep the space at 10°C or above for 48 hours before taping and finishing, and for at least 48 hours afterwards. A frame that has been dried with good heat and air movement meets that easily; one that’s still damp will make the drywall crew’s job harder and the finished walls worse.

If you’re having a frame built this winter, these are fair things to ask about before insulation and drywall go in.

See the framing stages in our project photos, and plan the rest of a winter build.