Before Ontario's freeze-thaw season starts, clean the gutters, extend the downspouts, fill low spots at the foundation, recaulk exterior gaps while it's still above 4°C, drain the hose bibs and test the sump pump. Then check attic venting, deck railings and masonry joints. Fix anything that lets water sit against or inside the house now, because every freeze makes it bigger. Big jobs like regrading, tuckpointing and deck rebuilds can wait for spring.
- Water is the real problem. Freeze-thaw just makes small water problems bigger, faster.
- Most exterior sealants need surfaces above about 4°C to cure, so late October is the last good window for caulking.
- Gutters, downspouts, hose bibs and the sump pump take one afternoon and head off most winter damage.
- Regrading, tuckpointing and deck rebuilds can wait for spring if you put a temporary fix in place now.
- Toronto homeowners may qualify for City subsidies on sump pumps, battery backups and backwater valves.
Why late October matters in Ontario
Southern Ontario winters aren't the coldest in Canada, but they're hard on houses. From November to April the temperature crosses 0°C again and again. Every time water in a crack, a mortar joint or a pipe freezes, it expands. Then it thaws, more water gets in, and the next freeze pushes the gap wider.
A warmer climate won't make this go away. Researchers studying the Toronto region found that getting rid of freeze-thaw days there would take an unlikely warming of about 14° to 20°C. Freeze-thaw will stay part of owning a house here.
Late October is the sweet spot. It's still warm enough for caulk to cure and for you to work safely on a ladder. Most of the leaves are down, so you only need to clean the gutters once.
The printable fall checklist
| Item | What to do | Why it matters in freeze-thaw |
|---|---|---|
| Gutters and downspouts | Clear debris, check joints for leaks, extend downspouts away from the wall | Overflow soaks the soil at the foundation, then freezes and thaws against it |
| Grading | Look for low spots, sunken soil and patios that slope toward the house | Water pooling at the wall feeds foundation cracks and window wells |
| Exterior caulking | Recaulk open joints at windows, doors, vents and penetrations | Water gets behind the cladding, freezes, and rots the sheathing |
| Hose bibs | Disconnect hoses, close the inside shut-off, drain the line | A frozen line can split inside the wall and leak once it thaws |
| Sump pump | Test with a pail of water, check the check valve and discharge line | Midwinter thaws and the spring melt are when pumps work hardest |
| Windows and window wells | Check weatherstripping, clear the wells, make sure the drains are open | Leaves in a well hold water right against the basement window |
| Attic | Check soffit vents, bath fan ducts and insulation for damp | A warm attic causes ice dams and frost under the roof deck |
| Deck and masonry | Shake railings, probe stringers, look for open mortar joints | Water in open joints freezes and pops the faces off bricks |
Gutters, downspouts and grading
Start here, because these handle the most water. Every litre that lands on your roof ends up wherever your downspouts point.
- Clean the gutters once most of the leaves are down. Flush them with a hose and watch for drips at the seams and corners.
- Check that every downspout runs clear. If the elbow is clogged, water overflows at the top and dumps right at the wall.
- Extend each downspout at least 1.5 to 2 metres out, onto lawn or a splash pad that slopes away. Never let it empty into a garden bed against the house.
- Walk around the house after a rain. Look for puddles within a couple of metres of the wall, soil that has sunk below the brick line, and interlock that now tips toward the house.
On our jobs, we want the ground to drop about 15 cm (6 inches) over the first 3 metres out from the wall. A wheelbarrow of clay-rich fill, packed down and sloped away, fixes most small low spots in an hour. Don't use mulch or loose topsoil for this. Both soak up water and hold it against the foundation.
Exterior caulking, windows and doors
Check the joints around window frames, door trim, dryer and bath vents, hose bibs, gas and electrical penetrations, and anywhere siding meets brick. If the bead is cracked, pulling away on one side, or you can slip a fingernail behind it, cut it out and redo it.
Temperature matters more than people think. GE's technical data sheet for its Supreme Silicone window and door sealant says the product, the surfaces and the work area all need to be above 40°F (5°C), and that frost or moisture on the surface slows the cure. Tremco's cold-weather bulletin gives 4°C to 27°C as the best range for applying sealant. Pick a dry afternoon and keep the tubes indoors overnight so they're warm.
Which caulk we use
- Window and door perimeters on brick or vinyl: 100% silicone or a hybrid polymer. Both stay flexible through a Canadian winter.
- Painted wood trim: a paintable hybrid polymer. Acrylic latex is fine indoors, but outside it shrinks and cracks within a couple of seasons.
- Gaps wider than about 10 mm: push in foam backer rod first, then caulk over it. Packing a deep gap with caulk alone wastes a tube, and the joint fails sooner.
Inside, check the weatherstripping on your exterior doors. If you can see daylight at the corners or feel a draft with your hand, replace it. It's an inexpensive fix you can do in an hour.
Hose bibs and exterior plumbing
This is the cheapest item on the list, and the one we see go wrong most often. When the water left in an outdoor tap line freezes, it can split the pipe inside the wall. Usually nobody notices until spring. Someone turns the tap on, and the water runs into the basement ceiling instead of out the spout.
- Disconnect every hose, including on frost-free sillcocks. A hose left on traps water in the long valve body that sits inside the warm wall, and that's the part that bursts.
- Find the inside shut-off for each outdoor tap. It's usually in the basement ceiling near the wall. Close it.
- Open the outside tap and leave it open so the line drains. If the inside valve has a small bleed cap, open it over a bucket.
- Blow out or drain irrigation lines and any outdoor kitchen or pool plumbing.
In older houses with no inside shut-off for a hose bib, have one added now. In October that's a small plumbing call. In March it's a big insurance claim.
Sump pump, backwater valve and window wells
Test the sump pump before the ground freezes. Take the lid off the pit and slowly pour in a pail of water until the float rises. The pump should start, empty the pit and shut off cleanly. If it hums without pumping, cycles on and off quickly, or the check valve slams loudly, call a plumber now. Don't wait for spring.
Then go outside and follow the discharge line. The above-ground section can freeze solid in winter, and then the pump has nowhere to send the water. Make sure the line drains away from the house, isn't buried where you pile snow, and doesn't empty onto a walkway where it will turn to ice.
If you have a backwater valve, open the access cap and check that the flap moves freely and nothing is stuck in it. Scoop the leaves out of the window wells and make sure each well drain is open.
In Toronto, the City's Basement Flooding Protection Subsidy Program helps pay for these devices. In October 2025 the City proposed raising the maximum per property from $3,400 to $6,650, including a new $300 subsidy for sump pump battery backups. The City's program page now lists separate amounts for work completed on or after November 12, 2025. It also says you have to be the registered owner of a single-family home, duplex, triplex or fourplex, and you have to apply within two years of the installation. Halton, Peel, Hamilton and Niagara municipalities run their own programs, so check yours before you book the work.
Attic ventilation and ice dams
Ice dams form when heat leaks into the attic and melts the snow on the upper roof, and the meltwater refreezes at the cold eaves. Natural Resources Canada's Keeping the Heat In guide treats attic ventilation as the second line of defence, after air sealing. For peaked roofs, the guide uses 1 unit of unobstructed vent area for every 300 units of insulated ceiling area.
Here's what to check with a flashlight from the attic hatch:
- Daylight at the soffits. If insulation is packed into the eaves with no baffles, air can't get in at the bottom.
- Bathroom and kitchen fan ducts. They have to run to an exterior vent cap, not just stop in the attic.
- Dark staining or rusty nail tips under the roof deck. That's condensation, which means warm, moist air is getting up there.
- Gaps around the hatch, pot lights and plumbing stacks. These are the air leaks behind the whole problem.
Weatherstripping the hatch and fixing a loose bath fan duct are jobs for this fall. Bigger air sealing and insulation top-ups can happen in winter too, because attic work doesn't depend on outdoor temperatures the way caulking does.
Decks and masonry
Shake every railing post hard. If it moves more than a little, tighten it or add fasteners now. Icy stairs and a loose railing are a bad combination. Check the ledger, where the deck attaches to the house, for rot or missing flashing. Probe the stair stringers and post bases with a screwdriver. If the wood is soft, it's rotting.
On brick and stone, look for mortar that's recessed, sandy or missing, especially at the top of the chimney, under window sills and at ground level. Proper repointing needs mild weather for the mortar to cure, so major masonry work usually belongs in spring. For now, a bead of masonry sealant over a badly open joint at the chimney crown keeps water out until then.
Fix now or wait for spring
| Problem | Fix now | Can wait for spring |
|---|---|---|
| Clogged or leaking gutters | Yes | No |
| Short or disconnected downspouts | Yes | No |
| Small low spots at the foundation | Yes, with packed fill | Full regrade or landscaping |
| Cracked caulk at windows and penetrations | Yes, while above 4°C | Window replacement |
| Hose bib with no inside shut-off | Yes | No |
| Sump pump not cycling properly | Yes | No |
| Bath fan venting into the attic | Yes | No |
| Loose deck railing | Yes | Full deck rebuild |
| Open mortar joints | Temporary seal at chimney and sills | Tuckpointing and brick repair |
| Dry hairline foundation crack | Mark and photograph it | Repair if it grows or leaks |
One more indoor item: CMHC's maintenance checklist recommends servicing a gas furnace every two years and an oil furnace every year, or as the manufacturer recommends. Fall is the time to book it.
What we see on site
When we open up basements for a renovation, the water damage we find almost always traces back to something on this list. These are the ones that keep coming up:
- The downspout that got moved. Someone took the extension off to mow and never put it back. We find a damp corner, white mineral staining on the block wall and mould on the back of the drywall, all within a metre of that one downspout.
- Garden beds built up against the brick. The soil gets topped up every spring until it sits above the weep holes and the foundation parging. Then water goes straight in behind the wall.
- Hose bib bursts inside finished ceilings. These usually show up in March or April as a stain on a basement bulkhead. By then the insulation and drywall are soaked.
- Sump pumps nobody tested. The float is stuck against the side of the pit, or a sag in the discharge line froze. A pail of water in October would have caught it.
- Bath fans dumping into the attic. In older Oakville and Burlington homes, we regularly find flex duct just lying on the insulation, with black roof sheathing above it.
Before we finish any basement, we deal with the outside water first: gutters, grading, downspouts and window wells. Interior waterproofing and a good sump system help, but they shouldn't be the only thing keeping water out. If your fall checks turn up staining or a musty smell, fix the source before anyone puts up drywall. Our basement renovation process starts with that moisture check. It matters even more for a legal basement apartment, where a tenant's home and belongings are at stake.
Planning bigger work for spring
Your checklist might turn up something bigger than a weekend job, like a deck that needs rebuilding, windows past saving, or a basement that has been damp for years. If so, winter is a good time to plan. Design, drawings and permits can all happen while the ground is frozen, so the crew can start once the weather turns. Our whole-home renovation projects often start this way, with the exterior repairs and interior work planned together so nothing gets done twice. Our Oakville home renovation and Burlington home renovation pages show local examples.
If your fall walk-around shows water getting into the basement, start with our basement renovation page and cost estimator. It explains the moisture fixes we do before finishing. Our basement projects typically run $25,000 to $100,000+ before HST. If you'd rather have someone look in person, book a consultation and we'll walk around the outside of the house with you first.
