Quick answer: Attic air sealing closes the hidden gaps between your living space and your attic: wall top plates, pot lights, plumbing and wiring holes, the attic hatch and the chimney chase. Natural Resources Canada says air leakage is about 20–30% of the heat lost from an older home, and insulation alone does not stop it. Sealing comes first, then insulation goes on top. On Ontario’s bundle path, air sealing that meets the air-change target earns up to $250, and amounts can change.
Updated November 2026
On this page
- 7 common attic air leaks
- How to spot air leaks in your attic
- Air sealing and rebates
- Air leakage by the numbers
- Air sealing vs insulation: what each one does
- Our attic air sealing process
- Attic air sealing checklist
- example project
- Framework: an air sealing scope to ask for
- Frequently asked questions
- Get a free attic assessment
Insulation slows heat moving through your ceiling. Air sealing stops warm, moist air from pouring through the holes in it. Pro Home Insulation air seals every attic before we add insulation, because doing it in the other order buries the leaks.
7 common attic air leaks
- Wall top plates. The tops of interior and exterior walls often have gaps where drywall meets framing.
- Pot lights. Older recessed lights can leak a lot of air into the attic.
- Plumbing stacks and vent pipes. Holes cut for pipes are often much larger than the pipe.
- Electrical wires and boxes. Every wire that runs into the attic leaves a small hole, and ceiling boxes leak around the edges.
- The attic hatch. An unsealed, uninsulated hatch is a large leak in the ceiling.
- The chimney chase. The gap around a chimney or flue can be a big open path to the attic and must be sealed with fire-rated materials.
- Bathroom fan housings and duct runs. Gaps around fans and ducts let moist air into the attic.
How to spot air leaks in your attic
- Look for dark streaks in the insulation. Insulation acts like a filter, so dirty patches often mark where air is leaking through.
- Check for frost on the roof deck in winter. Frost or ice on nails and boards points to warm, moist air reaching the attic.
- Feel for drafts at the hatch. If you feel air around the edges, the hatch is not sealed.
- Watch for ice dams. Leaking warm air helps melt snow on the roof, which refreezes at the eaves.
Our guide to the signs your attic needs insulation covers more warning signs.
Air sealing and rebates
Air sealing has its own rebate on the bundle path of the Home Renovation Savings Program. On the standalone attic path, there is no separate air sealing rebate, but we still air seal as part of every attic job.
| Rebate path | Air sealing rebate | What it takes |
|---|---|---|
| Bundle path | up to $250 | Pre- and post-work energy assessments, 2 or more upgrades, meet the air-change target |
| Standalone attic path | No separate air sealing rebate | Attic rebate of up to $1,250, based on insulation |
On the bundle path, you also get $600 back on the assessment, and attic insulation can earn up to $1,500. See all current rebates.
What air leaks cost (Natural Resources Canada estimates):
| Home age | Yearly cost of air-leakage heat loss, natural gas | Electricity |
|---|---|---|
| Built in the 1950s | about $390 | about $860 |
| Built 2000 or later | about $280 | about $610 |
| Difference | $390 − $280 = $110 | $860 − $610 = $250 |
These are NRCan’s general estimates, not a prediction for your home.
Air leakage by the numbers
- Air leakage is about 20–30% of the heat lost from an older home (Natural Resources Canada, Keeping the Heat In).
- One small air leak can let in 100 times more moisture than diffusion through the same area (Natural Resources Canada).
- Air-leakage heat loss in a 1950s home costs about $390 a year on natural gas or $860 on electricity (Natural Resources Canada).
- More than 10% of Canada’s yearly energy use goes to heating homes (Natural Resources Canada).
- Nearly 1.2 million Ontario residential properties were built in 1960 or earlier (Statistics Canada).
Air sealing vs insulation: what each one does
| Air sealing | Insulation | |
|---|---|---|
| Stops | Air moving through gaps | Heat moving through materials |
| Main benefit | Fewer drafts, less moisture in the attic | Slower heat loss and gain |
| Where | Top plates, penetrations, hatch, chimney chase | Across the whole attic floor |
| When | First | After sealing |
| Rebate (bundle path) | up to $250 | Attic up to $1,500 |
You need both. Air sealing without insulation leaves the ceiling thin, and insulation without air sealing leaves the leaks. Learn more about attic insulation.
Our attic air sealing process
- Assessment. We find the main leak points and check bathroom fans, ventilation and the chimney area.
- Move or remove insulation where needed. We pull back existing insulation to reach top plates and penetrations, or remove it if it is damaged. See attic insulation removal.
- Seal top plates and small gaps. We use sealant or spray foam on cracks and holes.
- Seal pipes and wires. Larger gaps get foam or rigid material, sealed in place.
- Handle pot lights safely. Older recessed lights are covered or sealed with methods suited to the fixture, keeping proper clearances.
- Seal the chimney chase. We use fire-rated materials around chimneys and flues, never ordinary foam.
- Seal and insulate the hatch. We weatherstrip the hatch and add rigid insulation to the back.
- Insulate on top. Baffles go in, then insulation is blown to R-50 or R-60.
Attic air sealing checklist
- Wall top plates sealed
- Plumbing stacks and vent pipes sealed
- Electrical wires and ceiling boxes sealed
- Pot lights covered or sealed with proper clearance
- Chimney chase sealed with fire-rated materials
- Bathroom fan housings sealed and fans vented outside
- Attic hatch weatherstripped and insulated
- Baffles installed before insulation goes on top
example project
example — not a specific customer.
A 1950s bungalow in Scarborough has about R-12 in the attic, several older pot lights, an open chimney chase and a loose hatch. The homeowner is also upgrading basement walls, so the bundle path fits.
- Air sealing: meets the air-change target in the post-work assessment: up to $250.
- Attic insulation: R-12 or less topped up to R-60: up to $1,500.
- Basement walls: adding R-10 to R-22: up to $900.
- Energy assessment: $600 back.
- Possible rebate total: $250 + $1,500 + $900 + $600 = up to $3,250, subject to the energy advisor’s results.
Framework: an air sealing scope to ask for
Use this list when you review any attic quote.
| Area | Included? | Material |
|---|---|---|
| Top plates | Yes / No | Sealant or foam |
| Plumbing and vent pipes | Yes / No | Foam or rigid material |
| Wires and boxes | Yes / No | Sealant or foam |
| Pot lights | Yes / No | Method suited to fixture |
| Chimney chase | Yes / No | Fire-rated materials |
| Hatch | Yes / No | Weatherstripping and rigid insulation |
Frequently asked questions
What is attic air sealing?
Air sealing closes the gaps that let air from your home leak into the attic. Common spots are top plates, pot lights, pipes, wires, the hatch and the chimney chase. It is done before insulation is added.
Why air seal before insulating?
Once insulation is installed, the leaks are buried and hard to reach. Sealing first stops warm, moist air from moving into the attic, where it can cause frost, mould and ice dams.
Is there a rebate for air sealing in Ontario?
Yes, on the bundle path of the Home Renovation Savings Program, air sealing that meets the air-change target earns up to $250. That path needs pre- and post-work energy assessments and 2 or more upgrades. Amounts can change, so check current rebates.
Can I seal around my chimney with spray foam?
No. The gap around a chimney or flue needs fire-rated materials and proper clearances. That is why we treat the chimney chase separately from other gaps.
Does air sealing help with ice dams?
It often helps. Ice dams form when warm air leaks into the attic and melts snow on the roof. Sealing those leaks, along with good insulation and ventilation, keeps the roof deck colder.
How long does air sealing take?
In most attics, air sealing is done the same day as the insulation top-up. Attics with many pot lights or a lot of old insulation to move can take longer.
Get a free attic assessment
With more than 10 years of experience, Pro Home Insulation air seals and insulates attics across Toronto, Scarborough, Pickering and Richmond Hill. We will show you where your attic is leaking. Call (647) 250-0606 or Book online.