Air Sealing vs Insulation: Which Matters More?
They do different jobs and neither replaces the other. Insulation slows heat moving through a surface; air sealing stops heated air escaping through gaps. In an older GTA home the air leakage usually costs more than the missing R-value — which is why sealing first, then insulating, is the order that works.
Two different physics problems
Insulation resists conduction. It is measured in R-value and it works only when air is not moving through it. Blown insulation with air streaming past it performs far below its rating.
Air sealing addresses convection: warm air rising out of the house through every penetration in the ceiling plane, pulling cold air in low down to replace it. That is the draft you feel at floor level in winter.
Where the leaks actually are
The usual list is short and consistent: top plates where interior walls meet the attic, plumbing and vent stacks, chimney chases, recessed lights, and the attic hatch itself. Together they can add up to a permanently open window.
None of it is visible from inside the house, which is why an attic inspection is the only reliable way to know. It is also why we do not price air sealing as an optional extra.
What each one does
| Insulation | Air sealing | |
|---|---|---|
| Stops | Heat conducting through surfaces | Heated air escaping through gaps |
| Measured in | R-value | Air changes per hour |
| Felt as | Cold surfaces and rooms | Drafts at floor level |
| Works without the other | Poorly | Partially |
| Cost | The larger share of the job | A small share, disproportionate effect |
Follow-up questions
Can a house be too airtight?
A very tight house needs mechanical ventilation to manage indoor humidity and air quality. Most existing GTA homes are nowhere near that threshold.
Is air sealing extra on your quote?
No. It is part of the attic work, because insulation without it does not deliver what it is rated for.
General guidance for homes in the Greater Toronto Area. Every building is different — treat this as background, not as a specification for your project.
Want this checked on your own house?
The assessment is free and there is no obligation. You get the findings explained on site and the quote in writing afterwards.
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