Will air sealing raise humidity in a Moncton home?

Yes, air sealing will raise indoor humidity levels — and in Moncton's climate, that's mostly a good thing, but it does require attention to ventilation.

When you seal a leaky house, you stop the constant exchange of indoor air with cold, dry outdoor air. In winter, outdoor air in Moncton is extremely dry — even when it feels damp outside, cold air holds very little moisture. That dry air infiltrating through gaps in your building envelope has been acting like an uncontrolled dehumidifier all winter long, pulling moisture out of your home and your lungs. Most older Moncton homes (built in the 1960s through 1990s) test at 8 to 15 air changes per hour at 50 pascals (ACH50) — meaning the entire air volume of the house leaks out and is replaced multiple times per hour. These homes are chronically dry in winter, often sitting at 15-25% relative humidity, which causes static electricity, dry skin, cracked wood trim, and respiratory irritation.

After proper air sealing, indoor humidity typically rises to a healthier 35-50% relative humidity in winter. That range is better for your health, your wood floors and furniture, and your comfort. Many Moncton homeowners who air seal their homes report that they no longer need to run a humidifier — the moisture generated by normal daily activities (cooking, bathing, breathing, houseplants) is enough to maintain comfortable humidity levels when the house isn't leaking that air straight outside.

The critical caveat is controlled ventilation. A house that's been tightened to 3.5 ACH50 or better — the current NB Building Code target for new construction — cannot rely on random air leakage for fresh air. You need a Heat Recovery Ventilator (HRV) or Energy Recovery Ventilator (ERV) to bring in fresh outdoor air in a controlled way while recovering 70-80% of the heat from the outgoing stale air. Without an HRV, a very tight home will accumulate excess humidity, CO₂, cooking odours, and volatile organic compounds. The HRV solves all of this while keeping your heating costs low.

For most older Moncton homes, the realistic scenario is that air sealing brings you from dangerously leaky to reasonably tight — not Passive House tight — and the humidity increase is modest and welcome. You're unlikely to create a moisture problem in a home that still has normal ventilation through windows, bathroom fans, and kitchen exhaust. But if you're doing a comprehensive retrofit — spray foam, new vapour barrier, dense-pack walls, the works — an HRV becomes essential, not optional.

The moisture risk to watch for is not high indoor humidity itself, but rather what happens when that humid indoor air finds a cold surface inside your wall or ceiling assembly. This is why air sealing and vapour barrier integrity matter so much in Moncton's climate. If you seal the house but leave gaps in the vapour barrier, warm moist air will still find its way into wall cavities and condense on cold sheathing. The solution is to do the job properly — continuous vapour barrier on the warm side, all penetrations sealed with acoustical sealant, and no shortcuts.

The short version: air sealing raises humidity from uncomfortably dry to comfortably healthy in most Moncton homes. Pair it with an HRV for fresh air exchange, ensure your vapour barrier is intact, and you'll have a home that's warmer, healthier, and significantly cheaper to heat through a Moncton winter.

If you're planning a significant air sealing project, a pre-retrofit EnerGuide evaluation through NB Power's Total Home Energy Savings Program will establish your baseline and make you eligible for rebates up to $5,000. That evaluation also includes guidance on ventilation requirements specific to your home's current tightness. You can find energy advisors and insulation contractors through the New Brunswick Construction Network at newbrunswickconstructionnetwork.com.