Stop Heating the Street: Your Niagara Air-Sealing Checklist

Causa Construction Group
Oct 16
6 min read

(OBC Part 9 Friendly — What Every Homeowner Should Know)

Introduction: Why Air Movement = Biggest Winter Energy Loss

In a cold climate like Niagara’s, your furnace isn't just warming the air inside your home — it’s battling a hidden foe: air leakage. Even with great insulation, uncontrolled air flow (infiltration and exfiltration) can drive 50 % or more of winter heating losses in older or leaky homes. Warm indoor air seeks lower pressure, exits through cracks; cold outdoor air follows in. That means you’re essentially heating the street.

Sealing your home tightly yields multiple wins: lower heating bills, fewer drafts, better comfort, and reduced moisture risk in wall cavities. But to do it right, you need to respect building science and local code (especially Ontario’s OBC, Part 9).

In this post, I’ll walk you through the fundamentals, the zones to attack, a weekend plan, safety and code considerations, and when to call in the pros.

Air Barrier vs Vapour Barrier — Let’s Clarify

Before grabbing foam and tape, get clear on air barrier and vapour (or vapour-retarder) barrier — two distinct roles.

Air barrier: A continuous barrier against air movement (inward or outward). It must be durable, sealed at joints and penetrations, and integrate across assemblies.
- Ontario’s OBC mandates that wall, ceiling, and floor assemblies separating conditioned space from unconditioned space include an air barrier system. buildingcode.online +2free.bcpublications.ca +2
- Per OBC 9.25.3.3, joints and penetrations in the air barrier system must be sealed (panels sealed, flexible sheets taped or sealed) to maintain continuity. buildingcode.online
- Materials used for principal resistance to air leakage (sheet / panel types) must not exceed an air leakage characteristic of 0.02 L/(s·m²) at 75 Pa. buildingcode.online
Vapour barrier (or vapour retarder): A layer controlling moisture diffusion through assemblies.
- OBC requires vapour barriers to have permeance ≤ 60 ng/(Pa · s · m²) (approx 1 US perm) if they’re intended for that function. buildingcode.online
- Placement matters: they should be installed on the warm side (interior) of the insulation, close enough to minimize condensation risk. buildingcode.online
- The code also anticipates that air barrier materials may also act as vapour barriers (or vice versa) — but each function must satisfy its own criteria. guides.co +1

Why this distinction matters: You might slap up polyethylene (poly) as a vapour barrier, but unless it’s sealed and continuous, it won’t function well as an air barrier. Likewise, tight but high-perm materials could let moisture through if not managed correctly.

Here’s a simple diagram to visualize how air and vapour layers interplay. (Above image illustrates continuous air barrier paths in a wall/roof stack.)

The 5 Leak Zones You Must Attack

When you go hunting for drafts, think in these five priority zones:

Attic / ceiling plane
- Recessed lights, plumbing stacks, attic hatches, wiring penetrations, chases, chimney/vent flashings.
Rim joist / band joist / top of foundation
- Joist ends, rim boards, rim-to-wall intersections, plumbing/electrical penetrations.
Walls / window & door openings
- Window frames, door frames, sill–top plate gaps, wall penetrations for wiring/venting.
Basement / foundation & slab interface
- Gaps at slab perimeter, rim-to-foundation interface, sump pit covers, utility penetrations.
Doors, hatches, and garage-to-house transitions
- Exterior doors, attic hatches, access panels, garage-house doors (especially in attached garages).

When you present this as a carousel (for your site), match each of those with a photo (e.g. attic hatch, rim joist, window frame, slab gap, door transition).

Quick Materials List: What You’ll Need

Material	Purpose / Use Case	Notes / Tips
Low- or medium-density spray foam (1-component, minimal expansion)	Sealing larger gaps, rim joist, voids under beams	Watch expansion so it doesn’t bow sheathing
Gasket foam tape / EPDM foam	Sealing around rim, subfloor, sill plates	Good for 3–10 mm gaps
Acoustic sealant / flexible caulk	Tight seal around wiring, conduits, small gaps	Use for penetrations that may move
Butyl tape / sheathing tape / air-barrier tape	Sealing joints on membrane or rigid board systems	Choose tapes rated for building envelope use
Door sweep / weatherstripping	Sealing bottom of doors and casings	Use brush, silicone or PVC strip style
Attic hatch / access cover kit	Rigid lid + gasket to seal hatch/perimeter	Make sure it’s well insulated too
Electrical box foam gaskets	Under outlet/switch covers to limit leakage	Ultra cheap – big bang for buck
Rigid foam board cut-offs / plywood blocking	To fill big voids, back up foam or tape surfaces	Useful as backing behind spray foam or tape

Optional extras: window plug blanks, vacuum hose for dust extraction, protective gloves & goggles.

Step-by-Step Weekend Plan

Here’s a suggested flow if you want to tackle air sealing over one or two weekends. Always work from “top down” (attic first, then rim, then wall/doors, etc.).

Day 1: Attic & Ceiling Plane

Safety first: Use proper PPE (dust mask, goggles). Watch for exposed nails, wiring, etc.
Unplug or turn off any electrical circuits near work areas, cover wire ends.
Remove old insulation flush to ceiling where needed to expose ceiling joist / drywall interface.
Inspect all penetrations (plumbing stacks, electrical boxes, HVAC ducts, chase walls).
Seal penetrations: use caulk or spray foam for small ones; expanding foam or gaskets for bigger.
Recessed lights: if not IC-rated or sealed, consider replacing with airtight, IC-rated cans, or build a barrier box and seal it.
Attic hatch: install a gasketed lid / cover. Seal the perimeter with foam tape or gasket and caulk any gaps.
Chimney / flues / vent stacks: seal gaps around flashing with high-temp caulk or sheet-metal flashing integration (see code note below).
Replace insulation as needed, ensuring airflow to soffit vents is maintained (don’t block vents).

Day 2: Rim Joist / Band Joist & Walls

Clear rim joist area: remove old insulation or debris that blocks access.
Seal rim joist: Use gasket foam tape across rim board and subfloor, or back-spray with minimal-expansion foam, finishing with caulk or tape.
Block rim-to-wall intersections and seal transitions.
For windows and doors:
- Remove interior trim carefully if needed.
- Use low-expansion foam or gaskets to seal the gap between rough opening and frame.
- Apply compatible flashing, tape, or caulk on the exterior or interior side to tie into the air barrier.
- Reinstall trim carefully, then seal the trim-to-wall junction.
Add foam gaskets behind all electrical boxes (switches, outlets).
Seal plumbing penetrations, ventilation pipes, gas lines, etc., with caulk or foam, paying attention to keeping combustible clearances.

Day 3 (optional / overflow): Basement / Slab & Doors

At slab perimeter (where slab meets foundation wall), seal any visible gap with caulk or foam.
Seal the bottom of rim-to-foundation wall junctions.
Install weatherstripping and door sweeps on exterior (or semi-exterior) doors (basement, side doors).
In homes with attached garages: ensure air barrier continuity between garage and living space per OBC 9.10.9.16. buildingcode.online +2buildingcode.online +2
Check sump pit cover — it should be sealed to maintain air barrier continuity (OBC 9.25.3.3). buildingcode.online

You’ll often find that after sealing the obvious gaps, comfort improves immediately — less draftiness, steadier wall/ceiling temperatures, and your furnace runs more steadily.

Safety & Code Notes (Don’t Skip These)

Mechanical vent clearances: Do not trap combustion appliance vents, chimneys, or gas vents behind airtight sealing. OBC requires clearances and that penetrations through air barriers be sealed with noncombustible material where relevant. buildingcode.online
Air barrier continuity is critical per OBC 9.25.3.3 — sealing all joints, penetrations, and maintaining sealing at transitions (wall, ceiling, floor) is mandatory. buildingcode.online +2guides.co +2
In new or major renos, OBC Subsection 9.25.3.1 requires that building envelope assemblies include a continuous air barrier system to prevent condensation or moisture issues. buildingcode.online +2free.bcpublications.ca +2
The air-barrier material selected must satisfy air leakage properties (esp. panel/sheet types). buildingcode.online +2free.bcpublications.ca +2
For vapour barriers, OBC 9.25.4.2 limits permeance ≤ 60 ng/(Pa·s·m²). buildingcode.online
In OBC 9.32 (Ventilation for dwellings), rooms must have ventilation (natural or mechanical) to ensure indoor air quality. You cannot seal so tightly that you destroy adequate fresh air inflow. Township of Leeds & the Thousand Islands+3buildingcode.online+3codenews.ca+3
For garage-to-house interfaces: OBC 9.10.9.16 demands an air barrier that separates exhaust/gas from living space. Every door between garage and house must comply with article 9.10.13.15. buildingcode.online +2tarion.com +2
Also beware fire-stop and fire-separation requirements (OBC section 9.10) when sealing walls, especially if walls are fire separations. buildingcode.online +1
If using spray foam, avoid interfering with required clearances around flues/vents and make sure foam is compatible and certified.

Because the Ontario Building Code is updated periodically (e.g. 2024 changes include revised ventilation rules) keep your references current. Township of Clearview+1

When to Call a Pro

Even with a DIY heart, some jobs call in the experts:

You want a blower door test (before/after) to quantify your leakage in ACH50 (air changes per hour at 50 Pa).
You suspect hidden issues (mold, moisture, insulation gaps, structural defects).
Your combustion appliances (furnace, gas water heater) may backdraft under tight conditions.
You’re doing a major retrofit or re-roof / re-clad project — the air barrier transitions get complex.
You don’t feel comfortable working in attics, on roofs, or with spray foam around vents.

A certified energy auditor or blower door technician will help you validate your work and catch areas you might miss.

Want a ready-to-use checklist for your home? Download the Winter-Ready Air Sealing Checklist (PDF).Have questions about your home, or want a guided plan? Book a 15-minute call with me, and I’ll walk you through your specific situation.