London homeowners shopping for insulation upgrades quickly run into this question: spray foam or blown-in? Both improve your home's thermal performance, but they work in fundamentally different ways, cost differently, and are right for different applications in London's housing stock.
The honest answer: for most London homes — particularly the pre-1960s stock in Old East Village, Wortley, and Old North — spray foam wins for critical air sealing locations. Blown-in is a better value for open attic top-up. Understanding which applies where saves thousands and avoids over-speccing a job that doesn't need it.
| Factor | Spray Foam | Blown-In |
|---|---|---|
| R-value per inch | Open-cell: R-3.7. Closed-cell: R-6 to R-7 | Cellulose: R-3.2–3.8. Fibreglass: R-2.2–2.7 |
| Air sealing | Spray Foam Wins — expands to fill gaps completely, seals air channels | Does not air seal — fibres settle into cavities but don't block air flow |
| Moisture control | Spray Foam Wins — closed-cell acts as vapour retarder; open-cell is vapour-permeable | Cellulose absorbs moisture and dries; fibreglass can trap moisture if improperly installed |
| Cost | Blown-In Wins — spray foam is 2–4× the cost per sq ft of coverage | Lower cost for large flat areas; attic top-ups are very cost-effective |
| Attic floor application | Over-engineered — expensive for limited gain unless air sealing is the goal | Blown-In Wins — industry standard for attic floor insulation upgrades |
| Rim joist application | Spray Foam Wins — only option that achieves both R-value and air seal in tight space | Batt insulation is used but doesn't air seal; blown-in not applicable in rim joists |
| Basement wall application | Spray Foam Wins — handles vapour drive from masonry; no secondary air barrier needed | Requires additional vapour barrier; less effective at handling moisture from London's masonry walls |
| Disruption | Requires cleared work area; off-gassing period for 2-cell (24h before occupying) | Low Disruption — can be done in occupied homes; attic work is fast |
| Longevity | Spray Foam Wins — doesn't settle or compress over time; permanent air seal | Cellulose settles 15–20% over 10 years; periodic top-up may be needed |
London's older housing stock — particularly the pre-1960s homes in Old East Village, Wortley Village, Old North, and Woodfield — presents specific conditions where the choice between products matters more than in newer construction.
London's oldest homes have rim joists exposed to the cold. Closed-cell spray foam is the only product that creates an effective air seal + R-value in a tight rim joist cavity. High-impact, low-cost application.
Brick and block construction common in London's older neighbourhoods requires vapour management. Closed-cell spray foam handles the outward vapour drive from masonry without the risk of moisture trapping at the wall.
For an attic that's already accessible and unfinished, blown-in cellulose from R-20 to R-60 is extremely cost-effective. Much cheaper than spray foam for the same coverage area.
London's older homes often have dozens of air penetrations into the attic — pot lights, top plates, plumbing stacks. Spray foam seals these before adding blown-in on top. The sequence matters.
Where the goal is making a garage conditioned space, spray foam on walls and roof deck achieves the continuous air barrier needed for a space that isn't part of the home's thermal envelope.
For upgrading wall insulation without opening the wall, dense-pack blown-in cellulose is injected through holes drilled in the siding or drywall. Much less disruptive than a full spray foam application.
The single most important insight for London homeowners in older neighbourhoods: R-value is not the same as air sealing. Most of the heat loss in an older London home is through air movement, not conduction through the insulation. Adding more blown-in cellulose on top of existing insulation improves the R-value on paper, but does nothing to stop the drafts moving through gaps at top plates, around pot lights, and at structural penetrations.
The right approach for an older London home is:
This hybrid approach — spray foam for sealing, blown-in for bulk R-value — is the cost-optimized solution for most pre-1960s London homes. Pure spray foam is over-engineered for an open attic; pure blown-in without air sealing first often fails to deliver the comfort improvement homeowners expect.
Common disappointment: London homeowners who add attic insulation without air sealing first often don't see the heating cost reduction they expected. The heat is still escaping; it's just taking a different path. An energy audit — or an experienced insulation contractor — can identify where the air is moving before you invest in insulation.
London falls in Ontario Climate Zone 6 — the same zone as Kitchener-Waterloo, Hamilton, and much of Southern Ontario. Climate Zone 6 requires minimum R-49 for attic insulation (NBC 2020 guidance). Most pre-1980s London homes were built to R-12 or R-20 attic standards — well below current code. Upgrading to R-49 or R-60 is the highest-ROI insulation project for most London homes.
The vapour drive direction in Zone 6 is outward in winter — moisture from the conditioned interior tries to move toward the cold outside. This is why vapour management matters in basement wall assemblies and rim joists — and why closed-cell spray foam, which functions as a vapour retarder, is the right tool for those specific applications.
We assess your current insulation state and recommend the right product for each application — not a one-size-fits-all solution.
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