Spray foam seals air leaks and handles moisture better. Cellulose costs less per square foot of cavity and works well where the building can dry. For most major Toronto renovations the best answer is neither alone: foam where air and moisture control matter most, cellulose (or another economical fill) for the rest. Below we explain how each material behaves, where each one goes wrong in older homes, and how to decide before the walls are closed.
TL;DR
- Spray foam is an air seal as well as insulation. Closed-cell foam also acts as an air and vapour barrier, which makes it the usual choice for moisture-sensitive spots such as rim joists and foundation walls.
- Cellulose is a treated, wood-based loose fill. It suits attics and wall cavities, and it costs less than foam when you are filling a large volume.
- Hybrid assemblies are common in major renovations: a layer of foam against the sheathing, then a cheaper fill in the rest of the cavity.
- Foam brings extra rules. It must be covered by a fire-resistant finish, it needs a cure period before you move back in, and it can cause trouble on old roofs if it blocks ventilation.
- Toronto inspects insulation and the air/vapour barrier before it is covered. Plan the sequence so nothing has to be torn open.
Table of Contents
- What each material actually is
- Spray foam vs cellulose, side by side
- Air sealing: where spray foam earns its cost
- Moisture and old Toronto houses
- The hot roof problem
- Fire protection and curing: the rules that catch people out
- Inspections: get the order of work right
- Which one for which part of the house
- What we think
- How to compare insulation quotes
- Building it into a full renovation budget
- Planning a whole-house renovation or addition?
- FAQ
- Sources
What each material actually is
It helps to be precise, because "spray foam" covers two quite different products.
According to Natural Resources Canada, spray foam comes in two primary types:
- Closed-cell (high density). It provides an air and vapour barrier and is often used in structural or moisture-sensitive areas.
- Open-cell (low density). It is more cost-effective for filling large cavities, but it needs a separate vapour barrier.
The same NRCan page describes cellulose fibre as a wood-based, treated loose-fill product used in attics and wall cavities. Type 1 is meant for pneumatic injection into closed cavities or for open attic use. Type 2 is often sprayed with liquid adhesives so it sticks better. The national evaluation criteria for cellulose, CAN/ULC-S703 Type 1, apply to treated, wood-based cellulose fibre in new and existing buildings.
So the real comparison is usually closed-cell foam against dense-packed or blown cellulose, with open-cell foam sitting somewhere in the middle on cost and moisture behaviour.
Spray foam vs cellulose, side by side
| Question | Closed-cell spray foam | Cellulose |
|---|---|---|
| Air sealing | Seals gaps and acts as an air barrier | Slows heat flow but is not an air seal on its own |
| Moisture and vapour | Acts as an air and vapour barrier | Needs a separate, well-planned vapour control layer |
| Best locations | Rim joists, foundation walls, moisture-sensitive areas | Attics, wall cavities, large open volumes |
| Cost to fill a cavity | Higher, so often used strategically | Lower, so suited to bulk fill |
| Fire protection | Plastic foam must be covered by a fire-resistant material | Treated product, no equivalent covering rule for the insulation itself |
| Occupancy after install | Cure and off-gassing period required | No comparable wait |
| Environmental profile | Petrochemical product | Wood-based, largely recycled fibre |
Two caveats. First, the row on cellulose's environmental profile reflects the product's wood-based makeup, not a claim about any specific brand. Second, installed prices swing with thickness, access and season. We do not publish a per-square-foot figure here, because the number that matters is the one on a written quote for your walls, with the thickness and R-value stated.
Air sealing: where spray foam earns its cost
A lot of heat loss in older houses is not about the insulation's rating. It is air moving through gaps at the rim joist, around windows, at the top plates and where floors meet walls. Foam expands into those gaps and stays bonded to them.
Natural Resources Canada's guidance, as we read it, is that foam's cost often makes it a strategic barrier rather than a full-cavity filler. The sensible order is to fill the critical gaps first, then use a more economical material to complete the required thermal resistance. That is why a hybrid wall is not a compromise. It is the point at which each material does what it does best.
Cellulose still has a real place in an air-tight house. Dense-packed into a wall cavity, it fills a partially insulated frame well. NRCan notes that professional contractors can blow in loose-fill or inject approved foam into even partially insulated wood-frame wall cavities, and that dense-pack techniques work with cellulose, glass fibre and approved foams. That matters when you want to improve a wall without stripping it.
Moisture and old Toronto houses
This is where choosing by R-value alone goes wrong. A century-old brick house in the Annex, Riverdale or Roncesvalles has a wall that has dried both ways for decades. Change the insulation and you change how it dries.
The City of Toronto's Net Zero Building Retrofit Guide on insulation covers retrofit practice, including attic upgrades with added insulation and a vapour barrier. Its common attic insulation types include fibreglass batts, cellulose and blown-in products. The takeaway for owners of older homes is that the vapour control strategy deserves as much thought as the insulation, including using vapour retarders that let a wall dry in summer rather than trapping moisture behind it.
In practice:
- Basements. NRCan lists batt, glass fibre loose fill, polyurethane spray and rigid board among common interior basement options, and says closed-cell polyurethane foam should be applied only by a certified installer. Cellulose is not the usual choice against a damp foundation wall.
- Walls above grade. Dense-packed cellulose can work well, provided the assembly is designed to dry and the air barrier is handled properly.
- Roofs. Here foam can hurt as well as help, as covered next.
The hot roof problem
Spraying closed-cell foam to the underside of a roof deck creates what is called a hot roof: the roof is no longer vented. That can be a good solution on a complex roofline where ventilation is impossible. It can also trap moisture and lead to rot in the roof structure if the assembly is not suited to it.
In a heritage or complex roof, have a building inspector or engineer confirm the approach before anyone sprays. For a simple gable with an accessible attic floor, blown cellulose over a properly air-sealed ceiling is often the more forgiving option. NRCan's roofs and attics section lays out the options for an air barrier system in an unfinished attic, including spray foam between the joists, so the choice is a real design decision and not a default.
Fire protection and curing: the rules that catch people out
Two foam-specific points belong in your schedule.
Fire protection. Plastic-based foam insulation must be covered by a fire-resistant material. Per NRCan's materials guidance, that is typically 13 mm (1/2 in.) drywall, mechanically fastened to the structure. If your design leaves foam exposed in a basement ceiling or utility area, ask how it is being covered.
Curing time. Closed-cell foam needs a curing and off-gassing period before you move back in, which the research we reviewed puts at about 24 hours. If that downtime is skipped, lingering chemical odours and health complaints can follow. Ask your project manager to schedule the time explicitly, and if anyone in the household has asthma or chemical sensitivities, raise it with your family doctor before the work starts.
Cellulose has no equivalent wait, though installation is dusty, so the area should be protected and cleaned like any other trade.
Inspections: get the order of work right
In Toronto, insulation is inspected. The City's inspection schedule includes an insulation and vapour/air barrier stage, and anything covered before inspection must be uncovered at the owner's expense. That page is written for larger buildings, so confirm the exact inspection list on your own permit with the City, but the principle applies to any renovation: the inspector sees the work before drywall goes up.
That has a practical effect on material choice:
- Foam is applied, then cured, then inspected, then covered.
- Cellulose is blown or dense-packed after the air and vapour layers are in place, and before the interior finish.
- Mixed assemblies need both steps sequenced correctly, with drywall booked only after sign-off.
What the City says on building permits is that they exist so projects are structurally sound and follow the Ontario Building Code and municipal zoning. For additions especially, see our guide to Toronto addition permits, zoning and Committee of Adjustment.
Which one for which part of the house
Use this as a starting point, not a prescription. Your house, your permit and your engineer's notes decide.
- Rim joists and band areas: closed-cell foam is the usual answer because air sealing matters most there.
- Foundation walls in a basement: closed-cell foam, installed by a certified applicator, or another approved basement system.
- Wall cavities in a gut renovation: a thin foam layer against the sheathing with the rest filled by cellulose or mineral wool, or a fully conventional approach with careful air barrier detailing.
- Existing walls you are not opening: dense-pack cellulose, which can be blown into closed cavities.
- Open attics with accessible floors: blown cellulose over an air-sealed ceiling plane.
- Sloped or cathedral roofs with no ventilation path: foam may be the only practical choice, with inspector or engineer approval.
- New second-storey or rear additions: decide on the hybrid at design stage, because wall thickness, window depth and mechanical routing all depend on it.
What we think
We get asked "foam or cellulose?" early, usually before the scope is even settled. Our answer is that it is the wrong first question. The first question is what the wall or roof is made of, how it will dry, and where the air leaks are. The material follows from that.
On a full-home renovation the insulation sits in the middle of a chain: structural changes, mechanical upgrades, permit inspections, drywall. Get the order wrong and someone is paying to open a finished wall. That is why we manage the whole sequence ourselves, with designers and engineers coordinated through one accountable builder, rather than leaving insulation to a trade that does not see the rest of the job.
We lean toward the hybrid for most major Toronto jobs: foam where air and moisture control are critical, a lower-cost fill where bulk matters. It keeps the budget honest, and it is easier to explain line by line. We would rather show you a quote where foam is used in three places and cellulose in the rest than sell you foam everywhere because it sounds premium. Where an older house has a roof or wall assembly we are not sure about, we say so and bring in the engineer before anything is sprayed.
— Cory
How to compare insulation quotes
Two quotes for "insulation" can describe very different work. Ask for each of these in writing:
- Product and type: open-cell or closed-cell foam, Type 1 or Type 2 cellulose.
- Thickness and target R-value for each area, not a single blanket figure.
- Where the air barrier and vapour control layer are, and who installs them.
- Fire-protection covering for any foam left in occupied or accessible spaces.
- Cure time and re-entry date for foam.
- Inspection timing: who books the City inspection and what happens if it fails.
- Installer credentials, particularly for foam applied in basements.
A low foam quote with no thickness stated is not a bargain. It is an unfinished question.
Building it into a full renovation budget
Insulation is a modest share of a large project, but it drives other costs: wall depth, drywall, extra inspections and any rework. We keep it as its own line in the scope so you can see what the hybrid saves against an all-foam approach. For wider context, see our Toronto renovation cost guide and our write-up of the eight stages of a renovation, where the insulation and inspection step sits between rough-in and closing the walls.
Planning a whole-house renovation or addition?
If you are gutting a Toronto home, adding a rear or second-storey addition, or weighing a house that needs serious work, we handle the feasibility study, budget, permits and construction under one point of contact. Insulation strategy is decided in that process, not bolted on. See our full-home renovations and home additions pages, or contact us to talk through your house.
FAQ
Which is better, cellulose or spray foam insulation?
Neither wins everywhere. Spray foam is better for air sealing and moisture-sensitive areas, while cellulose is more economical for filling large cavities and attics. Many Toronto renovations use both in one assembly.
Can spray foam cause problems in an older home?
Yes, if it is used without thinking about how the structure dries. Closed-cell foam on the underside of a roof deck removes ventilation, so it should be approved by a building inspector or engineer first, especially on heritage or complex roofs.
Does cellulose insulation have downsides?
It does not seal air leaks by itself, so air sealing and vapour control must be handled separately. In walls and roofs that need a drying path, the assembly has to be designed with that in mind.
Do I have to leave the house after spray foam is installed?
Plan to, for the curing and off-gassing period, which the guidance we reviewed gives as about 24 hours for closed-cell foam. Ask your project manager to schedule it. If you have a respiratory condition, check with your doctor beforehand.
Does Toronto inspect insulation?
Yes. The City has an inspection stage for insulation and the vapour/air barrier, and work covered before inspection must be uncovered at the owner's expense. Confirm the stages on your own permit with the City.
Sources
- Keeping the Heat In, Section 3: Materials, Natural Resources Canada
- Keeping the Heat In, Section 7: Insulating walls, Natural Resources Canada
- Keeping the Heat In, Section 6: Basement insulation, Natural Resources Canada
- Keeping the Heat In, Section 5: Roofs and attics, Natural Resources Canada
- CAN/ULC-S703-09 Type 1 evaluation requirements, National Research Council Canada
- Net Zero Building Retrofit Guides: Insulation, City of Toronto
- When to Call for Inspection of Large Buildings, City of Toronto
- BuildSafeTO: Learn About Building Permits, City of Toronto