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# Spray Foam vs Blown Cellulose vs Batt: Toronto Attic Comparison 2026
The three primary attic insulation materials behave very differently in Toronto's freeze-thaw climate, and the wrong choice for your specific attic geometry can cost you 30–50% of theoretical R-value within five years. This guide compares spray foam, blown cellulose, and fiberglass/mineral wool batt across every variable that matters: thermal performance, air sealing, moisture, settling, fire, environmental impact, cost, and lifespan.
For the broader pillar guide, see [Attic Insulation Toronto: Complete 2026 Upgrade Guide](/blog/attic-insulation-toronto-2026). For the cost angle specifically, see [Attic Insulation Cost Toronto: R-Value Tier-by-Tier Pricing](/blog/attic-insulation-cost-toronto-r-value).
The 60-Second Decision Framework
- Standard rectangular attic with adequate ventilation: Blown cellulose. Best $/R, good air-blocking, recycled content.
- Cathedral ceilings, complex framing, or air-leakage problems: Closed-cell spray foam at roof deck (hot-roof) or hybrid.
- Rim joists, knee walls, fire-rated assemblies: Mineral wool batt (Rockwool/Roxul).
- Standard attic when fiberglass is preferred: Loose-fill fiberglass (Owens Corning, Knauf, CertainTeed).
- Almost never in attic floors: Fiberglass batts. They don't fill irregular cavities and air-leak heavily.
R-Value per Inch
| Material | R-Value per Inch | Inches Needed for R60 |
|---|---|---|
| Closed-cell spray foam | R6.0–R7.0 | 9"–10" |
| Open-cell spray foam | R3.5–R4.0 | 15"–17" |
| Blown cellulose | R3.2–R3.8 | 16"–19" |
| Loose-fill fiberglass | R2.2–R2.7 | 22"–27" (settled) or R2.5 dense-pack |
| Fiberglass batt | R3.0–R3.7 | 16"–20" |
| Mineral wool batt | R3.7–R4.3 | 14"–16" |
R-value per inch matters when ceiling height in the attic is limited. In a typical Toronto bungalow with truss-framed attic, you have 18"–30" of clearance — plenty for any material. In a 1920s East York attic with shallow rafter bays, closed-cell spray foam may be the only way to hit R60 without losing usable space.
Air-Sealing Performance
Air sealing is where the materials diverge most dramatically. Air leakage causes 30–50% of total heat loss in poorly sealed homes — sometimes more than conduction.
| Material | Air-Sealing Rating | Notes |
|---|---|---|
| Closed-cell spray foam | Excellent | Air barrier built-in, no separate sealing needed |
| Open-cell spray foam | Good | Air barrier built-in but lower density |
| Blown cellulose (dense-pack) | Good | At 3.5+ lb/cuft density, near-air-barrier performance |
| Blown cellulose (loose-fill) | Fair | Reduces convection but not an air barrier |
| Loose-fill fiberglass | Poor | Air passes through readily |
| Fiberglass batt | Poor | Air passes through, edges leak |
| Mineral wool batt | Poor | Same as fiberglass |
The takeaway: only spray foam is itself an air barrier. Every other material requires separate air sealing of penetrations before installation.
Moisture Behavior
Toronto's climate creates two moisture stresses on attic insulation: winter condensation (warm interior moisture meets cold roof deck) and summer humidity (hot humid attic air meets cool ceiling).
| Material | Moisture Performance | Risk |
|---|---|---|
| Closed-cell spray foam | Excellent — vapor retarder | Can trap moisture if installed over wet substrate |
| Open-cell spray foam | Fair — vapor permeable | Can hold moisture; not recommended for cold climates without vapor control |
| Blown cellulose | Good — manages moisture | Borate-treated, dries slowly but doesn't lose R-value when damp |
| Loose-fill fiberglass | Fair — water passes through | Loses R-value when wet, recovers when dry |
| Fiberglass batt | Same as loose-fill | Same |
| Mineral wool batt | Excellent — hydrophobic | Sheds water, doesn't lose R-value when damp |
For a Toronto-specific issue: many old homes have intermittent ice dam leaks that wet the attic insulation. Cellulose and mineral wool tolerate this best. Closed-cell spray foam tolerates it but masks the leak (you don't see water staining). Open-cell spray foam can hold moisture and grow mold.
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| Material | Settling | R-Value at 5 Years |
|---|---|---|
| Closed-cell spray foam | None | 100% |
| Open-cell spray foam | None | 100% |
| Blown cellulose | 10–15% | R52–R54 (from R60 install) |
| Loose-fill fiberglass | 2–5% | R57–R58 (from R60 install) |
| Fiberglass batt | None (but compresses if walked on) | 100% if undisturbed |
| Mineral wool batt | None | 100% |
The settling number is the strongest argument for fiberglass over cellulose in Toronto attics where you want sustained R-value 10+ years. The counter-argument: cellulose is cheaper per inch of install, so over-installing to R65 to settle to R55 is roughly cost-equivalent to installing R60 fiberglass.
Fire Performance
| Material | Fire Behavior |
|---|---|
| Closed-cell spray foam | Combustible — requires thermal barrier (drywall) below in conditioned attics |
| Open-cell spray foam | Combustible — same |
| Blown cellulose | Class A fire rating — borate-treated to resist ignition |
| Loose-fill fiberglass | Non-combustible (glass) but binders can burn |
| Fiberglass batt | Same as loose-fill |
| Mineral wool batt | Non-combustible — melts at 1,000°C+ |
For Toronto attics, fire performance matters most around recessed lights, chimneys, and attic-floor penetrations. Mineral wool batts are often used as a fire-rated transition between insulation and chimney cleanouts.
Environmental Impact
| Material | Recycled Content | GWP (CO2 Equivalent) |
|---|---|---|
| Closed-cell spray foam (HFO blowing agent) | 0–10% | Low (HFO replaces high-GWP HFC) |
| Closed-cell spray foam (HFC blowing agent — older formulations) | 0–10% | Very High — being phased out |
| Open-cell spray foam | 0–5% | Low — water-blown |
| Blown cellulose | 80–85% (recycled newsprint) | Very Low |
| Loose-fill fiberglass | 30–60% recycled glass | Low-Medium |
| Fiberglass batt | 30–60% recycled glass | Low-Medium |
| Mineral wool batt | 40–75% recycled slag | Medium |
For homeowners pursuing LEED or Passive House certification, blown cellulose is typically the lowest-impact choice. For homes pursuing Net Zero retrofit, low-GWP closed-cell spray foam (Demilec Heatlok HFO) provides the best thermal performance with acceptable carbon footprint.
Cost per Square Foot (1,500 sqft Toronto attic, install only, no removal)
| Material | Cost per SqFt | Total |
|---|---|---|
| Blown cellulose | $1.20–$1.60 | $1,800–$2,400 |
| Loose-fill fiberglass | $1.40–$1.80 | $2,100–$2,700 |
| Fiberglass batt R60 | $1.80–$2.40 | $2,700–$3,600 |
| Mineral wool batt R60 | $2.20–$3.00 | $3,300–$4,500 |
| Open-cell spray foam (10") | $3.50–$4.50 | $5,250–$6,750 |
| Closed-cell spray foam (3" floor) | $2.80–$3.70 | $4,200–$5,500 |
| Closed-cell spray foam (full hot-roof) | $4.50–$7.00 | $6,750–$10,500 |
Lifespan
| Material | Functional Lifespan |
|---|---|
| Closed-cell spray foam | 50+ years |
| Open-cell spray foam | 40+ years |
| Blown cellulose | 30+ years (with periodic top-up to maintain R-value) |
| Loose-fill fiberglass | 50+ years |
| Fiberglass batt | 50+ years |
| Mineral wool batt | 75+ years |
In practice, all materials outlast the homeowner's tenure if installed correctly and not damaged.
Common Toronto Use Cases
Case 1: 1960s Leaside bungalow, 1,500 sqft attic, truss framing, R30 existing. Tier 2 with blown cellulose to R60. Cost: $5,500. Reasoning: standard scope, best $/R, no geometric complications. Case 2: 1920s East York 1.5-storey, complex framing with knee walls, R20 existing, ice dam history. Hybrid: closed-cell spray foam at knee walls and roof deck transitions, blown cellulose at flat attic floor. Cost: $8,500. Reasoning: spray foam handles the geometry that cellulose can't fill cleanly. Case 3: 1990s High Park two-storey, 1,200 sqft attic, R40 existing, no ice dams. Top-up only with blown cellulose to R60. Cost: $2,800. Reasoning: existing insulation is already adequate; just need a refresh. Case 4: 2010 Leslieville townhouse with cathedral ceilings (no attic). Closed-cell spray foam at the underside of the roof deck. Cost: $7,000. Reasoning: only material that fits the assembly. Case 5: 1955 Beaches detached, suspected vermiculite. Vermiculite testing first; if positive, abatement, then blown cellulose. Cost: $9,000–$13,000. Reasoning: standard cellulose scope after the abatement, since the geometry isn't complex.When to Avoid Each Material
Avoid closed-cell spray foam if: The roof deck has a known leak (foam masks the leak; water rots the deck under the foam). Or if the home is being sold within 5 years to a buyer who values "natural" materials (some buyers see spray foam as a negative). Avoid open-cell spray foam in Toronto attics: Toronto's climate has too much moisture stress. Open-cell holds moisture and can grow mold. Use only with explicit vapor control. Avoid blown cellulose if: Attic has chronic moisture issues that haven't been resolved (cellulose holds moisture and dries slowly). Avoid fiberglass batt if: You're insulating an attic floor (it doesn't fill irregular geometry). Use loose-fill fiberglass or cellulose instead. Avoid mineral wool batt as primary attic floor insulation: Cost is too high vs cellulose for equivalent R-value. Use mineral wool for fire-rated transitions, rim joists, or knee walls.Brand Notes
Closed-cell spray foam: Demilec Heatlok HFO is the dominant Toronto product (low-GWP, ULC-listed). Icynene ProSeal HFO is the runner-up. Huntsman Building Solutions and BASF Walltite are also available. Blown cellulose: GreenFiber Cocoon is the most common in Toronto. Applegate is regional but available. Both are borate-treated for fire and pest resistance. Loose-fill fiberglass: Owens Corning ProPink is the most-installed loose-fill in Toronto. Knauf Jet Stream Ultra is a higher-density premium option. CertainTeed InsulSafe SP rounds out the top three. Mineral wool: Rockwool (formerly Roxul) is the dominant brand. Comfortbatt for residential, Comfortboard for exterior continuous insulation.For brand-specific R-value certificates and warranty terms, see [Attic Insulation Toronto: Complete 2026 Upgrade Guide](/blog/attic-insulation-toronto-2026).
What to Specify in Your Scope of Work
When asking for quotes, specify:
- 1. R-value target (R60 minimum for OBC compliance)
- 2. Material (or "any of cellulose/loose-fill fiberglass — please quote both")
- 3. Density (for cellulose, request 1.2–1.5 lb/cuft minimum for blown attic floors)
- 4. Settled R-value, not installed R-value (cellulose settles 10–15% — install R65–R68 to settle to R60)
- 5. Air sealing scope (comprehensive, not just attic hatch)
- 6. Baffles (every rafter bay, not just visible ones)
- 7. Pot light covers (specify quantity)
- 8. Documentation (photo, R-value certificate, depth markers)
Bottom Line for Toronto Material Choice
For 80% of Toronto attics: blown cellulose at R65 (settles to R60) with comprehensive air sealing. Cheapest, environmentally best, performs well in Toronto climate.
For attics with complex geometry, ice dam history, or cathedral elements: hybrid with closed-cell spray foam at problem areas + cellulose at flat floor.
For attics where settling is a major concern (you don't plan another insulation top-up for 20+ years): loose-fill fiberglass (Owens Corning ProPink or Knauf Jet Stream Ultra) at R62.
For specialty applications (knee walls, rim joists, fire transitions): Rockwool batts.
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Choosing materials for your Toronto attic insulation? RenoHouse installs all four primary attic materials and will recommend based on your home's specific geometry, age, and rebate strategy. Visit our [attic insulation upgrade service page](/services/exterior/attic-insulation-upgrade) or schedule an [insulation thermal audit](/services/inspections-diagnostics/insulation-thermal-audit) to scope materials precisely for your home.
