Four Control Layers
| Layer | Function | Typical Material |
|---|
| 1. Water (WRB) | Bulk water defence | Self-adhered or fluid-applied membrane |
| 2. Air barrier | Stops uncontrolled air movement | Self-adhered membrane, fluid-applied |
| 3. Vapour control | Manages moisture diffusion | 6 mil poly (≤60 ng/Pa·s·m²) |
| 4. Thermal | Resists heat flow | CI outboard + cavity batt |
All four layers must be continuous — no gaps. Air leakage = 25–40% of heating load.
Continuous Insulation (CI)
| Product | R/inch | Vapour Perm | Notes |
|---|
| EPS | R-3.8–4.2 | Moderate | Stable R, cost-effective |
| XPS | R-5.0 | Low | R-value degrades over time |
| Polyiso | R-5.7–6.5 | Low | Derate to R-5.0 for ON winter |
| Mineral wool | R-4.0–4.3 | High (open) | Non-combustible, allows drying |
Steel studs reduce cavity-only R-value by 40–60%. CI is mandatory (NECB).
Air Barrier — Self-Adhered Membrane
- Side laps: 75 mm min. | End laps: 150 mm min. (shingle style)
- Substrate must be clean, dry, primed, ≥5°C
- Roll all laps with steel J-roller; watch for fish-mouths
- Detail penetrations before field membrane
- Wrap 100 mm into window rough openings
Fluid-Applied Alternative
- Spray: 40–60 mils WFT; roller: 20–40 mils DFT
- Verify thickness with mil gauge every 10 m²
- Embed polyester mesh at dissimilar material joints
Vapour Barrier & Batt Insulation
Vapour Barrier (6 mil Poly)
- Warm side of insulation — always interior in Ontario
- Laps: 100 mm, sealed with acoustic sealant
- Seal every penetration (boxes, pipes, HVAC)
- Poly slightly slack — not drum-tight (tears with movement)
Batt Insulation
| Property | Fiberglass | Mineral Wool |
|---|
| R/inch | R-3.2–3.8 | R-3.8–4.2 |
| Moisture | Absorbs, slow dry | Hydrophobic |
| Sound (NRC) | 0.90–0.95 | 0.95–1.05 |
No compression, no gaps, split around wires. 2% void = 10–15% R-value loss.
Window & Curtain Wall
Window Flashing Sequence
- 1. Sill pan (sloped out, end dams) → 2. Jambs over sill → 3. Head over jambs
- Shim at hinge/lock points; horseshoe shims only
- Seal frame to air barrier continuously
Curtain Wall
- Mullion tolerance: ±3 mm
- Verify embeds with total station before delivery
- Sequence: embeds → mullions → glazing → perimeter seal
- 421A Glazier certification required (compulsory trade)
Cladding & Rain Screen
Rain Screen Principles
- Drainage cavity: 19 mm min. (25 mm preferred)
- Weep openings at base; vents top & bottom; bug screens
- Pressure equalization reduces water penetration
Cladding Types
- Metal panel (ACM): FR mineral core ONLY — PE core prohibited
- Fibre cement: stainless/galv. ring-shank nails, flush heads; 3 mm gap at butts
- EIFS: drainage type only — avoid barrier EIFS
Sub-Girt Systems
- Thermal break clips maintain 80–95% of CI R-value
- Clip spacing: ~600 mm vert. × 400–600 mm horiz.
Code References
- OBC Part 5: Environmental separation — air/vapour barriers, insulation, rain control
- NECB 2020: Effective R-values, air leakage, thermal bridging (Climate Zone 6)
- OBC Part 12 / SB-10: Energy efficiency — CI requirements
- NAFS / CSA A440: Window & curtain wall performance
- CAN/ULC-S134: Fire test of exterior wall assemblies
- OHSA O. Reg. 213/91: Fall protection, scaffolding
- OHSA O. Reg. 833: Chemical exposure — silica, isocyanates
Safety & Critical Rules
- Spray foam: Evacuate area 24 h; supplied-air respirators for applicators. Isocyanate sensitization is permanent.
- Fibre cement cutting: Crystalline silica — N95 min., dust extraction, OEL 0.025 mg/m³. No dry circular saw cuts.
- Working at heights: Certification above 3 m (O. Reg. 297/13). Harness + engineered anchors.
- Compulsory trades: Glazier 421A, Sheet Metal 308A, Heat & Frost 298A. Verify cards before work starts.
- ACM panels: FR mineral core ONLY. PE core = fire hazard, prohibited by OBC >3 storeys; ban it on ALL projects.
- Thermal barrier: All spray foam requires 12.7 mm gypsum between foam and occupied space.
Pro Tips
- #1 air leak path: membrane-to-window-frame junction. Seal every single window with fluid-applied or gun-grade sealant.
- Pre-drywall insulation walk: Inspect every cavity before closing up. Compressed batts, gaps, and missed headers are invisible after drywall.
- Mock-up everything: Curtain wall, rain screen cladding, EIFS — build and approve a mock-up before production.
- Photo document every concealed layer (WRB, flashing, CI, sill pans) before cladding covers it.