Building Envelope Assessment (Insulation, Air Sealing, Windows and Doors)
Building Envelope Assessment
This domain tests whether you can inspect the envelope, identify defects, and specify improvements that actually perform. You need working knowledge of insulation types, installation quality, air-sealing locations, window ratings, and door leakage.
Core rules
- Insulation performance depends on material, thickness, density, and installation. RESNET grades installations from Grade I (best) to Grade III (substantial gaps or compression).
- Common air-sealing targets include the attic floor, top plates, penetrations, chases, rim joists, attic hatches, and basement band joists.
- Fiberglass batts, blown cellulose, spray foam, and rigid boards have different R-values per inch and different air-sealing behavior. Spray foam and rigid foam can act as air barriers; batts generally do not.
- Windows are rated by NFRC: U-factor (heat loss), SHGC (solar gain), visible transmittance, and air leakage. In cold climates, prioritize low U-factor; in cooling-dominated climates, low SHGC matters more.
- Doors leak at weatherstripping, sweeps, and frames. Adjust or replace before replacing the door.
Worked example
A 1,000 ft² attic floor has R-11 and is upgraded to R-49. HDD = 6,000, fuel costs $1.20/therm, AFUE = 80%, installed cost = $1,800. Annual savings = 24 × 6,000 × 1,000 × (1/11 − 1/49) / 0.80 = 126.9 therms, or about $152/year. Simple payback ≈ 11.8 years. Air sealing should be priced separately and usually improves the result.
Traps
- Compressing insulation and still claiming full R-value.
- Replacing windows before addressing attic air leakage and insulation.
- Ignoring the rim joist, attic hatch, and recessed lights.
- Specifying insulation without a pressure-boundary air seal.
- Using center-of-glass U-factor instead of whole-window NFRC ratings.