Combine Layers to Hit Targets
Shallow rafters are the classic attic challenge. To meet energy code without raising the roof dramatically, stack insulation types: high-density batts or spray foam in the bays plus a continuous layer that breaks thermal bridges. In re-roof scenarios, rigid foam above the deck (polyiso or GPS) with taped seams delivers continuous R and protects sheathing temperatures; inside-only projects can add continuous insulated panels or service-channel furring below rafters to increase depth.
Vented vs. Unvented Approaches
For vented assemblies, install baffles to maintain soffit-to-ridge airflow—even around hips/dormers—then dense-fill the cavity and add continuous insulation below rafters before drywall. For unvented roofs, achieve the required ratio of exterior (or closed-cell foam in-bay) to interior insulation so winter dew point stays outside the sheathing. Pair with a vapor-smart interior membrane that allows seasonal drying.
Thermal Bridges & Details That Matter
Bridge-break the knee-wall caps, ridge, and skylight returns; use insulated attic hatches with compression gaskets; gasket electrical boxes and choose IC/AT fixtures or wafer LEDs so the air barrier isn’t Swiss cheese. At transitions (dormer cheeks, valleys), draw continuity lines for both air and thermal layers—then build exactly to those lines.
Prove Performance
Commission with blower-door and duct-leakage testing prior to drywall. Infrared scans on a cool morning will flag missed bays and leaky penetrations before it’s too late.
Assembly diagrams and shopping lists for slim rooflines live in our energy-efficient attic remodeling in NYC overview.