Roof Insulation and Thermal Envelope Continuity

Roof insulation must connect continuously to the wall and work with air and water control. Between-rafter thickness is only part of the assessment.

Where the boundary runs

A cold loft usually places the thermal boundary at ceiling level; a conditioned attic may follow the slopes. Do not mix these strategies without coordinating layers and ventilation.

Rafters and junctions

Repeating timber or metal elements affect heat transfer. Assess eaves, ridges, gables and wall connections separately from the clear area.

Air barrier

Detail the membrane or other air barrier at wall plates, walls and penetrations. Plan sealing access before lining installation.

Water and drying

Roof covering, underlay and vapour control serve different functions. Define ventilation spaces and build-up for the particular system; one arrangement does not suit every roof.

Common mistakes

Compressed insulation, empty corners and uncoordinated penetrations undermine the design. Before covering, inspect layers, record details and consider an interim airtightness test.

ZeroHouse assessment diagram; not a construction detail.

Project review matrix
Item	Parameter	Check / result
Slope	Repeating members	Thermal assessment
Eaves	Connection	Detail
Penetration	Air + water	Sealing

What this means for your project

Request eaves, ridge and penetration details with the installation sequence. Confirm concealed joints remain accessible before covering.

Sources and scope of review

Checked: 2026-09-09. Editorial guidance; not evidence of compliance for an individual building.