Roof Insulation Systems
Insulation Systems for Pitched and Flat Roofs
Roof insulation can be installed in both pitched and flat roof constructions, depending on the structural design of the building.
Pitched roofs can be insulated either over the rafters or under the rafters, while flat roofs allow installation over joists or beneath the structural deck. Each system is designed to optimise thermal performance, reduce build-up depth and simplify installation.
Below, you can explore the appropriate insulation system based on your roof construction type.
Engineered for performance. Designed for real-world construction.
Roof Insulation System Comparison
Pitched Roof – Over Rafter
Insulation installed above the rafters, creating a continuous external thermal layer.
Reduces thermal bridging and preserves internal ceiling height.
Typically uses breathable multifoil systems for secondary weather protection.
Best suited for:
• New build projects
• Full roof renovations
• High-performance external build-ups
Pitched Roof – Under Rafter
Insulation installed internally beneath rafters.
Improves thermal performance without removing roof coverings.
Often used in refurbishment and loft conversions.
Best suited for:
• Internal upgrades
• Retrofit applications
• Projects with limited external access
Flat Roof – Over Joist
Insulation installed above joists, forming part of a warm or hybrid roof build-up.
Creates a continuous thermal layer and reduces structural heat loss.
Best suited for:
• Warm roof construction
• New flat roof systems
• Structural deck upgrades
Flat Roof – Under Joist
Insulation installed internally at ceiling level.
Commonly used in cold roof constructions where ventilation above insulation is required.
Best suited for:
• Refurbishment projects
• Internal ceiling upgrades
• Situations where external roof covering remains intact