Warm Roof Insulation for Retrofit Roof Upgrades
Warm roof insulation is an effective way to improve the energy efficiency, comfort and moisture performance of a pitched roof. By insulating at rafter level, the roof space becomes part of the thermal envelope, helping to reduce heat loss while supporting a breathable, airtight and durable roof build-up.
Recommended U-Values for Warm Roof Insulation
When upgrading a pitched roof, the insulation specification should be designed to meet current Building Regulations and the required U-value for the project. Exact requirements vary depending on whether the work is a retrofit, renovation or new build, so always confirm the target U-value with Building Control or a qualified professional before installation.
Natural fibre insulation, wood fibre sarking boards and airtightness membranes can work together to create a high-performance warm roof system that manages heat, air movement and moisture.
Retrofit Warm Roof Insulation Options
Warm Roof Installation from Above
This retrofit warm roof system is suitable when the external roof covering is being removed while the ceiling below the rafters is retained. It is a practical option for roof refurbishments where the aim is to improve insulation, airtightness and weather protection from the outside.
- Install Pro Clima Dasatop membrane (1) over and between the rafters, sealing joints and laps with Pro Clima Tescon Vana tape (2) to improve airtightness.
- Fit flexible natural fibre insulation (3) between the rafters to reduce heat loss through the roof structure.
- Add wood fibre sarking board (4) above the rafters for additional thermal performance and breathability.
- Install Pro Clima Solitex Plus (5) Sealed with the Tescon Vana Airtight tape as the external windtight and weather-resistant membrane layer.
- Secure counter battens (6) with Heco Topix screws to hold the sarking board and membrane in place.
- Fix horizontal battens (7) ready for the chosen roof covering, such as slate or tiles (8).
Warm Roof Installation from Below
- Assess the existing roof covering and felt (9) before installing insulation from inside the roof space*.
- Where a breathable felt is required, install Pro Clima Solitex Plus and seal with Pro Clima Orcon F.
- Fully fill the rafter zone with flexible natural fibre insulation (10) for improved thermal and acoustic performance.
Option 1: Wood fibre board with Lime Plaster Finish
- Fix rigid wood fibre board (11) beneath the rafters to reduce thermal bridging and create a continuous insulation layer.
- Finish the wood fibre boards with lime plaster and reinforcing mesh to create a breathable internal surface (12).
Option 2: Service Gap and additional Airtightness Layer
- Install Pro Clima Intello Plus as an internal airtightness and vapour control layer (13).
- Fix horizontal battens (14) to create a service cavity and support the internal finish.
- Add wood wool boards (15) as the backing layer for a breathable plaster finish
- Finish with lime plaster and reinforcing mesh (16)
* If a modern draped breather membrane is in place, insulation may be fitted up to the membrane. Where counter battens and a taut membrane are already installed, the rafter zone can be fully filled with insulation.
If a non breathable underfelt is in place, a ventilation gap of 50mm should be left between the insulation and the felt.
Warm Roof Installation from Above and Below
Where access permits, a complete roof system can be created by combining the above-rafter and below-rafter installation methods described in the preceding diagrams and guidance.
Choosing the Correct Warm Roof Insulation System
The best warm roof insulation build-up depends on the condition of the existing roof, the required U-value, the available rafter depth and whether the installation is being completed from above, below or both. For breathable roof insulation systems using wood fibre boards, natural fibre insulation and Pro Clima airtightness products, choose compatible materials and confirm the specification before work begins.
Need help selecting materials for a warm roof retrofit? Our team can advise on natural insulation, wood fibre boards, breather membranes, airtightness tapes and vapour control layers for sustainable roof upgrades.
Flexible, natural fibre insulation options:
Thermafleece Cosywool Insulation
Pavaflex flexible woodfibre insulation