Retrofitting sloping ceilings can be a challenge, particularly in top-floor rooms or loft conversions where space, breathability, and performance are critical. Thermoroom offers a practical, high-performance internal insulation system using rigid wood fibre boards installed onto sloped ceilings with mechanical fixings.
Made with a carbon-negative manufacturing process, Gutex Thermoroom wood fibre provides excellent thermal resistance, helping to improve comfort in top-floor rooms prone to overheating in summer and heat loss in winter. Its dense structure also delivers soundproofing benefits, enhancing acoustic comfort.
Thermoroom is breathable and hygroscopic. It helps manage moisture within the building fabric, preventing the build-up of condensation and reducing the risk of mould, essential for maintaining building health over time. Sloping ceiling insulation should always be installed at the same time as internal wall insulation to achieve the best thermal performance, to minimise thermal bridging and to simplify the airtightness detailing.
The boards can be fixed directly to existing lime plaster sloping ceilings or, where plaster has been removed exposing rafters, a 25mm wood wool board such as Cewood or Celenit can be installed to the rafters followed by Gutex Thermoroom. The Thermoroom is secured to the rafters in both cases using approved thermally broken mechanical fixings. E.g. Fischer TermoFix 6H-NT.
Once installed, the junctions with the vertical walls and horizontal ceiling are primed with Tescon Sprimer, then taped with Contega Solido SL. This ensures that, once plastered with Lime Green Solo, it will be airtight and ready for decoration. As an alternative to Tescon Sprimer and airtight tape, the wall and ceiling junctions can be sealed with Aerosana Visconn Fibre.
This system is ideal for retrofit projects where roof coverings cannot be disturbed. It offers an effective internal solution that enhances thermal performance while retaining the existing structure. Paired with appropriate Internal Wall Insulation and airtightness measures, Thermoroom helps meet regulatory U-values and creates healthier, more energy-efficient living spaces without compromising breathability.
About Sloping Ceiling Insulation
Thermoroom is a rigid, breathable wood fibre insulation board specifically designed for internal wall and ceiling upgrades. For sloped ceilings, it can be installed directly onto lime-plastered ceilings or onto a structural board fixed to rafters. Using thermally broken mechanical fixings, it provides an effective way to insulate from the inside without disturbing the external roof covering.
The dense wood fibre board delivers excellent thermal resistance, helping to reduce heat loss and improve comfort in loft-conversions or top-floor rooms. It also offers strong acoustic insulation, softening external noise and improving internal sound quality.
Being vapour open and hygroscopic, Thermoroom supports moisture movement within the building fabric, an essential feature for preserving older structures and reducing the risk of condensation and mould.
Once installed, the boards are finished with Lime Green Solo lime plaster for a breathable wall system. The result is a dry, effective, and sustainable retrofit solution that improves thermal performance while maintaining building breathability.
A typical uninsulated sloping ceiling has a U-Value of 3.76W/m²K.
With 100mm Gutex Thermoroom, the U-value is 0.36W/m²K, an improvement of 90.4%.
Thermoroom is a natural, breathable wood fibre insulation board that is ideal for internal retrofitting of sloping ceilings. It improves thermal performance, reduces overheating, and enhances acoustic comfort in loft-conversions and top-floor spaces. Mechanically fixed from the inside, the system is ideal where external roof coverings remain untouched. Thermoroom’s hygroscopic qualities allow it to absorb and release moisture safely, helping to regulate indoor humidity and prevent condensation. As a material with a carbon-negative production process, it supports sustainable building goals and contributes to healthier indoor environments. Combined with appropriate airtightness and vapour control measures, it offers a practical solution for low-energy retrofits.
Key Benefits
Ideal for retrofitting
A simple high-performance insulation solution for sloped ceilings
High thermal performance
Regulates temperature to protect against cold in winter and overheating in summer
Moisture & condensation management
Helps manage both moisture and condensation
Quiet
Enhances sound insulation for quieter indoor environments
Compatible
can be used with lime plaster finishes
Sustainable
Made with low carbon, recycled wood chips
Lime plastered sloping ceilings
If the existing plaster is lime-based and therefore vapour open, it does not need to be removed prior to installing the Gutex Thermoroom boards, however any existing wallpaper or non-breathable paint should be removed or scratched off before installation. If you are unsure of the type of plaster, you can test it; lime plaster when submerged in vinegar will create bubbles. Always contact our technical team for advice if you are unsure what type of plaster is on the ceiling or if there is impervious wallpaper or thick plastic-based (non-breathable) paint on the sloping ceiling.
Thermoroom boards are installed on the internal face of sloped ceilings using thermally broken mechanical fixings such as Fischer TermoFix 6H-NT. There should be 6 mechanical fixings per board. The screws should be long enough to go through the Thermoroom and plaster and at least 30mm into the rafters.
Once installed the vertical wall junctions and horizontal ceiling junction can be primed with Tescon Sprimer or Tescon Primer RP and taped with Contega Solido SL airtight tape. Or the junctions can be sealed (without Tescon Sprimer) using Aerosana Visconn Fibre airtight liquid membrane.
The Thermoroom is plastered with Lime Green Solo finishing plaster. The first 5mm layer is applied, followed by reinforcing mesh, then a final layer of 5mm Lime Green Solo. Auro natural paint completes the finish.
This method delivers a robust, breathable insulation from the inside. As it is installed over the top of the existing ceiling, this is a non-invasive method ideal for retrofit projects where roof coverings cannot be disturbed and ceiling plaster cannot be removed. The system improves thermal and acoustic performance while maintaining moisture movement through the structure.
Gypsum plastered sloping ceilings
If the sloping ceiling is currently plastered with gypsum or finished with plasterboard, this must be removed to expose the rafters underneath. Gypsum plaster is not compatible with the vapour open Gutex Thermoroom system and plaster board may not be robust enough for the additional weight of the wood fibre boards.
Once the rafters are exposed, a 25mm thick vapour open wood wool board such as Cewood or Celenit is fixed to the rafters with suitable woodscrews to create a strong background support for the Thermoroom. Thermoroom can then be fixed to the board using thermally broken mechanical fixings (Fischer TermoFix 6H-NT), six fixings per board. The fixings must be long enough to go through the Thermoroom and at least 30mm into each rafter. Once the Thermoroom is installed, the vertical wall junctions and horizontal ceiling junction can be primed with Tescon Sprimer or Tescon Primer RP and taped with Contega Solido SL airtight tape. Or the junctions can be sealed (without a primer) using Aerosana Visconn Fibre airtight liquid membrane.
The Thermoroom is plastered with Lime Green Solo finishing plaster, a 5mm first layer is applied, followed by reinforcing mesh, then a final layer of 5mm Lime Green Solo. Auro natural paint completes the finish.
This method delivers a robust, breathable insulation from the inside. This method is ideal for retrofit projects where roof coverings cannot be disturbed. The system improves thermal and acoustic performance while maintaining moisture movement through the structure.
Pro Clima Contega Solido SL
Pro Clima Aerosana Visconn Fibre
