Building thermal insulation · Glass wool
SCG STAY COOL
- Thickness
- 75–150 mm
- Thermal resistance (R)
- 1.79 m²·K/W (75 mm)
How to choose roof insulation
In short
Choose roof insulation on four things: where it goes (under the roof sheet, on the roof structure or on the ceiling), thermal conductivity (λ) — lower is better, thickness, which raises the thermal resistance (R), and the facing, such as foil, which reflects heat and resists moisture.
1. Where it goes
| Position | Suits | Good to know |
|---|---|---|
| --- | --- | --- |
| Under the roof sheet / on purlins | New builds or re-roofing | Stops heat before it reaches the roof space |
| On the ceiling | Finished houses | Easy to do; cover the whole area |
| Under factory roofs | Large metal-sheet roofs | Some types also reduce rain noise |
Use the product the maker specifies for that position.
2. Thermal conductivity (λ) and R-value
- λ (lambda, or k-value) in W/m·K — the lower it is, the less heat the material conducts
- R in m²·K/W — the thermal resistance of the insulation at a given thickness: thickness (m) ÷ λ
- Compare products by R at the thickness you will actually use, and check the mean temperature at which λ was measured
3. Thickness
More thickness gives a higher R, but consider the space available, the weight the ceiling can carry and the cost.
4. Facing
- Foil reflects heat well when there is an air space in front of it, and acts as a vapour barrier
- Unfaced products are used where another layer already covers them
Installation safety
Safety
- Roof work is work at height — use fall protection
- Wear gloves, long sleeves, eye protection and a dust mask when installing glass or stone wool
- Do not cover hot light fittings or electrical equipment
- Follow the manufacturer's installation guide
See the fix: House too hot / hot roof · Compare materials: Stone wool vs glass wool
Related products
Categories and example products for this topic
- SCG STAY COOL — On the ceiling: foil-encapsulated glass wool, 75 and 150 mm, laid without opening the roof
- ROCKWOOL Cool 'n' Comfort RL — Under single-skin metal roofs: stone wool roll laid over foil and wire mesh on the purlins
- ESKIMO FOIL 101F — Reflective facing: double-sided foil under the roof structure or combined with insulation
- ROCKWOOL Cool 'n' Comfort SL — Double-skin metal roofs: stone wool slab between the outer and inner sheets, 25–100 mm
Building thermal insulation · Stone wool
ROCKWOOL Cool 'n' Comfort RL
- Thickness
- 25–50 mm
- Density
- 40–60 kg/m³
- Thermal conductivity (λ)
- 0.034–0.035 W/m·K
Building thermal insulation · Stone wool
ROCKWOOL Cool 'n' Comfort SL
- Thermal conductivity (λ)
- 0.034–0.035 W/m·K
- Thermal resistance (R)
- 1.43–1.47 m²·K/W
- Sound absorption (NRC)
- 1.00–1.05