New EPDM Flat Roof Over New DeckingSteven Dickinson
Here you can start to see the buildup of the complete new flat roof, including the decking and insulation. Thermal bridging through the joists is prevented because of the use of the wood fibre insulation – this bridges across the tops of the joists in a continuous slab.
The buildup of the flat roof will be as follows:
- EPDM rubber.
- 18mm Ply or OSB.
- 22mm Isolair (wood fibre with paraffin impregnation for water resistance).
- 40mm Pavatherm (wood fibre insulation).
- LBD breathable membrane.
- 150mm sheeps wool between joists.
- Plasterboard ceiling.
This build up give us a U-value in the region of 0.20 W/m2K when building regs require 0.25 for flat roofs.
It must also be noted that there is no vapor barrier stoping the transfer of vapor up from the room below into the flat roof insulation.
Wool’s unique advantage is its breathability. When wool fibres absorbs moisture, they generate tiny amounts of heat. This warmth acts to prevent condensation in construction cavities by maintaining the temperature above the dew-point in damp conditions.