If the tiles are being removed during a loft conversion a modern breathable roofing membrane is fitted above the rafters. This helps to make the roof more airtight, and energy efficient.

Existing rafters are generally at 400mm centres and either 75 or 100mm deep. To achieve the required U-value of 0.18 W/m².K the rafters need to be battened to increase the depth to 125mm. Rigid insulation is installed between the rafters, leaving a small unventilated air space below the membrane.

Solutions with PIR: TLX Silver BM & PIR

Solutions with mineral wool: TLX Silver BM Glass Wool

If the tiles are not being removed during a loft conversion, and an older non-breathable type 1F felt is in place, then a 50mm ventilated air space is required below the felt.

Existing rafters are generally at 400mm centres and either 75 or 100mm deep. To achieve the required U-value of 0.18 W/m².K the rafters need to be battened to increase the depth to 180mm. Rigid insulation is installed between the rafters, leaving a 50mm ventilated air space below the felt.

Solutions with PIR: TLX Silver 1F PIR