Non-Habitable Roof in retrofit data sheet

Technical information

The total thickness of roof insulation we recommend is 400mm, laid in 3 layers. The first layer is laid between the ceiling joists and should be the same depth as those joists. The second and third layers should be cross laid over the top of the first layer and ceiling joists. If an external wall insulation system is being installed then the loft insulation should continue over the internal skin of the external walls and down to touch the external wall insulation.

Ensure void between rafters and gable walls are filled with insulation to the same height as the main insulation to avoid heat loss.

The roof space above the insulation should be adequately ventilated using felt lap vents installed within the overlaps of the existing roofing felt to allow air movement above the insulation and thereby reducing the formation of condensation on the underside of the felt.

Hints & Tips

Although not harmful, when dealing with fibre insulation gloves and respiratory protection should be worn to avoid irritation.

Make sure insulation is fitted snugly between joists and butted up over joist to avoid any air gaps that can contribute to unwanted heat loss.

Adequate ventilation space should be provided around recessed ceiling lights. Alternatively proprietary recessed light protection boxes should be installed.

All electrical cables within the roof space should either be tacked to the sides of joists or laid on top of the insulation. Do not encase cables within the insulation.

Ensure all pipework within loft space is fully lagged with pipe insulation.

Ensure any loft hatches are well sealed and are themselves insulated.