Roof insulation at rafters

Detail for insulation installed to the ceiling of a room in roof, to replace existing thin insulation.To increase thermal efficiency and prevent heat loss through the roof of the building. Insulation is shown in-plane of rafters where existing roof membrane is non-breathable. Ensure adequate ventilation between insulation and roofing membrane- minimum: 25mm or as shown on detail.

Target U-value: 0.18W/m2K

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Roof insulation- Existing non-permeable membrane (HR)

Detail for the insulation of roof rafters, internally, where the existing roofing membrane within a roof is impermeable/ High resistance (HR underlay to BS 5250: 2011); and as such: a minimum ventilation gap must be provided to the eaves in order to ventilate the roof space.

This detail demonstrates the installation of new insulation, to a depth of 200-250mm to achieve the target U-value, to the existing rafters with a 50mm ventilation gap behind to ensure adequate ventilation of the new insulation.

Target U-value: 0.18W/m2K

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Roof insulation to flanking wall of a room-in-roof

A roof insulation detail for the flanking wall of a room-in-roof or a storage space in roof, with additional loft insulation buildup as required to a minimum depth of 400mm to achieve the target U-value.

In this detail, insulation is installed to the upright stud walls between a room-in-roof and the loft space; along with insulation and membranes in plane of the existing rafters (where the existing roof membrane is non-breathable). It is important to ensure adequate ventilation over any insulation installed in the plane of the existing rafters.

In most cases, some loft insulation will already be installed (typically to a depth of between 50-200mm) in which case it is only required to add enough insulation to increase this to 400mm.

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