Roof insulation to existing underdrawn ceiling

Insulated plasterboard fitted to the underside of existing ceiling rafters. For use where roof void is well ventilated or has breathable membrane and where existing ceiling is to be retained.

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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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Roof Insulation for Increased depth Rafters

Detail for the internal installation of woodfibre insulation to an existing roof; where existing rafters are not deep enough to allow 200-250mm insulation to be installed. In this detail the existing rafters are extended with additional timber to fit insulation to the required depth.

To be used only where a suitable vapour-permeable roofing membrane is present above. (check brand and sd value upon inspection of roof).

Target U-value : 0.18W/m2K

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Roof Insulation- Existing membrane LR

Roof insulation to existing rafters, where the existing roofing membrane below tiles/slates is a Low Resistance (LR) membrane. [See Technical Description for definition as of BS 5250: 2011]

Insulation in plane of rafters where existing roof membrane is low resistance vapour permeable. Need to ensure adequate ventilation behind insulation.

Insulation boards and proprietary basecoat finish with vapour control render applied to inside face of insulation.

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