Knauf Insulation rolls out the benefits

Knauf Insulation has added two new thicknesses to the Crown® Rafter Roll 32 range of glass mineral wool insulation. Specifically designed for use as inter-rafter insulation in room-in-the-roof construction, Crown® Rafter Roll 32 has an impressively low thermal conductivity along with excellent acoustic and fire insulation properties. Used in combination with Knauf Breatheline, a vapour permeable underlay, the two products provide the most cost-effective insulation solution for creating a ‘living loft’.

To maximise the amount of available living space, many new homes are now built with a room-in-the-roof and converting existing lofts is becoming increasingly popular. Constructing a living loft means insulating the pitch of the roof but, although there are a number of methods of doing this, the easiest – and least expensive – is to build a roof structure that ‘breathes’ rather than one that has to be ventilated.

Rafters used for new-build room-in-the-roof construction are generally 200 mm deep. But having to use 50 mm of this depth to provide a ventilated air space above the insulation has meant – until now! – that the remaining inter-rafter void is too shallow to accommodate a layer of mineral wool thick enough to meet the Elemental U-value of 0.20 W/m2K required by the Building Regulations. Fortunately, Knauf Insulation’s recommended solution uses two of its high-performance products, Crown® Rafter Roll 32 and Knauf Breatheline, to overcome this and provide a winning combination.

Knauf Breatheline is a multi-purpose, vapour permeable underlay ideal for use beneath tiles. Its permeability allows vapour created inside the building to escape, overcoming the need for the ventilated space above the insulation. And doing so gives some ‘Big Benefits’: it means the entire depth of the inter-rafter void can now be filled with insulation; there’s no need to fix battens to the sides of the rafters to accurately position it and there’s no need for ventilators. The whole job becomes much easier, much faster and a lot less expensive.

Crown® Rafter Roll 32 is a glass mineral wool product specifically designed for inter-rafter insulation. Its low thermal conductivity, just 0.032 W/mK, along with the opportunity to use the full depth of the inter-rafter void means the thermal performance required by the Building Regulations can be comfortably met – in fact, there’s room to spare! In roofs with 200 mm deep rafters, a layer of Crown® Rafter Roll 32 just 170 mm thick is needed for those with rafters at 600 mm centres and only 185 mm thick for those at 400 mm centres.

And the benefits keep rolling in! The Robust Details created to help builders meet Part E of the Building Regulations in England and Wales and avoid Pre-completion Testing, specify that, for adjoining properties, a layer of mineral wool insulation at least 100 mm thick must be installed in room-in-the-roof construction. Done!

Crown® Rafter Roll 32 is supplied in roll form for easy storage and handling but, when unrolled, has the same characteristics as a semi-rigid slab of glass mineral wool insulation. To provide greater flexibility, rolls are now available in five thicknesses – 50, 65, 75, 85 and 100 mm – and at 1200 mm wide are designed to be cut to fit between rafters spaced at either 400 mm or 600 mm centres. Installation is quick and easy; the material is easy to cut and its semi-rigid nature allows a friction-fit between the rafters, its ‘scrunchiness’ overcoming timber variations and preventing air gaps.

Knauf Breatheline is a non-woven material made by melding a micro-porous polypropylene film between two layers of spunbond polypropylene. Classified as a breather membrane, the film acts as a barrier to water in liquid form but allows the passage of water vapour: 0.24 MNs/g against the defining limit of 0.60 MNs/g set by BS 5250:2002 (Part 3.2). Knauf Breatheline is supplied in rolls 50 m long by 1500 mm wide.

For further information, please visit or call the enquiries hotline on 01270 824024 quoting CR 405 05.

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