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Specifying natural insulation

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Sustainability editor Hattie Hartman reports on the growing market for cellulose, wool, hemp and flax

When space and budget permit, most green architects specify natural insulation. Online sustainable specification tool GreenSpec recommends organic insulations first, natural mineral insulations second, and those derived from non-renewable petrochemicals last. The Scottish Ecological Design Association’s 2008 guide to reducing toxic chemicals in buildings advises using cellulose, wool or flax in place of mineral fibre insulation and foamglass in place of polystyrene.

But choosing the right insulation for a project can be a daunting task. Products range from sheep’s wool, hemp and flax to high-tech aerogels and multifoils - and everything in between. New products are constantly being developed. Over the last five years, these products have increasingly been specified as an alternative to conventional mineral wool fibre and polystyrene products.

Natural insulation comprises a small but important market niche. Neil May of Natural Building Technologies estimates that between £8 million and £10 million was spent on natural insulation products in the UK last year - that’s around 0.8 per cent of all insulation sold (up from 0.2 per cent five years ago). Second Nature, a Cumbria-based manufacturer of sheep’s wool insulation, reports a 30 per cent annual increase in sales for the last five years. In Germany, natural insulation represents 6 per cent of the market.

Mass-market supplier Wolseley has capitalised on the trend for natural insulation and offers Pavatex softwood fibre and Hemcrete insulation through its Sustainable Building Centre, in addition to conventional Rockwool and Knauf mineral wool and foam products.

Natural insulation products usually require a thicker profile to achieve the same thermal performance (see table on page 44) and they often cost more. But thermal performance and depth of profile are not the only criteria for selecting insulation. As buildings become more and more airtight, breathability and toxicity are of increasing concern, but there is a paucity of research on indoor air quality.

Manufacturers of conventional insulation products have responded to the growth of natural insulation products with intensive marketing campaigns that demonstrate the relative insignificance of embodied energy in the overall energy equation, such as the 2002 Kingspan report ‘Insulation for Sustainability’, which was written by energy consultant XCO2.

Almost all green building experts agree that when it comes to insulation, more is better than less, and proper detailing is as important as the actual choice of product. It’s better to insulate with conventional materials than to insulate poorly. ‘We always tell clients on a tight budget to use more of a conventional insulation rather than less of a pricier natural one,’ says Chris Herring of the Green Building Store.

The current emphasis on retrofitting existing stock means that a massive market is beginning to open up. Russell Smith of eco-consultancy Parity Projects has just completed the renovation of his own home in Carshalton, London, where he has trialled eight types of insulation, with some fitted side-by-side in the same wall in order to directly compare their performance. Smith is currently monitoring U-values for the different products.

One of the main lessons from Smith’s experience is the information about the products that manufacturers fail to disclose, such as ease of cutting, fixing and availability. ‘The endgame is lots of insulation. If we want to get this into every house in the country, we need to sort out the logistics and know what’s easy to install. Some of the modern materials just aren’t,’ says Smith.

The ultimate guide to insulation, which takes into account all these factors and their relative weighting, is still to be written. In the meantime, architects must decide for themselves which product is the best.

Earthwool Loft Roll

Manufacturer and supplier Knauf
Material Glass mineral wool
Special properties Incorporates Ecose, a natural, formaldehyde-free binder with a high content of recycled glass bottles
Format Glass mineral wool roll
Application Loft insulation
U-value 0.13W/m2K
Thermal conductivity 0.04W/mK at 300mm
Fixing Usually laid in two layers, with the first layer between the joists and the second layer overlapping the first layer at right angles to joists
Layers 100mm base layer overlaid with a 200mm layer
Place of origin Cwmbran, Wales
Distributed in the UK from August 2009

NBT HempWood

Manufacturer Buitex
Supplier Natural Building Technologies
Material 55 per cent wood fibre, 30 per cent hemp and 15 per cent textile fibre binder
Special properties Higher density (50kg/m3) than other natural insulation products. It has excellent slump resistance and delivers tight-fit breathability
Application Lofts, walls and floors in timber new build and renovation-conservation jobs
U-value Not available
Thermal conductivity 0.038W/mK
Fixing Pressed into place between studs to ensure a snug fit with no gaps
Place of origin France
Distributed in the UK from March 2009


Manufacturer Pavatex
Supplier Natural Building Technologies
Material Offcuts and woodchips of native Swiss softwoods and a mineral layer of silicates sourced from German quarries, bound with lignin, timber’s natural binding agent
Special properties Breathability and moisture control. The dense board of 98 per cent woodfibre locks up approximately 1.2kg of CO2 for every 1kg of product
Application Internal walls in refurbishment projects, suitable for masonry and timber in dry areas
U-value Up to 0.34W/m2K
Thermal conductivity 0.042W/mK
Fixing Screw fixings or wide staples
Place of origin Switzerland
Distributed in the UK from July 2008

Thermafleece PB20

Manufacturer and supplier Second Nature
Material Sheep’s wool and recycled polyester
Special properties Easily compressed and packaged into a tight roll without losing any thickness once unrolled
Format Rolls of 100mm and 70mm thickness, with widths of 370mm and 570mm
Application New build and refurbishment, loft, wall and timber-framed buildings
U-value 0.16W/m2K at 270mm
Thermal conductivity 0.042W/mK
Place of origin Dacre, Cumbria
Distributed in the UK from February 2009

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