Wed 1 Aug 2007
Thermal innerwear
Good insulation is vital to the new breed of low carbon homes, and many of the latest insulation products are made using environmentally friendly manufacturing methods. Roger Hunt reports.Creating a thermally insulated and airtight building envelope is the single most important means of cutting a home’s energy use and therefore its carbon emissions. Indeed, homes that are designed appropriately and are sufficiently well insulated have the potential to need little or no space heating. To achieve this requires a careful choice of materials matched by good detailing and a high standard of workmanship on site.
Insulation solutions abound, ranging from blocks and prefabricated panels to natural fibres. For the specifier the choice of system should depend not only on the level of insulation required but on issues such as the space available for the insulation and the speed of the build programme, together with consideration of factors such as embodied energy, health and safety, cost, lifecycle performance and the eventual disposal of the materials.
Blocks
Rather than adding insulation, one solution is to use construction materials that are designed to be good insulators in their own right. At its flagship scheme at Lincoln Grove in Bladon, Oxfordshire, one of the UK’s first dedicated eco-developers, Kingerlee Homes, has opted to build with a ‘Zeigel’ block called Thermoplan from Natural Building Technologies. These create a single skin building envelope which provides insulation and prevents air leakage.
The Thermoplan blocks combine the traditional qualities of clay with modern technology to produce a sophisticated, thermally efficient and easy to use construction system. This is based upon a combination of thin bed mortar and a ‘tongue and groove’ design which allows the block to be joined with dry vertical joints.
The micro-porous structure of the block, combined with perforations that are extruded during the manufacturing process, makes the block thermally efficient and minimises cold bridging and damp/cold cavities, achieving the highest possible levels of insulation. The system is designed to be fully breathable as well as airtight, which ensures water vapour does not get trapped in the building’s structure, eliminating the risk of internal condensation.
Aircrete is another structural system claiming good environmental credentials due to its cellular structure and thermal mass. For example, H+H Celcon claims that inner skins built with its blocks, and with a cavity of 100 millimetre or less, can achieve a U-value of 0.25W/m²K.
Pulverised fuel ash (PFA) accounts for up to 80 per cent of the raw material used in the manufacture of blocks produced by H+H Celcon. PFA is a by-product of coal-fired power stations and would otherwise be sent to landfill. The company claims that the best results with aircrete are obtained by using its Rå House system. This concept uses thin-joint technology for the external and internal walls and includes a weather-tight roof with the option of foundation blocks and a flooring system.
Fibres
Recycled newspaper is increasingly used for insulation. Excel Building Solutions’ Warmcel cellulose fibre insulation is created using a purely mechanical process to transform the newspaper back into its raw fibrous state. As such, it has extremely low embodied energy. It is also free from CFCs, VOCs or other harmful substances and has zero ozone depletion potential.
The product’s insulation performance is further enhanced by its ability to create a high level of airtightness to prevent thermal convection currents. Warmcel products are available for the insulation of walls, floors and ‘warm roofs’ in timber frame homes, and for loft insulation for any house structure. Warmcel’s loose-fill nature means that the fibre completely fills all gaps around pipework, wiring and other obstructions, thus ensuring optimum performance.
The product is extremely resistant to fire and comfortably meets the fire protection standards required for timber-frame construction. Its fire resistance is achieved through the addition of simple, inorganic salts and it is also resistant to biological and fungal attack, is treated against insects and is unattractive to vermin.
Wool is a natural fibre from a fully renewable resource. Thermafleece, sheep’s wool insulation manufactured by Second Nature UK has now been used for the first time within a volume house build, with a thickness of 250 millimetres installed in the attics of new, but traditionally designed, three-storey homes at the Paul Newman New Homes Upton One development in Northampton.
Because of its ability to rapidly absorb and release water vapour, Thermafleece can help to keep buildings cool in summer and warm in winter. When installed, the fibre adapts to the shape of rafters, joists and studs to provide a tight fit and will retain its thermal performance. At the end of its useful life, it can be recycled for other environmentally friendly applications.
The manufacture of Thermafleece consumes minimal energy and it is claimed to use only 14 per cent of the embodied energy that is used in the manufacture of glass fibre insulation. In addition it is harmless and not irritating to the skin, eyes or respiratory tract so can be installed without gloves or protective clothing and any fibres which happen to reach the living space will present no hazard to health. The necessary insect proofing and fire resistance rating is achieved by the inclusion of naturally derived additives.
Another natural fibre insulation product is Isonat. Available in batts, it is made from hemp and recycled cotton fibres and is flexible, self-supporting and robust, making for ease of use within timber studs in walls and between rafters in roofs and floors. The hemp is grown on British farms without the use of agrichemicals. The fibres (30 per cent of the biomass) are extracted in an entirely waste free and chemical free mechanical process. The remaining biomass is used in the production of other materials. Like wool, Isonat can absorb and release water vapour and does not irritate the skin, eyes or respiratory tract, which makes installation and handling simple. As the fibres are based on cellulose there is no food source for insects or rodents and the product is treated with a fire retardant to meet the requirements of the Building Regulations. On disposal it can either be burnt for energy recovery or composted.
Panels and boards
Structural insulated panels (SIPS), essentially a sandwich construction comprising two layers of sheet material bonded to a foam insulated core, are no longer a new concept. As well as offering a rapid construction method they have the advantage of better thermal performance than normal framed panels because of the absence of thermal bridges associated with studs. One example is the Palgrave Brown SIPS building system with Kingspan TEK, which claims to offers U-values of 0.2W/m2K without the need for additional insulation. The insulation material is CFC-free urethane.
Another system manufactured offsite is Space4 which, having now produced 10,000 units, claims to be the UK’s largest producer of prefabricated housing. The key feature of the product is the high performance insulation injected in the panels before delivery to site, a process which ‘guarantees’ no gaps in the insulation. As a result, it is claimed that the system’s high thermal performance means that the home is kept sufficiently warm to warrant almost no other form of heating.
Insulating board products are another means of introducing thermal insulation. Just one example of their use is at Linden Homes’ Market Quarter development in Chippenham, Wiltshire, where the goal was to reach EcoHomes Excellent standard. Rigid polyurethane (PUR) insulation boards from EcoTherm were selected for both conventional pitched roofs and a green ‘living’ roof. These boards produce no ozone depleting chemicals in the manufacturing process and, it is claimed, the energy consumed during manufacture is repaid within only eight months of being utilised.
Glass-Therm, the EcoTherm product selected at Market Quarter, is particularly suitable for use with single-ply non-bituminous waterproofing membranes because the product is faced with clay-filled glass tissue on the top surface and plain glass tissue on the underside, thus providing a much better substrate for adhesive bonding than foil facings.
Latest innovations
Neopor is BASF’s new insulation material based on EPS (expanded polystyrene) and it exhibits a particularly good thermal insulating effect. Foams made of Neopor are silver-grey because they contain graphite which has the effect of reflecting heat radiation almost completely. BASF has been selling Neopor throughout Europe for about six years and its use can save up to 50 per cent in raw material. At the same time installers can work with panels that are 50 per cent lighter in weight or up to 20 per cent thinner, so the product is particularly useful where only limited space is available for insulation.
Another space saving product comes from Va-Q-tec, a Germany based company. It is now offering vacuum insulation panels (VIPs) which are claimed to have only one tenth of the conductivity of conventional insulation materials like mineral wool or foams. VIPs are formed from open pore materials wrapped in a high gas barrier film which is then evacuated and sealed.
First published in Show House Magazine August 2007.
The greatest care has been taken to ensure accuracy but some information contained within this article may have changed since it was first published.
Posted by Roger Hunt
in EcoTherm, Excel Building Solutions, H+H, Isonat, Natural Building Technologies, Neopor, Palgrave Brown, Second Nature UK, Space4, Sustainability, Va-Q-tec on Wed 1 Aug 2007
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