There is an increasing demand for eco-insulation materials that are obtained from natural sources. The most popular up to the present is cellulose fibre derived from recycled newspaper.
The material is treated with boron to give fire resistance and protect against vermin infestation. It is suitable for wet spray or dry blown application. One of the most popular proprietary brands is 'Warmcell', supplied by Excel Industries which belongs to Fillcrete. It has a thermal conductivity of 0.036 W/mK, which puts it in the same category as most of the main insulants on the market. It has BBA (British Board of Agreement) certification. Warmcell is an integral part of Fillcrete's 'breathing wall' panel system suitable for structural walls, floor and roof components. The panels have a U-value of 0.19 W/m2K. The panels incorporate service ducts on the internal face to facilitate rapid on-site fixture of services.
Prefabrication is becoming increasingly popular. This is because elements are produced in controlled conditions and safe from the elements. Because of their extremely tight tolerances they can offer guaranteed air tightness, which is a prerequisite for highly energy efficient buildings.
Other manufacturers of cellulose fibre insulation include Construction Resources supplying Isofloc, and 'Save It' (Nottingham) producing Ecofibre. These also are BBA certified.
Coming more into prominence is sheep's wool. One of the first buildings to use wool as an insulant was the exhibition House of the Future within the Museum of Welsh Life in south Wales. It uses 200 mm of wool in its cavities. At the time it had to be imported from France. Now the UK has its own treatment facilities and it can be obtained from the Wool Marketing Board. It has to be treated with water-based boron.
The most ambitious use of sheep's wool for insulation in the UK is in what is claimed to be the largest commercial ecobuilding in the UK, erected by the Centre for Alternative Technology (CAT) at Machynlleth in Wales. The installed thickness is 325 mm and the wool was hand-sprayed with boron during installation.
A demonstration project in Scotland is currently being evaluated to test the effectiveness of hemp as an insulation material. The verdict so far is that the hemp homes are using significantly less energy than was predicted by the SAP ratings and U-value calculations. They are consistently outperforming the control houses which have conventional masonry construction with cavity insulation. This is a material to watch.
Natural Building Technologies of High Wycombe was established to promote the widespread use of natural building products. These include cellulose fibre, cork and sheep's wool. All these natural materials are hygroscopic, that is, they absorb moisture without any damage to their functional integrity. Water vapour can move through them, which makes them ideal for 'breathing' walls which offer short-term protection against condensation. The big benefit is in offsetting the need for vapour barriers, which are notorious for being at the mercy of operatives on site.
The emergence of transparent insulation materials (TIMs) offers the double benefit of providing insulation and space heating. One product, StoTherm Solar, consists of a honeycomb structure of glass-coated polycarbonate. It is produced by the external insulation specialists Sto AG. It is claimed that a southerly façade using StoTherm Solar could achieve an energy gain of 120 kWh/m2 per year. In winter the outside temperature might be as low as — 10°C. Despite this, the back of the TIM could be as high as 60°C, benefiting from the low angle of the sun. Since the TIM is bonded to the inner wall surface this warmth would be transmitted to the interior, producing a room temperature of around 20°C. That is on the assumption that the wall is of solid construction with a density of at least 1200 kg/m3. Even on north-facing elevations this technology could offer an energy gain of up to 40 kWh/m2 per year.
Saving energy is one thing; buildings as carbon sinks is another, yet this is the destiny of buildings according to John Harrison, a technologist from Hobart, Tasmania. He has produced a magnesium-carbonate-based 'ecocement'. In the first place it only uses half the energy for process heating required by calcium carbonate (Portland) cement. The roasting process produces CO2 but most of this is reabsorbed by a process of carbonation as the cement hardens. Using ecocement for such items as concrete blocks means that nearly all the material will eventually carbonate, resulting in an absorption rate of 0.4 tonnes of CO2 for every tonne of concrete. The ultimate ecocredential of this material is the rate of carbon sequestration. According to Harrison, 'The opportunities to use carbonation processes to sequester carbon from the air are just huge. It can take conventional cements centuries or even millennia to absorb as much as ecocements can absorb in months'.5 This means that an ecoconcrete tower block can perform the same function as growing trees as it steadily fixes carbon. Harrison estimates that a shift to ecocement could ultimately cut CO2 emissions by over one billion tonnes since it could replace 80% of uses currently served by Portland cement.
There is one further attribute to this material. Being less alkaline than Portland cement it can incorporate up to four times more waste in the mix than conventional cement to provide bulk without losing strength. This could include organic waste which would otherwise be burnt or added to landfill, sawdust, plastics, rubber and fly ash.
Ecocement is not unique in its pollution-absorbing properties. Mitsubishi is producing paving slabs coated with titanium dioxide which remove most pollutants from the air. In Japan 50 towns are already using them and in Hong Kong it is estimated that they remove up to 90% of the nitrogen oxides that create smog. Magnesium-based concrete coated with titanium dioxide could be the basis for ecocities of the future.
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