Maximising the insulation in a building is one of the most effective ways of improving its environmental performance but being out of sight it is not being given the attention it deserves.
“There is more interest in promoting the use of renewable energy than reducing energy consumption through high levels of insulation,” comments John Fairley, company secretary of the Thermal Insulation Manufacturers and Suppliers Association. However, the loss of heat through a building’s structure is now becoming widely recognized. According to the Energy Saving Trust about half the heat in a home is lost through the walls and loft. It is a more reliable way of improving the environmental performance of a home. “One of the advantages of insulation, over other measures, is that it is not dependent on the behaviour of the occupiers unlike the use of energy efficient light bulbs, which can be easily replaced,” Fairley said.
As part of the move to achieve the zero carbon homes, building regulations are being made more demanding in terms of the u value required in new buildings and when major renovations are undertaken. The u value is a measure of the thermal conductivity of a material. New homes are incorporating high levels of insulation but improving the performance of existing homes is a major challenge in terms of physically fitting the insulation into the structure as well as getting the owners to carry it out (see panel).
Improving energy performance
The 2006 review of the building regulations sought a 20-28% improvement in the energy performance standard on new and refurbished homes The code for sustainable homes is not specific about the exact measures required to achieve different levels. However, one of the major manufacturers of urethane-based insulation Kingspan is suggesting that to achieve code level three, the walls should achieve a u level value of 0.18 and for level four a 0.15 value was necessary.
High levels of insulation are being achieved with ever thicker layers of the material which will affect the design of a building. “If you need to put 270mm insulation into a wall to achieve the necessary environmental performance, the design has to accommodate it,” Fairley points out. “Simple issues such as sufficient space around pipes needs to be allowed to fit insulation,” he points out. “It is also important that the right materials are chosen for the building’s structure,” he says.
There are some slimline products on the market which aim to achieve high performance without the thickness which is necessary for traditional insulation materials. Vacuum insulation panels are made up of core materials sealed in a vacuum and are claimed to offer a performance ten times that achieved with the equivalent thickness of traditional materials. These panels are designed for developments in high density urban areas where architects want to maximise a building’s internal floor area and provide increased return on investment or in tight loft conversions. There has been some debate about their performance because of problems in measuring it against traditional insulation materials and their acceptance in terms of meeting part L of the Building Regulations, points out John Tebbit from the Construction Products Association.
Better fitting equals better performance
According to John Fairley from TIMSA skilled construction workers are required to fit the materials. The quality of fitting can affect the thermal performance of the insulation particularly if it is punctured by plumbers and electricians installing equipment after the panels have been fitted. “Builders have up to now taken the view that if a problem can’t be seen, it doesn’t exist, but if the insulation is not performing, then it will come to light,” said Peter Morgan from Kingspan. He suggests that construction works need to be more closely supervised. The code for sustainable homes includes inspections of the plans and also post-construction testing by building control, Morgan points out.
Natural products use less energy
The environmental impact of manufacturing some of the products has been of concern in the past. Natural products are gaining in popularity but are still confined to specialist one-off buildings and have yet to make the big breakthrough with volume housebuilders specifying it. The suppliers emphasise both the thermal properties and the other contributions they make to a home and the wider environment. These products tend to use less energy in their production and offer similar environmental performance as other synthetic materials. Thermafleece which is based on sheep’s wool absorbs moisture which can help to increase temperatures when it is cold and when the outside temperature heats up, this moisture is released so helping to cool the inside of the building.
Paul Ashford from the environmental consultancy Caleb questions the longevity of sheep’s wool. “If it gets wet, then it loses its insulation qualities,” he points out. Insulation materials need to be judged on how they perform over their lifetime – and whilst they might use more energy in their manufacture, their longevity makes up for it Hemp lime is another traditional product now used in one-off buildings for insulation. Hemp grows fast and the plant acts as a carbon dioxide store. The hemp combined with lime is mainly used in timber buildings for insulation to the walls and floors. John Fairley, who also represents the Hemp Lime Construction Products Association says that one of the benefits of lime is that, like fleece, it absorbs moisture. A study by the volume housebuilder Taylor Wimpey comparing the options for insulation for a small housing development in Northern Ireland concluded that hemp lime showed the best overall performance, particularly in terms of social and environmental benefits.
However, when additional weighting was given to the supply chain management costs, the cost of materials and insurance costs, the top ranking insulation material was no longer hemp lime but expanded polystyrene instead. The report by Tom Woolley from architects Rachel Bevan Associates highlights the challenge in sourcing the materials as a particular problem. “Sourcing materials is a particular challenge in Northern Ireland. Some are easily obtainable from local suppliers, but others have to be imported from the Irish Republic or England.,” says the report.
The traditional urethane products have been improving their environmental impact. They no longer use CFCs and have reduced waste in manufacture and on site. Kingspan’s TEK system was one of the first products to get an A rating according to the BRE’s green guide in 2005. It uses structural insulated panels to create thermally efficient homes. The energy efficiency provided by the system also exceeds the levels proposed in the Government’s 2010 version of Part L of the Building Regulations. Rockwool’s stone wool is made by melting rock, limestone and recycled briquettes with other raw materials at 1500°C in a coke-heated cupola furnace. The resultant liquid stone melt is spun into fibres.
Like many companies Rockwool claims in its 2007 environmental appraisal that it is a major energy saver. “A typical 250 mm Rockwool loft insulation product – manufactured and installed in Denmark and used over 50 years – will save 128 times more primary energy than was used for its production, transport and disposal,” says the appraisal. It suggests that the energy balance becomes positive only five months after installation. The company has introduced a scheme to take back and reconstitute its insulation materials from buildings being dismantled.
Insulation grant schemes
Several measures are being introduced to promote and encourage higher levels of thermal insulation in existing homes. Grant schemes are now being developed which subsidise the supply and fitting of loft and cavity wall insulation. Under the government’s carbon emissions reduction target (Cert) scheme, the seven major energy companies are required to spend £1.5bn over the next three years to install energy efficiency measures in the homes of people on low incomes and the elderly. With the introduction of energy performance certificates as part of the home information pack the government is hoping that the choice of home will be influenced by its energy performance and will encourage homeowners to increase the insulation in their homes.
Other European countries are taking a more proactive approach. The German government now requires that buildings undergoing renovation, irrespective of size, must be upgraded in terms of their environmental performance. The government has allocated more than €1.4 bn/yr subsidies to improve the performance of existing buildings. The renovated building must be at least as energy efficient as the minimum requirement for new buildings. In France a 40% tax credit is given to landlords for insulating houses built before 1977.
Injecting homes built since 1920 with cavity walls with insulation material can make a major difference according to the Energy Saving Trust. Otherwise when a home is undergoing major renovation, more radical measures can be taken but even then finding space for 270mm of material round the walls, in the roof space and under the floors is problematic.
It can be difficult to get the detailing right around windows and doors because of a lack of space under the edge of the roof for the walls to gain thickness. Skirting and ceiling coving have to be altered or replaced, radiators may have to be moved. External insulation has some advantages because it maximises the thermal mass of the brickwork. The bricks will more effectively absorb heat and gradually release it back into the house, so helping to maintain an even temperature. In tower blocks, local authorities are generally using external insulation when the cladding is replaced.