The National Autistic Society

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Founded in 1962, The National Autistic Society (NAS) is the UK’s leading charity for people affected by Autism. With over 18,000 members and 80 branches, the charity operates many day services, schools and registered homes across the UK.

The NAS has been undertaking a programme to upgrade the quality of its existing building stock and as part of this has been developing various new buildings over the last three years.

As part of this programme, the NAS has taken the opportunity to look at ways of substantially improving the energy performance of those buildings planned for refurbishment. The new buildings are also are specified to perform better than currently required by the building regulations, and to be extremely cost-effective to run and – as a result of these factors – more environmentally friendly.

It was found that specifying high levels of insulation in new buildings achieved significant levels of energy efficiency, whilst also offering a far lower payback period than renewable energy generation technologies.

Bill Finn, Head of Property and Project Management at the NAS, explained the approach: “Insulation will sit in a building for the next 50-60 years, probably the entire life of the building and usually requires low or zero maintenance, whereas higher-tech solutions often have high initial capital costs and will need ongoing maintenance, technical input and monitoring throughout their life to ensure they continue to perform correctly to achieve the forecasted savings.”

Even heat pumps and solar panels require electrical power to operate, meaning that the energy provided will not be completely free, says Finn. Often, these systems will require partial or total replacement during the life of the building and this – the whole life cost – needs to be factored in to the total costing.

“We looked at the payback periods of heat pumps, photovoltaic and solar panels on one of the new NAS buildings” says Finn, “and found that these were incredibly long once the benefits of installing high levels of insulation were factored in – in some cases probably longer than the building’s useful life – therefore it was very difficult to justify even solar panels to pre-heat the domestic hot water.

“We have decided it would be better just to spend the money on higher levels of insulation and air tightness than required by the building regulations, and good heating and lighting controls.”

However, it looks likely that the cost of at least some renewable energy generation technologies, such as photovoltaics, will fall in the near future, as the government tries to make these technologies easier to implement in energy efficiency schemes by lowering the cost for consumers.

The NAS also uses underfloor heating in many of its new buildings, as this method is particularly suitable for their service users. A high level of floor insulation ensures that underfloor heating performs effectively, thus also making underfloor heating cost-effective to run. The energy savings and financial savings can be significant.

This focus on insulation is crucial, explains Finn, as around 25% of heat loss in a building occurs from the floors.

One of the NAS’ buildings currently being constructed in Somerset utilises a suspended concrete floor construction; a jetfloor. These are essentially large slabs of polystyrene over 200mm thick, placed between pre-cast concrete beams, with additional insulation over this. This lightweight structure then acts as a supporting floor achieving a U value of better than 0.13 w/m2k.

High levels of insulation are being used to great effect in the walls and roof of the building, with at least 100mm of high performance cavity insulation in the cavities and 400mm thickness of insulation quilt in the roof space, achieving U values of at least
0.17 w/m2k and 0.10 w/mk2 respectively.

“As we generally need robust construction”, says Finn, “this tends to require us to use wider cavities to accommodate thicker insulation. It would probably be cheaper and easier to achieve high quality insulation standards with timber frame buildings, but these are not always practical for our needs.”

Finn also mentions that substantial heat loss is often due to gaps in buildings and junctions in walls, so these are other important areas to consider carefully in the specification and design of all new-build properties.

When constructing energy efficient buildings, great attention to detail is required to achieve levels of air-tightness better than that required to achieve basic building control requirements. This can drastically improve the energy rating of a structure.

However, although this initial detailing is very important, it is the day-to-day control of quality on-site by the contractor, and supervision by consultants, that determines if high levels of energy efficiency are successfully achieved.

There are also issues with high levels of air tightness with regard to air quality in a building, which needs to be considered to maintain a good environment. This can be partly addressed by the inclusion of ventilation systems that permit fresh air but transfer much of the heat from the warm, stale air being extracted to the incoming fresh air in order to avoid wasting energy.