Sorry if this comes as a shock, but new build is not the answer to the zero-carbon challenge. The sobering fact is that less than two percent of the nation's building stock is renewed every year, which means that 90 percent of the buildings we have now will still be around in 2016 - the government's first zero-carbon target.
New build will also become more of a privilege as lending for capital projects gets expensive and the cost of fuel climbs higher. Add to that increasing control over energy use in buildings through legislation, and it's clear that we need to do far more with what we've already got. Retrofit, then, is going to be the next big thing.
The passive solar buildings of the 1990s that we got so excited about, with their natural or mixed-mode ventilation, night cooling algorithms, intelligent controls, and smart solar shading, are coming round for their first major refit. The headquarters of the Charities Aid Foundation (CAF) is typical of this mid-1990s take on what constituted a low energy building, so what can we learn from its refurbishment?
Details of the building's construction was well documented in the March 1996 edition of BSJ. Suffice to say that the mainly open-plan 3700m2 (treated), three-storey building began life as a home for around 200 administrative staff. It's located on the former West Malling aerodrome in Kent and was developed as a pre-let by Rouse Kent (a joint venture between Rouse and Kent County Council).
The steel-framed, U-shaped building is brick-clad. Largely open-plan offices occupy the 13.5m plan depth and are arranged around a south-east facing open-sided courtyard. Entry to the building is through a full-height glazed reception area, onto which the top two floors once opened out but which is now enclosed by new meeting rooms.
Ventilation was by openable windows and fanlights, with mechanical displacement ventilation via a pressurised floor plenum. In keeping with the times, mechanical refrigeration was avoided by the use of an innovative indirect evaporative cooling system, whereby a fine water spray was used to cool the exhaust air. The extract air then passed through a plate heat exchanger which cooled the incoming air.
The floor slabs were exposed to provide thermal mass and some beneficial radiant cooling, while the building's insulation values were in excess of that demanded by the Building Regulations of the time.
The glazing was of a high standard, comprising double-glazed Pilkington Suncool solar glass for the south-east and south west elevations, and low emissivity glass on the remaining elevations.
The CAF still occupies its building 12 years after it was constructed, so there's no change of use to take into account. True, the organisation has got larger, and the occupant density has increased to 360 on average, but by and large the tenant's requirements (and the maintenance resources) have stayed about the same.