HOUSING SPECIAL NEW-BUILD CASE STUDY
AIR TIGHTNESS
Target thermal transmission values Measured air permeability, based on two tests of completed houses, was 2.1 cu m/sq m/hr for a three- bedroom house and 3 cu m/sq m/ hr for a fi ve-bedroom house The heat loss parameter, expressed per unit surface area of the building envelope, is between 0.61 and 0.68 W/sq m K
Projected U-values: External walls = 0.15 W/sq m K
Roof = 0.10 W/m sq m K Ground fl oor = 0.13 W/ sq m K Windows = 0.78 W/ sq m K Doors = 1.00 W/sq m K
that supplies 1,000 apartments. The houses were commissioned by Woking Borough Homes (WBH), a subsidiary of Thameswey that is tasked with providing affordable homes in the area. Back in 2008, when WBH was contemplating a new housing development at Brookwood Farm in Knapp Hill, Woking, Morgan intervened personally to insist they be built to Level 5 of the Code. The scheme was completed in September 2010 and comprises 10 semi-detached homes, six with three bedrooms and four with two bedrooms (available on a shared ownership basis), plus two detached fi ve- bedroom homes that were sold on the open market for £615,000 each, which helped towards the cost of the ‘affordable’ properties.
Code Level 5 How Brookwood Farm measures up
Brookwood Farm scored 92 points out of a possible 100 under the Code for Sustainable Homes, suffi cient for a Code 6 rating, although only a Code 5 was applied for and awarded, according to project manager Jim Walter. High-scoring features include:
Dwelling emission rate: 14 credits out of 15, with a target
40 CIBSE Journal June 2011
emission rate of 19.2 – 23.2kgs of CO2/sq m per year and a dwelling emission rate of below zero, which means no net energy use, thanks to the PV installations (see table three).
Environmental impact of materials: 13 credits out of 15, at least three from a list of fi ve building elements (for example, walls, windows) must achieve a
Green Guide rating of A+ to D
Health and wellbeing: Ten out of 12, with high scores for meeting Lifetime Homes principles and good insulation.
Management : Nine out of nine, with guidance for occupiers on using the homes effi ciently, Considerate Constructors Scheme and on-site security.
John Thorn, group managing director of Thameswey, and Jim Walter, the council’s project manager for Brookwood Farm, are both concerned that there are few signs that many other councils are ready to follow Woking’s lead. ‘A lot of people
What we’re trying to do here is a very low-key form of social engineering [on energy reduction]
from other councils have come to see the development, but because they don’t have a similar climate change strategy to Woking, nor the political support, very few of them can
replicate what we’ve done,’ says Thorn. Although the land was gifted to Woking Borough Homes by the council, Thorn insists that the council does not subsidise Thameswey’s environmental activities. It borrows money from the council at 7% interest. The result is a range of benefi ts, he says: ‘Council tax payers get a profi t on the loan to Woking Borough Homes, there’s a CO2 reduction and affordable homes are available in the borough.’ However, some may question just how
affordable these homes are, with the two-bedroom properties each priced at £286,000, and the three-bedroom ones at £350,000. Yet there has been no shortage of potential buyers, with offers made on all the homes within days of their completion. The Code 5 homes use insulated concrete, which is poured between two layers of polystyrene, producing low U-values, says Walters. They also have
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‘Invisible’ solar panels on the Brookwood Farm development in Woking, Surrey
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