Quebec Park in Bordon, East Hampshire, is a medium-size development of two, three and four-bedroom homes on the site of the old Quebec Barracks, and was the pilot site for the implementation of the Assured Performance Process.
The 100 homes on the Quebec Park site were designed to the Zero Carbon Homes standard and use a timber-frame construction, with additional rigid insulation inside the frame. Some units have photovoltaic panels on the roofs and there is a mixture of house types ranging from detached houses to flats.
Both the developer and design team have considerable previous experience of sustainable buildings. The developer, Radian Homes, has a number of developments that achieved Code for Sustainable Homes Levels 5 and 6 (with Level 6 theoretically a zero-carbon home).
Radian also carried out post-occupancy evaluations of these past projects, with lessons feeding into their new developments.
The Assured Performance Process included reviews of each house type planned for the site, at key stages of design, and construction. Using APP allowed a range of risks to be identified and mitigation measures implemented. A selection of these includes:
- Changing orientations to make it easier to provide summer shading and to maximise the output from the PV.
- Careful attention to the summer overheating risk (a particular risk for timber frame homes with low thermal mass), using shading and night-time ventilation to lower temperatures.
- Adopting better U-values than the minimum requirements of Part L of the Building Regulations.
- Multiple instances of reduced thermal bridging, and improved buildability of junction details.
- Multiple instances of changed site management and trades practices addressing key construction risk issues.
- Reducing boiler capacity to better suit heat losses and reduce boiler cycling, while reducing capital costs.
- Highlighting needs for clear accountabilities associated with energy, carbon, indoor air quality and overheating risk.
- Improving the clarity of handover documentation.
The in-use performance of the homes is now being assessed, and early results suggest that APP brought significant benefits. For the first three months of occupation, among 22 homes installed with monitoring equipment, 14 used less energy for space heating than the SAP as-constructed estimate. This is an extremely impressive result, in contrast to the strong evidence from Innovate UK’s Building Performance Programme that new homes commonly use twice or three times as much as the design estimate when they are monitored.
However, we also identified four homes where energy use for space heating was significantly higher than the design estimate, and we recommend additional scrutiny and forensic work for these homes.
Analysing the monitoring data also showed huge variations in energy use for hot water, with the highest water-use household using nearly 12,000 kWh a year to generate hot water (factored up to 12 months). This is close to four times the expected energy use for space heating over the course of a year.
Compared to the design estimates, average energy use for hot water across the 22 homes was 73% more than expected. This has more to do with residents’ water-use habits than how the homes were designed or built. There is an argument here for speaking to residents, exploring why some use a lot of hot water, and providing tips on using less. Allowing them to compare energy use for hot water (and bills) with other households on the site may also provide an incentive for reducing hot water use.
The monitoring suggested average carbon emissions of 909 kgCO2 a year for heating and hot water in each home. This is roughly a third of equivalent emissions from existing UK homes – another very impressive result.
“The National Energy Foundation provided an excellent service in supporting East Hampshire District Council to deliver its Green Town aspirations for the regeneration of Whitehill & Bordon. They helped us take another step along a journey in securing higher environmental standards for the town, specifically identifying activities which the Council could undertake with project partners to influence the planning and development process. I would recommend the National Energy Foundation to other local authorities wishing to take the lead on raising environmental standards within new and existing communities.”
Bruce Collinson, Environmental Sustainability Lead, Whitehill & Bordon Project, East Hampshire District Council
We made regular visits to the site to examine energy related elements of the construction; checking on assembly of details, insulation type, thickness, and installation quality. We also advised on detailing and best practice to avoid thermal bypass and ensure thermal bridges are reduced as per the design intent.
We also examined the timber fraction and made recommendations to reduce the risk of under-performance as the site build out progresses.
Developer: Radian Housing
Contractor: Drew Smith Ltd
Architects: Architecture PLB
Planning Authority: East Hampshire District Council
Energy Consultant: Greenbox Associates