Building to Code Level 4 Case Study

Client: Contour Housing Group Ltd
Contractor: Bullock Construction Ltd
Completed: April 2011
Architect: Pozzoni LLP

HOUSING – WILMSLOW ROAD, HANDFORTH

The 21 no 2B apartments in Handforth have been designed to HCA requirements, Lifetime Homes standards and Secured by Design. The design team pushed to increase the specification from Level 3 to 4 long before it was required by regulations, making this development our first completed Level 4 building.

44% reduction in carbon emissions was achieved through a combination of a highly insulated timber frame with triple glazed windows and Photovoltaic panels. The air tight building fabric reduces the total energy demand of the building so that the PV array supplies a higher percentage of that reduced demand. The PVs on the east-west facing pitched roof supply electricity to the communal lights in the corridors reducing electricity bills and generating an income from the Feed in Tariff scheme.

A natural ventilation strategy and high levels of daylight further reduce energy demand and contribute to the health and well being of the residents. Careful specification of insulation with low Global Warming Potential, and efficient heating systems with reduced NOx emissions ensured maximum credits in the Pollution category. The sanitary ware and rainwater harvesting systems were selected to reduce water consumption and the surface water run-off from site.

Although the site has been classed as having ecological value, an ecologist was not appointed to enhance the landscaping therefore credits were lost in this section. Further credits were lost in the Health and Well Being section mainly due to the Robust Details E-FT-1 and E-WT-2 only achieving 1 credit for their sound attenuation properties. Both of these categories have high weighting factors applied to them therefore maximum credits had to be sought in the remaining ones. For example, A rated white goods were supplied (which is not usually the case in community housing) in order to gain a valuable extra energy credit. In this way, the Code for Sustainable Homes assessment can be considered flexible with numerous strategies for compliance.

Ground Floor 0.12W/m2K:
75mm screed on 150mm rigid insulation on beam and block floor

External Walls 0.15W/m2K:
Facing brickwork, 50mm cavity, 140mm timber frame (insulation between studs) with insulated plasterboard.

Roof 0.09W/m2K:
500mm mineral wool insulation.

Windows 0.90W/m2K:
Triple glazed UPVC (Green Guide A-rating)

y Value 0.08W/m2K:
This thermal bridging value results from the use of Accredited
Construction Details which minimise air leakage.

Air Permeability 5m3/h/m2:
The design air permeability rate of 5m3/h/m2 was significantly
exceeded proving the building envelope to be air tight.

Heat Loss Parameter:
0.58 – 0.81W/m2K depending on apartment location.

Space Heating & Hot Water:
Vaillant EcoTech Pro 24 Condensing combi gas boiler with
programmer, at least 2 no room thermostats including a delayed start thermostat AND a weather compensator.

Special Features:
Zenex Superflow Gas Saver SF50 saves >400kWh/yr by extracting heat from the flue gases for reuse in the dwellings as space heating.

Low and Zero Carbon Technology:
14 no Solarcentury C21e integrated tiles installed on East/West 30o roof pitch to achieve 0.63 KWp per apartment.

Surface Water Run Off 0m2 impermeable area pre-development, 500m2 post:
50m3 underground storage to attenuate surface water and 20,000 litre rainwater harvesting tank to collect water for use in the WCs and ground irrigation.

Conclusion:
Some site specific credits could not be achieved placing extra emphasis on those within our control. This project has proved how important it is to consider the Code right through from project inception, and then constantly throughout to ensure the required level is achieved and all team members are aware of the
requirements.