Wimbish Passivhaus

 

Wimbish Passivhaus

 

Project lead
Jane Keiller, Hastoe Housing Association

Building type, sector and stage
Domestic, social housing, shared ownership, essex

Keywords
Passivhaus, blockwork, external wall insulation, solar thermal, MVHR, rural

Time
12 months into a 2-year monitoring programme

Wimbish Passivhaus 2

Context
The Wimbish Passivhaus development derives from Hastoe Housing Association's track record in sustainable housing, and their desire to tackle rural fuel poverty. With the intention that Wimbish will be the first of many Passivhaus developments, Hastoe were keen to confirm that the buildings are performing as anticipated.  The project is in a rural location in Hastoe, Essex.
An East-West orientation was employed to profit from passive solar gain    and the houses arranged so that the private gardens benefitted from this private ‘solar' space. The development comprises 14 units: a block of 6      one-bedroom flats, and two rows of 4 two/three bedroom houses.

Targets
High levels of thermal insulation were required because the small UK house size standards make the Passivhaus requirement of 15 kWh/(m2a) difficult to achieve.
The following u-values were needed:

Externall wall 0.107 W/(m2K)
Floor 0.091 W/(m2K)
Roof 0.078 W/(m2K)
Window 0.79 W/(m2K)

In practice the external walls were designed to 0.0879 W/(m2K). The properties were designed to exceed the Passivhaus air-tightness requirements of 0.6 air changes per hour. Window and door frames were carefully taped to the block wall, the latter forming a fairly air-tight barrier even before application of the plaster.
Solar gain was managed by large eaves overhangs, brise-soleil at ground floor and external blinds at first floor level. The brise-soleil is designed to passively shade the large south facing windows during summer but allow warm sunshine through in the cooler seasons when the sun is lower.

Performance
This domestic new-build study, (contact Martin Ingham, Linktreat Ltd.) started with handover end-June 2011, is of 8 houses and 6 flats. It is looking at performance of the fabric as well as from the occupant perspective. The occupants are looking for low bills, and a comfortable environment; analysis of ten months' data indicates that the building scores highly on both fronts.
Gas consumption for space and water heating aligns with design expectations. Electricity use is a little higher than desirable; the appliance audit is expected to confirm that old appliances brought with them by the occupants, are a major factor. The Building Use Studies survey recorded high levels of satisfaction; this is confirmed by the monitoring data. A University of East Anglia PhD Researcher is investigating occupant practices; in particular, how they influence energy consumption, and how they may be modified to reduce consumption.

Conclusion
Lessons have been learned from the build process, and from the design, installation, commissioning and operation of the systems, especially the MVHR. While this provides excellent thermal comfort, it seems a little less successful in running cost and air quality. Measured thermal performance of the construction is lower than predicted; further investigations into this are being conducted. An interim report covering winter performance has been reported on www.buildwithcare.eu.