The Pheasantry

The first iteration of our site design included two site entrances, with an informal layout and a predominantly south orientation. However, single-storey dwellings are not suitable from a Passivhaus design perspective, and some homes' orientation would also not support Passivhaus design. As the site had been designated a Rural Exception Site by the local authority, there were several constrictions to the site by the strong tree line around the perimeter and the associated encroaching root protection areas.

Through consulting with highways and an arboriculturist we developed the masterplan to create views throughout, retain the boundary trees, and include a single entrance, with improved pedestrian links. However, following the Design Review Panel, we received feedback that the configuration was still too rigid, with more variation needed and more parking required.

In our final layout the meandering streets create more of a village-like feel and we have increased the parking provision. By including a variety of house types and layouts, we have increased the public realm available, whilst still adhering to Passivhaus principles. Houses are grouped together and face a southerly direction, reducing the external area and providing a Heat Loss Factor of 3.3-3.5.

We have also not disturbed any existing Tree Preservation Orders, which now act as a natural screen, creating a sense of enclosure and a feeling of nature within the development.

Building fabric In Passivhaus buildings wall, roof and floor elements should aspire to a U-value of between 0.10 W/m²K to 0.15 W/m²K, with minimal thermal bridging; and ideally, an internal service void so that services do not penetrate the airtight/vapour barrier. We used two timber double stud frames as these were lighter, easier to install and required less time on-site and a higher specification blown in insulation.

Thermal bridging When designing a building to the Passivhaus standard, there is great emphasis on thermal continuity and avoiding cold bridges. ‘Weak spots’ can be avoided by overlapping insulation to wrap the whole building or using blown in insulation of an equal density throughout.

Airtightness Passivhaus buildings need to achieve 0.6 air changes/hour @ 50 Pascals, approximately 5 x more airtight than the present UK Building Regulation requirements. To deliver a robust airtight design, there must be great attention to detail when sealing junctions and penetrations. By conducting rigorous air-testing we were able to highlight risk areas.