Case history: passivhaus project Forge Bank and Heron Bank at Halton, near Lancaster, are an ecological cohousing project, developed by Lancaster Cohousing, designed by Ecoarc and built by Whittle Construction. When complete it will include 41 homes, workshops, offices and studios and a common house for the community. The houses are being built to the Passivhaus standard and this is one of the largest Passivhaus projects in the UK. The characteristics of a Passivhaus include passive solar design and energy efficient landscaping,.
Meaning the building is compact to reduce the external surface area, with the main windows facing towards the midday sun for solar gain. There will be some internal thermal mass to reduce peak temperatures in the summer and to retain warmth in the winter. In hot countries, trees, pergolas, vertical gardens or green roofs can be used to reduce excessive summer heat.
High performance or superinsulation reduces heat loss through the walls, roof and floor. The thermal bridges often found at joints or holes in the structure are eliminated as far as possible. Advanced window technology is used. Normally triple glazing with lowemissivity coatings, argon or krypton gas fill and thermallybroken frames. Passivhaus buildings are made as airtight as possible. Porous surfaces are skimmed or parged, joints are sealed or taped.
Although the windows can be opened in summer, ventilation is mechanical. Heat is extracted from the waste air and used to warm the incoming fresh air. Conventional central heating is not required. A single raiator is often sufficient. Hot water can be from an instant, ondemand electric heater. Heating can be supplemented by a solar thermal installation on the roof or groundsource heat pump. The electrical demand of a Passivhaus is reduced by use of lowenergy light bulbs and appliances.
Lighting can be controlled by motion sensors and the mains supply supplemented by photovoltaic panels on the roof. The Lancaster houses are built in southfacing terraces with most windows southfacing to maximise solar gain. The floor slab is insulated with 250mm Jabfloor expanded polystyrene laid onto a gasproof membrane with taped joints.
This is screeded over. The walls are 500mm thick, including a 300mm cavity. Below floor level, these are insulated with a recycled plastic material. Above floor level the cavities are filled with Knauff Earthwool glass mineralwool insulation. The wall ties are made of basalt rather than steel to prevent thermal bridges. Another measure to prevent thermal bridges is to support the floor trusses on a wooden plate.
Attached to the wall with bolts set in resin, rather than bedding the trusses into the wall. As far as possible services are not chased into the structure. Where they are, for example for electric sockets, the chasings are parged before the services are fitted. High performance doors and windows are fitted. Particular emphasis is put on preventing thermal bridges or drafts around the door and window openings. Roof insulation is 500m thick and covered with a membrane to make it air tight.
Mike neate is a specialist air tightness contractor on the project . There’s four, five, six different areas that we have to concentrate on, it’s always the junctions between the different planes, so youve got the walls and the floors, so youve got the junction along the floors here. Then youve got the timber frame, southern elevation there. Where youve got membranes and you have to fix a membrane to the masonry, membrane to the frames,.