England’s first Passivhaus house

A house built beneath a 300-year old derelict barn in the Cotswolds has been certified this week as Passivhaus standard and is the first Passivhaus house in England.

Located in an Area of Outstanding Natural Beauty (AONB), Seymour Smith ArchitectsUnderhill House is designed for minimal visual and environmental impact. Constructed underneath and adjacent to a restored barn, the house is completely invisible from the surrounding countryside.

A concrete structure, largely pre-cast, is a critical element of the project’s environmental performance and was supplied by project partner Aggregate Industries. The precast concrete is exposed internally for thermal mass and also reduces waste through off-site construction. Dow Building Solutions‘ StyrofoamTM-A  and FloormateTM 300-A beneath the floor slab enclose the entire structure. South-facing glazing maximises passive solar gain.

Air tightness tests on the building achieved 0.2198 air changes (ac/h) an hour at 50 pascals (pa), compared to the demanding Passivhaus requirement of 0.6 ac/h @ 50pa. The UK equivalent q50 result was 0.23 m3/h/m2.

Architect Helen Seymour-Smith said, ‘The Passivhaus design achieves a staggering 90% energy savings over that of an average house. With much of the concrete structure exposed internally, the interior has been carefully designed to show that concrete can play a positive part in environmentally friendly construction. Using the thermal mass from the concrete structure alongside highly-durable insulation has resulted in a highly energy efficient building.’

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