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Dundon Passivhaus

Dundon Passivhaus

Private

Category: Private

Location: Compton Dundon, Somerset

Architect: Prewett Bizley Architects

Structural Engineer: Structural Solutions

Joinery Company: Allwood

Staircase: Fowler & Co.

Interiors: Heartwood Cabinet Makers Ltd

Wood Supplier: Luton Green Sawmill

Wood Species: Green Oak, European Oak, Birch Plywood, Pine, Softwood

The design for the Dundon Passivhaus developed around an interest in how one might build in harmony with a rural setting, enhancing rather than dominating the surrounding countryside. The house sits at the foot of a wooded hill overlooking the expansive landscape of the Somerset levels. The woods are partly deciduous native species interspersed with planted conifers with tall, straight trunks. Timber was chosen for its ability to define the character of the building and for its excellent energy performance.

The primary structure of the house is a softwood timber frame. To minimise thermal bridging the frame is made up of an inner 140mm frame which sits on the concrete ground slab, and an 89mm outer frame suspended off the inner frame on 12mm plywood gusset plates. The roof is made from timber I-joists. Cellulose insulation was blown between the timber frame and hemp insulation has been used in the service zone and partitions.

On three sides the shallow pitched roof extends beyond the footprint to create sheltered outdoor spaces that catch the sun at different times of day. An out-rigger structure of green oak posts supports the roof, makes a visual connection with the pine trunks on the hillside and frames views through the covered spaces, binding the building into the landscape. The roof overhangs work in harmony with the energy strategy by providing summer shading to the large areas of glazing.

The thermal envelope is defined by thick walls clad with green oak boards. Green oak was used to match the outrigger structure. We were keen that the fixings were unobtrusive so the boards were rough-sawn to 70mm widths so that they would only require a single central fixing with slightly over-sized holes and no washers.

Where softwood has been used for exposed joists, plywood soffits or the internal ceilings it is painted to contrast with the oak. The only timber exposed in the house is oak. The roof overhangs cast the facade in shadow and the oak cladding is already turning grey, so from a distance the house blends into the hillside. The weathered oak has a similar tone and colour to the local blue lias stone used on houses in the area. The roof pitch and structural proportions are similar to those on a Dutch hay barn that the house directly faces at the bottom of the field.

The internal spaces connect with particular external spaces or features in the landscape via large windows, making each room distinct and drawing the surrounding countryside in. The two floors have particular architectural characters. The upper floor entrance hall and reception rooms are lined in planed oak with oak joinery, a more refined version of the rough sawn external cladding. Elsewhere the walls are lined with plywood and painted in warm shades of grey to create a more serene atmosphere.

Further Sustainability Information: The house is being certified to Passivhaus standard. The architect wanted to build a house that uses as little energy as possible so took a fabric first approach, using a highly insulated envelope with a very low space heating demand. The wall construction is vapour permeable to moderate humidity and create a healthy internal atmosphere. A mechanical ventilation system with heat recovery provides constant fresh air throughout the colder months when it is undesirable to open the windows.