ARCHITECTURAL DESIGN COMPETITION

FOR PASSIVE HOUSE IN BULGARIA

John Moran Architect

(198 - user rating)

Building-Metric-Sheet-19.xls

Design Approach

The design takes as its starting point the task of reconciling the spatial demands of a family with a wheelchair user and those of good Passivhaus design. In thinking about this problem it was decided to exclude lifts as a solution because of their expense and their tendency to divide the wheelchair user from the everyday circulation patterns followed by the rest of the family.

The ideal lift-free house form for a wheelchair user would be a single storey layout. However Passivhaus favours compact building forms and multi-storey layouts in order to minimise the ratio of surface area to volume. This design adopts a storey and a half approach with the majority of the accommodation at ground level and the master bedroom, bathroom and study located at first floor level. This achieves an effective compromise between the two competing design drivers of accessibility and compactness.

Detail Design

The disposition of spaces is driven by orientation with the main living spaces facing south into the garden and the bedrooms and service spaces occupying the northern portion of the plan. The master bedroom occupies a large dormer structure looking south over the garden.

The main living space enjoys a generous double height under the sloping roof with a dramatic structural glass open stair dividing it from the dining area. The space is overlooked by the master bedroom and first floor balcony. Privacy for the bedroom is provided by large sliding screens which can be slid back to provide maximum openness. The double height living space is lit at the apex by a continuous rooflight which allows daylight to wash the rear wall. A wood burning stove provides a focus for the living space.

The kitchen is open plan with the dining area and living area and is served by a generous side window. Behind the kitchen sits the utility room. The hall and bathroom are generous to accommodate wheelchair users. A large store adjacent to the front door provides space for cycles and refuse recycling.

The fenestration is designed to maximise solar gains with large areas of glazing facing south. The north, west and east facades are mostly solid with optimally sized windows to achieve adequate daylight inside. The south facing glazing is shaded by a large overhang which provides protection from excessive summer gains whilst allowing low angle winter sun to penetrate. The house is positioned on the site to achieve an appropriate balance of space between the entrance forecourt and the garden facing south.

Regulating Geometry

Embedded within the design are ideal geometrical figures and ratios. Both the plan and the elevations have been composed using the Square and the Golden Section so as to achieve good proportions.

Heating and Ventilation

The central plant room is located at the heart of the house to achieve optimal ducting layouts for the mechanical ventilation system. Its position adjacent to the apex of the double height living space allows the space to be efficiently ventilated. In winter heat build up in the apex is extracted directly through the rear wall to the plant room behind. In summer the continuous rooflight can be opened to provide stack ventilation of the living spaces. Energy is supplied by a solar PV array on the south facing roof slope and by a ground source heat pump connected to a borehole.

Materials and Fabric

The building is constructed from timber frame with insulated studs to minimise thermal bridging. The walls are made of a double sandwich of insulation with OSB board providing the air tightness layer. The OSB layer and the windows have been aligned to simplify air sealing. The roof is built up using the same principle. Windows are triple glazed with stained softwood frames to Passivhaus certified standard. The walls, roof and floor all achieve a U value of 0.13W/m²K.

The palette of external materials has been kept simple. The building is clad in dark stained larch cladding. The roof and dormers are clad in zinc. The elevations are unified by a light grey stained timber string course at first floor level.