ARCHITECTURAL DESIGN COMPETITION

FOR PASSIVE HOUSE IN BULGARIA

Seymour-Smith Architects, Rob Statham BArch, BA[Hons], Helen Seymour-Smith B.Arch [hons], Dip. Arch, RIBA

(341 - user rating)

Building-Metric-Sheet-37.xls

first thoughts
The first stage in our design process was to familiarise ourselves with the village of Lozen in order to gain a contextual understanding of what is considered to be the local ‘style’, including commonly used materials, forms, building heights, landscaping, colours, and the general character of the village.
Using websites such as Google Maps, Flickr and Panoramio we were able to piece together a picture of what makes Lozen, Lozen. In summary, the elements of the local vernacular that stood out were:-

  • a variety of roof typologies - commonly ‘hip’, ‘saltbox’ and ‘gabled’
  • large roof overhangs on all elevations with timber clad soffit boards
  • red/orange roof tiling [Red Marseille typically]
  • rendered walls, varying in colour and texture
  • buildings often clad in a variety of materials - most commonly render, stone and timber cladding
  • abstract window layouts, consisting of a mix of rectangular and square openings placed at unusual heights and spacing
  • framed views of the surrounding mountains and forests

In response to our contextual research findings, we decided that a contemporary fusion of the local vernacular would be appropriate for the design of a new Passive House for the large open site in Lozen.
Immediately, a number of the local vernacular characteristics were excluded from the design due to their lack of suitability in Passive House and environmentally conscious design/construction. For instance, the Red Marseille roof tiles that dominate the aerial view of Lozen contain large amounts of embodied energy, primarily from the inefficient manufacturing process and transportation of the tiles.
Having chosen an orientation for the site, positioning the building at the North end of the plot was an obvious decision for maximising the potential for absorbing solar gains. From there on, the aim was simply to design a beautiful, contemporary, family house, applying passive design principles and airtight detailing, specifying locally sourced materials with low embodied energy wherever possible.

the concept
The roofscape of Lozen stood out as being one of the strongest elements of the village’s character. After studying the typologies of roof forms in the village, we decided that the most attractive form to use as the backbone of our design was the asymmetry of the ‘saltbox’, however for economy and efficiency, we wanted to maintain the two-storey across the full building platform rather than the traditional ‘saltbox’ design.
This theme, combined with the need for thick, highly insulated walls on the North half of the building and large areas of glazing to the South, led us to the concept of having a thick line [i.e the walls and roof] that wraps over the two storeys of internal space, starting with a shallow pitch to the North, descending more sharply on the South facing pitch, with the line thinning out and becoming intermittent as it wraps over the South elevation.
In reality, we thought that the thick line should be of one continuous material that forms the cladding of the North Elevation, the roof, and a solar shading device covering a glazed South elevation.

the design
The plan of the building has a simple hierarchy, common in Passive House design. The ancillary spaces [mechanical room, bathrooms, closets and kitchen] are all in the North half of the plan, whilst the primary spaces [living room, dining and bedrooms] are given the South aspect, in doing so, providing bright, comfortable living spaces. An open-plan arrangement has been designed into the ground floor plan, to suit the modern family.
The main living spaces are positioned on the ground floor, with full height triple glazing to the South and West providing views out to the surrounding mountains and forests. Aside from the aforementioned glazing wrapping around the living spaces, the window openings are far more traditional in terms of their size, shape and their spacing on the elevations. The percentage of glazing area to wall area is appropriate for each elevation, to minimise heat loss and maximise heat gains where necessary.
A striking roof overhang on the West elevation exaggerates the concept of a thick element wrapping over the building, also providing solar shading in the afternoon/evening. This concept echoes the form of many buildings in Lozen which feature a stepped façade with large overhangs.

environmental credentials
As is the case with all Passive Houses, the building has been designed to use the sun for heating, thermal mass for heat retention and cooling, solar shading for solar gain control, and high levels of insulation to prevent heat loss. Our competition scheme however takes the extra step to provide a platform for a healthy, sustainable lifestyle for the building occupants.
We are constantly being bombarded with information about how we can cut the carbon emissions involved in construction in the residential sector, by designing to Passivhaus standards, using low embodied energy materials and integrating renewable energy technologies. These are all important objectives and should be the international standard for new homes, however, producing efficient, low-impact houses is one thing, but in order to sustain the planet’s resources we need to promote sustainable living.
Self-sufficiency is at the core of sustainable living. Our Passive House encourages this by providing for food production on the land surrounding the building. These food gardens will be capable of producing seasonal vegetables and herbs, therefore reducing the carbon emissions accumulated by the family driving to the supermarket to buy food which may have travelled tens, hundreds or even thousands of miles. A submerged rainwater-harvesting tank will store rainwater from the roof of the Passive House, for watering the garden and vegetables.
A third bedroom in the house has been designed to be used as an office when not needed for accommodating guests etc. thereby providing a work/live/play environment to reduce the occupants’ carbon footprint.
The Passive House is powered by, heated, cooled and ventilated by a holistic system. The catalyst for the self-sufficiency of the building is a 4.6kW array of photovoltaic panels positioned to the far west of the plot with unobstructed solar energy potential. Once inverted, the electricity provided by the PV panels will provide the power for a ground source heat pump, which pumps a mixture of antifreeze and water around a 200m long network of pipes buried 1-2m underground, absorbing the heat from the sun naturally stored in the earth. The heat pump then tops up the temperature of the liquid to between 30 and 45 oc and feeds it around a network of underfloor heating pipes located in the layer of screed on both the ground and first floor, providing carbon neutral heating that is four times more efficient than a condensing gas boiler. A thermal store will be installed in the mechanical room of the Passive House to store the hot water provided by the GSHP to feed the underfloor heating system as well as mains pressure hot water, for showers, baths etc.
The fabric of the Passive House will be made airtight, which is great for reducing heat losses but in the process eliminates the draughts found in most. To prevent the internal environment of the building from becoming humid and smelly, a mechanical ventilation heat recovery unit will be integrated into the mechanical room [alongside the GSHP, thermal store and PV inverter], powered by the PV array. The MVHR unit is linked to a network of insulated pipes concealed in suspended ceilings, which extracts heat from the ‘wet’ rooms [kitchen, bathrooms, mechanical room] and feeds this heat through a heat exchanger into a fresh air supply to the ‘dry’ rooms - living spaces and bedrooms.
construction

Floor
Both the ground and first floors are exposed concrete, for optimum thermal mass properties in order to regulate the internal room temperatures. The ground floor is built up of a layer of screed on top with underfloor heating pipes, a reinforced insitu concrete slab, and a 300mm layer of rigid insulation boards, with a 200mm perimeter layer surrounding the slab on each side, forming a permanent formwork for the concrete slab to be poured in to. All concrete used in the construction will include locally sourced recycled aggregates, including glass, and will use ground granulated blast furnace slag/pulverised fuel ash as a proportion of cement replacement.

Roof
Despite the aerial view of Lozen being covered in red/orange roof tiles, we have chosen [locally sourced] timber shingles for the roof covering since they can replicate the effect of clay tiles if treated, and have a much lower embodied energy. These shingles are fixed onto timber battens on TJI roof joists at 600mm centres. The roof is highly insulated, with 240mm of recycled newspaper fill insulation between the TJI joists, a layer of Panelvent board underneath [the airtightness layer] and two layers of 150mm sheepswool insulation below.

Walls
In order to realise the ‘wrapping roof’ concept, the North elevation will be clad in timber shingles to match the roof covering. These too will be fixed to battens, on vertically fixed TJI ‘joists’ with 240mm EPS insulation between. The loadbearing structure/internal skin will be constructed with thin-joint blockwork, plastered internally for airtightness using lime plaster. This system will be used on the external walls of the West elevation and the section of the South elevation under the roof overhang.
All other external walls will consist of external lime render on 280mm EPS insulation, adhered to 200mm thin-joint blockwork, again, with lime plaster internally.
All junctions between structural elements [e.g. externall wall - to - floor slab, roof eaves, window openings] will be made airtight using airtightness tapes and membranes [e.g. ProClima].