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Monday28 July 2014

Scotland’s Housing Expo homes previewed

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We examine four of the innovative projects under construction for this summer’s long-awaited Housing Expo in Inverness

Scotland’s Housing Expo has to be as close to a win-win architectural competition as they come. In 2007, a consortium of Scottish public agencies held an open architectural competition for experimental houses on the Expo site in Scotland’s boom city of Inverness.

Some 88 designs were entered for 28 plots accommodating 55 dwellings. Twenty-four Scottish architects won commissions to build their schemes, and four managed to walk off with a couple of plots each. Competitors weren’t even required to have a housebuilder in tow: those that didn’t were paired with a builder later on.

Now, three years later and in the depth of the worst recession in living memory, all but one of these 28 sites is under construction. For the entire month of August, the architects’ show homes will be on public exhibition. And after that they will be sold off, some 40% as affordable housing. The fact that the recession has delayed the Expo for a full year may well be forgotten amid all the back-slapping of the show and sales.

All entries had to meet the equivalent of Eco-homes “excellent” standard, while in design terms, the houses tend more towards traditional Highland cottages with double-pitched roofs rather than avant-garde forms.

Natural renewable materials make up a recurring theme. Softwood is used in all its forms, from basic shingles and boarded cladding in larch, through wood fibre insulation and orientated strandboard to Trespa cladding panels in wood fibre composite and hefty cross-laminated spruce panels that resemble jumbo plywood. Larch boarding is a favourite cladding material as it flaunts its locally grown origins. But the more exciting wide-span structures are supported on cross-laminated panels, manufactured in Austria and Germany.

The houses illustrated here all show ingenious variants on the highly insulated building envelope, with the schemes by Richard Murphy Architects and Graeme Massie Architects both introducing exciting technical innovations.

Shrink-wrapped Houses

Architect ; Graham Massie Architects

Structural engineer : ECC Timber Engineering

Contractor : O’Brien Homes

The big technical innovation in Graeme Massie Architects’ pair of houses on adjacent plots is a spray-on finish that shrink-wraps the external walls and roof alike in a seamless membrane. In this way, walls and roof appear uniform and homogeneous so as to express the building’s crisp geometric forms. The sharp-edged effect is enhanced by eliminating

clip-on clutter such as gutters and downpipes and instead sinking them into the building fabric.

For the houses’ underlying concept, Massie has harked back to the classic modernist notion of space flowing freely between interior and exterior. Accordingly, the upper floor of one house has been entirely given over to an open-plan living room with wall-to-wall opening windows, and this was made possible by a clear-span, self-supporting shell of cross-laminated timber panels.

The spray-on external finish is manufactured by BASF with BBA approval, and marketed as the roofing product Coniroof. It is applied by spraying on in four coats. It is waterproof and uv-resistant, and BASF claims it is also elastic and seamless enough to bridge gaps in the substrate.

For the first time in the UK, Coniroof will be used to cover the entire building envelope of walls and roofs of Massie’s two show homes.


massie house

Massie’s houses will sit on adjacent plots at the expo.

Dynamically Breathing House

Architect :Richard Murphy Architects

Structural engineer:Halcrow

Contractor: Tulloch

Beneath Richard Murphy Architects’ trademark ridge skylight lies a house that is “dynamically breathing” through its jacket of innovative permeable insulation. The house draws its fresh air directly through the insulation in walls and roof, and in the process the air heats up passively.

The insulation system of permeable polystyrene panels was invented and patented by its supplier, Energyflo Construction Technologies, a fledgling company formed at Aberdeen University in 2004.

External air is drawn in through vents at the foot of the walls and the eaves. It then rises up through the wall and roof cavities while the same time percolating through the insulation panels. As it does so, the air picks up as much as 8°C of heat that is trying to escape by conduction out of the warm interiors. On hot summer days, the incoming air is cooled down by the building fabric.

At roof level, the air passes into the roof void, where it gains more heat extracted by a mechanical heat exchanger from exhaust air discharged through the rooflight. The doubly heated fresh air is then circulated throughout the house.

In Richard Murphy’s design, the walls and roof are timber-framed and plasterboarded on the inside. The roof is covered in standing seam zinc and the external walls in natural larch boarding.

The double action of insulation and ventilation improves the building envelope’s thermal efficiency by recycling heat that would otherwise escape. By using 140mm thick insulation panels, the U-value is effectively reduced to below 0.1W/m2K. But this high thermal efficiency is achieved within relatively thin walls and roofs, so that the space saved can be more profitably added to usable floor areas. It also provides constant fresh air to the building interior, with airborne pollutants filtered out as it passes through the insulation.


Murphy

The house draws fresh air through insulation in the walls and roof.

Flower house

Architect: A&J Burridge

Structural engineer :A Fairhurst & Partners

Contractor: O’Brien Homes




Behind the children’s book decorations of A&J Burridge’s Flower House stands another shell of cross-laminated timber with double-pitched roof.


Walls and roof are both finished in rainscreen cladding of 125mm timber boards with 6mm open joints. Local larch is used on the walls and more stable heat-treated Platowood across the roof. The insulation below the boarding is Pavatex wood fibreboard, which is made weatherproof by laytex impregnation on the walls and Tyvek membrane on the roof.

PassivHauS

Architect: HLM Architects
Structural and services engineer : Buro Happold
Contractor : O’Brien Homes


Though not the first Passivhaus to be built in Scotland, the three terrace houses by HLM Architects have been certified as achieving the low-energy standards of the German model. High thermal insulation and airtightness should reduce energy consumption by 80%, enough to make conventional space heaters unnecessary.


Within the larch-boarded walls are prefabricated boxed panels of oriented strand board stuffed with 265mm-deep mineral wool insulation plus another 40mm of rigid insulation fixed in the inside behind the plasterboard lining.

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