Scotston Hill, Auchterhouse, Angus 2012

The Bivvi

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Completed in 2012, this project is located on an incredible site in a small disused quarry on the side of Scotston Hill in Auchterhouse, Angus. The client had a great vision to build a house on the site nurtured during his childhood building ‘bivvi’s’ in the woods behind the site. The house is designed to make the most of its spectacular site while trying to minimise its visual impact on the landscape. Designed as a passive house, it will also have very a low requirement for energy in use.

Completed in 2012, this project is located on an incredible site in a small disused quarry on the side of Scotston Hill in Auchterhouse, Angus. The client had a great vision to build a house on the site nurtured during his childhood building ‘bivvi’s’ in the woods behind the site. The house is designed to make the most of its spectacular site while trying to minimise its visual impact on the landscape. Designed as a passive house, it will also have very a low requirement for energy in use.

Siting and Contextual Response

The house is half buried in a small disused quarry on Scotston Hill, its south elevation is extensively glazed to make the most of the views, the other external finishes are natural stone walls and a green sedum roof. Earth is then bunded against the house and over the garage and has been left to return to hillside rather than being planted as garden.

The original brief was for a ‘hobbity’ house but I struggled to conceive a house with curves in all directions and round doors on a reasonable budget! The design evolved as a faceted planform reflecting the topography of the existing quarry with a single aspect and a plan just deep enough to accommodate two useful rooms with a mono-pitch green roof and clerestory glazing above the quarry at the rear for balanced natural light and ventilation. Given that the clients own a large area of farm land surrounding the house, a traditional garden was not a priority and two useful, low maintenance, terraces were proposed at ground and first floor level where curves are re-introduced to reflect the brief in landscape and balcony features where they are relatively easy to build. Everything else would return to the wild hillside landscape on completion.

Inside, the house has a double height, open plan kitchen and living space with mezzanine floor at its centre and a massive internal stone wall serving to mitigate some of the effects of solar gain by helping to maintain a steady internal temperature. This wall also acts as a visual continuation between inside and outside and accommodates a ‘floating’ cantilevered staircase. There are two bedrooms at ground floor and two upstairs with bathrooms on both levels and a living room at first floor level with access to a balcony and terrace.

Siting and Contextual Response

The Big Question?

Having obtained planning permission for the house, with its south west elevation extensively glazed across two stories, the client asked the big question: ‘will it overheat?’. At the time, the answer was; ‘I don’t know’! However, the client had come across the Passive House standard which uses a highly detailed spreadsheet to calculate building physics and could tell us whether the house would overheat. This began a wonderful journey of discovery and learning for me that I had not anticipated and I became a Certified Passive House Designer in 2012.

Using this house as my learning project throughout the course, I discovered that the house, as designed would overheat. But by pulling out the roof overhang to 1.2m across the whole south west elevation, the summer overheating was mitigated and a natural ventilation strategy with automatic opening windows at ground and first floor level set with a simple thermostat in the double height central space, the house can regulate its own temperature and avoid overheating

Low Energy Strategy

Technically, the house is highly insulated with floor, wall and roof U-values of 0.13, 0.14 and 0.09 respectively and triple glazed Katzbeck windows with a U-value of 0.72. Careful attention has been paid to air tightness and avoiding cold bridges in detailing and on site in order to ensure the rigorous requirements of 'Passive House' design are met; these being a heating demand of 15kW/m2 per year and airtightness of less than 0.6 air changes/hour at 50pa. A very efficient Paul MVHR (Mechanical Ventilation with Heat Recovery) whole house ventilation system takes the heat out of extracted air and imparts it on incoming air to provide ample fresh air while losing a minimum of heat energy. The house achieved an air tightness of 0.53 Air Changes per Hour @ 50 Pa.

Although the house is to be well sealed and mechanically ventilated for the majority of the time, there is nothing to stop occupants from opening a window. Indeed there are large sliding doors from most of the rooms onto the ground and first floor terraces that will allow the house to open up to the landscape better than most in the summer months when it is warm.

As Archid Architects first new build house commission that we have carried through to site,..

this house has been a tremendous opportunity. We are now believers in the 'Passive House' standard but also have a far better understanding of how to design and build low energy buildings even if they don't meet passive house standards.