When Steve and Deborah Macken set about building a new farmhouse on a beautiful, elevated spot in Loch Lomond and Trossachs National Park, they were serious about their desire to make a thoroughly energy-efficient home.

So serious, in fact, that the new farmhouse at East Cambusmoon is, unlike many others built with the best of green intentions, no token eco-house. Such was the Mackens’ commitment to achieving a sustainable home that, when they embarked on the project, they joined the Association of Environmentally Conscious Builders.

“We both work within the renewables industry, so we’re well placed and well briefed, and we were keen to have a house that incorporated this type of technology as far as possible,” says Deborah.

From an office in the farm’s former tool shed, she and Steve run a windpower company, Lomond Energy, for which Deborah is the surveyor. “For the new farmhouse, we adopted the association’s CarbonLite Silver Standard as a specification for energy efficiency. This aims for about an 80% improvement on current building standards.”

As a result, the new house on the five-acre East Cambusmoon Farm estate, which the couple bought in 2006, has energy-efficiency credentials with bells on. Its attributes include superinsulation, airtight construction and draughtproofing, and heatrecovery ventilation.

The low-energy heating system includes a high-efficiency gas boiler and ground-source heat pump. Argon-filled double glazing, A+-rated appliances, low-energy lighting and solar panels complete the picture.

The building has also been orientated to take advantage of sunlight to heat it naturally.

The Mackens’ reward has been a heating and hot water bill of just £300 for the entire first year of occupancy. “Our objective was to achieve all of these specifications without breaking the bank or giving local builders a problem,” says Steve, an engineer.

The £300,000 project went ahead without any “Grand Designs-type catastrophes”, according to Deborah. “We did our homework, and we had a good relationship with the architect and the builder, and this teamwork paid dividends.

“The bottom line is that the more work you do in advance, the better the build goes. We had looked into the technical detail of what we were doing quite thoroughly, and all that attention to detail before you’ve actually dug the first part of the foundation really makes a huge difference.”

The couple also prepared a “mood board” — a cut-and-paste compilation of all the features they wanted in their new house>.

Then they spent a year planning and designing it with the help of Thomas Robinson Architects, of Blanefield.

“We were intending to be hands-on clients and we were keen to have a firm nearby that we could work closely with. The architects have completed other projects around the Loch Lomond and Trossachs National Park, and this was also important,” says Steve.

In design terms, the Mackens had in mind a family house — for them and children Molly, 6, and Finlay, 4 — with a simple form in the tradition of the rural longhouse, which would fit sympathetically into the landscape. “We were also keen to have high ceilings and open-plan, airy spaces, and a lot of light in the house — because this is important for the energy-efficiency aspect, too,” he says.

A somewhat rundown, Victorian farmhouse was what confronted Fiona Robinson, the project’s architect, when she arrived to carry out an appraisal of the site.

“We considered developing the existing house but it was too small for modern family living and it could never have been as energy-efficient as Steve and Deborah were hoping for,” she says.

So the house was demolished to make way for the new timber-framed, one-and-a-half-storey, contemporary longhouse, which has white render, untreated larch cladding and a slate roof made from the old tiles from the original building. “We retained as much as possible. Even our veggie patch has been constructed using the old roof timbers,” says Deborah.

The building’s timber frame has been over-clad in wood fibre, which adds about 50% to the thickness of the walls and contributes to the airtightness. The roof contains superinsulation and the 6in-thick concrete floor has underfloor heating, “floating” on 8in of insulating polystyrene.

The site did pose a design quandary, says Robinson: “There was a bit of a conflict, as the main views are to the north, which would normally mean using big windows to capture these views.

“With sustainability key to the whole concept of the building, this meant creating smaller openings — because it’s colder on the north side. As a result, the main living area and kitchen have been placed at the south-facing end of the house, which traps the sun all day.”

The open-plan living, kitchen and dining area sits within the larch-clad section of the house. “We decided to keep it a long, linear building, which is typical of traditional farm buildings of the area,” says Robinson. “But since it’s such a long building, we chose the timber cladding to create the effect of shortening it, as well as marking that part the main public space.”

This area also has a greater floor-to-ceiling height and, as a result, is a large, airy space that makes the most of the light flooding in from the large, glazed openings.

In addition to the kitchen, dining and adjoining family room, the ground floor also has a roomy utilities area, a main sitting room, a guest bedroom, a shower room and a large entrance and reception space.

A bespoke oak staircase leads to the upper level, which has a family bathroom and three more bedrooms, including a master with an en-suite bathroom. Steve and Deborah were responsible for finding most of the interior finishes, from the striking, red Ikea kitchen with bespoke granite worktops, to the dark, stone flooring, from Strathearn Stone and Timber, which absorbs heat and distributes it throughout the ground floor via the concrete foundations.

East Cambusmoon’s location in the national park meant that the design of the new farmhouse was subject to planning constraints. “The planning authorities stipulated that they wanted to see a sensitively designed building that would fit well into the landscape,” says Robinson.

“We had paid a lot of attention to how the building would fit into the farm complex and I initially presented a design statement detailing our sustainable-design idea. Throughout the whole process, the planners were very supportive and encouraging.”

The eight-month construction period did prove to be slightly more arduous for Steve and Deborah, though,particularly when the family had to move from their home in the neighbouring village into a caravan on the site in the summer of 2007.

“I’ve got say that living in the caravan got pretty tough, especially in the winter with the rough weather,” says Steve. “Sometimes it would rock in the wind.”

But, ultimately, the Mackens were unwavering in their commitment to the project and have no regrets. “If I were building another house, I probably wouldn’t live in a caravan,” says Deborah. “We wanted to be very hands-on, which was one of the reasons that we lived on-site.

“Although we’ve never built a home before, professionally we’re involved in project management, so we do have the right background to tackle this sort of project.

“But it is hard work, and we have to give credit to the architect and the excellent builder. And we’re here to stay — we have no intention of moving. We love the house and its views, and the energy-efficient aspect.”

Steve and Deborah are already planning the next phase of East Cambusmoon’s development, and with the same architect and team of builders. Two outhouses will be renovated and turned into holiday lets, using the same low-energy approach.

“So, in answer to the standard question of whether we would do it again,” says Deborah, “the answer is clearly yes.”

Steve and Deborah Macken wrote a blog about their self-build experience on http://eastcambusmoon.blogspot.com ; www.thomasrobinsonarchitects.co.uk

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