01 Oct 2013

Going underground in an area of outstanding natural beauty

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Bryn and Pam Owen wanted to build a house of their own, but were restricted by an Area of Outstanding Beauty.

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The retired couple wanted to create a home that was efficient to run, comfortable and carbon neutral. Planning restrictions in an Area of Outstanding Beauty demanded a design that would have minimal visual impact, so the sloping site was turned to advantage by the inventive plan to opt for a subterranean house. Adding a basement level was a great way to increase floor space in their new property without impacting on the landscape. The large roof window allows light to flood into the lowered floor.

“We decided we would have nothing above the road level which would not normally be found in a large country garden,” explains Pam. “We wanted to make a minimal impact and as one as our grandsons so nicely put it, it also has the advantage that when we die we will already be six foot under!”

Their so-called ‘Green House’ is built on a plot of land sloping away from what was Bryn and Pam’s rear garden. “Until the ground was removed we could not be sure what we would find as nobody could know for sure what was hiding below the surface,” describes the couple. 87 20-ton truck loads of spoil later, a sloping rural garden had been reduced to a large hole in the ground. 100 tons of concrete transformed this hole into the frame work of the dwelling and 1,000 concrete blocks were laid.

“All this concrete does have a carbon footprint, but there was no way in which we could build the subterranean structure we needed with wood and straw,” the couple continues. “We have, however, used natural stone from a local quarry for the back wall of the house which is non-structural and this means that the only completely exposed wall which can be seen from the back garden of the house looks satisfactorily natural.”

With a design aimed at achieving standards equivalent to level 6 of the Code for Sustainable Homes the Owen's designed insulation, heating and lighting systems to ensure the house would be carbon neutral. This meant installing efficient insulation which would deliver required U-values and maintain effective thermal performance even in a harsh, underground environment.

“We decided to work to target U-values of 0.15W/m2K for surfaces next to air and 0.2W/m2K where they were in the ground, as the temperature rarely drops to -5⁰C in our region and the calculated heat requirement of 3KW could easily be provided by a simple heating system,” adds Bryn.

Key to achieving the U-value targets for the floor was below-slab insulation which needed to withstand the load of the building and perform in an external environment. The Owen’s structural engineer recommended a thickness of 100mm to achieve the desired U-value at the same time as meeting mechanical strength requirements.

Basement walls were insulated with a STYROFOAM-A product, chosen for its effective moisture resistance and good thermal performance. PERIMATE DI-A was specified for the underground walls as it contains vertical drainage channels protected by a geo-textile fabric to help prevent them becoming clogged with soil.

“The erection of the roof top building was a significant milestone,” continues Bryn. “This building forms the above-ground entry to the dwelling and provides a vital platform for the solar panels. We did consider using structurally insulated panels (SIPs), but chose, because of cost, to go with a more traditional timber frame. For cladding of the timber frame building we wanted a material which would look like wood so the whole appearance would resemble a large garden building, but we did not want the long term maintenance problems associated with wood. After much investigation we found a British company, Euroform, who make a weatherboard finished to any colour. Surprisingly, although it is made from fibre cement, it has a Green Product Label Award issued by the National Environment Protection Bureau. We found this cladding easy to fit and most people who have seen it have thought it was wood and were surprised to learn of its composition.”

The house is built into the hillside, with the main living rooms looking through large east-facing windows. The design incorporates a central courtyard with a glass lantern to allow light into bedrooms and a large planter has been constructed in the stairwell. The couple plan to grow a large lemon tree in the planter, which will grow the full height of the building up towards the light from the Velux roof lights. The evergreen lemon tree will flower and fruit throughout the year, promote the courtyard feeling and provide fruit for Bryn and Pam.

Enhanced eco-credentials

A green roof supports the chalet-style building, with solar panels and rainwater collection facilities. “The location and planning constraints on the design of our eco dwelling gave us unusual challenges,” explains Pam. “The planning consent stated that we had to be carbon neutral and that the dwelling had to be subterranean. To achieve carbon neutral status and to be able to use electrical appliances we needed to generate electricity on site from renewable sources.”

Six months after completion Bryn and Pam have already managed to establish the start of the gardens and have a rockery outside the front door. All the stones in the rockery were extracted from the excavation and most of the plants were previously in the garden and carefully preserved during the build.

“We can already see the advantages of the new house,” enthuses Bryn. “We have created rooms with excellent views of the surrounding countryside with the sea in the near distance; we have created rooms overlooking a secluded back garden; we have created bedrooms which we expect to be quiet and peaceful places to sleep; and linking all of this and bringing light to the centre of the house is the stairs and courtyard, which is already creating an inside/outside feel. With no heating installed we can already tell from the inside temperatures in the middle of winter that we will have a house with low heating costs. Our water usage with our plentiful supply of rainwater will be at least 50% lower than a comparable conventional house and the maintenance costs, with no outside woodwork to look after, should be low.”

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