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    30th Jan 2019

    Underground Eco-Haven; The long term efficacy of the ground source heat pump

    In true Grand Designs style, we take the opportunity to re-visit the fabulous Long Crendon Underground House. Since its completion in 2016, Stephen and Neil Bentley-Gockman’s self-designed home has been featured in the Saturday Telegraph’s Property section, with a focus on achieving planning for subterranean builds, and won the Federation of Master Builders Southern Region Eco-Build of the Year Award.

    To recap, for anyone not familiar with this project, The Underground House was built on a sloping site with protected views and next to the thirteenth-century village church. According to Stephen “The local planners explained very clearly from the start that we could build a house, but only if it wasn’t visible… therefore building underground was the only viable option. The upside was that we could benefit from the ground's natural heat and create an energy efficient abode.” The StuartBarr CDR team were delighted to prove that this largely underground project was not just possible, but also a highly sustainable way to build.

    Stephen goes on to say “The Underground House is toasty and warm. The ground source heat pump is brilliant – we have endless hot water and heating and it has functioned perfectly in the cold weather. Guilt-free heating! The sensors on the system keep track of the outside temperature so as it gets colder outside the pump kicks in to raise the temperature of the hot water, so we never need to worry about the house getting cold or running out of hot water. Having high performing glazing/roof lights and well-insulated walls also helps, and all were well worth the investment of the extra capital costs because our quarterly energy bills are the lowest we have ever had.

     

    The end result is a truly remarkable dwelling, invisible from the front, bar a blue front gate leading to a wildflower meadow roof. One approaches the house by descending via a narrow set of steps, finished in simple black slate and flanked by tall white rendered walls, towards a deep ‘secret’ entrance. On entering the house, however, the very distinct feeling of being underground is turned on its head. One is immediately hit by a bright open plan living space. Clever use of roof lights and south facing glazing, as well as the all-white interior splashed with bold feature colours, make for a delightfully bewildering sense of space and light.

     

    The build project itself involved a massive excavation, down to a final-max depth of eleven metres. The eco-advantage of ‘the big dig’ was that it put us in just the right place to install the infrastructure required for the ground source heat pump. In the case of The Underground House, a borehole system was deemed to be the most efficient and cost-effective option. Nine boreholes, each three metres deep and half a metre-wide run in sequence into a main water reservoir manifold.

     

    “The finished residence is incredibly energy efficient,” says David Noonan, Construction Director for the project. “Deep roof insulation and rooflight seals negate any of the usual flat roof heat loss and were proven effective by results from the airtightness test and ECP ratings. The underground heat pump and MVHR system (mechanical ventilation with heat recovery) aids the naturally insulated house to remain as carbon neutral as possible. In addition, the ‘Durasol’ blocks used for the build were made from a recycled, renewable, and energy efficient material and timber was sustainably sourced.”

    It is no surprise that one of the greatest benefits of underground living is energy efficiency. The earth's subsurface temperature remains stable, so underground dwellings benefit from geothermal mass and heat exchange, staying cool in the summer and warm in the winter - saving around 80% in energy costs. An additional benefit of the surrounding earth is noise insulation making The Underground House an exceptionally peaceful place to live.

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