‘The roof ridge is lower than the previous approved scheme and the foot print is considerably smaller, being more appropriate for the scale of the site and more in keeping with adjoining neighbours’ properties,’ said Andrew. ‘The house faces almost due south, to maximize passive solar gain and allow the house to function as a Passivhaus, with a mechanical ventilation heat recovery system providing heating / ventilation and a small wood-burning stove for back up. This orientation also ensures that thermal and PV solar panels will operate at optimal efficiency throughout the year – further reducing the carbon footprint of the house.’
Andrew was also committed to designing a Passive House within Karen and Ian’s budget of £200,000. ‘We wanted to prove that we could build an affordable passive house and demonstrate to others that it’s a viable way forward for future self-builders,’ says Karen. ‘Ian was quite sceptical at first – we had built three houses before this but I wanted to go for a passive house and was prepared to take on the project management myself to achieve it.’
After selling their last house in 2011, Karen, Ian and their two children moved lock, stock and barrel into ‘the cave’ – effectively a very large garage with a small kitchen and a shower room – so they could build at their own pace. ‘It was cheaper than moving into a rented house and more comfortable than a static caravan,’ says Karen. The ‘cave’ already had under floor heating and they insulated the garage doors, to make very small but cosy home. ‘ It made us realise that you don’t really need a lot of space or possessions to live comfortably – although we hadn’t envisaged living there for four and a half years.’
Before the build started, Ian and Karen built a barn, not only as a shelter for their horses but also to provide a dry storage area for building materials. Then they asked Andrew Devenney, (Transition Joinery) who had been on Strathclyde University’s passivhaus course, to take their new project on board. ‘He was ‘air tightness champion’ and really understood what we wanted to achieve. We pulled together a team of local trades people who were prepared to get involved and up for the challenge,’ says Karen. ‘Ian and I got stuck in where we could. Ian did more of the physical work, including the ground works which were his domain, while I was more involved in project management. I spent hours in on the phone and computer getting the best deals for materials.’
The concrete foundations, layered with Visqueen and an Eco-membrane slip sheet, was finished in concrete slab to take the main thermal breezeblock structure, strengthened with basalt wall ties and all the 300mm insulation was installed by Karen and Ian to ensure it was completely airtight.
The walls are a substantial half a meter thick and the roof is insulated with a further 600mm layer of insulation. Any gaps, however small, were sealed ‘with green gunk and airtight tape’ to prevent any leakage.
‘It went everywhere you can think of,’ says Karen. ‘Wherever there was a hole or the tiniest gap, out came the gunk and tape. There are no air leaks anywhere. At our initial meeting, Ian and I suggested having geothermal heating but Andrew Yeats said ‘Why do you need it?’ and he was absolutely right. The house maintains a steady temperature all year round thanks to its airtightness, solar gain and heat recovery system. Once the temperature is up, it stays up and the MVHR is constantly refreshing the air, so it’s never stale or damp inside.’ With the combination of free solar power, feed-in tariffs for the 14 solar panels and RHI payments for two solar thermal panels heating the hot water, the house alone costs around £100 per annum in electricity.
‘There were no big disasters during the build but it was hard work, especially on top of our jobs and looking after the children,’ says Karen. ‘We often had to be creative when problems arose – fortunately I like problem solving – and we had Andrew as a back up if we didn’t know or understand anything. We followed his plans to the letter. Sometimes things seemed counter-intuitive, but you have to do it anyway and then it falls into place. If you can maintain the principles of airtightness (and avoid cold-bridging) you have the basis of the whole house.’