The Knowledge MAKinG ExisTinG HOMEs EFFiciEnT
Although John and Jean knew what they wanted to achieve, their plans only really came to life when they employed architect Paul Testa, who they could work closely with and who was willing and able to project manage the entire renovation.
Paul was also highly instrumental to the energyefficient scheme. “From the outset we aimed to achieve as close to the AECB building standard as was spatially and financially reasonable on the project,” he explains. “It
follows the broad methodology that is used for Passivhaus but has a lower performance threshold and a less onerous process for certification. We find it a very useful office benchmark for all the projects we do that aren’t specifically aiming for Passivhaus.
“The existing bungalow was cold, dark and damp. It was a priority for Jean and John that this became a warm, comfortable and healthy home in which to retire,” continues Paul. “The existing construction had almost no insulation, despite the elevated and exposed hillside location. The block and stone cavity walls were not suitable for retrofit cavity wall insulation and the timber floors and roof were not insulated.
“The priority was to improve the thermal performance of the building fabric — a fabric-first approach. This involved three key aspects:
l insulation
“We insulated between the suspended timber floor joists with rigid insulation, as well as insulating the exterior walls with a drylining system and adding rigid insulation between and above the roof trusses. The glazing throughout the building is also highly efficient as we used high-performance triple-glazed Velfac windows and Fakro rooflights.
l airtightness
“We overboarded the floor joists with OSB and taped the joints to prove an airtight structural deck; the walls were sealed with an intelligent vapour control membrane as was the roof. This was carefully taped at all joints, penetrations and to the window frames.
l ventilation
“A considered and properly designed ventilation strategy is key to the comfort and health of a building. In this house we utilised a mechanical ventilation with heat recovery (MVHR) system. This is ducted around the building supplying fresh, pre-heated air to the bedrooms and living spaces and extracting dirty, moist air from the kitchen, bathroom and
utility. The heat recovery element ensures that minimal heat is lost through ventilation but the occupants are still guaranteed a consistent supply of fresh air to give the best possible internal air quality.
“Retrofit work is highly challenging because houses like this are pretty fixed in their geometry and orientation. There were various building elements that inevitably led to coldbridges [which can allow heat to escape and/or cold air to enter] in the construction, and there were some minor spatial constraints also on internal wall insulation and the duct routing for the MVHR system. So this also needed careful planning and delivery on site.
“As we took a fabric-first approach to the project we didn’t particularly consider renewables such as heat pumps and biomass heating as the budget wouldn’t stretch that far. However, the house benefitted from a large array of existing solar panels on the south-facing roof which were carefully removed and refitted after the re-roofing works. These were old enough to be paying the best Feed-in Tariff (FiTs) rate, so were well worth retaining.
The house now has combined gas and electric bills of £800/year but with a FiTs payment of £1,800/year, the couple are making a handsome annual profit of £1,000.”
Concludes John: “It was good to have someone who was able to suggest possible options including calculating the effect on thermal efficiency of each potential cut when we needed to reduce costs. Ultimately, that was an invaluable part of the decision-making process.”