Situated in Cirencester, the Barrel Store was constructed around 1820 as a warehouse to serve the adjacent brewery, which closed in the early 20th century. By the 1970s, the derelict but solidly built Cotswold limestone building narrowly escaped demolition and instead was converted into a theatre. The building sustained this use for several decades, but the theatre recently closed as it was no longer fit for purpose.
The ambitious scheme put together by Greengauge and Potter Church & Holmes Architects proposed a Passivhaus Enerphit retrofit for the building.
“I believe our proposal was chosen because it was the only scheme that included Passivhaus,” says Peter Holmes the Architect and director at Potter Church & Holmes Architects. “It may also have been that we proposed a ground-breaking, low energy hostel that would attract people and would result in minimal running costs. We were a good, local team of consultants that were very committed and enthusiastic about the project.”
Despite the brief’s simplicity, the project still had its own unique set of challenges. One of the most testing aspects involved the insulation. Given that the building is situated in a conservation area, the insulation required to help achieve Passivhaus could not be fixed to the outside of the stone building. Instead, it had to be fixed on the inside.
This decision had a knock-on effect on the hostel’s proposed layout. As the building is long and narrow, the insulation thickness required would take up valuable internal space resulting in fewer beds.
The specialist skills offered by Greengauge played a major role here by modelling the proposed structure in WUFI to check how it was likely to perform.
“We had to make sure we managed the risk of moisture accumulation,” says Cambray. “The dynamic movement of water, vapour and liquid form is something that the WUFI software can assess, which other simpler assessment methods don’t.”
A lime plaster parge layer was applied to the internal stone walls and then a continuous 100mm thick rigid wood fibre insulation layer was fixed to the masonry. The new timber structure, filled with 80mm thick flexible wood fibre insulation, was then built inside the rigid woodfibre board which is thermally separated from the walls and floor.
Minimising thermal bridging and ensuring air-tightness in the building were other critical factors that helped to achieve Passivhaus. Greengauge drew up two-dimensional models of proposed key junctions using the THERM software to analyse heat transfer and to evaluate any potential problems with condensation and moisture risk.
Hot water demand at the Barrel Store was anticipated to be high given its hostel use. Greengauge specified a direct gas-fired water heater that heats a 370-litre cylinder, which supplies approximately 40 showers in two hours. Some of this heat is diverted into space heating when needed. A small 10kw plate heat exchanger takes heat from the cylinder and sends it around the hostel’s small radiator circuit.
Like all Passivhaus projects ventilation is important. This is provided via two mechanical ventilation with heat recovery units, which serve the left and right halves of the building. Ventilation is demand controlled based on relative humidity and is supplemented with fresh air via the windows.
Another contributing factor which helps to achieve Passivhaus certification is a good builder. One who is meticulous about ensuring against air leakage and keeps a clean, dust-free site. David Gilkes, managing director at DJP Construction, who was the Barrel Store builder, says it was the first Passivhaus project he had worked on and he is now a Passivhaus convert.
“It was a very rewarding job and it has had a huge impact on how we construct other projects,” says Gilkes. “We realise that to achieve Passivhaus is not as difficult as we had thought as long as you follow specific criteria. Toby [Cambray] at Greengauge was fantastic and because of his knowledge and experience in Passivhaus he was very considerate and supportive. Greengauge is at the forefront of Passivhaus and is miles ahead of any other consultants we’ve worked with.”
Holmes agrees adding: “Greengauge is not just a services engineer, it also has energy consultants with specialist knowledge about low energy buildings. They are a young firm that is growing very fast and has a really interesting range of skills. This broadening skills base within this overall area of expertise is uniquely theirs.”
The Barrel Store has been open for two years and to date, has received only positive feedback from guests. Many regard the Passivhaus aspect as a novelty and particularly enjoy its eco-friendly credentials.
The energy efficiency of the hostel means that the client should use less than 50% of the energy of a traditional construction. The client has confirmed that the building requires very little maintenance, which maximises the time the hostel is open. This is particularly important as the Barrel Store forms an integral part of the New Brewery Arts financial model; its efficiency therefore directly benefits its charitable organisation.