sustainable buildings & energy management
Barrel Store
The first and only Passivhaus certified hostel in the UK is expected to use less than 50 per cent of the energy of a traditional construction.
specifying and doing the calculations for the insulation, the triple glazed windows and supporting the architect in the detailing. Greengauge and insulation supplier Natural Building Technologies worked on different elements of the moisture risk analysis using WUFI - a specialist software tool which simulates how moisture moves through a building’s structure.
BUILT in the 1820s, the Cotswold limestone warehouse in Cirencester was converted into a theatre in the 1980s, but by the 2010s was considered no longer fit for purpose. The New Brewery Arts charity, which
had managed the theatre along with two other nearby former brewery buildings, decided to convert the Barrel Store into a youth hostel to generate revenue and provide accommodation for residential arts and crafts courses. Completed in 2016, the building won the
Cirencester Civic Society Design Award in the same year and was a finalist in the UK Passivhaus Awards 2018.
low energy hostel The ambitious scheme proposed a Passivhaus Enerphit retrofit (the Passive House Certificate for retrofits) for the building. “I believe our proposal was chosen
because it was the only scheme that included Passivhaus. 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,” says Peter Holmes, architect and director at Potter Church & Holmes Architects. The project brief called for a hostel that
provided 48 beds, a kitchen, dining area, entrance, laundry, office and storage. A Passivhaus Enerphit retrofit is inherently
more difficult than a new build. However, the project was simpler than most retrofits as everything internal was stripped out leaving the building’s shell, which was in good condition. Two new floors were formed requiring new load-bearing internal structures and the roof space was used to house the mechanical plant. Working with the architects, building
physics and services engineer Greengauge provided a holistic advice package on the remodelling and retrofit of the building. The company did all of the M&E design, the Passivhaus consultancy, which involved
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leisuredab.co.uk
insulation issues The insulation proved one of the most testing aspects of the project. The building is situated in a conservation area so 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 affected the hostel’s
proposed layout. The building is long and narrow, and the insulation thickness required would take up valuable internal space resulting in fewer beds. The realised scheme provides 14
bedrooms, 13 with en-suite bathrooms, and 48 beds, while still insulating to the level required for Enerphit. A semi-circular oak staircase lined with ash boarding, like a barrel, was introduced into the centre of the hostel. This architectural feature elevates the interior and draws in daylight via a new rooflight. Internal Wall Insulation (IWI) has to be
specified carefully because the masonry behind the insulation in a heated building will become colder than before. This increases the risk of moisture accumulation and slows down the rate at which the masonry can dry out. This in turn can increase the risk of mould and damage to the existing stone, new timber structure and the insulation. To solve this, a highly insulated timber-
framed ‘building’ was constructed inside the existing stone walls. This structure was built off an insulated concrete slab, which helped to thermally isolate the new timber structure from the ground and walls. The semi-basement was filled in with compacted granular material and 350mm of polystyrene insulation below a concrete raft to create level access. Greengauge modelled 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. The dynamic movement of water, vapour and
liquid form is something that the WUFI software can assess, which other simpler assessment methods don’t,” explains Toby Cambray, co-founder of Greengauge. A lime plaster parge layer was applied to
the internal stone walls and 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.
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