Refurb Projects - November 2018

200 year old warehouse converted
to first Passivhaus hostel in the UK
Building physics and services
engineer Greengauge has
provided a complete holistic
advice package on the
remodelling and retrofit of the
Barrel Store, the first and only
Passivhaus certified hostel in the UK.
Completed in 2016, the
exceptionally performing building
won the Cirencester Civic Society
Design Award 2016 and is a finalist
in the UK Passivhaus Awards 2018.
But these accolades belie a humbler
beginning.
BACKGROUND
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 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. This use would provide much
needed affordable and stylish visitor
accommodation for people
attending New Brewery Arts courses
and workshops.
PASSIVHAUS ENERPHIT RETROFIT
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 groundbreaking,
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.”
The project brief was fairly
straightforward, asking for a hostel
that provided 48 beds, a kitchen,
dining area, entrance, laundry, office
and storage. But a Passivhaus
Enerphit retrofit is inherently more
difficult than a new build.
Thankfully, this 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.
“This project touches on all of
our key services,” says Toby Cambray,
co-founder of Greengauge. “We did
all of the M&E design, the
Passivhaus consultancy, which
involved specifying and doing the
calculations for the insulation, the
triple glazed windows and
supporting the architect in the
detailing. We also completed a
moisture risk analysis using WUFI [a
specialist software tool which
simulates how moisture moves
through a building’s structure].”
INSULATION CHALLENGES
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 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 high
quality 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 this end the solution
employed involved the construction
of a highly insulated timber-framed
‘building’ 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.
MOISTURE RISK ANALYSIS
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 twodimensional
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 AND VENTILATION
Hot water demand at the Barrel
Store was anticipated to be high
given its hostel use. Greengauge
PROJECTS
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.
AT THE FOREFRONT OF
PASSIVHAUS
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 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.
01225 862605
hannahrayner@
greengaugebuildingenergy.co.uk
REFURBISHMENT PROJECTS, NOVEMBER 2018 41