MMC 5542 48 Feb '16 cc

Cross code project
nears completion
Technical Editor Bruce Meechan reviews a highly energy conscious, mixed tenure social housing
development down near the Bristol Channel which is drawing on two of the industry’s best
proven design standards.
The continuing relevance of the Code
for Sustainable Homes to the social
housing sector has been
demonstrated by the development of 25
new homes near to Minehead on the Bristol
Channel, which is making use of both the
points based system and the even more
energy sensitive PassivHaus Standard..
Known as Townsend Farm, the project for
Hastoe Housing is seeing Halsall
Construction Limited build a total of 20
houses to full PassivHaus requirements,
while a further five for market sales also
offer excellent energy performance.
Significantly, the project team which includes
Bristol based architectural consultant, gcp
and WARM Associates as the PassivHaus
certification specialist, is also being specified
to meet Code Level 4 in order to address
wider sustainability issues.
Beyond this site by the Bristol Channel,
Hastoe is constructing all of its new housing
to Code for Sustainable Homes Level 4 as a
minimum standard, while 20 per cent of its
developments are set to achieve the
PassivHaus Standard.
Design and Sustainability Manager at Halsall,
Nicola Thorogood has been involved with the
Townsend Farm project from early on and
commented: “It’s a site that has been
identified for a long time for housing and has
been a challenge to get to this point, but
pleased we are now moving forward
providing high quality, low maintenance, low
energy cost homes for local people in and
around Carhampton.
“This design and build project is an exciting
challenge for Halsall building on the
knowledge and experience of low energynear
PassivHaus design, Code for
Sustainable Homes levels 5 and 6 housing
the company has successfully completed
over the past few years.”
The construction, while featuring a highly
insulated timber frame system from Taylor
Lane, brings together a selection of other
products in order to achieve the required
standards of airtightness and insulation
across the building envelope.
For example, at the critical floor/wall junction
the designers have incorporated a course of
Thermoblocks; manufactured by Marmox.
These feature miniature columns of concrete
encapsulated within high performance XPS
insulation. They can be used at upper floor
levels and other locations as well as around
the perimeter to the oversite.
The Site Agent for Halsall Construction
Limited, John Gray, explained: “The
PassivHaus properties feature the use of 150
mm wide Celcon aircrete blocks up to floor
level then the course of Marmox
Thermoblocks and another single course of
blocks above, which ultimately carries the
timber frame. The elevations to the buildings
then features either local stone or render
outside a further 200 mm thickness of
insulation. The Thermoblock is employed to
help achieve the very low U-value, while the
airtightness figure required is 0.6 (m 3 /
m 2 /hr)”.
In fact the 140 mm timber frame is factory
insulated with Kingspan Kooltherm insulation
and then encased externally by 200 mm of
Rockwool. The latter has the twin benefits of
offering very good fire protection and sound
reduction while remaining vapour permeable.
Internally the frame has an Intello Smart air
barrier to restrict movement of moisture
vapour into the structure where it could
cause interstitial condensation. Then there is
also a batten cavity for the routing of
building services.
Although gcp Chartered Architects has
designed past PassivHaus projects with slabs
of high density polystyrene beneath the
oversite, the challenging ground conditions
on the former farmland did not lend
themselves to a raft solution. As a result, the
mix of one, two and three bedroom homes
are raised on conventional footings spanned
by a beam and block ground floor. This then
has substantial insulation over and is
protected against cold-bridging by the
Thermoblocks and very energy efficient wall
construction.
Project Architect Colin Powell commented:
“In order to maintain the very good
airtightness and insulation offered by the
fabric of the walls, roof and floor, the
contract to supply the windows was awarded
to TRC, an eastern European manufacturer.
These are timber to respect the village
setting of the development and triple glazed
to keep heat loss within PassivHaus
guidelines. The entrance doors were supplied
by IG.
“Then the properties all feature Zehnder
mechanical ventilation with heat recovery
systems which are ideal for PassivHaus
requirements. In terms of the overall primary
energy the places are heated with a couple
of convector radiators in the bathroom and
hall; while Baxi solar thermal systems will
provide the domestic hot water through
much of the year.
“Overall the aim of the project was to design
it to be as conventional as possible –
adapting standard materials and techniques
to keep the cost down and the appearance
traditional.
“Then of course the PassivHaus performance
gives you a very good starting point in terms
of energy standards to go onto achieve Code
for Sustainable Homes Level 4, where the
houses will be provided with facilities such as
bike stores and water butts.”
As well as the private market sale properties,
the homes at Townsend Farm will offer the
opportunity for both shared equity and
affordable rent. The project is expected to be
completed before the summer.
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