significantly change their lifestyles in order
to live in such a building. This house is
flexible, comfortable, it has high quality
design features and includes the spaces
and volumes which many modern homes
omit. Yet it is eminently affordable to
construct and to run.
The building does not look out of place
in its suburban setting, but is bold and
responds carefully to its site location.
Internally the spaces feel generous without
being excessive and the varied volumes of
the rooms makes living there an enjoyable
experience. Natural light pervades the
home.
This house is ground breaking by
being simple and economical to build,
comfortable to inhabit and by having low
running costs and a tiny carbon footprint
of just 11Kg/year. Any small house builder
could construct a house like this with very
little extra skill being required. Attention to
detail is needed, particularly in relation to
the air tightness, but thin joint blockwork
lends itself to this as a matter of course.
Yet no part of the aesthetics have been
sacrificed to the functional brief.
By addressing all of the ways that
buildings waste energy, exceptionally
low energy bills for the householder have
been accomplished. The 5 main issues
of orientation, insulation, air tightness,
thermal mass and volume were carefully
considered along with heating, ventilation
and energy generation to maximise the
thermal performance of the house.
Orientation:
The house is located on a plot which has
an open aspect to the south, but due to
the Planning constraints this is a short
façade; nevertheless, the architects have
maximised the window openings to gain
the most solar energy gain in winter.
Overhanging eaves and soffits provide
shading in summer to limit overheating.
Along with this a series of roof windows
allow light and warmth to penetrate
reducing lighting loads and provide heat
gains and natural ventilation control.
Insulation:
The house is exceptionally well insulated
to achieve a minimum U value of 0.1W/
m2K. There are no traditional foundations,
with the ground floor raft floating on
200mm of insulation. Windows and doors
are triple glazed with a U value of between
0.7 and 1.0 W/m2K. The insulation on the
walls wrap round in front of each of the
window and door frames preventing cold
bridging.
Air tightness:
There are no draughts! The house is
hermetically sealed so a whole house
ventilation system is used – see below. No
draught equals comfort!
Thermal mass and volume:
This house is largely built of concrete to
retain heat in winter and maintain a stable
temperature in summer. The volume of
the 3m high south facing rooms allows the
hot air to rise and stratify, transferring the
summer warmth to the 200mm concrete
first floor structure. The stair void in the
centre of the house rises 8.6m drawing
warm air through the house and out
through the roof windows in summer.
Heating:
The air to water heat pump (COP of 3)
delivers warm water very efficiently to the
underfloor heating which serves most
of the ground floor rooms. There is no
heating to the upper floor as the house is
kept at a constant temperature with the
upper rooms achieving the design intent
of 2°C lower than the ground floor rooms.
Ventilation:
As the house is sealed against wasteful air
leakage a heat recovery ventilation system
has been installed, gently extracting warm
moist air out of the wet rooms and input
fresh air into all the living spaces, through
a heat exchanger.
Generation:
Using the south facing PV panels which
generate 3,380kW hours/year, electricity
is fed back to the house to run appliances,
the heating and hot water production.
Excess electricity is sold back to a green
energy supplier, reducing the carbon
footprint of the house to 8Kg/year when
utilising the green electricity supplier,
Ecotricity. This amounts to 3% of the
carbon produced by an average UK house
of the same size with the same supplier.
The running cost of the house is £0.00.
Cost:
The cost of constructing the house was
£240,000 which includes all the fixtures
and finishes. This equates to £1,340 per
m2, which is comparable to the build
cost of a one-off high spec ‘traditional’
property with much lower environmental
performance. However this includes
the cost of the PV array and associated
installations. Without this the build cost
would have been closer to £1,250 per m2.
www.johnmccall.co.uk