deciding how to renovate. “It was a
probate sale and there hadn’t been much
done to it since it was built, so we knew
we were going to have to spend a lot to
upgrade it,” Jonathan says.
The big question wasn’t what colour
to paint the living room walls or what
kitchen to buy, but whether or not to
insulate under the ground floor. “This
would be the only chance to do that,”
says Jonathan, who employed Heather
McNeill at the local architecture
company AD Practice, which had
just been certified by Passivhaus,
the international design standard
for cutting energy use. “Once
we’d decided to do that, which
meant digging up the whole
floor and replacing it with a
highly insulated slab with
underfloor heating inside the
screed, we thought we might as
well go the whole hog.”
The whole hog meant removing
large sections of the external walls and
replacing them with highly insulated
timber-framed sections, which were
clad in Siberian larch. The remaining
walls were filled with cavity insulation
and externally insulated with wood-fibreJ
onathan and Emma Dixon’s
Hertfordshire home was built
in 1964 before anyone had
heard of having solar panels
or ground source heat pumps.
Now it is only the third
certified retrofit home in the
UK that generates more
energy than it uses. It is so energy
efficient it costs almost nothing to
run, needs no heating upstairs and has
walls half a metre thick.
“We didn’t buy this house to do this
scale of project. We thought we would
put in triple-glazed windows but weren’t
sure what else,” says Jonathan, 45, a
software engineer. “But reducing our
carbon footprint was always a goal.”
The couple moved to Harpenden from
south London to get away from the city,
and chose to live in the four-bedroom
detached house for a while before
Jonathan
and Emma
Dixon’s home
generates
more energy
than it usesWe don’t need
to turn on the
heating from late March
until November
‘Retrofitting has cut our
energy bills by 90 per cent’
Meet the Hertfordshire couple who ditched gas, super-insulated
their home — and installed a £1,500 cat flap. By Cherry Maslen
board, while the inside of the house was
lined with an airtight plywood skin to
Passivhaus standards. These layers of
insulation have made the walls half a
metre thick, which, together with the
insulated floor and roof, has drastically
reduced the house’s energy needs. The
house is also gas-free, using an air source
heat pump and harnessing solar energy
with an entire roof pitch of solar panels.
“We’re in a conservation area so
having the whole roof pitch covered in
panels helped with getting planning
permission because they’re less
noticeable. It just looks like a glass roof,”
Jonathan says. A mechanical ventilation
with heat recovery (MVHR) system
provides fresh, filtered air.
The insulation has the extra benefit
of soundproofing, so you can’t hear road
noise or the railway line nearby. “I’m a
light sleeper, so the quiet at night really
helps,” Jonathan says. “And because the
house is airtight we don’t get dust or
spiders either.”
The Dixons extended the
house at the rear to create
a spacious kitchen/diner,
with a big picture
window on to the
garden and two large
skylights that open
automatically at
night to cool the
house in hot weather.
Emma, 44, a data
analyst, hated the
original gloomy hallway,
so they took out the
ceiling to create an
atrium extending into
the loft with another
large skylight flooding
light downwards, and
installed a dramatic curved staircase.
“When we got the build quotes in we
considered knocking the house down
and building from scratch,” Jonathan
says. “But it would have taken longer to
start the whole process again, and a total
rebuild would have meant more
embodied carbon.”
The project took a year to build, from
January 2020 to February 2021 — three
months longer than planned because of
delays caused by Covid. They have now
been back in the house a full year, so
know they are consuming just a tenth
of the energy they were before.
“We have so much floor insulation
we only need a very low level of
underfloor heating, which is
programmed to come on for just
four hours at night when it’s
cheapest,” Jonathan says.
“In fact, we don’t need any
heating from late March
until November.”
Because warm air rises
the house doesn’t need any
heating at all upstairs, which
is always one or two degrees
warmer than downstairs.
“We do have electric
underfloor heating mats in
the bathroom and en suite,
but that’s it,” Jonathan adds.
The Dixons bought the house
for £900,000 and spent about
£300,000 on the retrofit, including
£10,000 to dig out and reinstate the
floor, £35,000 for the insulation and
£30,000 for the fenestration, including
an airtight electronic cat flap at £1,500.
“Before we started this project an eco
house might have had a lower resale
value than a standard house because
people didn’t want anything unusual,”
Jonathan says. “Now it’s the opposite.
The standard appreciation on this house
since we bought it would make it
£1.3 million, but because of the retrofit it
has been valued at £1.6 million. Estate
agents have been asked if there are any
houses like ours on the market.”AKIRA SUEMORI FOR THE SUNDAY TIMESAirtight plywood
layer on the inside toPassivhaus standards
No heating upstairs
(except heat mats
in the bathrooms)Whole roof pitch
of solar panels
Walls half a metre
thick with cavity andexternal insulation
Highly insulated floor slab
with heating in the screedSkylights automatically
open at night to coolhouse in hot weather
How it adds up
Bought: £900,000
Spent: £300,000
Valued at: £1.6 million
Heating bill before: £770 a year
Heating bill now: £90 a year
Profit from excess solar sales: £255Airtight
triple-glazed
electroniccat flap
Bricks
& MortarFriday April 8 2022 9
the times