Refurbishment of semi-detached houses in Bedford
Part L1 (2002) in existing dwellings
Part L1 (2002) in existing dwellings – Case Study
Bedford case study
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Introduction
In 2000 Bedfordshire Pilgrims Housing Association completed a largescale project to externally clad 650 of their properties. The houses
were solid-wall semi-detached houses built around 1937 and were
of the typical construction of the time. Many of the houses had been
suffering from rainwater penetration as a result of cracked render.
Many of the more fuel-poor households were also suffering from
damp and condensation problems. Four years after the work was
completed the Housing Association and their tenants are very pleased
with the results and the properties are no longer affected by damp or
condensation issues.
Wall insulation
The solid wall properties were externally clad with 60 mm of expanded
polystyrene, mechanically fixed to brickwork joints. The boards were
covered with a reinforcing scrim material and then 10-15 mm of epoxy
resin render and dashed with 5-10 mm gauge pebble-dashing. The
cladding system was an Alumasc ‘Swisslab’ product.
For all the detailing where such a thickness would be a problem, for
example the window reveals, thinner phenolic boards of a similar
U-value were used.
BRE has calculated that the U-value of such a wall would be in the
order of 0.45 W/m2K, which was the new-build standard at the time of
the refurbishment. This U-value is higher than the current new-build
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value of 0.35 W/m2K. The same thickness of phenolic board would
have reduced the U-value, but would have been more costly.
The insulation system used rates as ‘A’ rated for sustainability in the
BRE ‘Green guide for Housing Specification’,
Infrared thermography1
Infrared themograms of a semi detached pair where the right hand
house is owned by the Housing Association and the adjacent left
hand house is privately owned show that the improvement due to the
wall insulation is evident. Compared to the even surface temperature
of the insulated house, the adjacent house shows greater heat loss
particularly from the upper bedroom wall which probably has a
radiator under the window leading to much greater heat loss from
this area of the wall.
▲ The right-hand house of this pair has been refurbished,
the left-hand house is privately owned
Although the windows in the Housing Association house have been
recently upgraded to low emissivity K glass, both dwellings have
double glazing as indicated by the similar heat loss shown by the
thermogram of the windows.
A thermogram of the north-facing upper façade and roof of the
recently refurbished ‘Community’ House shows a uniform external
wall temperature indicating good thermal performance. As would be
expected in a vented loft design, the differing roof tile profile does not
appear to have an effect on the roof’s thermal performance.
Infrared thermography is a valuable tool for evaluating the thermal performance of whole buildings and for assessing the thermal performance of building components. Being a remote
sensing technique, a thermographic survey can be carried out with minimal disturbance. As there is no ‘natural’ colour associated with infrared, all colour thermograms are reproduced
using a false colour scheme. For this survey, the colour rendering is known as the “Iron” scale where the blue/black colours are cooler than the yellow/white end of the scale.
▲ Infrared thermograph showing uniform temperature in the
insulated house but heat loss under the bedroom window (as
indicated by the yellow colouring) from the un-insulated house
Part L1 (2002) in existing dwellings – Case Study
Bedford case study
3
The north façade, ground floor, again shows the uniform external wall
temperature indicating good thermal performance from the external
wall insulation, however, a thin strip of the original solid wall can be
seen at ground level and some heat loss can be seen from this strip in
the thermogram.
Costs and benefits
An average of £10,000 was spent on each property during this
refurbishment project. This price included new rainwater goods,
upvc fascias and gutters, some repairs to chimney stacks and the
replacement of some roofs.
External insulation cladding is relatively expensive compared with
internal insulation. However, there are advantages to be had by
‘economy of scale’. In 1998 BRE looked at 42 recent contracts for
external insulation taken from the Register of Installers. Although
there was considerable fluctuation in the contract prices due to the
size of the properties and the cladding system chosen, there was
also a visible trend in the unit price of the jobs and the size of the
contract. The trend line suggested that contracts for single figures
of properties were likely to be up to twice the unit price of contracts
for over 100 properties.
Advantages
• Thermal mass of the building is on the inside so that any heat is
retained in winter and summertime overheating is reduced
• Helps to reduce fuel poverty
• Eliminates damp and mould
• Reduces structural disintegration
• Improves value and appearance of property
• Do not need to decant residents during works
• Increases residents’ feelings of worth
Disadvantages
• Relatively expensive, especially for one-off jobs, but some
economy of scale can be achieved.
• Have to remove and re-fit waste and electrical services
▲ The refurbished roof of the ‘community’ house
▲ The back of the ‘community’ house showing some heat loss
below the level of the cladding