38
OCTOBER 2015 PRO INSTALLER
TOP TIPS UNLEASHED
www.proinstaller.co.uk
How to avoid cold
bridging
on bay windows
BAY WINDOWS
10.0
ZERO CARBON HUB BUILDERS' BOOK
Cold bridging is a common problem, often arising where a gap occurs in the insulation of a building.
Whenever there is a break in the
continuity of a property’s outer envelope, there is a risk of a cold bridge
appearing. Such an area will often be
colder than the main areas surrounding it and can lead to condensation
and the added headache of mould
for occupants.
PROBLEM TO AVOID
COLD BRIDGING
COLDSPOT
A challenging area likely to cause a cold
bridge is bay windows. Whilst very popular
with designers and occupants alike, these
areas present several thermal performance
problems if not well understood and built
correctly.
The Local Authority Building Control
(LABC) and the Zero Carbon Hub have
recognised this common issue and have created instructions for tradespeople on how
to avoid cold bridging.
How to get it right:
• Encourage early discussion between the
designer, energy assessor, window and
lintel manufacturers at design stage to
help avoid many of the common errors
• Provide the site contractors with clear
cross sections of the key junctions and
their build sequence to increase the likelihood that components are assembled as
intended
• Ensure you provide a continuous layer
of insulation between the external wall,
lintel and bay roof area to minimise the
chances of gaps around the bay opening
• Insulation should be compressed by cutting it ‘proud’. This means it is under pressure when the window unit is installed
– which prevents air leakage
• Avoid specifying large window frame
profiles. This can reduce the overall energy performance of the bay window by
increasing heat loss
• Don’t install window units with excessive
gaps between the walls and bay roof as this
will make it more difficult to achieve a robust airtight junction and increase heat loss.
The most effective way of countering cold
bridges is to design them out, but even
good designs cannot succeed if the workmanship is dodgy. The recently launched
Zero Carbon Hub Builder’s Book, produced
alongside CITB, PTE Architects and LABC,
offers practical examples that can help you
get it right on site.
To view the full booklet or for more
information visit www.zerocarbonhub.
org or for more from the LABC visit
www.labc.co.uk
THICK FRAME AND POSTS INCREASES HEAT LOSS
OPTION 1
WHAT TO DO?
OPTION 2
Reduce cold bridges
of steel or concrete
or timber through
insulation layer
Continuous insulation
inside
Install slimmer frames
to be more energy
efficient
INTERNAL INSULATION
TO FULL DEPTH
Less than 10mm
tolerance between
window frame
and opening
GOOD PRACTICE
Continuous insulation throughout bay window
Please print and use in your site office,
INSULATED
PLASTERBOARD