Clearview National September 2019 - Issue 214 | Page 54

SOLIDROOFTECHNOLOGIES
New code sets
new standards
for flat roofing
The British Standards Institute (BSI) has
published the BS 6229: 2018 - flat roofs
with continuously supported flexible
waterproof covering - code of practice.
» » A NUMBER OF CHANGES
in relation to general good
practice guidance, updated
terminology and definitions
for flat roofs. These include an
update of the previous definition
for a “vapour control layer” to
an “air and vapour control layer”
(AVCL), as they perform two
important functions. Changes
now recommend avoiding the
traditional cold roof construction,
where the insulation is on the
underside or cold side of the deck,
due to the difficulty in forming an
effective AVCL, cross ventilation
and the subsequent increased risk
of condensation. An additional
“breather layer” is now shown
over the insulation to provide an
external air-leakage barrier and to
help protect the insulation against
any detrimental environmental
factors.
More specific reference on the
minimum design and finished
falls in formed gutters and a new
definition for “zero falls” (roof
slope between 0 and 1:80 with
no back falls or ponding) is also
now included. A small relaxation
to minimum upstand heights
at door thresholds to balconies
and terraces only is adopted
(following NHBC guidance)
to allow designers to meet the
Building Regulations for level
access. For all other abutments,
the waterproofing should still be
terminated a minimum of 150mm
from the finished roof level.
Updated advice is available for
the thermal design of inverted
roofs, having now obtained
improved practical experience of
the actual performance of inverted
roofs incorporating a water
flow reducing layer (WFRL),
designed to reduce the ‘cooling
effect’ from rainwater. Interstitial
condensation is covered in detail
under its own standard, BS 5250,
so has been removed from this
standard. However, the updated
code of practice does advise
minimum thermal values for
heated buildings (0.35W/m^2K)
are achieved at any point, to avoid
surface condensation, all as per
legislation guidance.
Although it is anticipated
many of the above mentioned
amendments will take time to
become established industry
practice, those within the
building sector should now be
familiarising themselves with the
code and following this updated
guidance.
Martin Bidewell, Head
of Technical and Product
Management for Sika Roofing
said: “Manufacturers, specifiers
and the like should be obtaining
copies of the standard. People
need to understand what the
detailed changes are and the affect
it might have on our buildings.
From here on in, companies
should be doing their utmost to
ensure all new designs incorporate
the latest recommendations.”
54 » SE P 2019 » CL EARVI E W- UK . C O M
Martin Bidewell, Head of Technical and
Product Management for Sika Roofing
‘The latest guidelines are more defined
and help eliminate some of the grey areas
that existed within the previous code’
The code relating to flat roofs
with continuously supported
coverings was previously updated
in 2003. Martin said the new
guidelines provide more clarity for
users. “The latest guidelines are
more defined and help eliminate
some of the grey areas that existed
within the previous code,” he
said. “The 2003 version really
was an old standard, therefore the
2018 code brings it into line with
the latest Building Regulations
and other codes of practice. In my
opinion, the latest guidelines are
more streamlined and easier to
understand, which can only be a
good thing.”
“The guidelines are vital to
successful flat roofing,” Martin
added. “The standard sets out the
basics of how to properly design
a flat roof. There will always be
instances when the guidelines
cannot be adhered to completely,
particularly when the project
involves the refurbishment of
an existing roof. However, there
should be no excuse to ignore
the code in new-build scenarios.
The BS 6229 code of practice is
the go-to flat-roofing document,
and along with relevant trade
association guidance, should
form the minimum standards the
industry is looking to achieve for
every roofing project.”
For copies of BS 6229: 2018,
visit: shop.bsigroup.com