November/December 2019

Rooflight Specification
KEY KNOWLEDGE FOR INSTALLERS
The growing popularity of flat roofs is generating new opportunity in rooflight supply, but are
installers up to speed on their specification? Total Installer talks to Mark Norcliffe, of
Cornwall Glass, who says perhaps due consideration isn’t being given to every installation…
Flat roofs offer almost immeasurable design
flexibility, which is why they make up a
growing percentage of home extensions.
More often than not, their design incorporates
rooflights, something which commentators
suggest is a bonus for the window and door
industry – but one which carries significant risks,
if specifications are wrong.
“Don’t get me wrong. It’s great that we and our
customers are being asked to supply more and
more IGUs for rooflights”, said Mark Norcliffe,
Joint Managing Director, Cornwall Glass
Manufacturing. “What concerns me, however, is
that not everyone is always giving those
installations due consideration. The
consequences and the penalties attached to that
are immense”, he warned.
He suggests this is attributable to two causes.
The first is that ‘jobbing builders’ don’t
necessarily understand rooflight specification
thoroughly either, so installers aren’t being given
the right direction.
The second is that guidance on IGU specification
for rooflights is ‘advisory’ rather than regulatory,
leaving in Mark’s opinion, far too much room for
misinterpretation.
“I’m always slightly surprised that in an industry
which is highly regulated in most areas, rooflight
IGU specification – something that you can
actually fall through and do yourself very real
injury – isn’t. There are so many considerations,
usage, design, loadings, which you need to plan
for to develop the right specification. It seems a
gap in building regulation and control”, he said.
Is rooflight IGU specification regulated?
The challenge, according to Mark is, that while
standards exist for rooflights installed at greater
height, for example they’re being installed at
more than 5m above floor level, the inner pane
must be laminated – this doesn’t apply to most
domestic installations.
“In the vast majority of cases a single storey
extension comes in at a fraction of the 5m height
required to trigger regulation. The point is that even
at half that, say 2.5m or eight foot, you’re still going
to get hurt – especially if you’ve fallen through
glass, or if it falls on you. This, for me, puts the
onus on installers to get it right. It’s not only a
moral responsibility but a legal one because while
there aren’t regulations for rooflight IGU
specification, there are still legal consequences
where someone suffers injury and professional
negligence can be proved”, Mark argued.
So, what does guidance say about IGU
rooflight specification?
“There are a number of key questions which you
should be asking in rooflight IGU specification”,
continued Mark. “The first is an assessment of
risk. How likely is it that someone will fall through
a roof, what classification is it? This will be
defined by its location and usage. For example, at
one end of the scale you have walk-on roofs. The
requirement is self-explanatory and in this
respect it’s easy to define the specification – the
IGU needs to be designed to be walked on. At the
other end of the spectrum you have fragile roofs.
Again, it’s self-explanatory; you, or someone,
else could fall through it, so access should be
strictly limited and warnings and mitigating
controls need to be in place. It’s the area in the
middle which becomes confusing, partly because
of the fundamental complexity associated with
getting it right, but also terminology.”
Above: Mark Norcliffe, Cornwall Glass.
‘Fragile’, ‘non-fragile’ and ‘walk-on’ roofs
Rooflight IGUs can be classed as ‘fragile’ ‘nonfragile’,
and ‘walk-on’ or ‘walkable’.
Walk-on are designed to do what they say on the
tin, with a loading strength which should be more
or less equal to the floor around it.
As a minimum, this should be designed for typical
domestic floor loadings of 1.5kN/m², with a
concentrated load of 2.0kN as set out in BS EN
1991-1-1:2002, depending on its use.
“If someone wants a walk-on IGU rooflight, they’ll
know that that’s what they want and will want to
discuss the specification in detail. We generally
advise use of either a three-ply outer pane made
up of 10mm toughened laminate or two-ply 12mm
toughened laminate, with a suitable robust and
safe toughened glass on the underside or
depending on size, toughened laminate” Mark said.
It’s terminology like ‘non-fragile’ and ‘mansafe’
– the ‘middle ground’, which tends,
according to Mark, to cause greatest confusion:
“The point is a rooflight IGU has to do two things.
It has to protect the people below from injury and
it has to prevent someone falling through it from
above. Non-fragile does not by default mean
‘walk-on’ – only that it is designed to prevent
injury by preventing someone or something, from
falling through it. Even then there are a series
54 TINOV/DEC 2019 PRACTICAL CONTENT FOR THE GLAZING INSTALLER & HOME IMPROVEMENT SPECIALIST