Memorandum by Stephen Ledbetter, Centre
for Window and Cladding Technology (ROF 45)
FIRE AND FACADES
Modern buildings of medium to high rise invariably
comprise a loadbearing structure and a non-loadbearing cladding
system. Hence, the cladding system becomes a load on the structure
and attempts are made to minimise its weight.
The facade also fulfils many functions to moderate
the internal climate of the building. The filtering of light,
heat and sound leads to energy efficient buildings and greater
comfort levels that lead to greater productivity in commercial
Last but not least, the facade provides the
aesthetic of the building and contributes to the cityscape.
Any changes to the facade to satisfy a single
requirement such as fire performance will impinge on all other
aspects of the wall's performance as well as its cost.
Walls may be constructed as single layer curtain
walling in which an aluminium (or other material) frame holds
infill panels of glass and opaque materials. More commonly, a
wall may be constructed as a layered construction. In these walls
a metal frame contains infill panels and acts as the structural
part of the wall. It also serves to seal the building against
air leakage and frequently provides the thermal insulation of
the wall. An outer layer then serves to shed water from the wall
and provide the aesthetic of the facade.
Currently walls may be required to prevent the
spread of fire into exit routes and from floor to floor but not
suffer disproportionate damage in a fire.
Fire resistant walls are constructed to protect
stairways where, say, they are at a re-entrant corner of a building.
Such constructions are expensive as a result of the material and
skills used and are not economically viable for the prevention
of fire spread from floor to floor in a building.
Spread of fire from floor to floor may occur
by the passage of hot gases between the floor edge and the inner
face of the wall. Fire spread may also occur as a result of fire
breaking out through the wall and burning back in again. Spread
of fire behind the wall can be restricted by placing a fire stop
with a fire rating equal to that of the floor slab and this is
normal practice. Spread of fire by burning out through the wall
will depend on the form of wall. For a layered wall with separate
air barrier and rainscreen there is an internal cavity that can
promote the spread of fire by acting as a flue. This happened
at Knowsley Heights but may be prevented by the use of fire stops
within the cavity. Guidance on this is given in publications by
the BRE, and the Building Regulations. Standard and Guide to good
practice for ventilated rainscreen walls by CWCT gives guidance
on all aspects of layered walls. For a single-layer wall, spread
will be from floor to floor and will depend on the nature of the
fire and the materials used. In these respects the LPC report
has looked at a restricted number of facade types. There is a
European Standard under development for a method of testing fire
The LPC report has identified the glass as being
a weakness in the glass/aluminium wall. It should be understood
that in many constructions we want the glass to break early so
that it falls in its broken state as small pieces with rounded
edges. If the aluminium frame or fixings failed first the large
sheets of glass would fall from the building to the possible injury
of those fighting the fire. I would argue that the mode of failure
during the fire is as important as the period of fire resistance
in many cases.
I am a cladding engineer not a fire engineer
but am sure that the use of sprinklers has a role to play in the
performance of cladding in fires. As is so often the case in the
construction industry, it seems that the costs of these solutions
are seen in isolation. It would be possible to build fire-resisting
walls on all buildings but the costs would be unreasonable and
unnecessary. It would require elaborate testing for each project
and yet for most walls (layered walls) we have no clearly defined
tests and I believe that test specimens would have to be large
(several storeys high).
Before any radical changes are made to the way
in which buildings are constructed inthe UK, it would be advisable
to look at the very few incidents of spread of fire in medium
and high rise buildings and to establish the contributory factors.
A proper risk assessment should then be undertaken. I feel the
work of the LPC has been driven by a few incidents that have hit
the insurance industry and that we run the risk of using a test
method because it exists not because it delivers real benefits
to building owners or users.