External cladding on frames - Walls, Windows and Doors - page 115

Thermal properties
Lack of thermal insulation leading to
high heating costs was common in
many systems. Unheated bedrooms,
combined with other factors, gives
rise to mould growth following
condensation.
It is difficult to give typical
thermal insulation values, for no
single construction can be said to be
entirely typical. However, many
systems were originally built just to
better the 1965 Building Regulations
target of 1.7 W/m 2 K or the 1976
target of 1.0 W/m 2 K.
Care must be taken in deciding
whether and how to upgrade the
thermal insulation of steel framed
walls. Where the basic construction
of the wall is little different from one
of conventional construction - that is
to say with masonry inner and outer
leaves, and a cavity between - the
main point of concern in considering
the use of cavity insulation will be
the possible poulticing effect of
thermal insulation beads wetted by
contact with the outer leaf against the
steelwork contained in the cavity, or
being drawn by capillary attraction
into the interstices
formed when certain kinds of
insulation shrink (Figure 3.11). The
condition of the surface protection to
the steel is of crucial importance for
durability. Other points to watch for
include electric wiring in the cavity
and frost damage to the external
masonry leaf (cavity insulation may
have the effect of slightly reducing
the temperature of the outer leaf,
making it more vulnerable to frost
damage).

Steel frames
Steel beams and columns may be
partly embedded in floors and walls
in buildings. These elements may
also be used outside the building
façade where, subject to their
position in relation to windows
through which heat may radiate and
flames can jet, they can be found with
no protection against fire. In both
applications the elements are
subjected to non-uniform heating
such that large temperature
differences across the steel section
can be attained. These temperature
differences cause differential
expansion in the material and, when
unrestrained, result in thermal
bowing towards the fire (134) .

Risk of rain penetration being held in
contact with steel frame

Figure 3.11
There are significant risks of deterioration
when cavities of steel framed houses are
filled

Reinforced concrete frames
Reinforced concrete frames provide
their own inbuilt protection.

Noise and sound insulation
For performance of masonry
cladding, see the same sections in
Chapters 2.1 and 2.2.

Durability
Steel frames
The greatest incidence of corrosion of
frames in the steel systems examined
has been observed in areas with high
driving rain. Where dwellings also
have a clear line of sight to open
country, the problem may be
exacerbated. In exposed locations,
most steelwork paint protective
systems were observed to be in
process of deterioration, but this will
not automatically mean that such
coatings need renewal. It depends
what service life is required from the
dwelling.
BRE site observations of the
corrosion rates of steel in low rise
systems indicates typical rates of
3 mm in 20 years for steelwork in
contact with wet cladding. The
expansion caused by the rusting
exerts considerable force on
claddings, sufficient to crack
brickwork (Figure 3.12).
Some Preswelds had fully
galvanised frames, but these houses
were in a minority.
BISF ground floor elevations,
Dorloncos and Cranes are prone to

Fire
One general point to note is that if the
structural frame is external to the
external wall, it does not have to be
fire-resisting, though the wall itself
does. This may seem rather
anomalous, but it stems from the fact
that fire resistance of elements of
structure is considered only in
relation to fires generated within the
building.
See also the same sections in
Chapters 2.1 and 2.2.

Figure 3.12
Cracked brickwork in a Dennis Wild house
caused by rusting of the corner stanchion