Civil Engineering Reference
In-Depth Information
condensation can be a problem.
Dampness in a solid wall from any
source will further reduce even the
minimum insulation it possesses and
increase the risk of condensation on
internal surfaces. Mould growth is
often an unfortunate indication that
surface condensation is occurring.
Reduced wall thicknesses (and
hence reduced insulation) may exist
in porches, previously bricked-up
openings and where fireplaces have
been removed. Half brick solid walls,
often found in projecting back rooms
to 'byelaw housing', are highly
susceptible to surface condensation
and mould growth (Figure 2.14).
Condensation can be a nuisance at
window and door reveals, where
there may be locations with reduced
wall thickness. Corroding metal
corner beads around window or door
openings indicate that condensation
has been a problem. Impervious
external wall coatings may prevent or
restrict drying out of water vapour
from the wall and lead to dampness
and an increased risk of
condensation. Changes to heating,
ventilation or occupancy patterns on
the other hand can often lead to
condensation and mould where
previously no problems were
encountered.
Fire
Masonry external walls, whatever
their thickness, have an inherent fire
resistance considerably in excess of
the half hour or one hour normally
required for low-rise buildings.
Structural components within a
wall and tested with it, such as
lintels, require an equal fire
resistance. In the case of conversion
schemes (eg a three-storey house into
multiple flats), an enhanced
resistance may be required.
Lintels may have inadequate fire
protection (typically only plaster);
steel lintels being the most
vulnerable. Loadbearing window or
door frames will almost certainly
have inadequate fire resistance
(corner windows are most likely to be
in this category).
Building Regulations 1991
Approved Document B
(52)
is the best
reference for current requirements. In
the case of proprietary components,
for example lintels, information on
fire resistance may be found in a
relevant Agrément certificate. The
BRE report,
Results of fire resistance
tests on elements of building
construction
(88)
though now quite
old, may contain relevant
information. See also BRE
Information Paper IP 21/84
(89)
and
Chapter 1.8.
Half brick external
walls are highly susceptible
to mould growth internally
Figure 2.14
Projecting back rooms in 'byelaw' housing
may have external walls only half a brick
thick
Noise and sound insulation
Figure 2.15 gives a rough guide to
the insulation that can be expected
from solid walls of different mass/m
2
in the mid frequency range; it does
not take account of other factors, such
as stiffness, air flow resistance and
junctions with flanking walls, which
may also be important for some
materials.
60
55
50
45
40
35
30
25
The effects of windows
The effect on sound insulation of the
insertion of windows into solid walls
can be dramatic. If a solid wall has a
performance, say, of 50-55 dB
without windows, the insertion of
openable single glazed windows,
even if they are closed, will not
usually give more than around 20 dB.
Permanently sealed windows will
enable the wall to achieve a higher
performance, up to 30 dB, with
20
15
10
5
0
1
2
4
6
8
10
20
40
60
100
200
500
1000
Surface mass of wall in kg/m
2
Figure 2.15
Approximate relationship of sound insulation to surface mass for single leaf construction
