Civil Engineering Reference
In-Depth Information
Chapter 2.2
Brick and block, cavity
Cavity walling as a means of
resisting rain penetration is usually
associated with modern buildings (ie
post-1945). Naturally, the older the
building, the less likely it is to have
cavity walls. However, cavity walls
became an established form of
construction at different times in
different regions. In parts of south
east England, solid brick walls were
still being built up to the late 1950s,
but in more exposed regions, cavities
were being used in the late nineteenth
century.
It is reported that in England, just
under two thirds of all dwellings have
masonry cavity walls as their
predominant structure, with the
proportion of dwellings built before
1918 at around 1 in 22, and those
post-1980 at 9 out of 10 (Figure
2.20). The EHCS
(2)
does not
distinguish between brick and stone.
Of the dwellings built before the
end of the nineteenth century, only
3% had cavity walls. It has already
been observed that 7 out of 10
dwellings in Scotland have cavity
external walls.
Housing Association Property
Mutual reported that, in the new
dwellings which they inspected
during 1991-94, about 1 in 10 had
unfilled cavities, with the remainder
split almost equally between partial
fill and full fill of insulation material.
Characteristic details
Basic structure
External facings
There is an enormous variety of clay
facing bricks which have been used
over the years, and some aspects have
already been covered in Chapter 2.1.
Although not generally used in solid
walls, calcium silicate bricks and
concrete bricks are to be found in
cavity walls - during the period
1991-94 it was reported that about 1
in 25 dwellings had external walls
which used calcium silicate or
concrete bricks in the external leaf.
Occasionally a surveyor may come
across innovative external walls built
from horizontally or vertically
perforated through-the-wall units
built with divided joints to maintain
weathertightness.
Cast stone, although it may be
intended to be used in substitution for
a natural stone, and indeed made to
look like it, is in effect a concrete
block made with Portland cement and
a suitable aggregate, sometimes
pigmented. Cast stone is unlikely to
be found in buildings dated before
1900, although the occasional one
may be encountered. It is now widely
used in areas with planning
restrictions (eg Bath) which require
the use of a 'stone' finish. The
relevant standard for the material is
BS 1217
(96)
.
Generally dense concrete block
faced walls are either left untreated,
if the surface is relatively closed, or,
if of a more open texture, finished
externally with a two-coat rendering
and roughcast or dry-dash finish;
alternatively, a proprietary resin-
based mineral-filled finish may
Figure 2.20
A post-1980 detached house. Around 9 out of 10 dwellings of this period are built in
loadbearing masonry and the majority will have cavity masonry for all their external walls
