Civil Engineering Reference
In-Depth Information
fire separating elements in buildings,
such as walls, are undertaken on
representative elements of
construction of limited size. Modern
buildings, however, can have
elements which are many times larger
and the real fire exposure can differ in
timing, severity and extent. Careful
engineering design and construction
is needed to ensure that thermal
movements and restraining forces do
not impair the stability, integrity and
insulation of large assemblies
(203,204)
.
The resistance of no-fines
separating walls to the passage of
smoke (as indeed for sound too) self-
evidently will depend on the integrity
of the plastering.
brick walls will give similar values to
solid, although the variability will be
somewhat greater and will be
influenced, for example, by wall tie
design and junctions with external
walls
(205)
.
Dense concrete separating walls of
150 mm thickness will give values
ranging from 47 to 53 dB, and the
normally thicker no-fines concrete
walls will also give around these
figures.
The sound insulation of separating
walls is now covered in the various
Building Regulations, Part E in
England and Wales
(206)
, Part H in
Scotland
(207)
, and Part G in Northern
Ireland
(208)
. The Building Regulations
require walls between dwellings to
provide reasonable resistance to
airborne sound. 'Reasonable' is made
explicit in England and Wales in
Approved Document El/2/3 by means
of acceptable construction or
performance criteria. While
compliance with building regulations
may not be mandatory for conversion
or rehabilitation schemes,
performance which does not reach the
building regulation standard is a
common cause of occupant
dissatisfaction.
The following constructions
should meet the requirement for
sound insulation of masonry
separating walls:
●
solid dense concrete block of at
least 415 kg/m
2
of wall area
plastered both sides
insulation standards of the Building
Regulations Approved Document E.
Some of the more common causes
are:
●
pressed bricks laid frog down
●
walls of inadequate mass
●
non-butterfly ties in cavity
separating walls
●
lightweight flanking external walls
●
unfilled perpends in masonry,
particularly within floor zones and
loft spaces
●
joists built into the separating
walls with inadequate beam-filling
between them
deep chases for services cut back-
to-back in the separating wall
●
lack of dry-packing under walls in
concrete panel systems
●
lightweight linings touching the
masonry core
Noise and sound insulation
Separating walls built under the old
local byelaws created following the
passing of the Public Health Act
made no specific provision for sound
insulation, since the stability and fire
resistance requirements governed
wall thicknesses in any case.
A half brick separating wall could
be expected to give a single figure
sound insulation value of around
44 dB when combined with the
massive construction of fireplaces
and flues on the separating wall
(205)
.
This value does depend on frequency.
When complaints of sound
transmission through a separating
wall have been investigated, that part
of the separating wall within the roof
space has been found often to be a
major contributing route. In some
cases, BRE investigators have found
there to be no separating wall
whatsoever in the roof space. The
material of a separating wall, or its
thickness, may change above ceiling
level, or there may be unfilled joints
in masonry, or even large holes.
Rough rendering the separating wall
within the roof space may provide a
partial solution.
A solid one-brick (225 mm) wall
with plaster on both sides is usually
regarded as adequate for sound
insulation, but the actual performance
achieved, measurable by standard test
procedures, will depend also upon the
surrounding construction. Single
figure values of around 52 dB or
slightly more can be expected. Cavity
●
Where sound insulation of walls
consisting of units of adequate mass
proves to be deficient, the cause may
be found in unfilled perpends within
the wall construction; perhaps where
the bricklayer has simply buttered the
arrises of the units before laying
(Figure 6.7).
Holes or cracks through separating
walls are often found and can
seriously reduce the sound insulation
objective. Walls of inadequate
thickness or built of low-density
blockwork may not meet
performance standards. Even
localised reductions in thickness can
reduce overall performance
significantly. Masonry walls that are
dry-lined rather than plastered have a
in situ or precast dense concrete of
at least 415 kg/m
2
of wall area
plastered both sides
●
cavity brick or dense concrete
block wall of at least 415 kg/m
2
of
wall area plastered both sides
●
cavity lightweight aggregate block
(maximum density of 1600 kg/m
3
),
75 mm cavity and overall weight,
including plaster, of 300 kg/m
2
of
wall area
●
single leaf brick or dense concrete
core of at least 300 kg/m
2
of wall
area lined on both sides with
isolated lightweight panels of
cored or glued plasterboard
●
It has been estimated that around one
third of all separating walls in
dwellings fail to meet the sound
Figure 6.7
Poor filling of perpends in separating walls
can lead to deficiencies in sound insulation
