Civil Engineering Reference
In-Depth Information
history of poor performance, largely
owing to the lack of sealing
of joints.
The actual performance achieved
can be established only by field tests
which are expensive and are not
practicable if the building is in an
incomplete state, or if access to both
sides of the wall is not available for
testing.
BRE tests demonstrate that the
field performance of lightweight
aggregate and aerated block cavity
walls, when plastered, can meet the
standards inherent in Approved
Document E.
A comparison between the
insulation ratings found in field
measurements across stepped-and-
staggered walls with those for similar
in-line party walls confirms that
displacement significantly enhances
insulation
(209)
.
Solid autoclaved aerated concrete
block walls, plastered or dry-lined,
perform very poorly, whereas cavity
autoclaved aerated concrete block
walls, plastered or dry-lined, are
capable of good performance.
Information from site surveys
indicates that the cavity closer
between the external wall and the
separating wall is often missing. It
certainly needs to be present; it can
offer up to 2 or 3 dB improvement in
performance.
due to the design of the separating
wall rather than to flanking paths, the
following strategy may be effective.
A completely separate timber stud
framework is erected on one side of
the wall with a sound absorbing quilt
between and two layers of 12.5 mm
plasterboard fixed to the studs
(Figure 6.8). Where space is at a
premium, proprietary partition
systems may be useful provided the
mass is not reduced.
If the joists are built into the
separating wall, inadequate beam-
filling between the joists may cause
air paths between dwellings
(Figure 6.9). In the worst situations
the joists should be cut back and
supported on joist hangers built into
the separating wall. Redundant holes
in the brickwork should be filled
(Figure 6.10).
Sometimes the separating wall in
the loft space is only a half brick
thick. This provides adequate fire
resistance but may be inadequate for
sound insulation if it is not well built.
It is usually impracticable to render
this wall in its entirety because of the
proximity of the roof trusses, but the
render that can be applied will make
an improvement. Sound insulation
can usually best be improved by
reducing transmission through the
ceilings by adding an additional layer
of plasterboard to the ceiling on
either side of the wall (Figure 6.11).
Sound absorbing quilt hung
against existing wall
(min 25 mm)
Double layer of
12.5 mm plasterboard
Timber stud work preferably
fixed only to floor and ceiling
Figure 6.8
Separating walls: a new insulated stud wall
constructed against the existing wall
Air paths (eg through
unfilled perpends) allow
sound transmission
between dwellings
Figure 6.9
Separating walls: inadequate filling
between joists provides sound paths
Air paths blocked and all gaps
filled
Strategies for upgrading
Where the lack of sound insulation is
Lightweight wall in loft space
Joists cut back and
supported on joist hangers
Recessed switch and socket
outlets back to back reduce
sound insulation
Potential
air path
Insulation batts fitted tightly
between joists
Figure 6.10
Separating walls: joists cut back and
supported on joist hangers allows
brickwork to be inserted to improve sound
insulation
Additional plaster boar d on
ceiling on both sides of
separating wall
Figure 6.11
Separating walls: ceiling insulation helps
reduce sound transmission between
dwellings via loft spaces
Figure 6.12
Separating walls: back-to-back electrical
boxes may need relocating to reduce
sound paths
