Separating and compartment walls - Walls, Windows and Doors - page 196

On rare occasions, problems may
be caused by excessive chasing of the
wall for electrical services (Figure
6.12 on page 212). In these cases,
recessed switches and socket outlets
may have to be changed for surface-
mounted boxes and chases filled with
mortar.
Separating walls built in precast
concrete panels may sometimes be
encountered. For instance, the Taylor
Woodrow Anglian system of
prefabricated two storey housing had
7 inch precast concrete separating
walls (in four sections for easy crane
handling) that was claimed to ensure
a sound reduction of 50 dB (210) .
BRE Digest 333 (211) deals
generally with the sound insulation of
separating walls. BRE Digest 293 (212)
and BRE Defect Action Sheet 105 (213)
evaluate methods for improving the
sound insulation of existing
separating walls. General advice is
also given in BS 8233 (214) † .

Case study
Sound insulation of separating walls
which were dry-lined
Measurements were made in a row of
traditionally built terraced houses, all with
internal walls of studwork or paper cored-
type partitions and separating wall surfaces
dry-lined. The separating wall also contained
back-to-back flue blocks for a gas heater in
the living room area. Sound transmission
tests made between two of the houses in the
terraced block showed satisfactory results
compared to the performance standard
required by current building regulations.

Work on site

Inspection
The stability of existing separating walls
should be examined critically, even where
the existing construction appears to be
sound. The examination should consider, in
particular, the condition of the masonry; the
adequacy of connection to adjacent floors,
roofs and other walls; and the thickness of
masonry walls in relation to support from
adjacent walls and floors. Differential
movements should be investigated, and
measures taken to ensure that the walls act
as homogeneous panels and that structural
interaction between elements is achieved.
Vertical cracking is often identifiable in
unplastered areas of the wall such as the
apex within the roof or in a cellar. Special
attention should be given to the junctions
with other structural walls where movement
can show as cracking in corners. The
direction of span of floor joists should be
noted: where parallel to the separating wall
it is possible that no structural connections
have been provided to the wall. It will be
necessary to identify whether parts of the
original structure may have been removed
(eg a chimney breast or internal wall).
Obvious signs of rising damp should be
noted (presence of salts and tidemarks).
Moisture levels on walls at low level can be
measured, but the results obtained by
electrical resistance-type meters should be
interpreted with care.
The extent of subdivision in roof spaces
and floor voids should be checked; also
perforation and fire-stopping at junctions
with other elements, if necessary with an
optical probe.
The problems to look for are:

Case study
Sound insulation of separating walls
built of innovative bricks
Sound insulation between flats with
separating walls of single leaf, vertically
perforated, fired clay masonry units
(Calculon 'C' brick) was investigated in three
buildings. Measurements showed wide
variations in performance. The poorest
results, obtained in a particular set of
maisonettes, were found to be partly
brought about by the use of a resilient lining
on the external walls. There was a
resonance effect in the lining which led to
inadequate performance in the adjoining
part of the separating wall.

Durability
Normally there should be no
problems with masonry separating
walls, unless they project through the
roof. The durability of these
projections was dealt with in Roofs
and roofing .
However, one factor which can and
does affect masonry separating walls
is movement from the ground. These
movements can be quite serious, as
the case study on page 213 shows.

missing walls within roof spaces

◊

◊ unfilled mortar joints within floor

thicknesses and roof spaces

◊ wall ties too stiff in cavity walls

sound insulation deficient (walls too thin
or density too low)

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† Under revision.

◊ fire performance inadequate (eg cavity

barriers omitted)

inadequate bonding to external walls

◊

◊ services passing through (particularly in

conversions)

◊ walls of inadequate mass (eg pressed

bricks laid frog down)

◊ lightweight flanking external walls

◊ deep chases for services cut back-to-

back in separating walls

lack of dry-packing under walls in
concrete panel systems

◊

◊ lightweight linings touching the masonry

core

removal of buttressing effect of
intersecting partitions during rehab

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