SCOTTISH EXECUTIVE

11. Wall type 2: cavity masonry

The resistance to airborne sound depends on the mass of the leaves and on the degree of isolation achieved.

Points to watch

Fill masonry joints with mortar (to achieve the mass and to avoid air paths).

Maintain the cavity up to the underside of the roof.

Connect the leaves only where necessary for structural reasons. Use only butterfly pattern ties, spaced no more than 900 mm apart horizontally and 450 mm apart vertically. (BS 5628: Part 3: 1985 limits this tie type and spacing to cavities of 50 mm to 75 mm with a minimum masonry leaf thickness of 90 mm).

If external walls are to be filled with an insulating material other than loose fibre the insulating material must be prevented from entering the cavity in the separating wall.

Constructions

Two wall constructions (A and B) which give suitable resistance to direct transmission are specified.

Two other wall constructions (C and D) will be suitable between houses provided a step in elevation and/or a stagger in plan is incorporated at the separating wall.

Details of how junctions must be made to limit flanking transmission follow.

A. Two leaves of brick with 50 mm cavity, plastered on both room faces.

Mass including plaster 415 kg/m². 13 mm plaster each face.

Example: 102 mm leaves, lightweight plaster, 75 mm coursing; brick density of 1970 kg/m³ gives the required mass.

B. Two leaves of concrete block with 50 mm cavity, plastered on both room faces.

Mass including plaster 415 kg/m². 13 mm plaster each face.

Example: 100 mm leaves, lightweight plaster, 225 mm coursing; block density of 1990 kg/m³ gives the required mass.

diagram

diagram

11. Additional constructions permitted only where a step and/or stagger of at least 300 mm is used

C. Two leaves of concrete block with 50 mm cavity, plasterboard on both room faces.

Mass of masonry alone 415 kg/m².

12.5 mm plasterboard each face, use any normal fixing method.

Example: 100 mm leaves, 225 mm coursing; block density of 1990 kg/m³ gives the required mass.

D. Two leaves of lightweight aggregate concrete block (maximum density 1500 kg/m³) with 75 mm cavity, plastered on both room faces.

Mass including plaster 250 kg/m². 13 mm plaster each face.

Seal the face of the blockwork, with cement paint or plaster, through the full width and depth of any intermediate floor.

Example: 100 mm leaves, lightweight plaster, 225 mm coursing; block density of 1105 kg/m³ gives the required mass.

diagram

diagram

11. Junctions for wall type 2

Roof

Fire-stop the joint between wall and roof (see Part D).

Ceiling and roof space

Where there is a heavy ceiling with sealed joints (12.5 mm plasterboard or equivalent), the mass of the wall above the ceiling may be reduced to 150 kg/m². The cavity must still be maintained. If lightweight aggregate blocks are used to reduce mass, one face of the wall must be sealed with cement paint or plaster skim.

Intermediate and ground floors

With a timber floor use joist hangers for any joists supported on the wall.

With a concrete intermediate or suspended ground floor the floor may be carried through only to the cavity face of each leaf.

A concrete slab on the ground may be continuous.

diagram

External wall

The outer leaf of a cavity wall may be of any construction.

Where a cavity wall has an inner leaf of masonry -

a.

i. the masonry of the walls must be bonded together, or

ii. the masonry of the external wall must abut the separating wall and be tied to it with ties at no more than 300 mm centres vertically,

to create a homogeneous unit; and

b. the masonry must have a mass of
120 kg/m² except where separating wall type 2 is used when there is no minimum required mass.

Where a cavity wall has an inner leaf of timber construction it must -

c. abut the separating wall;

d. be tied to it with ties at no more than
300 mm centres vertically; and

e. have the joints sealed with tape or
caulking.

The cavity in the separating wall must only be sealed in accordance with Part D.

Partitions

There are no restrictions on partition walls meeting a type 2 separating wall.

diagram

12. Wall type 3: solid masonry between isolated panels

The resistance to airborne sound depends on the mass and type of core and on the isolation and mass of the panels.

Points to watch

Fill masonry joints with mortar (to achieve the mass and to avoid air paths).

Support the panels only from floor and ceiling - do not fix or tie them to the masonry core (to maintain isolation).

Constructions

Four masonry cores and two panels are specified which in any combination of core plus panels give suitable resistance to direct transmission.

Details of how junctions must be made to limit flanking transmission follow.

Basic construction

A masonry core, with an isolated panel on each side.

Minimum air space between panels and core 25 mm. Keep framing clear of core (at least 5 mm).

Masonry cores

A. Brick

Mass 300 kg/m².

Example: 215 mm core, 75 mm coursing; brick density of 1290 kg/m³ gives the required mass.

B. Concrete block

Mass 300 kg/m^2.

Example: 140 mm core, 110 mm coursing; block density of 2200 kg/m³ gives the required mass.

C. Lightweight aggregate concrete block (maximum density 1500 kg/m³).

Mass 200 kg/m².

Example: 140 mm core, 225 mm coursing; block density of 1405 kg/m³ gives the required mass.

Example: 215 mm core, 150 mm coursing; block density of 855 kg/m³ gives the required mass.

D. Autoclaved aerated concrete block. Mass 160 kg/m^2.

Example: 200 mm core, 225 mm coursing; block density of 730 kg/m³ gives the required mass.

diagram

diagram

12. Panels

E. Two sheets of plasterboard joined by a cellular core.

Mass (including plaster finish if used) 18 kg/m²

Fix to ceiling and floor only. Tape joints between panels.

F. Two sheets of plasterboard with joints staggered.

Thickness of each sheet 12.5 mm if a supporting framework is used, or total thickness of 30 mm if no framework is used.

Junctions for wall type 3

Roof

Fire-stop the joint between masonry core and roof (see Part D).

Ceiling and roof space

Where there is a heavy ceiling with sealed joints (12.5 mm plasterboard or equivalent), the free-standing panels may be omitted in the roof space and mass of the core above the ceiling may be reduced to 150 kg/m². If lightweight aggregate blocks are used to reduce mass, seal one side with cement paint or plaster skim. Seal the junction between ceiling and free-standing panels with tape or caulking.

Intermediate and ground floors

With a timber intermediate floor use joist hangers for any joists supported on the wall and seal the spaces between joists with full depth timber battens.

With a concrete intermediate floor the floor base may only be carried through where it has a mass of 365 kg/m². Seal the junction between ceiling and panel with tape or caulking.

The ground floor must be a solid slab, laid on the ground to prevent air paths.

12. External wall

The outer leaf of a cavity wall may be of any construction.

The inner leaf of a cavity wall must have an internal finish of isolated panels as specified for the separating wall except where the separating wall has core A or B when plaster or dry-lining with joints sealed with tape or caulking may be used.

A layer of insulation may be added to such internal finish provided the 25 mm and 10 mm gaps shown in the diagram are maintained.

The inner leaf may be of any construction if it is lined with isolated panels.

If the inner leaf is dry-lined it must be masonry with a mass of 120 kg/m², butt jointed to the separating wall core with ties at no more than 300 mm centres, vertically.

Partitions

Partitions abutting a type 3 separating wall must not be of masonry construction.

Other loadbearing partitions should be fixed to the masonry core through a continuous pad of mineral fibre quilt.

Non-loadbearing partitions should be tight butted to the isolated panels.

All joints between partitions and panels must be sealed with tape or caulking.