Section 2: Separating walls and associated flanking construction for new buildings

Introduction

2.1 This section gives examples of wall types which, if built correctly, should achieve the performance standards set out in Section 0: Performance - Table 1a.

2.2 The guidance in this section is not exhaustive and other designs, materials or products may be used to achieve the performance standards set out in Section 0: Performance - Table 1a. Advice should be sought from the manufacturer or other appropriate source.

2.3 The walls are grouped into four main types. See Diagram 2.1.

2.4 Wall type 1 Solid masonry

The resistance to airborne sound depends mainly on the mass per unit area of the wall.

2.5 Wall type 2 Cavity masonry

The resistance to airborne sound depends on the mass per unit area of the leaves and on the degree of isolation achieved. The isolation is affected by connections (such as wall ties and foundations) between the wall leaves and by the cavity width.

2.6 Wall type 3 Masonry between independent panels

The resistance to airborne sound depends partly on the type and mass per unit area of the core, and partly on the isolation and mass per unit area of the independent panels.

2.7 Wall type 4 Framed walls with absorbent material

The resistance to airborne sound depends on the mass per unit area of the leaves, the isolation of the frames, and the absorption in the cavity between the frames.

2.8 Within each wall type the constructions are ranked, as far as possible, with constructions providing higher sound insulation given first.

Junctions between separating walls and other building elements

2.9 In order for the construction to be fully effective, care should be taken to correctly detail the junctions between the separating wall and other elements, such as floors, roofs, external walls and internal walls. Recommendations are also given for the construction of these elements, where it is necessary to control flanking transmission. Notes and diagrams explain the junction details for each of the separating wall types.

2.10 Table 2.1 indicates the inclusion of guidance in this document on the junctions that may occur between each of the four separating wall types and various attached building elements.

Diagram 2.1 Types of separating wall

Table 2.1 Separating wall junctions reference table

Mass per unit area of walls

2.11 The mass per unit area of a wall is expressed in kilograms per square metre (kg/m2). The method for calculating mass per unit area is shown in Annex A.

2.12 The density of the materials used (and on which the mass per unit area of the wall depends) is expressed in kilograms per cubic metre (kg/m^3). When calculating the mass per unit area for bricks and blocks use the density at the appropriate moisture content from Table 3.2, CIBSE Guide A (1999).

2.13 The guidance describes constructions that use blocks without voids. For blocks with voids, seek advice from the manufacturer.

Plasterboard linings on separating and external masonry walls

2.14 The guidance describes some constructions with only wet finishes. For dry finishes, seek advice from the manufacturer.

2.15 Wherever plasterboard is recommended, or the finish is not specified, a drylining laminate of plasterboard with mineral wool may be used. For other drylining laminates, seek advice from the manufacturer.

2.16 Plasterboard linings should be fixed according to manufacturer's instructions.

Cavity widths in separating cavity masonry walls

2.17 Recommended cavity widths are minimum values.

Walls ties in separating and external cavity masonry walls

2.18 Suitable wall ties for use in masonry cavity walls are indicated in the guidance by reference to either tie type A or B.

2.19 Tie type A

Connect the leaves of a cavity masonry wall only where necessary by butterfly ties as described in BS 1243:1978 Metal ties for cavity wall construction, and spaced as required for structural purposes (BS 5628-3:2001 Code of practice for use of masonry. Materials and components, design and workmanship, which limits this tie type and spacing to cavity widths of 50mm to 75mm with a minimum masonry leaf thickness of 90mm). Alternatively, use wall ties with an appropriate measured dynamic stiffness for the cavity width. The specification for wall ties of dynamic stiffness, kxmm in MN/m with a cavity width of Xmm and n ties/m² is n.kxmm<4.8MN/m³.

2.20 Tie type B (for use only in external masonry cavity walls where tie type A does not satisfy the requirements of Building Regulation Part A – Structure)

Connect the leaves of a cavity masonry wall only where necessary by double-triangle ties as described in BS 1243:1978 Metal ties for cavity wall construction, and spaced as required for structural purposes (BS 5628-3:2001 Code of practice for use of masonry. Materials and components, design and workmanship, which limits this tie type and spacing to cavity widths of 50mm to 75mm with a minimum masonry leaf thickness of 90mm). Alternatively, use wall ties with an appropriate measured dynamic stiffness for the cavity width. The specification for wall ties of dynamic stiffness, kXmm in MN/m with a cavity width of Xmm and n ties/m² is n.kXmm<113MN/m³.

Note In external cavity masonry walls, tie type B may decrease the airborne sound insulation due to flanking transmission via the external wall leaf compared to tie type A.

2.21 Measurements of the wall tie dynamic stiffness, kXmm, should be carried out according to BRE Information Paper, IP 3/01.

2.22 The number of ties per square metre, n, is calculated from the horizontal and vertical tie spacing distances, Sx and Sy in metres using n = 1 / (Sx.Sy). Example: for horizontal and vertical tie spacing distances of 0.9m and 0.45m, n is 2.5 ties/m².

2.23 If kXmm is not available for the required cavity width, it is acceptable to use available kXmm data for Xmm values less than the required cavity width to calculate n.kXmm.

2.24 All wall ties and spacings specified using the dynamic stiffness parameter should also satisfy the Requirements of Building Regulation Part A – Structure.

Corridor walls and doors

2.25 The separating walls described in this section should be used between corridors and rooms in flats, in order to control flanking transmission and to provide the required sound insulation. However, it is likely that the sound insulation will be reduced by the presence of a door.

2.26 Ensure that any door has good perimeter sealing (including the threshold where practical) and a minimum mass per unit area of 25kg/m or a minimum sound reduction index of 29 dB Rw (measured according to BS EN ISO 140-3:1995 and rated according to BS EN ISO 717-1:1997). The door should also satisfy the Requirements of Building Regulation Part B – Fire safety.

2.27 Noisy parts of the building should preferably have a lobby, double door or high performance doorset to contain the noise. Where this is not possible, nearby flats should have similar protection. However, there should be a sufficient number of flats that are suitable for disabled access, see Building Regulation Part M - Access and facilities for disabled people.

Refuse chutes

2.28 A wall separating a habitable room or kitchen and a refuse chute should have a mass per unit area (including any finishes) of at least 1320kg/m². A wall separating a non-habitable room from a refuse chute should have a mass per unit area (including any finishes) of at least 220kg/m².

Wall type 1: solid masonry

2.29 The resistance to airborne sound depends mainly on the mass per unit area of the wall.

Constructions

2.30 Three wall type 1 constructions (types 1, 1.2, and 1.3) are described in this guidance.

2.31 Details of how junctions should be made to limit flanking transmission are also described in this guidance.

2.32 Points to watch

Do

• Do fill and seal all masonry joints with mortar.

• Do lay bricks frog up to achieve the required mass per unit area and avoid air paths.

• Do use bricks/blocks that extend to the full thickness of the wall.

• Do ensure that an external cavity wall is stopped with a flexible closer at the junction with a separating wall, unless the cavity is fully filled with mineral wool or expanded polystyrene beads (seek manufacturer’s advice for other suitable materials).

• Do control flanking transmission from walls and floors connected to the separating wall as described in the guidance on junctions.

• Do stagger the position of sockets on opposite sides of the separating wall.

• Do ensure that flue blocks will not adversely affect the sound insulation and that a suitable finish is used over the flue blocks (see BS 1289– 1:1986 and seek manufacturer’s advice).

Do not

• Do not try and convert a cavity separating wall to a type 1 (solid masonry) separating wall by inserting mortar or concrete into the cavity between the two leaves.

• Do not use deep sockets and chases in the separating wall, and do not place sockets back to back.

• Do not create a junction between a solid wall type 1 and a cavity wall type 2 in which the cavity wall is bridged by the solid wall.

2.33 Wall type 1.1 Dense aggregate concrete block, plaster on both room faces (see Diagram 2.2)

• minimum mass per unit area including plaster 415kg/m²;

• 13mm plaster on both room faces;

• use blocks that are laid flat to the full thickness of the wall.

Diagram 2.2 Wall type 1.1

Example of wall type 1.1

The required mass per unit area would be achieved by using

• 215mm block laid flat

• block density 1840kg/m³

• 110mm coursing

• 13mm lightweight plaster (minimum mass per unit area 10kg/m²) on both room faces.
This is an example only. See Annex A for a simplified method of calculating mass per unit area. Alternatively use manufacturer’s actual figures where these are available.

2.34 Wall type 1.2 Dense aggregate concrete cast in-situ, plaster on both room faces (see Diagram 2.3)

• minimum mass per unit area including plaster 415kg/m²;

• plaster on both room faces.

Example of wall type 1.2

The required mass per unit area would be achieved by using

• 190mm concrete

• concrete density 2200kg/m³

• 13mm lightweight plaster (minimum mass per unit area 10kg/m²) on both room faces

This is an example only. See Annex A for a simplified method of calculating mass per unit area. Alternatively use manufacturer’s actual figures where these are available.

Diagram 2.3 Wall type 1.2

2.35 Wall type 1.3 Brick, plaster on both room faces (see Diagram 2.4)

• minimum mass per unit area including plaster 375kg/m²;

• 13mm plaster on both room faces;

• bricks to be laid frog up, coursed with headers.

Example of wall type 1.3

The required mass per unit area would be achieved by using

• 215mm brick

• brick density 1610kg/m³

• 75mm coursing

• 13mm lightweight plaster (minimum mass per unit area 10kg/m²) on both room faces
This is an example only. See Annex A for a simplified method of calculating mass per unit area. Alternatively use manufacturer’s actual figures where these are available.

Diagram 2.4 Wall type 1.3

Junction requirements for wall type 1

Junctions with an external cavity wall with masonry inner leaf

2.36 Where the external wall is a cavity wall:

a. the outer leaf of the wall may be of any
construction; and

b. the cavity should be stopped with a flexible closer (see Diagram 2.5) unless the cavity is fully filled with mineral wool or expanded polystyrene beads (seek manufacturer’s advice for other suitable materials).

2.37 The separating wall should be joined to the inner leaf of the external cavity wall by one of the following methods:

a. Bonded. The separating wall should be bonded to the external wall in such a way that the separating wall contributes at least 50% of the bond at the junction. See Diagram 2.6.

b. Tied. The external wall should abut the separating wall and be tied to it. See Diagram 2.7. Also, see Building Regulation Part A – Structure.

2.38 The masonry inner leaf should have a mass per unit area of at least 120kg/m² excluding finish. However, there is no minimum mass requirement where there are openings in the external wall (see Diagram 2.8) that are:

a. not less than 1 metre high; and

b. on both sides of the separating wall at every storey; and

c. not more than 700mm from the face of the separating wall on both sides.

Diagram 2.5 Wall type 1 – external cavity wall with masonry inner leaf

2.39 Where there is also a separating floor then the requirement for a minimum mass per unit area of 120kg/m² excluding finish should always apply, irrespective of the presence or absence of openings.

Diagram 2.6 Wall type 1 – bonded junction – masonry inner leaf of external cavity wall with solid separating wall

Diagram 2.7 Wall type 1 – tied junction – external cavity wall with internal masonry wall

Diagram 2.8 Wall type 1 – tied junction – external cavity wall with internal masonry wall

Junctions with an external cavity wall with timber frame inner leaf

2.40 Where the external wall is a cavity wall:

a. the outer leaf of the wall may be of any construction; and

b. the cavity should be stopped with a flexible closer. See Diagram 2.9.

2.41 Where the inner leaf of an external cavity wall is of framed construction, the framed inner leaf should:

a. abut the separating wall; and

b. be tied to it with ties at no more than 300mm centres vertically.

The wall finish of the framed inner leaf of the external wall should be:

a. one layer of plasterboard; or

b. two layers of plasterboard where there is a separating floor;

c. each sheet of plasterboard to be of minimum mass per unit area 10kg/m^2, and

d. all joints should be sealed with tape or caulked with sealant.

Diagram 2.9 Wall type 1 - external cavity wall with timber frame inner leaf

Junctions with an external solid masonry wall

2.42 No guidance available (seek specialist advice).

Junctions with internal framed walls

2.43 There are no restrictions on internal framed walls meeting a type 1 separating wall.

Junctions with internal masonry walls

2.44 Internal masonry walls that abut a type 1 separating wall should have a mass per unit area of at least 120kg/m² excluding finish.

Junctions with internal timber floors

2.45 If the floor joists are to be supported on a type 1 separating wall then they should be supported on hangers and should not be built in. See Diagram 2.10.

Junctions with internal concrete floors

2.46 An internal concrete floor slab may only be carried through a type 1 separating wall if the floor base has a mass per unit area of at least 365kg/m². See Diagram 2.11.

2.47 Internal hollow-core concrete plank floors and concrete beams with infilling block floors should not be continuous through a type 1 separating wall.

2.48 For internal floors of concrete beams with infilling blocks, avoid beams built in to the separating wall unless the blocks in the floor fill the space between the beams where they penetrate the wall.

Diagram 2.10 Wall type 1 - internal timber floor

Diagram 2.11 Wall type 1 - internal concrete floor

Junctions with timber ground floors

2.49 If the floor joists are to be supported on a type 1 separating wall then they should be supported on hangers and should not be built in.

2.50 See Building Regulation Part C - Site preparation and resistance to moisture, and Building Regulation Part L - Conservation of fuel and power.

Junctions with concrete ground floors

2.51 The ground floor may be a solid slab, laid on the ground, or a suspended concrete floor. A concrete slab floor on the ground may be continuous under a type 1 separating wall. See Diagram 2.12.

2.52 A suspended concrete floor may only pass under a type 1 separating wall if the floor has a mass of at least 365kg/m².

2.53 Hollow core concrete plank and concrete beams with infilling block floors should not be continuous under a type 1 separating wall.

Diagram 2.12 Wall type 1 - concrete ground floor

2.54 See Building Regulation Part C - Site preparation and resistance to moisture, and Building Regulation Part L - Conservation of fuel and power.

Junctions with ceiling and roof

2.55 Where a type 1 separating wall is used it should be continuous to the underside of the roof.

2.56 The junction between the separating wall and the roof should be filled with a flexible closer which is also suitable as a fire stop. See Diagram 2.13.

2.57 Where the roof or loft space is not a habitable room and there is a ceiling with a minimum mass per unit area of 10kg/m² with sealed joints, then the mass per unit area of the separating wall above the ceiling may be reduced to 150kg/m². See Diagram 2.13.

2.58 If lightweight aggregate blocks of density less than 1200kg/m³ are used above ceiling level, then one side should be sealed with cement paint or plaster skim.

2.59 Where there is an external cavity wall, the cavity should be closed at eaves level with a suitable flexible material (e.g. mineral wool). See Diagram 2.14.

Notes A rigid connection between the inner and external wall leaves should be avoided. If a rigid material is used, then it should only be rigidly bonded to one leaf. See BRE BR 262, Thermal Insulation: avoiding risks, Section 2.3.

Junctions with separating floors

2.60 There are important details in Section 3 concerning junctions between wall type 1 and separating floors.

Diagram 2.13 Wall type 1 - ceiling and roof junction

Diagram 2.14 External cavity wall at eaves level

Constructions

2.62 Four wall type 2 constructions (types 2.1, 2.2, 2.3 and 2.4) are described in this guidance.

2.63 Two of these wall constructions (types 2.3 and 2.4) are only suitable when a step in elevation and/or a stagger in plan is incorporated at the separating wall.

2.64 Details of how junctions should be made to limit flanking transmission are also described in this guidance.

2.65 Points to watch:

Do

a. Do fill and seal all masonry joints with mortar.

b. Do keep the cavity leaves separate below ground floor level.

c. Do ensure that any external cavity wall is stopped with a flexible closer at the junction with the separating wall, unless the cavity is fully filled with mineral wool or expanded polystyrene beads (seek manufacturer's advice for other suitable materials).

d. Do control flanking transmission from walls and floors connected to the separating wall as described in the guidance on junctions.

e. Do stagger the position of sockets on opposite sides of the separating wall.

f. Do ensure that flue blocks will not adversely affect the sound insulation and that a suitable finish is used over the flue blocks (see BS 1289-1:1986 and seek manufacturer's advice).

Do not

a. Do not try and convert a cavity separating wall to a type 1 (solid masonry) separating wall by inserting mortar or concrete into the cavity between the two leaves.

b. Do not change to a solid wall construction in the roof space as a rigid connection between the leaves will reduce wall performance.

c. Do not build cavity walls off a continuous solid concrete slab floor.

d. Do not use deep sockets and chases in the separating wall, do not place them back to back.

Wall type 2: cavity masonry

2.61 The resistance to airborne sound depends on the mass per unit area of the leaves and on the degree of isolation achieved. The isolation is affected by connections (such as wall ties and foundations) between the wall leaves and by the cavity width.

Wall ties in separating cavity masonry walls

2.66 The wall ties used to connect the leaves of a cavity masonry wall should be tie type A.

Cavity widths in separating cavity masonry walls

2.67 Recommended cavity widths are minimum values.

Blocks with voids

2.68 The guidance describes constructions that use blocks without voids. For blocks with voids, seek advice from the manufacturer.

2.69 Wall type 2.1 Two leaves of dense aggregate concrete block with 50mm cavity, plaster on both room faces (see Diagram 2.15)

• minimum mass per unit area including plaster 415kg/m²;

• minimum cavity width of 50mm;

• 13mm plaster on both room faces.

Example of wall type 2.1

The required mass per unit area would be achieved by using

• 100mm block leaves

• block density 1990kg/m³

• 225mm coursing

• 13mm lightweight plaster (minimum mass per unit area 10kg/m²) on both room faces

This is an example only. See Annex A for a simplified method of calculating mass per unit area. Alternatively use manufacturer’s actual figures where these are available.

Diagram 2.15 Wall type 2.1

Wall type 2.2

2.70 Wall type 2.2 Two leaves of lightweight aggregate block with 75mm cavity, plaster on both room faces (see Diagram 2.16)

• minimum mass per unit area including plaster 300kg/m²;

• minimum cavity width of 75mm;

• 13mm plaster on both room faces.

*Example of wall type 2.2

The required mass per unit area would be achieved by using

• 100mm block leaves

• block density 1375kg/m³

• 225mm coursing

• 13mm lightweight plaster (minimum mass per unit area 10kg/m²) on both room faces.

This is an example only. See Annex A for a simplified method of calculating mass per unit area. Alternatively use manufacturer’s actual figures where these are available.

Diagram 2.16 Wall type 2.2

Additional construction: wall type 2.3 should only be used where there is a step and/or stagger of at least 300mm.

2.71 Wall type 2.3 Two leaves of lightweight aggregate block with 75mm cavity and step/stagger, plasterboard on both room faces (see Diagram 2.17)

minimum mass per unit area including plasterboard 290kg/m²;
lightweight aggregate blocks should have a density in the range 1350 to 1600kg/m³;
minimum cavity width of 75mm;
plasterboard, each sheet of minimum mass per unit area 10kg/m², on both room faces.

Note: The composition of the lightweight aggregate blocks contributes to the performance of this construction with a plasterboard finish. Using denser blocks may not give an equivalent performance.

Example of wall type 2.3

The required mass per unit area would be achieved by using 100mm block leaves

block density 1375kg/m³
225mm coursing
plasterboard, each sheet of minimum mass per unit area 10kg/m², on both room faces This is an example only. See Annex A for a simplified method of calculating mass per unit area.

Alternatively use manufacturer’s actual figures where these are available.

Note: Increasing the size of the step or stagger in the separating wall tends to increase the airborne sound insulation.

Diagram 2.17 Wall type 2.3

Additional construction: Wall type 2.4 should only be used in constructions without separating floors and where there is a step and/or stagger of at least 300mm.

2.72 Wall type 2.4 Two leaves of aircrete block with 75mm cavity and step/stagger, plasterboard or plaster on both room faces (see Diagram 2.18)

minimum mass per unit area including finish 150kg/m²;
minimum cavity width of 75mm;
plasterboard, each sheet of minimum mass per unit area 10kg/m², on both room faces; or
13mm plaster on both room faces.

Example of wall type 2.4

The required mass per unit area would be achieved by using 100mm aircrete block leaves

block density 650kg/m³
225mm coursing
plasterboard, each sheet of minimum mass per unit area 10kg/m², on both room faces This is an example only. See Annex A for a simplified method of calculating mass per unit area.

Alternatively use manufacturer’s actual figures where these are available.

Note: Increasing the size of the step or stagger in the separating wall tends to increase the airborne sound insulation.

Diagram 2.18 Wall type 2.4

Junction requirements for wall type 2

Junctions with an external cavity wall with masonry inner leaf

2.73 Where the external wall is a cavity wall:

a. the outer leaf of the wall may be of any construction; and

b. the cavity should be stopped with a flexible closer (for wall types 2.1 and 2.2 see Diagram 2.19, for wall types 2.3 and 2.4 see Diagram 2.20) unless the cavity is fully filled with mineral wool or expanded polystyrene beads (seek manufacturer’s advice for other suitable materials).

2.74 The separating wall should be joined to the inner leaf of the external cavity wall by one of the following methods:

a. Bonded. The separating wall should be bonded to the external wall in such a way that the separating wall contributes at least 50% of the bond at the junction.

b. Tied. The external wall should abut the separating wall and be tied to it. See Diagram 2.21. Also, see Building Regulation Part A – Structure.

2.75The masonry inner leaf should have a mass per unit area of at least 120kg/m² excluding finish. However, there is no minimum mass requirement where separating wall type 2.1, 2.3 or 2.4 is used.

2.76Where there is also a separating floor then the requirement for a minimum mass per unit area of 120kg/m² excluding finish should always apply, even when wall type 2.1, 2.3 or 2.4 is used.

Diagram 2.19 Wall types 2.1 and 2.2 – external cavity wall with masonry inner leaf

Diagram 2.20 Wall types 2.3 and 2.4 – external cavity wall with masonry inner leaf – stagger

Diagram 2.21 Wall type 2 – tied junction – external cavity wall with internal masonry wall

Junctions with an external cavity wall with timber frame inner leaf

2.77 Where the external wall is a cavity wall:

a. the outer leaf of the wall may be of any construction; and

b. the cavity should be stopped with a flexible closer. See Diagram 2.22.

Diagram 2.22 Wall type 2 - external cavity wall with timber frame inner leaf

2.78 Where the inner leaf of an external cavity wall is of framed construction, the framed inner leaf should:

a. abut the separating wall; and

b. be tied to it with ties at no more than 300mm centres vertically.

The wall finish of the inner leaf of the external wall should be:

a. one layer of plasterboard; or

b. two layers of plasterboard where there is a separating floor;

c. each sheet of plasterboard to be of minimum mass per unit area 10kg/m²; and

d. all joints should be sealed with tape or caulked with sealant.

Junctions with an external solid masonry wall

2.79 No guidance available (seek specialist advice).

Junctions with internal framed walls

2.80 There are no restrictions on internal framed walls meeting a type 2 separating wall.

Junctions with internal masonry walls

2.81 Internal masonry walls that abut a type 2 separating wall should have a mass per unit area of at least 120kg/m² excluding finish.

2.82 Where there is a separating floor, internal masonry walls should have a mass per unit area of at least 120kg/m² excluding finish.

2.83 When there is no separating floor with separating wall type 2.3 or 2.4 there is no minimum mass per unit area for internal masonry walls.

Junctions with internal timber floors

2.84 If the floor joists are to be supported on the separating wall then they should be supported on hangers and should not be built in. See Diagram 2.23.

Diagram 2.23 Wall type 2 - internal timber floor

Junctions with internal concrete floors

2.85 Internal concrete floors should generally be built into a type 2 separating wall and carried through to the cavity face of the leaf. The cavity should not be bridged. See Diagram 2.24.

Junctions with timber ground floors

2.86 If the floor joists are to be supported on the separating wall then they should be supported on hangers and should not be built in.

2.87 See Building Regulation Part C - Site preparation and resistance to moisture, and Building Regulation Part L - Conservation of fuel and power.

Junctions with concrete ground floors

2.88 The ground floor may be a solid slab, laid on the ground, or a suspended concrete floor. A concrete slab floor on the ground should not be continuous under a type 2 separating wall. See Diagram 2.24.

2.89 A suspended concrete floor should not be continuous under a type 2 separating wall, and should be carried through to the cavity face of the leaf. The cavity should not be bridged. See Diagram 2.24.

2.90 See Building Regulation Part C - Site preparation and resistance to moisture, and Building Regulation Part L - Conservation of fuel and power.

Diagram 2.24 Wall type 2 - internal concrete floor and concrete ground floor

Diagram 2.25 Wall type 2 - ceiling and roof junction

Junctions with ceiling and roof space

2.91 Where a type 2 separating wall is used it should be continuous to the underside of the roof.

2.92 The junction between the separating wall and the roof should be filled with a flexible closer which is also suitable as a fire stop. See Diagram 2.25.

2.93 Where the roof or loft space is not a habitable room and there is a ceiling with a minimum mass per unit area of 10kg/m² with sealed joints, then the mass per unit area of the separating wall above the ceiling may be reduced to 150kg/m² , but it should still be a cavity wall. See Diagram 2.25.

2.94 If lightweight aggregate blocks of density less than 1200kg/m³ are used above ceiling level, then one side should be sealed with cement paint or plaster skim.

2.95 Where there is an external cavity wall, the cavity should be closed at eaves level with a suitable flexible material (e.g. mineral wool). See Diagram 2.26.

Note A rigid connection between the inner and external wall leaves should be avoided. If a rigid material is used, then it should only be rigidly bonded to one leaf.

Diagram 2.26 External cavity wall at eaves level

Junctions with separating floors

2.96 There are important details in Section 3 concerning junctions between wall type 2 and separating floors.

Wall type 3: masonry between independent panels

2.97 The resistance to airborne sound depends partly on the type and mass per unit area of the core, and partly on the isolation and mass per unit area of the independent panels.

Note: Wall type 3 can give high resistance to the transmission of both airborne sound and impact sound on the wall.

Construction

2.98 Three wall type 3 constructions (types 3.1, 3.2 and 3.3) are described in this guidance.

2.99 The construction consists of either a solid or cavity masonry core wall with independent panels on both sides. These panels and any frame should not be in contact with the core wall.

2.100 Details of how junctions should be made to limit flanking transmission are also described in this guidance.

2.101 Points to watch

Do

a. Do fill and seal all masonry joints with mortar.

b. Do control flanking transmission from walls and floors connected to the separating wall as described in the guidance on junctions.

c. Do fix the panels or the supporting frames to the ceiling and floor only.

d. Do tape and seal all joints.

e. Do ensure that flue blocks will not adversely affect the sound insulation and that a suitable finish is used over the flue blocks (see BS 1289-1:1986 and seek manufacturer's advice).

Do not

Do not fix, tie or connect the free standing panels or the frame to the masonry core.

Wall ties in cavity masonry cores

2.102 The wall ties used to connect the leaves of a cavity masonry core should be tie type A.

Cavity widths in separating cavity masonry cores

2.103 Recommended cavity widths are minimum values.

2.104 Independent panels.

These panels should meet the following specification:

• minimum mass per unit area of panel (excluding any supporting framework) 20kg/m²;

• panels should consist of either

a. at least 2 layers of plasterboard with staggered joints, or

b. a composite panel consisting of 2 sheets of plasterboard separated by a cellular core;

• if the panels are not supported on a frame they should be at least 35mm from the masonry core;

• if the panels are supported on a frame there should be a gap of at least 10mm between the frame and the masonry core.

2.105 Wall type 3.1 Solid masonry core (dense aggregate concrete block), independent panels on both room faces (see Diagrams 2.27 and 2.28)

• minimum mass per unit area of core 300kg/m²;

• minimum core width is determined by structural requirements (see Building Regulation Part A – Structure);

• independent panels on both room faces.

Example of wall type 3.1

The required mass per unit area would be achieved by using

• 140mm block core

• block density 2200kg/m³

• 110mm coursing

• independent panels, each panel of mass per unit area 20kg/m², to be two sheets of plasterboard with joints staggered.

This is an example only. See Annex A for a simplified method of calculating mass per unit area. Alternatively use manufacturer’s actual figures where these are available.

Diagram 2.27 Wall type 3.1 with independent composite panels

Diagram 2.28 Wall type 3.1 with independent plasterboard panels

2.106 Wall type 3.2 Solid masonry core (lightweight concrete block), independent panels on both room faces (see Diagram 2.29)

• minimum mass per unit area of core 150kg/m²;

• minimum core width is determined by structural requirements (see Building Regulation Part A – Structure);

• independent panels on both room faces.

Example of wall type 3.2

The required mass per unit area would be achieved by using

• 140mm lightweight block core

• block density 1400kg/m³

• 225mm coursing

• independent panels, each panel of mass per unit area 20kg/m², to be two sheets of plasterboard joined by a cellular core.

This is an example only. See Annex A for a simplified method of calculating mass per unit area. Alternatively use manufacturer’s actual figures where these are available.

Diagram 2.29 Wall type 3.2 with independent composite panels

2.107 Wall type 3.3 Cavity masonry core (brickwork or blockwork), 50mm cavity, independent panels on both room faces (see Diagram 2.30)

• the core can be of any mass per unit area;

• minimum cavity width of 50mm;

• minimum core width is determined by structural requirements (see Building Regulation Part A – Structure);

• independent panels on both room faces.

Example of wall type 3.3

• two leaves of concrete block

• each leaf at least 100mm thick

• minimum cavity width of 50mm

• independent panels, each panel of mass per unit area 20kg/m², to be two sheets of plasterboard joined by a cellular core

Diagram 2.30 Wall type 3.3 with independent composite panels

Junction requirements for wall type 3

Junctions with an external cavity wall with masonry inner leaf

2.108 Where the external wall is a cavity wall:

a. the outer leaf of the wall may be of any construction; and

b. the cavity should be stopped with a flexible closer (see Diagram 2.31) unless the cavity is fully filled with mineral wool or expanded polystyrene beads (seek manufacturer’s advice for other suitable materials).

2.109 Where the inner leaf of an external cavity wall is masonry:

a. the inner leaf of the external wall should be bonded or tied to the masonry core;

b. the inner leaf of the external wall should be lined with independent panels in the same manner as the separating walls. See Diagram 2.31.

2.110 Where there is a separating floor the masonry inner leaf of the external wall should have a minimum mass per unit area of at least 120kg/m² excluding finish.

2.111Where there is no separating floor and the masonry inner leaf of the external wall is lined with independent panels in the same manner as the separating walls, there is no minimum mass requirement on the masonry inner leaf.

2.112Where there is no separating floor with separating wall type 3.1 or 3.3, and the masonry inner leaf of the external wall has a mass of at least 120kg/m² excluding finish, then the inner leaf of the external wall may be finished with plaster or plasterboard of minimum mass per unit area 10kg/m².

Diagram 2.31 Wall type 3 – external cavity wall with masonry inner leaf

Junctions with an external cavity wall with timber frame inner leaf

2.113 No guidance available (seek specialist advice).

Junctions with an external solid masonry wall

2.114 No guidance available (seek specialist advice).

Junctions with internal framed walls

2.115 Load-bearing framed internal walls should be fixed to the masonry core through a continuous pad of mineral wool. See Diagram 2.32.

2.116 Non-load-bearing internal walls should be butted to the independent panels.

2.117 All joints between internal walls and panels should be sealed with tape or caulked with sealant.

Diagram 2.32 Wall type 3 - external cavity wall with internal timber wall

Junctions with internal masonry walls

2.118 Internal walls that abut a type 3 separating wall should not be of masonry construction.

Junctions with internal timber floors

2.119 If the floor joists are to be supported on the separating wall then they should be supported on hangers and should not be built in. See Diagram 2.33.

2.120 Spaces between the floor joists should be sealed with full depth timber blocking.

Wall types 3.1 and 3.2 (solid masonry core)

2.121 An internal concrete floor slab may only be carried through a solid masonry core if the floor base has a mass per unit area of at least 365kg/m². See Diagram 2-34.

Wall type 3.3 (cavity masonry core)

2.122 Internal concrete floors should generally be built into a cavity masonry core and carried through to the cavity face of the leaf. The cavity should not be bridged.

Diagram 2.33 Wall type 3 - internal timber floor

Diagram 2.34 Wall types 3.1 and 3.2 - internal concrete floor

Junctions with timber ground floors

2.123 If the floor joists are to be supported on the separating wall then they should be supported on hangers and should not be built in.

2.124 Spaces between the floor joists should be sealed with full depth timber blocking.

2.125 See Building Regulation Part C - Site preparation and resistance to moisture, and Building Regulation Part L - Conservation of fuel and power.

Junctions with concrete ground floors

2.126 The ground floor may be a solid slab, laid on the ground, or a suspended concrete floor.

Wall type 3.1 and 3.2 (solid masonry core)

2.127 A concrete slab floor on the ground may be continuous under the solid masonry core of a type 3.1 or 3.2 separating wall.

2.128 A suspended concrete floor may only pass under the solid masonry core of a type 3.1 or 3.2 separating wall if the floor has a mass per unit area of at least 365kg/m².

2.129 Hollow core concrete plank and concrete beams with infilling block floors should not be continuous under the solid masonry core of a type 3.1 or 3.2 separating wall.

Wall type 3.3 (cavity masonry core)

2.130 A concrete slab floor on the ground should not be continuous under the cavity masonry core of a type 3.3 separating wall.

2.131 A suspended concrete floor should not be continuous under the cavity masonry core of a type 3.3 separating wall and should be carried through to the cavity face of the leaf. The cavity should not be bridged.

2.132 See Building Regulation Part C - Site preparation and resistance to moisture, and Building Regulation Part L - Conservation of fuel and power.

Diagram 2.35 Wall types 3.1 and 3.2 - ceiling and roof junction

Junctions with ceiling and roof space

2.133 The masonry core should be continuous to the underside of the roof.

2.134 The junction between the separating wall and the roof should be filled with a flexible closer which is also suitable as a fire stop. See Diagram 2.35.

2.135 The junction between the ceiling and independent panels should be sealed with tape or caulked with sealant.

2.136 Where there is an external cavity wall, the cavity should be closed at eaves level with a suitable flexible material (e.g. mineral wool). See Diagram 2.36.

Note A rigid connection between the inner and external wall leaves should be avoided. If a rigid material is used, then it should only be rigidly bonded to one leaf.

Wall types 3.1 and 3.2 (solid masonry core)

2.137 Where the roof or loft space is not a habitable room and there is a ceiling with a minimum mass per unit area 10kg/m² and with sealed joints, the independent panels may be omitted in the roof space and the mass per unit area of the separating wall above the ceiling may be a minimum of 150kg/m². See Diagram 2.35.

2.138 If lightweight aggregate blocks of density less than 1200kg/m³ are used above ceiling level, then one side should be sealed with cement paint or plaster skim.

Diagram 2.36 External cavity wall at eaves level

Wall type 3.3 (cavity masonry core)

2.139 Where the roof or loft space is not a habitable room and there is a ceiling with a minimum mass per unit area 10kg/m² and with sealed joints, the independent panels may be omitted in the roof space but the cavity masonry core should be maintained to the underside of the roof.

Junctions with separating floors

2.140 There are important details in Section 3 concerning junctions between wall type 3 and separating floors.

Wall type 4: framed walls with absorbent material

2.141 In this guidance only a timber framed wall is described. For steel framed walls, seek advice from the manufacturer.

2.142 The resistance to airborne sound depends on the mass per unit area of the leaves, the isolation of the frames, and the absorption in the cavity between the frames.

Construction

2.143 The construction consists of timber frames, with plasterboard linings on room surfaces and with absorbent material between the frames.

2.144 One wall type 4 construction (type 4.1) is described in this guidance.

2.145 Details of how junctions should be made to limit flanking transmission are also described in this guidance.

2.146 Points to watch

Do

a. Do ensure that where fire stops are needed in the cavity between frames they are either flexible or fixed to only one frame.

b. Do stagger the position of sockets on opposite sides of the separating wall, and use a similar thickness of cladding behind the socket box.

c. Do ensure that each layer of plasterboard is independently fixed to the stud frame.

d. Do control flanking transmission from walls and floors connected to the separating wall as described in the guidance on junctions.

Do not

a. Where it is necessary to connect the two leaves together for structural reasons, do not use ties of greater cross section than 40mm x 3mm fixed to the studwork at or just below ceiling level and do not set them at closer than 1.2m centres.

b. Do not locate sockets back to back. A minimum edge to edge stagger of 150mm is recommended. Do not chase plasterboard.

2.147 Wall type 4.1 Double leaf frames with absorbent material (see Diagram 2.37)

• minimum distance between inside lining faces of 200mm;

• plywood sheathing may be used in the cavity as necessary for structural reasons;

• each lining to be two or more layers of plasterboard, each sheet of minimum mass per unit area 10kg/m², with staggered joints;

• absorbent material to be unfaced mineral wool batts or quilt (which may be wire reinforced), minimum density 10kg/m³;

• minimum thickness of absorbent material:

a. 25mm if suspended in the cavity between frames,

b. 50mm if fixed to one frame,

c. 25mm per batt (or quilt) if one is fixed to each frame.

Note: A masonry core may be used where required for structural purposes, but the core should be connected to only one frame.

Diagram 2.37 Wall type 4.1

Wall type 4.1

2.147 Double leaf frames with absorbent material (see Diagram 2.37)

• minimum distance between inside lining faces of 200mm;

• plywood sheathing may be used in the cavity as necessary for structural reasons;

• each lining to be two or more layers of plasterboard, each sheet of minimum mass per unit area 10kg/m

• absorbent material to be unfaced mineral wool batts or quilt (which may be wire reinforced), minimum density 10kg/m

• minimum thickness of absorbent material:

• a25mm if suspended in the cavity between frames,

• b50mm if fixed to one frame,

• c25mm per batt (or quilt) if one is fixed to each frame.

Notes: A masonry core may be used where required for structural purposes, but the core should be connected to only one frame.

Junctions with an external cavity wall with masonry inner leaf

2.148 No guidance available (seek specialist advice).

Junctions with an external cavity wall with timber frame inner leaf

2.149 Where the external wall is a cavity wall:

a. the outer leaf of the wall may be of any construction; and

b. the cavity should be stopped between the ends of the separating wall and the outer leaf with a flexible closer. See Diagram 2.38.

2.150 The wall finish of the inner leaf of the external wall should be:

a. one layer of plasterboard; or

b. two layers of plasterboard where there is a separating floor;

c. each sheet of plasterboard of minimum mass per unit area 10kg/m²; and

d. all joints should be sealed with tape or caulked with sealant.

Diagram 2.38 Wall type 4 - external cavity wall with timber frame inner leaf

Junctions with an external solid masonry wall

2.151 No guidance available (seek specialist advice).

Junctions with internal framed walls

2.152 There are no restrictions on internal framed walls meeting a type 4 separating wall.

Junctions with internal masonry walls

2.153 There are no restrictions on internal masonry walls meeting a type 4 separating wall.

Junctions with internal timber floors

2.154 Block the air paths through the wall into the cavity by using solid timber blockings or continuous ring beam or joists.

Junctions with internal concrete floors

2.155 No guidance available (seek specialist advice).

Junctions with timber ground floors

2.156 Block the air paths through the wall into the cavity by using solid timber blockings or a continuous ring beam or joists.

2.157 See Building Regulation Part C - Site preparation and resistance to moisture, and Building Regulation Part L - Conservation of fuel and power.

Junctions with concrete ground floors

2.158 The ground floor may be a solid slab, laid on the ground, or a suspended concrete floor. A concrete slab floor on the ground may be continuous under a type 4 separating wall. A suspended concrete floor may only pass under a wall type 4 if the floor has a mass per unit area of at least 365kg/m².

2.159 See Building Regulation Part C - Site preparation and resistance to moisture, and Building Regulation Part L - Conservation of fuel and power.

Junctions with ceiling and roof space

2.160 The wall should preferably be continuous to the underside of the roof.

2.161 The junction between the separating wall and the roof should be filled with a flexible closer.

2.162 The junction between the ceiling and the wall linings should be sealed with tape or caulked with sealant.

Where the roof or loft space is not a habitable room and there is a ceiling with a minimum mass per unit area 10kg/m² and with sealed joints, either:

a. the linings on each frame may be reduced to two layers of plasterboard, each sheet of minimum mass per unit area 10kg/m

b. the cavity may be closed at ceiling level without connecting the two frames rigidly together and then one frame may be used in the roof space provided there is a lining of two layers of plasterboard, each sheet of minimum mass per unit area 10kg/m², on both sides of the frame.

2.163 Where there is an external wall cavity, the cavity should be closed at eaves level with a suitable material.

Junctions with separating floors

2.164 There are important details in Section 3 concerning junctions between wall type 4 and separating floors.