6.3 Internal walls


6.3 - S1 Sitework standards
6.3 - S2 Damp-proof courses
6.3 - S3 Masonry partitions
6.3 - S4 Timber stud partitions
6.3 - S5 Proprietary partitions
6.3 - S6 Separating walls
6.3 - S7 Partitions to rooms containing a WC
6.3 - S8 Walls providing fire resistance
6.3 - S9 Chimneys, flues and linings

6.3 - S1
All sitework shall:
(a) meet the Technical Requirements
(b) take account of the design
(c) follow established good practice and workmanship

Sitework that follows the design and the guidance below will be acceptable for internal walls, including separating walls and compartment walls.


6.3 - S2
Damp-proof courses shall be installed to prevent moisture entering the building

A dpc should be provided below all loadbearing walls built off foundation walls. The dpc should be linked with any adjoining dpm.

The dpm may be either continuous or formed by two separate overlapping pieces.

Dpc linked with dpm below partition. Dpm below slab

Dpcs should be provided below timber partitions where directly fixed to floor slabs, even if there is a dpm beneath the slab. This is to prevent residual moisture in the concrete affecting the timber.

Stud partition on dpc, dpm below slab

A dpc should be provided below all internal walls where the dpm is applied to the top surface of the slab.

The dpcs should be at least the width of the partition. Where dpcs join, the lap should be at least 100mm.

Partition on dpc above polyethylene dpm, screed on dpm above slab


6.3 - S3
Construction of masonry internal walls shall ensure adequate stability

Items to be taken into account include:

(a) setting out and workmanship

Partitions should be accurately set out in accordance with the design.

All work should be reasonably plane and true. Walls should be plumbed and courses levelled by using lines and spirit levels.

Openings should be formed to the correct size and shape. Templates should be used, where necessary.

Walls should be plumbed and courses levelled by using lines and spirit levels

(b) construction sequence

Walling should be constructed in lifts/stages to prevent distortion of wall panels during construction.

(c) mortar mix and joints


Make sure the correct mix is used. A mortar of 1 : 1 : 5½, cement : lime : sand, with plasticiser is suitable for both internal and external walls.

Unless otherwise specified, ordinary Portland cement may be used. Sulfate-resisting Portland cement should be used, where necessary (see Chapter 6.1 'External masonry walls' (Sitework)).

Mixers should be maintained and cleaned to function properly.

Mortar should be used within 2 hours, unless it is a retarded mortar. Mortar should not be re-tempered after setting has commenced.


Retarded mortar should not be used beyond the time specified by the supplier.

Retarded mortar should not be used during cold weather.


Where plasticisers or other additives are to be used, the manufacturer's instructions should be followed. An air entraining agent can help reduce frost damage but it is not an anti-freeze. The recommended quantity of air entraining agent should be carefully measured for each batch in accordance with the manufacturer's instructions.


All bricks and blocks should be laid on a full bed of mortar.

All perpends should be solidly filled.

If walls are to be finished with wet plaster, joints should be raked out square to a shallow depth to provide a key.

For dry lining, mortar joints should be struck off flush.

For information on dry lining masonry walls, reference should be made to Chapter 8.2 'Wall and ceiling finishes' (Sitework).

(d) bonding and tying

A regular bonding pattern should be maintained. All masonry walls and partitions should be fully bonded or tied, as required by the design.


  • tooth every alternate course, or
  • tie with expanded metal or equivalent, at centres not exceeding 300mm vertically.

Bonded connection

Tied connection

Joist filling should be brick or blockwork, without excessive mortar joints. Bricks and blocks should not be mixed.

To avoid cracking, bricks and blocks or blocks of different types should not be mixed in the same wall.

Incorrect use of different masonry types

(e) chasing for services

Chases can reduce the sound insulation value of a wall and should be cut only where required by the design. Impact power tools that can damage the wall should not be used.

The depth of horizontal chases should not exceed one-sixth the thickness of the single leaf, and vertical chases, one-third the thickness. Hollow blocks should not be chased, unless specifically permitted by the manufacturer.

Chasing for services

(f) size, location and support of lintels and beams

Lintels should be the correct size for the opening and have the correct bearing at each end:

Span [m] Minimum bearing [mm]
Up to 1.2 100
Over 1.2 150

Long lintels may require padstones. Lintels should bear on a full block where possible and be installed level on a solid bed of mortar. Soft or non-durable packing should not be used.

Small pieces of cut bricks or blocks should not be used around lintel bearings. Concrete lintels should be the right way up.

Support of lintels

Where steel beams are to be used, reference should be made to Chapter 6.5 'Steelwork support to upper floors and partitions' (Sitework) for guidance on steel beam sizes and the need for padstones.

(g) restraint strapping

Joists built into masonry walls provide adequate lateral restraint.

Restraint straps may be required by the design. If so, they should be fitted before new masonry is built above.

Restraint strapping


6.3 - S4
Construction of timber stud internal walls shall ensure adequate stability

Items to be taken into account include:

(a) setting out and workmanship

Partitioning should be correctly positioned, square and plumb.

Setting out

Studs should be spaced at centres to suit the plasterboard thickness. Extra studs should be provided at openings, as required by the design.

(b) size of timber members

Loadbearing timber partitions should be constructed in accordance with the design. Unless designed otherwise, the minimum specification for all partitions should be:

  • sill and head plates 63mm x 38mm
  • studs 63mm x 38mm at maximum 600mm centres
  • framing joints secured with not less than 2 nails per joint
  • blocking/nogging for support of plasterboard 43mm x 38mm
  • blocking/nogging for other purposes 63mm x 38mm.

(c) support and fixings

Partitions should be firmly fixed to each other and to abutting walls. Noggings or extra studs should be used, where necessary.

Extra stud

Partitions should be fixed at head and base to noggings or joists.

Partition parallel to joist - Fixing to nogging

Partition at right angles to joist - Fixing to joist

Internal partitions should not be wedged against ceiling joists or roof trusses. This does not allow for ceiling deflection/movement and can damage the ceiling boards.

Partitions should not be over-wedged at floor level. This could damage floor boarding.

Noggings should be provided to support fittings, such as radiators, wall mounted boilers, sanitary fittings, kitchen units, etc.

Nogging supports radiator

Fixing and finishing plasterboard partitions should be in accordance with Chapter 8.2 'Wall and ceiling finishes' (Sitework).


6.3 - S5
Proprietary partitions shall be erected in accordance with manufacturers' recommendations

Partitioning should be correctly positioned, square and plumb. The manufacturer's recommended construction sequence should be followed.

Timber or other additional fixings should be provided for radiators, electrical outlets, switches and the like.


6.3 - S6
Construction of separating walls shall ensure adequate sound insulation


The correct density of block should be used. Holes, voids, even hairline cracks, can significantly reduce the effectiveness of a sound-insulating wall.

To maintain sound insulation:

  • fully fill all mortar beds and perpends
  • use only butterfly or other approved wall ties for cavities up to 75mm wide
  • space wall ties 900mm minimum horizontally and 450mm minimum vertically
  • stagger the positions of electrical socket outlets on opposite sides of separating walls
  • tie in or tooth bond to adjoining walls to improve rigidity of separating wall
  • where joist ends are built into separating walls fully fill the spaces around the joists with mortar and point around the joist perimeter with silicone sealant as required by the design
  • chases for services should be well filled with mortar.

Solid separating walls should be taken through the inner leaf of a cavity external wall using metal ties to provide rigidity. However, if the same blocks are used for both walls, tooth bonding is acceptable.

Solid separating walls


The design details should be carefully followed. There should be no gaps in the:

  • mineral wool quilt
  • plasterboard layers
  • fire-stopping.

Services should not penetrate the plasterboard layers. They should be fixed in front of the plasterboard.


6.3 - S7
Partitions to rooms containing a WC shall provide adequate sound insulation, where required by the design

The guidance below applies in Scotland, Northern Ireland and the Isle of Man. In England and Wales the design should be checked to see how sound insulation is to be achieved.

A partition between a room containing a WC and a living room, dining room, study or bedroom (except where the WC is en-suite) should have adequate sound insulation.

Most masonry partitions provide adequate sound insulation without additional treatment.

Some methods of providing adequate sound insulation with a timber stud partition are shown below:

One layer of 12.5mm plasterboard each side + no insulation. One layer of 12.5mm plasterboard each side + 25mm mineral wool quilt

5mm plaster coat on one layer of 9.5mm plasterboard each side + 25mm mineral wool quilt. One layer of 12mm panel board each side + 75mm mineral wool quilt

Where two layers of plasterboard are used, the joints should be staggered and the joints in the outer layer properly filled.

Proprietary plasterboard partitions usually need an additional layer of plasterboard to one or both sides of the partition to provide adequate sound insulation.


6.3 - S8
Internal walls shall, where required, have adequate resistance to fire spread

Items to be taken into account include:

(a) separating wall construction


Junctions between separating walls and roofs should be firestopped to the underside of the tiling to prevent fire spreading between dwellings.

The separating wall should stop about 25mm below the top of adjacent roof trusses.

Soft packing, such as mineral wool, should be used above and below the roofing underlay, to allow for movement in roof timbers and prevent 'hogging' of the tiles.

Separating wall construction

It is important that a cavity barrier is provided within boxed eaves. The cavity barrier should be wire reinforced mineral wool blanket, at least 50mm thick, nailed to the rafter and carefully cut to shape to fully seal the boxed eaves.

penetration of fire-resisting walls by services

Pipes, cables and ducting should be firestopped where they pass through fire-resisting walls, including:

  • separating walls
  • compartment walls
  • walls to ducts serving flats.

The design requirements for firestopping should be checked and making good completed neatly.


6.3 - S9
Construction of chimneys, flues and linings

See Chapter 6.8 'Fireplaces, chimneys and flues'.