6.3 Internal walls


6.3 - M1 Materials standards
6.3 - M2 Masonry materials
6.3 - M3 Wall ties and related items
6.3 - M4-M5 Timber
6.3 - M6 Plasterboard
6.3 - M7 Proprietary systems
6.3 - M8 Damp-proof courses
6.3 - M9 Sound insulation materials
6.3 - M10 Fire-stopping materials
6.3 - M11 Fireplaces and flues

6.3 - M1
All materials shall:
(a) meet the Technical Requirements
(b) take account of the design

Materials that comply with the design and the guidance below will be acceptable for internal walls, including separating walls and compartment walls.

Materials for internal walls should comply with all relevant standards, including those listed below. Where no standard exists, Technical Requirement R3 applies (see Chapter 1.1 'Introduction to the Standards and Technical Requirements').

References to British Standards and Codes of Practice include those made under the Construction Products Directive (89/106/EEC) and, in particular, appropriate European Technical Specifications approved by a European Committee for Standardisation (CEN).


6.3 - M2
Masonry shall comply with relevant standards

Items to be taken into account include:

(a) precast concrete blocks

Concrete blocks should comply with BS EN 771.

When used in loadbearing partitions, blocks should have the minimum compressive strength required by the design. The table below gives recommended strengths of blocks to be used in specific cases:

Height of wall Minimum compressive strength of block unit

1 or 2 storeys blocks - 2.9N/mm2
Lowest storey of a 3 storey wall or where individual storeys exceed 2.7m

blocks - 7.3N/mm2
(unless calculations show that lower strengths are suitable)
Upper storeys of 3 storey wall
blocks - 2.9N/mm2

Where buildings are more than 3 storeys in height, masonry should be designed in accordance with Technical Requirement R5 using the block strength specified by the designer.

The maximum loadbearing capacity of the wall should not exceed the recommendations of the manufacturer.

In some partitions to WC compartments and all separating walls, blocks should have at least the minimum density required by the design in order to achieve the required sound insulation.

Where special blocks/pipes are used for flues, the manufacturer's recommendations should be checked. Special materials may be required around the blocks/pipes.

(b) bricks

Bricks should comply with the relevant British Standards:

  • clay bricks should comply with BS EN 771-1
  • calcium silicate bricks should comply with BS EN 771-2
  • concrete bricks should comply with BS EN 771-3.

When used in a separating wall, bricks should have at least the minimum density required by the design. A lighter brick may not provide a suitable level of sound resistance.

For bricks suitable for use in chimneys reference should be made to Chapter 6.8 'Fireplaces, chimneys and flues'.

(c) mortar

A mortar of 1 : 1 : 5½, cement : lime : sand, with plasticiser is suitable for both internal and external walls.

Unless otherwise specified by the brick or block manufacturer, ordinary Portland cement to BS EN 197 may be used. Sulfate-resisting Portland cement should be used, where necessary (see Chapter 6.1 'External masonry walls' (Materials)).

Admixtures, retarded mortars and pre-mixed mortars may be used in accordance with the manufacturer's recommendations, provided those of the masonry manufacturer agree.


6.3 - M3
Walls ties and related items shall be of the appropriate type and strength and shall have adequate durability


Wall ties should either:

  • be butterfly type, or
  • have been tested to show that their design meets with statutory requirements.

Wall ties for timber frame separating walls should be not more than 40mm x 3mm in cross section.


Joist hangers, restraint straps, bond ties, etc should be protected against corrosion. Ferrous metals with the following levels of protection are acceptable:

  • post-galvanizing to BS 729, or
  • pre-galvanizing to BS 2989.

Restraint straps for use in masonry construction should have a minimum cross section of 30mm x 5mm.


6.3 - M4
Timber shall be of the appropriate grades and sizes to support the imposed loads

Preferably, regularised timber should be used for stud partitions. Structural timber should be specified according to the strength classes in BS EN 338, eg C16 or C24. When using the BS 4978 grading rules, the timber species should be included in accordance with BS EN 1912 or class strength specified. The strength class can then be determined from BS EN 338.

Finger joints should comply with BS EN 385 and timber for dry lining with BS 8212.

6.3 - M5
Timber shall have a suitable moisture content

To minimise drying shrinkage, timber should have a moisture content not greater than 20%.

Structural softwood for internal use should be dry graded to BS 4978 and marked 'DRY' or 'KD'.


6.3 - M6
Plasterboard shall be of a suitable thickness for its intended use

Plasterboard should be to BS 1230. Plasterboard thickness should be:

  • 9.5mm for stud spacing up to 450mm
  • 12.5mm for stud spacing up to 600mm.

For sound-resisting walls (separating walls and walls to WC compartments), the correct thickness, number of layers of plasterboard sheets and sealing should be specified (see Design clause 6.3 - D9).

Tapered edge boards should be used where the plasterboard is to be jointed only before decoration.

Dry lining systems should comply with BS 8212. Reference should be made to Chapter 8.2 'Wall and ceiling finishes' (each section) for further details.


6.3 - M7
Prefabricated proprietary partition systems shall be suitable for their purpose

Proprietary partitions should be specified in accordance with the manufacturer's recommendations.


6.3 - M8
Materials for damp-proofing shall adequately resist the passage of moisture

Materials which are acceptable for use as dpcs include:

  • bitumen to BS 6398
  • polyethylene to BS 6515
  • proprietary materials assessed in accordance with Technical Requirement R3.

Dpcs should be not less than the width of the wall or partition.


6.3 - M9
Materials used for sound insulation shall be of a suitable thickness and density

Normally, mineral wool quilt should be used for acoustic insulation in partitions. The thickness and density should be as required by the design.


6.3 - M10
Fire-stopping materials shall be suitable to resist the passage of fire

Suitable fire-stopping materials include:

  • mineral wool
  • cement mortar
  • gypsum plaster
  • intumescent mastic or preformed strip
  • proprietary sealing systems (particularly those designed for service penetrations) assessed in accordance with Technical Requirement R3 to maintain the fire resistance of the wall.


6.3 - M11
Fireplaces and flues

See Chapter 6.8 'Fireplaces, chimneys and flues'.