Internal walls

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6.3.4Masonry walls

Internal masonry walls shall be designed to support and transfer loads to foundations safely and without undue movement. Issues to be taken into account include:

  1. structural elements
  2. mortar mix and jointing
  3. workmanship
  4. bonding and tying
  5. lateral restraint
  6. masonry separating walls
  7. lintels and beams.

Structural elements

Structural design of masonry walls should be in accordance with BS EN 1996-1-1.

Bricks and blocks should be selected in accordance with their intended use and as recommended in Table 1.

Table 1: Bricks and blocks in buildings up to three storeys high

Height of wallUnitMinimum compressive strength
One or two storeyBlocks
2.9 N/mm2
9.0 N/mm2
Lowest storey of a three storey wall, or where individual storeys exceed 2.7mBlocks
7.3 N/mm2
13.0 N/mm2
Upper storeys of a three storey wallBlocks
2.9 N/mm2
9.0 N/mm2

Where buildings are more than three storeys high, masonry should be designed in accordance with Technical Requirement R5 and the block strength specified in the design.

Precast concrete blocks

Concrete blocks should comply with BS EN 771. The maximum load-bearing capacity of the wall should not exceed the recommendations of the manufacturer.

Flue blocks should be in accordance with the manufacturer’s recommendations.


Bricks should comply with the relevant British Standards:

Clay bricksBS EN 771-1
Calcium silicate bricksBS EN 771-2
Concrete bricksBS EN 771-3

When used in a separating wall, masonry should:

  • be in accordance with the design information
  • provide a suitable level of sound resistance.

Mortar mix and jointing

Mortar should:

  • be the correct mix and used within two hours, unless it is retarded mortar
  • not be re-tempered if it has started to set
  • include sulfate-resisting cement where required.

Admixtures, retarded mortars and premixed mortars should be:

  • compatible with masonry and other components
  • used in accordance with the manufacturer’s recommendations.

Air-entraining agents:

  • can help reduce frost damage but cannot be used as anti-freeze
  • should be carefully measured for each batch and be in accordance with the manufacturer’s instructions.

Bricks and blocks should be laid on a full bed of mortar, with perpends solidly filled.

Where walls are to be finished with wet plaster, joints should be raked out to a shallow depth to provide a key. For dry lining, mortar joints should be struck off flush.


Internal masonry walls and associated works should be:

  • constructed in lifts/stages to prevent the distortion of wall panels during construction
  • accurately set out
  • reasonably plane and true
  • plumb, with courses level.

Bonding and tying

Internal masonry walls should:

  • maintain a regular bonding pattern
  • not include bricks or blocks of different types in the same wall, to avoid cracking
  • be fully bonded or tied, either with a tooth at alternate courses, or an expanded metal tie (or equivalent) at a maximum vertical spacing of 300mm.

Lateral restraint

Load-bearing masonry walls, including separating walls, should be provided with lateral restraint at:

  • each floor level
  • ceiling level below a roof.

Restraint straps should be provided to separating walls on each level, at a maximum of 2m centres, when the floor:

  • is not on, or near, the same level
  • does not provide adequate restraint.

Lateral restraint should be provided in accordance with Chapter 6.4 ‘Timber and concrete upper floors’.

Timber floors

Adequate restraint can be provided by timber floors where joists have a minimum 90mm bearing. Alternatively, restraint should be provided by:

  • restraint straps with a minimum 30mm x 5mm cross-section, or
  • restraint type joist hangers to BS EN 845-1 with a performance equivalent to restraint straps.

Concrete floors

Adequate restraint can be provided by concrete floors that have a minimum 90mm bearing on to the wall. Alternatively, restraint should be provided by:

  • restraint straps that are a minimum of 450mm long with the end turned down between a joint in the concrete floor or suitably fixed with screws.

Masonry separating walls

Both leaves of a masonry cavity separating wall should be tied together to provide structural stability. The type of tie and spacing should limit the sound transmission across the cavity in accordance with building regulations.

Lintels and beams

Lintels should be specified according to loads and spans:

  • in accordance with manufacturer’s recommendations, or
  • designed by an engineer in accordance with Technical Requirement R5.

For masonry:

  • concrete and steel lintels are suitable
  • timber lintels should not be used
  • lintels should extend beyond the end of each opening in accordance with Table 2.

Table 2: Lintel bearings

Span (m)Minimum length of bearing (mm)
Up to 1.2100
Over 1.2150

Lintels and beams should:

  • have padstones where required
  • be the correct way up
  • bear on a full block, and be level and bedded on a solid bed of suitable mortar
  • not have soft or non-durable packing.