Superstructure (excluding roofs)

6.1External masonry walls


This chapter provides guidance on external masonry which is used for the outer and inner leaves of a cavity wall construction, cladding to framed structures and to the limited solid wall construction used in housebuilding such as garages. General guidance on masonry cavity wall construction including the masonry inner leaf of a cavity wall are also provided within this chapter.

The guidance is consistent and complementary to that provided within Chapter 6.9 Curtain walling and cladding which should be used for products and systems falling under that description.

There is a strong link to all chapters in Part 6 of this standards, particularly chapters 6.2 – 6.5 and 6.10.

The aim of this chapter is to provide clarity for external and cavity walls constructed of clay and concrete bricks and blocks as well as natural stone.

Definitions for this chapter

Aggregate concrete masonry unitMasonry unit manufactured from cementitious binder, aggregates and water and which may contain admixtures and additions and colouring pigments and other materials incorporated or applied during or after unit manufacture
Aircrete masonry unitMasonry unit manufactured from hydraulic binders such as cement and/or lime, combined with siliceous based fine material, cell generating material and water and cured with high pressure steam in autoclaves
BlocksMasonry units which when used in its normal aspect exceeds the length or width or height specified for a coursing unit (typical brick size). A common block size is 440mm long x 100mm wide x 215mm high
BricksAre designated in terms of their intended use. The coordinating sizes for bricks is generally: 225mm long x 112.5mm wide x 75mm high. The work sizes are in effect coordinating sizes less a nominal thickness of 10mm for the mortar joint.
Clay masonry unitMasonry unit made from clay or other argillaceous materials with or without sand, fuel or other additives fired at a sufficiently high temperature to achieve a ceramic bond
Compressive strengthsWhere these are quoted in this chapter, they refer to the declared compressive strengths of masonry units
Coordinating sizeSize of a coordinating space allocated to a masonry unit including allowances for joints
Coursing unitMasonry unit, commonly of brick sizes, used to assist in achieving the storey height of a wall in conjunction with full height blocks
Fully filled cavityThe insulation thickness is such that the it will be in full contact with both leaves of masonry when the building meets normal construction tolerances.
Manufactured stone masonry unitFacing masonry unit having at least one exposed face with a close structure formed from either one or two homogeneous mixtures of aggregate, cementitious binder and other materials moulded under pressure and/or vibration and with or without further processing, intended to resemble and be used as an alternative to natural stone
MasonryAssemblage of masonry units laid in a specified pattern and joined together with mortar
Masonry unitPreformed component intended for use in masonry construction
Natural stone masonry unitMasonry unit manufactured from natural stone
Recessed jointsWhere the mortar is raked out, about 5 mm from the wall face. There are certain exposure
conditions where these should not be used (clause 6.1.6).
Work sizeSize of masonry unit specified for its manufacture, to which the actual size conforms within permissible deviations.