External masonry walls


Bricks shall be capable of supporting intended loads and have appropriate resistance to the adverse effects of freeze/thaw and sulfate attack.

The design strength of bricks should comply with:

  • BS EN 1996-1
  • the design.

Table 3: Classification of clay bricks according to their freeze/thaw resistance and active soluble salt content in accordance with BS EN 771-1

DurabilityFreeze/thaw resistanceActive soluble salt content
F2,S2Freeze-/thaw-resistant (F2), durable in all building situations(S2) low
F2,S1Freeze-/thaw-resistant (F2), durable in all building situations(S1) normal
F1,S2Moderately freeze-/thaw-resistant (F1), durable except when saturated and subject to repeated freezing and thawing(S2) low
F1,S1Moderately freeze-/thaw-resistant (F1), durable except when saturated and subject to repeated freezing and thawing(S1) normal
F0,S2Not freeze-/thaw-resistant (F0), liable to be damaged by freezing and thawing(S2) low
F0,S1Not freeze-/thaw-resistant (F0), liable to be damaged by freezing and thawing(S1) normal

Calcium silicate and concrete bricks contain no significant active soluble salts. Information on their durability is given in this chapter.

Clay bricks

Bricks that are freeze-/thaw-resistant (F2,S2 or F2,S1 to BS EN 771) should be used where there is a high risk of prolonged wetting and freezing including:

  • external facing work in Scotland
  • exposed parts, including copings, sills, parapets and chimneys which have no overhang to provide protection.
  • areas of the country subject to exceptionally severe freeze/thaw exposure. See Clause 6.1.6.

In areas of severe freeze/thaw exposure outside Scotland, bricks that are moderately freeze-/thaw-resistant (F1,S1 or F1,S2 to BS EN 771) may be used for general wall areas, provided they are classified in the manufacturer’s published recommendations as satisfactory for the exposure.

Bricks that are not freeze-/thaw-resistant (F0,S2 or F0,S1 to BS EN 771) are not acceptable for use externally, unless completely protected by a cladding which can satisfactorily resist the passage of water.

Where brickwork may become saturated, moderately freeze-/thaw-resistant bricks (F1,S1 or F1,S2 to BS EN 771) are not appropriate where there is a risk of vulnerability to frost. In saturated conditions, sulfate-resisting cement mortar is required for S1 designation bricks.

For one and two storey homes, clay bricks to BS EN 771, with a minimum compressive strength of 9N/mm2 should be adequate.

For three storey homes; clay bricks to BS EN 771 with a minimum compressive strength of 13N/mm2 are acceptable.

Concrete bricks

Concrete bricks have a direct relationship between strength and durability, including freeze/thaw resistance. Most concrete bricks have a strength of 20N/mm2 and are durable in most situations. For copings and sills, bricks with a compressive strength of 36N/mm2 should be used.

Calcium silicate bricks

Calcium silicate bricks do not contain significant amounts of soluble sulfates and may be suitable where sulfate-bearing soil and ground water conditions exist. Where calcium silicate bricks are used, it should be in accordance with the manufacturer’s recommendations.

Bricks of compressive strength Class 20 (BS EN 771-2) are suitable for most applications.

Bricks of strength Class 30 and declared as freeze-/thaw-resistant to BS EN 771-2 are recommended in the following areas:

  • severe freeze/thaw exposure
  • where bricks may be persistently wet, e.g. parapets, chimneys, sills and below the DPC.

Reclaimed bricks

Reclaimed bricks:

  • should be used in accordance with Technical Requirement R3
  • should be considered as F1,S1 or F1,S2 to BS EN 771 and used accordingly
  • may require independent certification of suitability
  • may be unsuitable for external work because of a high salt content or a lack of freeze/thaw resistance
  • which have previously been used internally or which were fully protected may be unsuitable in external situations.

It is advisable to know where reclaimed bricks came from, and if they were used internally or externally.

Special shaped bricks

Special shaped bricks should conform to BS 4729.