Above-ground unreinforced masonry, nominally reinforced masonry where vertical joints in adjacent courses are aligned [see Article 9.20.9.1.], loadbearing masonry of buildings of more than one storey in regions where the spectral response acceleration S_a(0.2) is greater than 0.55 that are reinforced in accordance with Sentence 9.20.1.2.(1), and loadbearing masonry of 3-storey buildings in regions where the spectral response acceleration S_a(0.2) is greater than 0.35 and less than or equal to 0.55 that are reinforced in accordance with Sentence 9.20.1.2.(2), made with cellular (foamed) concrete blocks, in buildings to which Part 9 applies [see Sentence 1.3.3.3.(1) of Division A for application of Part 9]:

• where the wall height above the foundation wall does not exceed 11 m, and
• in which the roof or floor system above the first storey is not of concrete construction.

Exceptions: 

To limit the probability of an inadequate resistance to sulfate attack or stresses resulting from water absorption and freeze-thaw cycling.

This is to limit the probability of compromised structural integrity, which could lead to:

• structural failure of masonry construction,
• where masonry construction is part of an environmental separator, the excessive deformation, displacement or failure of required environmental separation elements, which could lead to deterioration, which could lead to further compromised structural integrity, and
• in assemblies exposed to moisture or the exterior, damage and deterioration, which could lead to further compromised structural integrity.

This is to limit the probability of harm to persons.