Wall Construction Requirements for Masonry Buildings

What This Requirement Covers

Masonry construction (brick, block, and stone) is the most common form of wall construction in UK housing. Approved Document A Section 2C provides simplified rules for masonry walls in small buildings, while larger or more complex buildings require design to BS EN 1996 (Eurocode 6: Masonry Structures).

Key Requirements

Wall Thickness

Approved Document A simplified rules specify minimum wall thicknesses

1. External cavity walls: Minimum 90 mm inner leaf + cavity + 90 mm outer leaf (280 mm overall with standard cavity)
2. Internal load-bearing walls: Minimum 90 mm (100 mm blockwork is standard)
3. Separating (party) walls: Minimum 215 mm solid or two leaves of 100 mm with a cavity (also must meet Part E sound insulation and Part B fire resistance)
4. Single-leaf external walls: Minimum 190 mm (rare in modern construction)

Height and Length Limits

For the simplified rules to apply

1. Maximum building height: 15 metres to the ridge (12 metres to the eaves for 3-storey buildings)
2. Maximum wall length between returns or buttressing walls: varies by wall thickness and height (Diagram 9, Approved Document A)
3. Maximum storey height: 2.7 metres (floor to floor) for the simplified rules

Lateral Support

1. Floors and roofs must provide lateral restraint to walls at each storey level
2. Floor joists must be strapped to walls with 30 mm x 5 mm galvanised steel straps at maximum 2 metre centres
3. Straps must extend at least 300 mm over the floor structure
4. Roof trusses must be strapped to the wall plate and gable walls

Cavity Walls

1. Maximum cavity width: 100 mm for the simplified rules (wider cavities with full-fill insulation are common but may require engineering justification)
2. Wall ties must comply with BS EN 845-1 and be spaced at maximum 900 mm horizontally and 450 mm vertically (or 300 mm vertically within 225 mm of openings)
3. Cavity trays and weep holes must be provided above openings and at other locations where moisture could penetrate the inner leaf

Damp-Proof Courses

1. A damp-proof course (DPC) must be provided at least 150 mm above finished external ground level
2. DPCs must be continuous and lapped at junctions
3. Where internal floor levels are below external ground level, tanking or other damp-proofing measures are required

Practical Compliance Tips

1. Use the simplified rules for straightforward houses and small extensions; for anything outside the parameters, appoint a structural engineer
2. Ensure wall ties are correctly spaced and properly embedded in the mortar bed (minimum 50 mm embedment each side)
3. Check that cavity trays are correctly installed above lintels, at abutments, and at other locations specified in the design
4. Do not build masonry more than 1.5 metres above floor level in a single day to allow mortar to gain strength
5. Protect newly built masonry from frost, rain, and excessive drying during construction
6. Lateral restraint straps are frequently missed or incorrectly installed; check specification and spacing before plastering
7. Keep the cavity clean of mortar droppings that could bridge the cavity and transfer moisture to the inner leaf