Structural Stability Requirements Under Approved Document A

What This Requirement Covers

Approved Document A addresses the structural safety of buildings. Requirement A1 (Loading) requires that a building is designed and constructed so that the combined dead, imposed, and wind loads are sustained and transmitted to the ground safely. Requirement A2 (Ground movement) requires that the building is constructed so that ground movement does not impair its structural stability.

The Approved Document provides guidance on the use of British and European structural design standards (Eurocodes) and sets out the requirements for different building types and sizes.

Key Requirements

Loadings

All buildings must be designed for the following load types

1. Dead loads: The self-weight of the structure, finishes, and fixed equipment
2. Imposed loads: Loads from occupancy, furniture, and storage, as specified in BS EN 1991-1-1 (Eurocode 1)

- Residential floors: 1.5 kN/m² minimum - Office floors: 2.5 kN/m² minimum - Retail areas: 4.0 kN/m² minimum - Assembly areas: 5.0 kN/m² minimum

1. Wind loads: Calculated in accordance with BS EN 1991-1-4 (Eurocode 1, Part 1-4) based on location, terrain, building height, and shape
2. Snow loads: Calculated in accordance with BS EN 1991-1-3 based on location and altitude

Structural Design Standards

Buildings must be designed to the relevant Eurocodes

1. BS EN 1990: Basis of structural design
2. BS EN 1992 (Eurocode 2): Concrete structures
3. BS EN 1993 (Eurocode 3): Steel structures
4. BS EN 1995 (Eurocode 5): Timber structures
5. BS EN 1996 (Eurocode 6): Masonry structures

Small Buildings (Traditional Construction)

Approved Document A provides simplified rules for small buildings of traditional construction (Section 2C)

1. Houses and other small buildings up to 3 storeys and 15 metres in length
2. Minimum wall thickness: 90 mm for internal walls, 190 mm for external cavity walls (combined leaf thicknesses)
3. Minimum foundation width based on soil type and wall loading (Table 10)
4. Lateral support from floors and roofs at maximum intervals specified in the tables
5. These simplified rules do not apply to buildings on problem soils (shrinkable clay, former mining areas, etc.)

Disproportionate Collapse

1. Class 1 buildings (houses up to 4 storeys): No additional measures required beyond normal design
2. Class 2A buildings (5-storey residential, 4-storey office): Horizontal ties required
3. Class 2B buildings (6-15 storey residential, hospitals, public buildings): Horizontal and vertical ties, or alternative load path analysis
4. Class 3 buildings (buildings over 15 storeys or of unusual form): Systematic risk assessment required

Practical Compliance Tips

1. For simple houses and extensions, the simplified rules in Section 2C of Approved Document A may be sufficient without full structural calculations
2. For anything beyond simple traditional construction, appoint a structural engineer
3. Ensure the structural engineer's design is based on current Eurocodes with UK National Annexes
4. Foundation design must account for local ground conditions; obtain a ground investigation report for anything other than straightforward sites
5. Submit structural calculations to Building Control with the full plans application; late submission causes delays
6. Pay attention to lateral restraint; floors and roofs must be adequately connected to walls to provide stability
7. Disproportionate collapse provisions are frequently missed; check the building classification early in design