Approved Document A: Structure – Building Regulations 2010 Compliance Guide
Approved Document A provides practical guidance on meeting the structural requirements of the Building Regulations 2010 for building work carried out in England. This 2004 edition incorporates amendments made in 2004, 2010, and 2013. It sits under the wider legal framework of Schedule 1 to the Building Regulations, specifically addressing Requirement A1 (Loading), Requirement A2 (Ground movement), and Requirement A3 (Disproportionate collapse). While primarily for use in England, it also applies to specific excepted energy buildings in Wales as defined by the Welsh Ministers (Transfer of Functions) (No. 2) Order 2009.
The document is divided into five primary sections covering codes and standards for all building types, sizing for traditional construction, wall cladding, roof coverings, and measures to reduce sensitivity to disproportionate collapse. It defines essential technical terms such as Dead load, Imposed load, Wind load, Buttressing wall, and Key elements. For buildings of traditional construction, it provides specific rules for structural elements including timber floors, masonry walls, and foundations of plain concrete. The document also lists the specific British Standards and Eurocodes required for structural design, such as BS EN 1990 for the basis of structural design and BS EN 1991 for actions on structures.
The following sections detail the technical provisions for structural stability, material specifications, and the various consequence classes used to determine the necessary level of robustness against accidental damage. These guidelines serve as a reference for ensuring that buildings sustain and transmit loads safely to the ground without impairing the stability of the structure or adjacent buildings.
Loading and Ground Movement Requirements
Requirements A1 and A2 establish the fundamental necessity for buildings to sustain dead, imposed, and wind loads and transmit them safely to the ground. This must be achieved without causing deformations that impair the stability of any part of another building.
- Dead load: The weight of all walls, partitions, floors, roofs, finishes, and permanent services.
- Imposed load: Loads produced by occupancy, including movable partitions and snow, but excluding wind.
- Ground movement: The structure must resist movement caused by swelling, shrinkage, or freezing of subsoil, as well as foreseeable land-slips or subsidence.
Sizes of Structural Elements for Traditional Construction
Section 2 provides specific sizing rules for residential buildings of not more than three storeys and small non-residential buildings. These rules apply to traditional masonry construction and timber members.
- Wall Thickness: Determined by the height and length of the wall as specified in Table 3. For example, a solid external wall not exceeding 3.5m in height and 12m in length must have a minimum thickness of 190mm.
- Timber Members: Sizing for floors and roofs (excluding trussed rafters) refers to TRADA span tables or BS EN 1995-1-1.
- Cavity Walls: Leaves must be at least 90mm thick with cavities at least 50mm wide, using austenitic stainless steel wall ties conforming to BS EN 845-1.
- House longhorn beetle: Softwood timber in specific geographical areas, such as the Borough of Woking or Borough of Surrey Heath, must be treated to prevent infestation.
Foundations of Plain Concrete
Section 2E outlines design provisions for strip foundations on various ground types, including rock, gravel, sand, and clay. Foundations must be situated centrally under the wall.
- Minimum Depth: Foundations should have a minimum depth of 0.45m to the underside to avoid frost action, except when founded on rock.
- Shrinkable Clays: In clay soils subject to volume change, depths must not be less than 0.75m for low shrinkage, 0.9m for medium, and 1.0m for high shrinkage clays.
- Strip Width: Minimum widths range from the width of the wall for rock to 850mm for firm clay under a 70kN/linear metre load, as detailed in Table 10.
Reducing Sensitivity to Disproportionate Collapse
Requirement A3 ensures buildings do not suffer collapse to an extent disproportionate to the cause of an accident. Compliance is determined by the Consequence Class of the building.
- Class 1: Includes houses not exceeding 4 storeys; standard design and construction for A1 and A2 are typically sufficient.
- Class 2a (Lower Risk): Includes 5-storey single occupancy houses and offices not exceeding 4 storeys; requires effective horizontal ties.
- Class 2b (Upper Risk): Includes hotels and flats between 4 and 15 storeys; requires horizontal and vertical ties or notional removal checks.
- Class 3: High-risk buildings like grandstands for over 5000 spectators; requires a systematic risk assessment.
- Key Elements: Members designed to sustain an accidental design loading of 34kN/m² applied in any direction.
Frequently Asked Questions
What are the requirements for Requirement A1 regarding loading?
The building must be constructed so that dead, imposed, and wind loads are sustained and transmitted safely to the ground without causing instability in the building or adjacent structures.
What defines a material alteration for roof re-covering?
A structural check is required if the new roof covering increases the loading on the roof by more than 15% compared to the original construction.
Which geographical areas are at risk from the house longhorn beetle?
Specified areas include the Boroughs of Elmbridge, Runnymede, Spelthorne, Surrey Heath, Woking, and parts of Bracknell Forest, Hart, and Rushmoor.
How is the minimum thickness of a masonry wall determined for a small building?
It is determined based on the wall's height and length using Table 3, with solid walls in coursed brickwork required to be at least 1/16 of the storey height.
What is the maximum permitted span for a floor supported by a wall under Section 2?
The maximum span for any floor supported by a wall is 6m, measured centre to centre of bearing as shown in Diagram 10.
When is a building classified as Consequence Class 2b?
Class 2b includes hotels, flats, and apartments between 4 and 15 storeys, hospitals not exceeding 3 storeys, and public buildings with floor areas between 2000m² and 5000m².
What is the accidental design loading requirement for a 'key element'?
A key element must be capable of sustaining an accidental design loading of 34kN/m² applied horizontally and vertically, one direction at a time.
What are the rules for foundations in shrinkable clay soils?
Foundations must be taken to a depth where anticipated ground movements will not impair stability, with minimum depths of 0.75m to 1.0m depending on the clay's shrinkage potential.
