Approved Document A Frequently Asked Questions – Structural Compliance Guidance
The Approved Document A Frequently Asked Questions is a technical guidance document issued by the Department for Communities and Local Government (now the Department for Levelling Up, Housing and Communities) in March 2016. It serves as a formal clarification for the structural requirements set out in the Building Regulations 2010 for England and Wales. The document provides interpretations of Approved Document A: Structure, specifically addressing common queries from developers, structural engineers, and homeowners regarding the technical application of structural standards.
The scope of this guidance includes technical specifications for timber sizes, the regulatory process for unauthorised building work, and specific engineering requirements for foundations and basements. It defines the necessary compliance pathways for projects involving loft rooms, single storey extensions, and first floor conservatories. The document also directs users to external authoritative standards such as those from the Timber Research and Development Association (TRADA), the British Standards Institution (BSI), and the National House Building Council (NHBC).
The following sections provide structured details on structural member sizing, retrospective certification procedures, and the impact of soil conditions on foundation design as outlined in the official FAQ text.
Structural Timber Member Sizing
Specific timber sizes for floor joists and roofing members are no longer directly contained in the current version of Approved Document A. Instead, designers and contractors must refer to established industry span tables and British Standards.
- TRADA Guidance: ‘Span tables for solid timber members in floors, ceilings and roofs (excluding trussed rafter roofs) for dwellings’ published by TRADA Technology Ltd.
- British Standards: BS 8103 Part 3 2009 ‘Structural design of low-rise buildings – Code of practice for timber floors and roofs for housing’.
Retrospective Building Regulations Consent
When structural work, such as a loft room construction, is carried out without prior approval, a formal retrospective application is required to ensure the work meets safety standards.
- Regularisation Certification: Property owners must apply to the local authority Building Control office for a certificate covering unauthorised building work.
- Verification Procedures: The process may require exposing covered work, such as verifying the size of a steel beam or the spacing of floor joists, which can be disruptive to the existing structure.
Basement and Foundation Requirements
The construction of basements and deep foundations involves complex planning and structural considerations, particularly in areas with sensitive soil conditions.
- Basement Approval: Both Planning Permission and Building Regulations approval are required for new-build or retrofit basements.
- Foundation Depths: Foundations may need to exceed standard depths (e.g., reaching 2.5 metres) when situated near high-water-demand trees like the Lombardy poplar.
- Soil Type: The design must account for shrinkable clays and highly plastic sub-soil, which are susceptible to movement.
- Engineering Solutions: Options for difficult ground include mini piles for reduced spoil or a rigid reinforced raft foundation designed to accommodate differential movements.
Conservatories on Elevated Extensions
The placement of a conservatory on top of a first-floor extension is subject to specific regulatory oversight to ensure structural integrity and neighbor privacy.
- Planning Permission: Consent must be granted by the Local Authority.
- Building Control: The project must satisfy all relevant parts of the Building Regulations, as first-floor conservatories are not exempt from these requirements.
Frequently Asked Questions
Where can I find timber sizes for floor joists and roofing members?
These sizes are found in the TRADA publication 'Span tables for solid timber members' or in British Standard BS 8103 Part 3 2009.
How do I get Building Regulations approval for work already completed?
You must apply for a Regularisation Certification for the 'unauthorised building work' through your local authority Building Control office.
Does a new basement require planning permission?
Yes, basements require both Planning Permission and Building Regulations approval whether they are part of a new house or a retrofit.
Why would building control require foundations to be 2.5 metres deep?
This depth may be required due to nearby mature trees with high water demand, such as Lombardy poplars, in areas with shrinkable clay soils.
What are the benefits of using mini piles for an extension?
Mini piles are often an economic solution as they are quick to place, produce less spoil for disposal, and use less foundation concrete.
Are conservatories built on the first floor exempt from Building Regulations?
No, conservatories located at first-floor level are not exempt and must comply with all relevant parts of the Building Regulations.
Who provides technical standards for foundation design in various sub-soil situations?
Information is published by the National House Building Council (NHBC) Technical Standards and the Building Research Establishment (BRE).
