Approved Document A (Structure): What Homeowners Need to Know

Part A deals with three main structural concerns:

• Loading — ensuring floors, walls and roofs can carry the loads placed on them (people, furniture, snow, wind).
• Ground movement — foundations must be deep and wide enough to avoid settlement, especially on clay soils that shrink in dry weather.
• Disproportionate collapse — larger buildings must be designed so that local damage (e.g. a gas explosion) doesn’t trigger a catastrophic chain failure.

The document references British Standards (primarily BS EN 1990–1997, the Eurocodes) and provides simplified rules for small residential buildings so that not every minor project needs a full engineering calculation.

Virtually any building work that affects the structure of your home needs to comply with Part A. Common projects include:

• Rear and side extensions — new foundations, structural lintels over openings, and connections to the existing structure all fall under Part A.
• Loft conversions — adding floor joists, a new staircase opening, and dormer windows all impose new loads on the existing building.
• Removing load-bearing walls — an RSJ (steel beam) or concrete lintel must be correctly sized by calculation; guesswork is not acceptable.
• New storeys — adding a storey requires checking that existing walls and foundations can take the additional weight.
• Garage conversions — if the garage wall is load-bearing, structural work is needed before removing it.

For straightforward single-storey rear extensions, your architect or building designer may be able to specify standard elements (e.g. a catalogued steel lintel) without a full structural calculation. However, for any of the following, a structural engineer is strongly recommended:

• Removing or partially removing a load-bearing wall
• Loft conversions involving hip-to-gable or dormer extensions
• Extensions on poor ground conditions (clay, fill, near trees)
• Adding a storey to an existing property
• Any project where the building control officer requests calculations

Structural engineer fees typically range from £300–£1,500 for a residential project, depending on complexity. This is nearly always money well spent.

There are two main routes to building control approval. For structural projects, Full Plans is usually the right choice:

• Full Plans — you submit detailed drawings and structural calculations before work starts. Building control checks and approves the plans. If they approve, you have certainty the design meets regulations before a brick is laid.
• Building Notice — you notify building control and start work, with inspections as you go. No plans are approved upfront. This is riskier for structural work because you might build something that later fails inspection and needs to be altered or demolished.

For simple non-structural projects (e.g. a new bathroom), a Building Notice is fine. For anything involving beams, foundations, or load-bearing walls, Full Plans protects you.

Your building control officer (BCO) — from your local authority or an approved inspector — will carry out a series of site inspections at key stages. For structural work, the most important are:

• Foundation inspection — before concrete is poured, the BCO checks depth and width of trenches.
• Oversite inspection — checks damp-proof membrane and ground floor construction.
• Frame/beam inspection — checks steel beams, timber frames and connections match the approved drawings.
• Final inspection — a check that all work is complete and a completion certificate is issued.

Never cover up structural elements before they have been inspected — if you do, building control may require you to open up the work at your own expense.

The most common Part A problems encountered on residential projects are:

• Undersized lintels — a lintel that spans a new opening must be calculated for the load above it. Always get the size confirmed by an engineer or building control.
• Shallow foundations — in clay soils, foundations often need to be 1 metre deep or more to avoid heave and shrinkage movement. The BCO will check this before concrete is poured.
• Inadequate beam bearing — steel beams must have adequate ‘bearing’ (the length of wall supporting each end). Typically a minimum of 150 mm each end.
• Roof spread — older cut-timber roofs can spread outward under load. A loft conversion must address this, often with a structural ridge beam or collar ties.