Summary
- Part A (Structure) requires the building to safely sustain and transmit all loads to the ground without impairing stability — on domestic jobs this usually means engineer's calculations for beams, lintels, foundations and removed walls.
- Under the Building Safety Act 2022, the Principal Designer (BSA) must take all reasonable steps to ensure the design, if built, would comply with Part A — you need a documented evidence trail, not just a structural engineer's appointment.
- The highest-risk domestic moments are loft conversions (new floor loads), open-plan knock-throughs (steel beams and padstones) and extensions near trees (foundation depth).
What the Building Safety Act requires for Part A on non-HRB domestic jobs
Requirement A1 (loading), A2 (ground movement) and A3 (disproportionate collapse) apply to every extension, loft conversion and structural alteration, however small. Since the Building Regulations etc. (Amendment) (England) Regulations 2023 came into force on 1 October 2023, the Principal Designer under the Building Safety Act 2022 must plan, manage and monitor the design work so that, if built, it would comply with all relevant requirements — Part A included.
In practice that means you cannot simply pass structure to a consulting engineer and forget it. As PD you should record who is designing each structural element, confirm the engineer's competence, and hold the calculation package, beam schedules and connection details in your project evidence log so you can demonstrate coordination if Building Control or a future purchaser's solicitor asks.
For domestic clients, remember that if no PD is formally appointed in writing, the duties default to the designer in control of the design phase — usually you. An unmanaged Part A trail is exactly the kind of gap that surfaces when a cracked lintel becomes a claim.
Key design risks and evidence needed (RIBA Stages 2–4)
- Stage 2 (Concept): flag load-bearing walls proposed for removal, roof structure changes for lofts, and proximity of trees/drains to new foundations. Record assumptions to be verified by the structural engineer.
- Stage 3 (Spatial Coordination): confirm beam zones, padstone positions and steel sizes are coordinated with services and head heights; log the engineer's preliminary calculations against each element.
- Stage 4 (Technical Design): hold the full calculation package — beam and lintel schedules, wall tie specification, foundation design, connection details — cross-referenced to drawings. This is the package Building Control will assess and the golden-thread record you keep.
Standards and references you should be citing
- BS EN 1990–1997 (Eurocodes 0–7) — the design basis for structural calculations submitted with full plans applications.
- BS 8103 (Structural design of low-rise buildings) — the simplified route many domestic engineers use for masonry and timber elements.
- BS EN 845-1 — specification for wall ties, tension straps and hangers; record the declared type in your specification, not just "stainless ties".
- BRE guidance and NHBC Standards Chapter 4.2 for foundation depths near trees on shrinkable clay.
Evidence log: what Building Control expects vs what protects you
| Element | Minimum for Building Control | What a defensible PD evidence log holds |
|---|---|---|
| Steel beams / lintels | Engineer's calcs with application | Calc revision history, padstone details, drawing cross-references, engineer's PI confirmation |
| Foundations | Depth agreed on site with inspector | Trial pit/soil notes, tree survey, agreed depth recorded with date and inspector name |
| Wall ties & restraint | Noted on drawings | BS EN 845-1 specification clause plus site photo evidence at construction stage |
| Removed walls | Beam calc | Load-path sketch, temporary works note, party wall award reference where relevant |
Common pitfalls that catch out sole practitioners
- Assuming the structural engineer carries the Part A duty — the PD (BSA) coordination duty stays with you, and "the engineer did the calcs" is not a coordination record.
- No written trail for foundation depths agreed verbally on site during footing inspections.
- Lintel schedules that never get updated when window openings change at Stage 4.
- Loft conversions where the new floor is designed but the trimming around the stair opening and the wind post at the gable are left to "builder's detail".
Frequently asked questions
Do I need structural calculations for a single-storey domestic extension?
Almost always yes for any new openings, beams or lintels beyond simple catalogue lintels within their published span tables. Building Control will expect calculations to BS EN Eurocodes or BS 8103 for beams, and the Principal Designer (BSA) should hold them in the project evidence log with drawing cross-references.
As the architect, am I responsible for Part A if a structural engineer designs the structure?
The engineer is responsible for their design as a designer under the BSA 2022, but if you are the Principal Designer you retain the duty to plan, manage, monitor and coordinate design work so the project as a whole complies. You should record the engineer's scope, competence and outputs — coordination is your evidence, not theirs.
Does Part A apply differently to non-HRB buildings?
The functional requirements are the same, but non-HRB projects avoid the Gateway 2/3 approval process entirely. Compliance is demonstrated through your chosen Building Control route, supported by the design evidence the PD coordinates.
Track this natively instead of in Word templates
PD Pathway gives small practices an automated Parts A–T relevant-requirements tracker, stage-by-stage Principal Designer checklists and one-click compliance documents — built strictly for non-HRB projects. First project free, then from £10 per project or £99/yr unlimited.