Architectural engineering on a London house project is the coordination of the building design with its structure, so one drawing set satisfies building control. For an extension or loft that means beams and calculations under Approved Document A, drawn together with the fire, stair and insulation details required by Parts B, K and L.
Architectural engineering sits between two disciplines. The architectural design decides what the extension or loft looks like and how the rooms work. The structural engineering decides whether it will stand up. On a domestic job in London both are usually needed, and the part that goes wrong is the junction between them: the steel that clashes with a rooflight, the insulation that has nowhere to go because a beam fills the ceiling zone, the new stair that loses its headroom under a floor that got deeper.
We treat those as one piece of work. Our architectural technologists produce the building design and the building regulations drawings, and the structural calculations are prepared as part of the same set, from the same survey. The result is a drawing package in which the beam schedule, the sections, the fire strategy and the thermal details all describe the same building.
That matters because building control does not approve a design in parts. An inspector reads the structural calculations against the drawings, checks the stair against Approved Document K and the insulation against Approved Document L, and asks questions wherever they disagree. Every disagreement costs time on site.
Schedule 1 to the Building Regulations 2010 sets out the legal requirements, and the Approved Documents give the government’s guidance on meeting them. A domestic extension or loft conversion drawing set normally has to answer at least four of them.
| Part of Schedule 1 | Approved Document | What the drawings must show |
|---|---|---|
| Part A: structure | Approved Document A | Beam and lintel sizes, bearings, padstones, foundations, calculations |
| Part B: fire safety | Approved Document B, Volume 1 | Escape routes, escape windows, protected stairs, fire-resisting doors |
| Part K: protection from falling | Approved Document K | Stair rise, going, headroom, guarding |
| Part L: conservation of fuel and power | Approved Document L, Volume 1 | Insulation build-ups meeting the limiting U-values |
Source: GOV.UK, Approved Documents, retrieved 12 September 2026.
Approved Document A is the structural one. It is where beam sizes, bearing lengths, lintels and foundation depths are justified, normally by calculation. The others are where architectural decisions have structural consequences: a protected stair enclosure changes where the loads come down, an insulation build-up changes the depth of the roof, and an escape window has to fit between the rafters or the dormer framing.
Rear and side return extensions. Opening the back of a terraced house into a new kitchen means removing load-bearing wall and replacing it with a beam, often a steel bearing on padstones in the party walls. The size of that beam sets the ceiling line of the new room and whether the bifold doors can run the full width. Our structural engineering drawings size it; the architectural drawings decide where it sits.
Loft conversions. New floor joists, new steels to carry the dormer, and a roof that is being altered rather than merely opened. Once the loft becomes a habitable storey, the house usually gains a floor more than 4.5 m above ground, and Approved Document B then expects a protected escape route down through the house. The stair headroom figures in Approved Document K and the roof U-value in Approved Document L are both decided by how deep the new structure is.
Garage conversions. The Planning Portal notes that converting a garage to habitable space will normally require approval under the building regulations. The door opening is filled, a lintel or beam may be needed over a new window, the existing slab is checked, and the floor and walls are brought up to current insulation standards.
Party walls. On a London terrace almost every beam bears on a shared wall, so the Party Wall etc. Act 1996 is usually in play. The structural drawings are what the neighbour’s surveyor will read, so we produce them before notices are served.
These are the numbers that most often decide whether a domestic set is approved first time. Each one has to be visible on the drawings, not just assumed.
| Requirement | Figure | Approved Document |
|---|---|---|
| Escape window, clear openable area | at least 0.33 m² | B, Volume 1 |
| Escape window, clear opening height and width | at least 450 mm each | B, Volume 1 |
| Escape window, bottom of opening above floor | no more than 1,100 mm | B, Volume 1 |
| Height of upper floor that changes the escape rules | 4.5 m above ground | B, Volume 1 |
| Stair headroom | 2.0 m | K |
| Loft stair headroom where 2.0 m is impossible | 1.9 m at centre, 1.8 m at side | K |
| New roof in an extension, limiting U-value | 0.15 W/m²K | L, Volume 1 |
| New wall or floor, limiting U-value | 0.18 W/m²K | L, Volume 1 |
| New window, limiting U-value | 1.4 W/m²K | L, Volume 1 |
Source: Approved Document B, Volume 1 (2019 edition, as amended), retrieved 12 September 2026; Approved Document K (2013), paragraph 1.13 and Diagram 1.4, retrieved 12 September 2026; Approved Document L, Volume 1 (2021 edition incorporating 2023 amendments), Table 4.2, retrieved 12 September 2026.
More on each is in our explainers for Part B fire safety, Part K stairs and Part L insulation.
Coordination fails quietly when two versions of a drawing circulate. The UK construction industry moved from BS 1192 and PAS 1192-2 to BS EN ISO 19650-1 and -2, published in 2018, and ISO 19650-2 requires every information container, meaning every drawing or document, to carry a unique ID. A domestic project does not need a full information management plan, but it does benefit from the same habit: every sheet numbered, every revision lettered, and one current issue sent to the builder, building control and the structural engineer at the same time.
Source: NBS, From BS 1192 to ISO 19650, retrieved 12 September 2026.
There are two sets of costs: our fees for the design, drawings and calculations, and the building control body’s charge for checking the plans and inspecting the work. You can use the local authority or an approved private building control body.
| Service | Our fee |
|---|---|
| Structural calculations | £350–£1,050 |
| SAP and Part L compliance | £105–£315 |
| Building control submission and inspections | £350–£665 |
| Complete package: planning and building regulations drawings with structural calculations | from £1,750 |
Source: our fees from the pricing page, retrieved 12 September 2026.
Local authority charges vary by borough. As one published London example, the London Borough of Havering’s 2026–27 schedule is below.
| Work (Havering, 2026–27) | Standard charge | Fast track |
|---|---|---|
| Garage conversion, up to 30 m² | £673 | £740 |
| Extension or loft conversion, up to 30 m² | £859 | £945 |
| Extension, 30–60 m² | £1,183 | £1,301 |
| Extension, 60–100 m² | £1,406 | £1,547 |
Source: London Borough of Havering, Building control fees 2026–2027, Table 2, retrieved 12 September 2026. The same charge applies to Full Plans and Building Notice. Fast track plans are checked within 10 working days. We have not confirmed whether the figures include VAT, and every London borough sets its own charges.
If the project also needs planning permission, that comes first. In England, 93% of householder applications in the year to March 2026 were decided within eight weeks or an agreed extension (MHCLG, retrieved 12 September 2026), and we usually prepare the engineered building regulations set while the application is being decided. See our building regulations drawings for what that set contains.
No. Structural engineering sizes the beams, columns and foundations. Architectural engineering, as we use the term, is the coordination of that structure with the rest of the design: the fire strategy, the stair, the insulation and the way the parts meet, so that one drawing set works for building control and for the builder.
Approved Document A, which gives guidance on Part A (structure) of Schedule 1 to the Building Regulations 2010. Building control will expect calculations for any new beam, lintel or foundation, and the drawings must show how each member bears.
Our structural calculations are priced from £350 to £1,050 depending on the number of members and connections. They are included in the Complete package, from £1,750, alongside the planning and building regulations drawings.
Often. Converting a garage to a habitable room will normally require building regulations approval, and replacing the garage door with a wall and window usually needs a new lintel or beam, a check on the existing foundation, and an insulated floor and wall build-up.
Approved Document K asks for 2.0 m of headroom over a stair. Where a loft conversion cannot achieve that, 1.9 m at the centre of the stair falling to 1.8 m at the side is accepted.
Tell us the project and the size of the opening or loft. We reply with a fixed fee for drawings and calculations.
Get a quoteYou can browse every service and area to find the right fit, or contact us to talk it through. When you are ready, get a quote today — most homeowners have a fee in minutes — or contact us about your project and an architectural technologist will be in touch.
