For a full plans application on a London extension, building control needs construction drawings, not planning drawings: sections through the walls, floor and roof with every layer named, details at the junctions, a written specification covering structure, fire, insulation, ventilation and drainage, and structural calculations for any beam or lintel. We draw that set from a fresh survey for £545 drawings + £150 survey (£695 total), and building control is expected to decide a full plans application within 5 weeks, or 2 months with your consent (GOV.UK).
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The planning drawings that got you permission are the starting point, not the submission. Building control does not judge how the extension looks; it checks that it will stand up, keep heat in, let stale air out, and give people time to escape a fire.
What sheets go into a full plans set?
Plans, existing and proposed, at 1:50, with the new walls, the steel positions, the drain runs, the extract fans and the smoke alarms marked. These are developed from the planning plans, not copied.
Sections, at least one cut through the extension and into the existing house, showing the foundation depth, the floor build-up, the wall build-up, the roof build-up and the ceiling heights.
Details, at 1:10 or 1:5, where most defects start: the eaves, the threshold to the garden, the steel bearing on the old brick wall, the junction of the new flat roof with the existing back wall, and any parapet on the boundary.
Specification notes, organised by the parts of the regulations, naming the materials and the standards they meet.
Structural calculations from an engineer, for every beam, lintel and padstone. Part A sets three requirements, covering loading, ground movement and disproportionate collapse (Schedule 1), and the calculations are the proof. Our structural calculations are co-ordinated with the drawings.
What does building control check under Part L, B and F?
Part L, energy. For a new extension the walls must reach 0.18 W/(m2.K), the roof 0.15 and the floor 0.18 (Approved Document L, Table 3.2). Windows, rooflights and doors must not exceed 25% of the extension's floor area, plus any openings it removes (paragraph 10.8(d)). That 25% limit catches many London kitchen extensions with full-width sliding doors and a large roof light; above it, the drawings need an area-weighted U-value check or a SAP calculation, which our SAP cost post covers.
Part B, fire. Smoke alarms must be mains powered with a standby supply, at Grade D2 Category LD3 as a minimum (Approved Document B Volume 1). An open-plan kitchen that removes the wall between the hall and the back room changes the escape route, and the drawings must show how that is handled. For a loft, Part B is the heaviest part of the set; see our loft fire safety guide.
Part F, ventilation. Extract fans in the kitchen and any new bathroom, background ventilators in the windows, and purge ventilation for rooms that lose an openable window when the extension covers it. The drawings mark each one.
Parts C (moisture), H (drainage), K (glazing and falls) and M (access) also show up as notes.
What changes on a London house?
Three things come up again and again on the capital's Victorian and Edwardian terraces and semis.
Old solid walls. Most pre-1919 London houses have solid brick walls, not cavities. The new extension is built to current U-values, but the junction with the old wall, and any wall you open up, needs a detail showing how moisture and cold bridging are handled.
Shared drains. London terraces often share a drain run behind the houses. If the extension sits over or near it, the drawings must show its position, and the sewerage company's consent may be needed to build over it. That is another reason to survey first.
The party wall. A steel beam bearing on the party wall, or a new foundation dug close to the neighbour's, brings the Party Wall Act into play. Building control does not deal with it, but your drawings need to show what is happening at the boundary, and our party wall service serves the notices.
What gets a full plans application sent back?
Building control can approve, approve with conditions, or reject. Rejections and conditional approvals on London extensions usually trace back to gaps the drawings could have closed:
- A beam with no calculation, or a calculation for a different span from the one drawn.
- No bearing detail showing how the new steel sits on old brickwork, with the padstone size.
- Insulation named but not sized, so the U-value cannot be checked against Table 3.2.
- Glazing above 25% of the floor area with no area-weighted or SAP check to support it.
- No ventilation strategy for the back room that loses its only window when the extension is built.
- The drain not shown, when the extension sits over the shared run behind a terrace.
Each one is cheaper to answer on the drawing than to argue about on site. A conditional approval lets work start, but the conditions still have to be met, usually by sending the missing information before that part is built.
Do I need full plans, or is a building notice enough?
Before work starts you must give either a building notice or deposit full plans (regulation 12). GOV.UK describes the building notice as "only for smaller projects" (GOV.UK).
| Full plans | Building notice | |
|---|---|---|
| Drawings checked before work | Yes | No |
| Expected decision time | 5 weeks, or 2 months with consent | None; checks happen on site |
| Builder prices from approved drawings | Yes | From whatever drawings you have |
| Risk on site | Lower | Higher: the inspector may ask for changes to work already built |
On a London extension with a new steel opening the back of a terrace, we recommend full plans. A building notice suits a small, simple job where the builder knows exactly what to do.
You can also use a private registered building control approver instead of the council (GOV.UK); they work from an initial notice, but still expect the same construction drawings.
Frequently asked questions
Can I send my planning drawings to building control? You can send them, but they will not be enough for full plans approval. They show no construction, no insulation thickness and no beam sizes.
Who pays the building control fee? You do, directly to the council or the private approver. Our fee covers the drawings and the submission; the building control charge is set by the body you choose.
Do I need building control drawings if I don't need planning? Yes. Permitted development removes the planning application, not building regulations. Our regs and structural package is for exactly that case, at from £945 drawings + £150 survey (£1,095 total).
What if building control asks for changes? We revise the drawings to answer the comments and send them back; tell us at quote stage if your approver is already known.
