What Happens After Planning Permission Is Approved for a House Extension?
Planning permission doesn’t mean you can start building. It means you can start the three professional stages that have to happen before a builder ever picks up a tool: structural engineering, building regulations drawings, and appointing a builder. Only once all three are done does the actual build begin. Here’s what each stage involves, roughly how long it takes, and what Kirkwood does at each point.
Stage 1: Receive and File Your Planning Decision Notice
Your decision notice will come with conditions attached; materials, working hours, and boundary treatments are the ones that show up most often. All of them need to be satisfied at some point, whether that’s before work starts or during the build itself. Some are pre-commencement conditions, which means they have to be formally discharged with the council before anyone sets foot on site. Kirkwood goes through every condition on a client’s behalf and flags which ones need dealing with before the build can begin.
Stage 2: Appointing a Structural Engineer for Extension Work
This is the stage most homeowners don’t even know exists until they need it.
Once planning’s approved, a structural engineer for your extension takes the approved drawings and turns them into: foundation depth and specification, steel beam calculations for any wall removals or openings, floor joist sizing, and the roof’s structural design. Building Control won’t start inspections without this package, and no builder can quote accurately or start work without it either.
On cost: a structural engineer for a house extension in Essex typically charges £1,000 to £1,600 including VAT for a standard single-storey project. That covers foundations, steelwork, and the full set of building control drawings.
Kirkwood handles structural engineering in-house; the same team that produced the original drawings produces the structural package too, which closes the gap between design and structure that so often causes costs to creep up once work is underway on site.
Worth knowing: structural engineering only gets commissioned after planning approval, because the structural specification has to match whatever drawings the council actually approved.
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Kirkwood manages the structural engineering stage in-house as part of its complete service.
Stage 3: Building Regulations Drawings for a House Extension
Planning permission decides whether you’re allowed to build it. Building regulations decide how it actually has to be built. These are two completely separate processes; having approval for one tells you nothing about the other.
Building regulations drawings for a house extension form a detailed technical package: foundations, wall construction, roof build-up, insulation, ventilation, drainage, fire safety, and every structural element. These get submitted to building regulations control, either the council’s own department or a private approved inspector, for review before any work starts.
From there, Building Control inspects the work at set points as the build progresses: foundations before concrete goes in, steelwork before it gets covered up, insulation before plastering, and a final inspection once everything’s finished. Without a completion certificate from Building Control at the end of all that, you won’t be able to sell the property down the line.
Kirkwood produces the building regulations package in-house, running it alongside the structural engineering stage rather than after it, which shaves several weeks off the overall timeline.
Stage 4: Appointing a Builder
Once the structural engineering and building regulations drawings are both finished, the project’s actually ready for a builder. This is the right moment to start that search, not earlier, and definitely not during the design stage.
Here’s why the timing matters: only with a genuinely complete drawings package can a builder give you a fixed, itemised price. Without one, any quote is really just a guess dressed up as a number, based on assumptions that tend to turn into arguments once reality doesn’t match what was assumed. Get three builders quoting from the exact same finished package, though, and you’ve actually got something worth comparing.
Searching ‘extension builder Essex’ or ‘builder near me’ throws up a lot of names but not much certainty about quality. Kirkwood instead introduces clients to a small, hand-picked group of vetted local builders; their work gets checked, their past customers get spoken to, and they price from the complete drawings package rather than a rough guess. This introduction is built into Kirkwood’s design service, covering Chelmsford, Brentwood, Billericay, Wickford, Basildon, Rayleigh, Leigh-on-Sea, and Southend.
Stage 5: The Build and the Realistic Timeline
Roughly how long does this all take from the moment planning’s approved to the day the extension’s finished? Here’s a realistic breakdown:
Stage | Typical Duration | Notes |
Structural engineering and building regulations | 4 – 6 weeks | |
Building Control application processing | 5 – 8 weeks | Runs alongside structural stage |
Builder quotation and contract | 2 – 4 weeks | |
Build — single storey extension | 10 – 14 weeks |
Add it up, and you’re looking at somewhere around 5 to 7 months total, from planning approval through to a finished extension. The build phase itself depends heavily on the size of the project and whatever the builder’s own programme looks like; Kirkwood gives every client a realistic timeline upfront, based on their specific build, not a generic figure. For a fuller breakdown of what each stage costs, see our house extension costs guide.
One thing worth flagging early: if a party wall notice is needed, it should go out during the design stage or right after planning approval, not the week the builder’s due to arrive.
So: structural engineering, building regulations, appointing a builder, then the build itself- four stages, roughly 5 to 7 months, before you’re standing in a finished room. Kirkwood manages all three professional stages in-house as one coordinated service for homeowners across Chelmsford, Brentwood, Billericay, Wickford, Basildon, and Rayleigh, so you’re not left sourcing a structural engineer, a building regulations consultant, and a builder separately and hoping they all talk to each other properly. One team handles the lot.
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No, you don’t need a registered professional carrying that specific title for a house extension. What you do need is proper planning drawings, structural engineering, and building regulations drawings, and Kirkwood produces all three in-house for extensions across Chelmsford, Brentwood, Billericay, Wickford, Basildon, Rayleigh, Leigh-on-Sea, Southend, and the surrounding areas of Essex.
Frequently Asked Questions
What happens after planning permission is approved for a house extension?
Planning approval is not the green light to start building. It is the green light to start three further professional stages: structural engineering, building regulations drawings, and then builder appointment. These stages take approximately 3 to 5 months before the build can begin.
Do I need a structural engineer after planning permission?
Yes. Structural engineering is required after planning approval for almost all house extensions. The structural engineer works from the approved architectural drawings to produce foundation specifications, steel beam calculations, and structural drawings for Building Control. This stage costs from £1,000 to £1,600 including VAT for a standard single-storey extension.
How long after planning permission can I start building?
You cannot start building immediately after planning permission. Structural engineering and building regulations drawings must be completed first, and Building Control must receive the application before work begins. From planning approval to build start typically takes 3 to 5 months. The full project from planning approval to completion is usually 5 to 7 months.
What are planning conditions and do I need to comply with them?
Yes. Most planning approvals come with conditions attached, commonly covering materials, working hours, boundary treatments, or specific construction details. Some conditions are pre-commencement, meaning they must be formally discharged with the council before any work starts on site. Kirkwood reviews all planning conditions and advises which need to be dealt with before the build begins.
Do I need building regulations approval as well as planning permission?
Yes. Planning permission and building regulations are completely separate. Planning decides whether you can build it. Building regulations decide how it must be built. You need both. Building regulations drawings are submitted to Building Control after planning approval, and Building Control will inspect the work at key stages during the build.
When should I approach a builder after getting planning permission?
After the structural engineering and building regulations drawings are complete, not before. Only with a full drawings package can a builder provide an accurate, fixed, itemised quotation. Approaching a builder before this stage means getting estimates that are likely to change once the true technical requirements are known.
Can Kirkwood manage everything after planning permission is approved?
Yes. Kirkwood provides structural engineering, building regulations drawings, and vetted builder introduction as part of its complete service. All three stages are managed in-house by the same team, which means the transition from planning to build is coordinated rather than fragmented. Call 01268 944233 or book at kirkwoodbuild.co.uk/quick-quote/
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