A typical single-storey extension takes 10–16 weeks to build once on site. Including design, planning and Building Regulations, allow 6–9 months from initial consultation to moving in. A double-storey extension typically takes 16–24 weeks on site, with an overall programme of 9–14 months.
Initial Consultation & Design — Site visit, brief development, design drawings produced and agreed.
Planning Permission — Standard householder applications are determined within 8 weeks. In practice, allow 10–13 weeks. Permitted Development projects skip this stage entirely.
Building Regulations & Structural Design — Structural engineer produces drawings. Building Regulations application submitted and approved.
Construction on Site — Groundworks, structural build, roofing, first fix, second fix, finishing. 10–16 weeks for single-storey; 16–24 weeks for double-storey.
| Extension Type | On-Site Build Time | Total Programme (incl. planning) |
|---|---|---|
| Single-storey rear extension | 10 – 16 weeks | 6 – 9 months |
| Double-storey extension | 16 – 24 weeks | 9 – 14 months |
| Side return extension | 8 – 14 weeks | 5 – 8 months |
| First-floor extension | 12 – 20 weeks | 7 – 12 months |
| Wrap-around extension | 16 – 26 weeks | 9 – 15 months |
The local authority has 8 weeks to determine a householder application, but delays caused by consultation responses, requests for additional information, or officer workload can extend this to 12–16 weeks. In Hull, this is handled by Hull City Council; in the surrounding villages, by East Riding of Yorkshire Council.
Unexpected ground conditions — soft soil, high water tables, tree roots or existing services — can require additional foundation engineering and groundwork time. A trial pit investigation before finalising the design can identify these issues early and prevent costly delays during the build.
The structural steel required to open up the rear wall of the existing house has a lead time for fabrication and delivery, typically 2–4 weeks. Good contractors order this well in advance of when it’s needed so it doesn’t hold up the programme.
Bifold doors, large glazed roof lanterns and bespoke windows often have lead times of 6–12 weeks. These need to be specified, ordered and paid for well before installation is required on site.
Changes made during the build — to layouts, specifications or finishes — are one of the most common causes of programme delay. Finalising all decisions before work starts is the single most effective way to keep the project on track.
T3 Developments manages every trade in-house as a single team, which eliminates the coordination gaps that cause delays when homeowners manage multiple contractors independently. Kegan oversees the programme personally, orders materials and specialist items ahead of schedule, and communicates proactively with clients so there are no surprises.
Planning an extension in Hull or East Yorkshire? T3 will visit the site, talk you through the programme and give you a straight price — no commitment required.
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