Contents
The Typical Timeline Stage by Stage
- **Stage 1: Early design and feasibility — 4–8 weeks**
- The design process begins with briefing an architect (or design-and-build contractor) on the desired outcome. At this stage:
- •Initial concept design and feasibility assessment
- •Pre-application planning enquiry (optional but recommended for complex schemes)
- •Confirmation of planning route (permitted development vs. full planning application vs. Prior Approval)
- •Structural feasibility
- •Party wall consideration — which notices need to be served, and to whom
- **Stage 2: Planning application (where required) — 10–16 weeks**
- A standard householder planning application takes approximately 8 weeks to determine once submitted. Allow 2–4 weeks for drawings and application preparation before submission, then:
- •8 weeks statutory determination period (some authorities take 10–13 weeks)
- •Plus time for any amendments or additional information requested by the officer
If the scheme is permitted development (and Prior Approval is not required), this stage is eliminated or reduced to a Prior Approval application (approximately 6 weeks).
If the scheme requires Listed Building Consent (in addition to or instead of planning permission), allow an additional 4–8 weeks.
- **Stage 3: Technical design — 4–8 weeks (overlapping with planning)**
- While the planning application is being determined, the architect develops the technical design to a level sufficient for Building Regulations and contractor tendering:
- •Structural engineer input (beam and foundation design)
- •M&E (mechanical and electrical) coordination
- •Specification of materials and finishes
- •Building Regulations application
- **Stage 4: Party wall — 8–16 weeks (overlapping with planning and technical design)**
- Party wall notices should be served as early as possible — the 2-month minimum notice period for a party structure notice means that serving the notices during the planning stage can avoid delays at the construction stage. Where an Award is required:
- •Notice period: 2 months (or 1 month for excavation notices)
- •Award preparation: 4–8 weeks after notice period expires (if Award required)
- **Stage 5: Tendering and appointment of contractor — 3–6 weeks**
- Once planning permission is in place, technical design is complete, and party wall notices are in hand:
- •Tender documents sent to 2–3 contractors
- •2–3 weeks for contractors to price
- •1–2 weeks for evaluation and negotiation
- •Contract signed
- **Stage 6: Pre-construction — 2–4 weeks**
- Between contract award and start on site:
- •Building Regulations application submitted or approved inspector appointed
- •Material ordering (long-lead items — steels, glazing, windows may have 6–12 week lead times)
- •Scaffold booking
- •Utility isolation arrangements
- **Stage 7: Construction — 10–20 weeks on site**
- Construction programme for a standard rear extension:
- •Demolition and enabling works: 1–2 weeks
- •Foundations and groundworks: 2–3 weeks
- •Structure (brick/blockwork or steel frame): 3–5 weeks
- •Roof and weatherproofing: 2–4 weeks
- •First-fix M&E: 2–3 weeks
- •Plastering and screeds (plus 2–4 weeks drying time): 4–6 weeks total
- •Second-fix, kitchen installation, finishes: 4–6 weeks
- •Decoration and completion: 2–3 weeks
A simple single-storey rear extension: 10–14 weeks on site. A more complex scheme (structural openings, full kitchen replacement): 14–20 weeks.
**Total from first instruction to practical completion:**
- •**Simple extension, permitted development, no party wall complications:** 6–10 months
- •**Extension requiring full planning permission, party wall agreements, and comprehensive kitchen refurbishment:** 12–18 months
- •**Complex scheme (listed building, multiple neighbours, contested party wall):** 18–24+ months
The Factors That Cause Delay
Understanding what causes delay helps manage expectations and, in some cases, take steps to reduce the risk.
- **Planning delays:**
- •Many London boroughs consistently determine applications beyond the 8-week statutory target
- •Applications requiring neighbour consultation or committee determination take longer
- •Requests for additional information or amended drawings add weeks to the process
- •Conservation area or listed building consent applications are frequently slower than standard applications
- **Party wall delays:**
- •Adjoining owners who do not respond promptly, or who instruct difficult surveyors, can extend the Award process significantly
- •Multiple adjoining owners require multiple separate Award processes
- •Adjournments (for example, when the adjoining owner's surveyor is unavailable) add weeks
- **Contractor availability:**
- •Good London contractors are typically 2–4 months ahead in their programme
- •If the contractor must start immediately on contract award, the choice of contractors is limited
- •Building in some flexibility in the start date allows access to better quality contractors who are already committed
- **Long-lead materials:**
- •Structural steel may have a 4–8 week lead time
- •Glazing (bifold doors, rooflights) may have a 6–12 week lead time
- •Bespoke joinery may have an 8–16 week lead time
- •Ordering these items before construction starts (once the specification is fixed and the contractor is appointed) avoids on-site delays waiting for materials
- **Client decisions:**
- •Client decisions on tile selections, flooring, finishes, hardware, and fixtures are a very common cause of on-site delay
- •Agreeing a decision schedule with the contractor before works start (including when each decision is needed by) reduces this risk
Frequently Asked Questions
How long does a London rear extension take from start to finish?▼
A simple single-storey rear extension in London that is permitted development (no full planning application required) typically takes 6–10 months from first instruction to practical completion. An extension requiring full planning permission, party wall agreements, and a comprehensive kitchen refurbishment typically takes 12–18 months. The construction stage itself is typically 10–16 weeks on site.
When should I serve party wall notices for a London extension?▼
As early as possible — ideally at the same time as or shortly after the planning application is submitted. The 2-month minimum notice period for a party structure notice means that serving it early (while planning is being determined) ensures that the party wall process is not on the critical path of the project. If the notices are left until planning permission is granted, they add a minimum of 2 months to the timeline before construction can start.
How long do I need to wait between planning permission and building starting?▼
There is no statutory minimum waiting period between planning permission and construction starting (provided party wall notices are in order and Building Regulations are in place). However, the reality is that technical design, tendering, contractor appointment, and pre-construction preparation typically take 6–12 weeks after planning permission is granted before construction begins. Serving party wall notices during the planning stage avoids adding the party wall notice period to this pre-construction gap.
Important Note
This guide is for general information only. Building regulations, planning rules, and legal requirements change regularly and vary by local authority. Always seek professional advice specific to your project and location. To talk through your own project, book a project review.
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