Spring Planning: Get Your Extension Approved Before Summer

If you start now (March 2026), you could realistically have all approvals in place and start construction by July–August 2026. Here is why:

The key insight: Many stages run in parallel. Submit your planning or LDC application, building regulations application, party wall notices, and structural engineer instruction all within the same 1–2 week window. This is how you compress the timeline.

Week 1–2 (March): Check and brief

Check your PD rights — find out whether your project is PD or needs planning permission. This determines your timeline.

Find an architect or designer. Get recommendations, check portfolios, and brief them on what you want. If your project is straightforward (a standard rear extension under PD), an architectural technologist (£800–£2,500) may be more cost-effective than a full architect.

Consider pre-application advice — if your project needs planning permission and is borderline or complex, pay for pre-app advice from your council (£150–£600). This takes 4–6 weeks but can save months of delays from a refused application.

Weeks 3–6 (March–April): Design

Your architect produces the drawings you need:

• For a planning application: site plan, floor plans, elevations, sections
• For an LDC application: plans and elevations showing PD compliance
• For building regulations: detailed construction drawings (often produced later in parallel)

Tip: Do not over-design at this stage. Get the planning drawings done first. The detailed construction drawings for building regulations can follow while your planning application is being processed.

Week 6–7 (April): Submit everything

This is the critical week. Submit as many applications as possible simultaneously:

• Planning application (£548) or LDC application (£274) via the Planning Portal
• Building regulations application — Full Plans (£500–£900) via your council or private inspector
• Party wall notices — serve on all affected neighbours (1–2 months before construction)
• Structural engineer — instruct to produce calculations and beam designs

Weeks 7–14 (April–June): Wait (productively)

While applications are being processed:

• Get builder quotes. Aim for at least 3 detailed quotes.
• Finalise your specification. Kitchen layout, bathroom fittings, flooring, lighting — make as many decisions as possible now. Changes during construction are expensive.
• Sort insurance. Notify your home insurer about the building work.
• Arrange finance. If you are borrowing, finalise the arrangement. Lender surveys or revaluations can take 2–4 weeks.

Weeks 14–16 (June–July): Approvals received

By mid-June to early July, you should have:

• Planning permission or LDC granted
• Building regulations approved (or at least submitted and progressing)
• Party wall agreement in place (or consent from neighbours)
• Builder confirmed and start date agreed

Week 16+ (July–August): Start construction

Your builder starts on site. Make sure you have:

• A written contract with your builder (JCT Homeowner or similar)
• Building control notified of the commencement date
• Skip permit arranged (if the skip will be on the road)
• Scaffolding licence arranged (if scaffolding will be on the pavement)
• Neighbours informed of the start date and expected duration

If you are reading this in April or May and have not started yet, a summer start may still be possible — but only if your project is permitted development (no 8-week planning wait) and you act immediately.

For projects needing planning permission, a more realistic target is an autumn start (September–October). Building work can continue through winter — modern construction methods are not as weather-dependent as they used to be — but ground works (foundations) are best done before the wettest months.

• Check PD rights with BILTD's free checker
• Brief an architect or designer
• Submit planning/LDC application by mid-April at the latest
• Instruct structural engineer
• Serve party wall notices (if applicable)
• Submit building regulations application
• Get 3+ builder quotes
• Finalise specification and materials
• Notify home insurer
• Arrange finance (if borrowing)

Read our complete extension planning checklist for the full step-by-step guide.