What Happens Before an Extension Starts?

The pre-construction phase

The most successful extensions begin long before the first digger arrives. In fact, the pre-construction phase — the planning, design and approvals stage — is often the most important part of the entire project. Get this right and construction runs smoothly; skip steps and you'll face delays, extra costs and stress.

Here's what needs to happen before construction can begin.

1. Initial consultation

Before anything else, you need a clear understanding of what you want to achieve and whether it's feasible. A good consultation covers your goals, budget, timeline and the structural implications of your ideas. This is also where an experienced builder can flag potential issues early — things like foundation requirements, party wall considerations or planning constraints.

2. Architectural drawings

You'll need proper architectural drawings — not just sketches. These are required for both planning applications and building regulations, and they form the basis of your builder's quote. A detailed set of drawings means your quote will be accurate and your build will match your expectations.

Drawings typically include:

• Existing and proposed floor plans
• Elevations
• Cross-sections
• Foundation and structural details

3. Planning application (if required)

If your project needs planning permission, the application is submitted to your local council. Decisions usually take about 8 weeks. If you're under permitted development, we recommend obtaining a Lawful Development Certificate to prove compliance — it protects you when you come to sell.

4. Structural engineer

For any extension involving steelwork, wall removal or structural alteration, you'll need a structural engineer to design and calculate the beams, posts and foundations. Their calculations are submitted as part of your building regulations application.

5. Party Wall Agreement

If your extension affects a shared wall or boundary, or if you're excavating within 3 metres (or 6 metres for deeper foundations) of a neighbouring structure, you'll need a Party Wall Agreement. This is a legal requirement under the Party Wall etc. Act 1996, and it protects both you and your neighbour.

A party wall surveyor prepares the agreement, which typically takes 2–4 weeks.

6. Building regulations approval

Your drawings and structural calculations are submitted to building control (either the local authority or an approved inspector). They check compliance and issue an approval notice. Once approved, construction can begin — with inspections at key stages.

7. Final quotation and contract

With approved drawings in hand, your builder provides a final, fixed quotation. This should be itemised and reference the drawings, so there's no ambiguity about what's included. A proper contract protects both parties and sets out payment terms and timelines.

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This entire pre-construction phase typically takes 8–16 weeks, depending on planning requirements and party wall matters. It sounds long, but it's the foundation of a successful build.

We manage this entire process for our clients. Get in touch using the form on our contact page to get started.