Home Extension Build Phase: Timeline, Stages & What to Expect

The build phase is when your home extension finally takes shape – but it can also feel like the most uncertain part of the journey. Knowing what happens, in what order, and how it’s managed removes the stress and lets you enjoy the transformation. At HomeExtensionsRUs, our dedicated project management ensures every stage runs smoothly, on time and with clear communication.

Preparing for the Build Phase

Before any work starts on site, thorough preparation prevents most problems.

We handle:

Final contract and payment schedule
Site setup and worker welfare
Neighbour notifications and access agreements
Material ordering and delivery scheduling

This groundwork means day one runs smoothly. For instance, our Watford home extension projects often require careful coordination with neighbouring properties in terraced and semi-detached streets—securing access agreements and managing material deliveries in limited space are planned weeks in advance, not solved on the day.

Week-by-Week: Typical Build Timeline

Every project varies, but here’s a realistic guide for a single-storey rear extension:

Weeks 1–2: Groundworks and foundations
Weeks 3–5: Structural shell (walls, roof frame)
Weeks 6–8: Envelope (roof covering, windows, doors)
Weeks 9–12: First fix (electrics, plumbing)
Weeks 13–16: Internal finishes and second fix
Weeks 17+: Snagging and handover

Key Stages of Construction

Understanding the main phases helps you visualise progress.

Groundworks – excavation, foundations, drainage
Structural – walls, steelwork, roof structure
Weathertight – roof, windows, external doors
First fix – plumbing, electrics, insulation
Second fix – plastering, flooring, kitchen/bathroom
Finishes – decoration, final fittings

Our build project management service coordinates every stage, ensuring trades arrive in sequence, materials are on site when needed, and quality standards are maintained from groundworks through to final decoration.

Thinking about building an extending? Get personalised expert advice

How We Coordinate Builders and Suppliers

A successful build needs tight coordination.

Our dedicated manager:

Schedules trades to avoid delays
Orders materials for just-in-time delivery
Manages health & safety daily
Runs weekly progress meetings

This keeps momentum without chaos.

Inspections and Building Control Visits

Building Control sign-off happens at key stages:

Foundations
Pre-plaster (drainage, structure)
Completion

We arrange every visit and resolve any queries immediately.

Managing Changes and Unexpected Issues

Even the best plans can need adjustments.

We handle:

Transparent cost/time implications
Written variation orders
Quick decisions to keep momentum

Our contingency planning minimises disruption.

The Final Weeks and Handover

The last stages bring everything together:

Snagging list compiled and resolved
Final cleaning
Full demonstration of systems
Handover pack with warranties and manuals

You receive your completed extension exactly as envisioned.

Checklist: Prepare for Your Extension Build

Clear the site and protect valuables
Arrange parking/access for trades
Set up temporary kitchen if needed
Agree communication preferences
Keep contingency budget ready

Expert Insights

“The first two weeks of groundworks set the tone – good preparation here prevents 90 % of delays.”
“Daily oversight is what separates smooth projects from stressful ones.”
“A dedicated manager is worth far more than their fee in peace of mind.”

Michelle Dunbar (Director & Senior Project Manager)

Michelle oversees the day-to-day operations, manages client relationships, and ensures each project is delivered to a consistent, professional standard.

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Frequently Asked Questions

How long does the actual build phase of a home extension take?

Typically 10-16 weeks for a single-storey extension, depending on size and complexity. Groundworks and structural stages take longest – we provide a detailed timeline during planning.

How to prepare your home for the extension build phase?

Clear access areas, protect valuables, set up temporary facilities if needed, and discuss neighbour impacts. Early site surveys ensure minimal disruption during construction.

Will there be a lot of noise and disruption during the build?

Some disruption is inevitable, but we minimise it with careful scheduling, dust control and neighbour consideration. Most clients stay in their homes throughout.

Who is responsible if something goes wrong during construction?

Your dedicated project manager handles all issues immediately. We carry full insurance and only use vetted builders with proven reliability.

What role does Building Control play in home extension builds?

Building Control inspects at key stages like foundations and pre-plaster to ensure compliance. Professional scheduling makes these visits seamless and avoids rework.

Can I make changes once the build has started?

Yes – we manage variations professionally with clear cost/time implications. Early decisions reduce the need for changes, but flexibility is built into our process.

How often will I get updates during the build?

Weekly progress reports plus daily access to your manager. We also provide visual updates (photos/videos) at key milestones so you always know what’s happening.

What happens at the final handover?

We complete a full snagging review, demonstrate all systems, provide warranties and manuals, then hand over the keys once you’re completely satisfied.

Or call on 1462 342 040