What to Expect During a House Extension: Week by Week
April 2026·8 min read
You've signed the contract and your start date is confirmed. But what actually happens once the builders arrive? Here's a realistic week-by-week guide to a typical single storey rear extension in Essex — so you know exactly what to expect at every stage.
Important note
Every project is different. Timelines vary depending on size, specification, weather, and site conditions. This guide is based on a typical 4–5 metre single storey rear extension — the most common project we build. Double storey and wrap-around extensions follow a similar sequence but take longer.
Weeks 1–2
Groundworks & Foundations
Site set-up — skip delivery, materials drop, welfare facilities
Excavation of foundation trenches using a mini digger
Building Control inspection of the open trenches
Concrete poured into the trenches (strip foundations)
Below-ground blockwork built up to damp proof course (DPC) level
Drainage runs installed and connected
Oversite preparation — hardcore, compaction, and DPM
What to know: This is the noisiest and most disruptive stage. The garden will look like a building site — that's completely normal.
Weeks 3–4
Floor Slab & Masonry
Concrete floor slab poured (with insulation and DPM underneath)
External walls start going up — blockwork inner leaf and brickwork outer leaf
Cavity insulation installed between the two leaves
Window and door openings formed with lintels
Wall ties, DPC trays, and weep holes installed
Walls reach roof plate level
What to know: You'll start to see the shape of your extension. This is when it gets exciting.
Weeks 5–6
Roof Structure & Covering
Roof joists or rafters installed (timber or steel depending on design)
Roof decking boards fitted
Flat roof covering applied (EPDM rubber or GRP fibreglass) — or tiles for a pitched roof
Insulation installed above or between roof joists
Fascia, soffit, and guttering fitted
The extension is now watertight
What to know: Once the roof is on, the extension is weatherproof. Internal work can now proceed regardless of rain.
Weeks 7–8
Windows, Doors & First Fix
Windows and doors installed (bifolding, sliding, patio, or French doors)
First fix electrics — cables run for sockets, switches, and lighting
First fix plumbing — pipes run for radiators, underfloor heating, or kitchen/bathroom connections
Stud walls built for any internal partitions
Insulation fitted to walls and ceiling
Plasterboard fitted to walls and ceiling
What to know: The space starts to feel like a room. You can walk around and get a real sense of the finished layout.
Weeks 9–10
Plastering & Second Fix
All walls and ceilings plastered — smooth, flat finish ready for decoration
Second fix electrics — sockets, switches, and light fittings installed
Second fix plumbing — radiators, taps, and connections fitted
Skirting boards, architraves, and door linings fitted
Internal doors hung
Window boards installed
What to know: The plastering stage is a big milestone. Once the walls are smooth and white, the room transforms overnight.
Weeks 11–12
Decoration, Flooring & Finishing
Walls and ceilings painted or decorated to your specification
Flooring installed — tiles, engineered wood, laminate, or carpet
Kitchen or utility units fitted (if part of the project)
Final electrical and plumbing connections
External works — patio, landscaping, or driveway reinstatement
Thorough clean throughout
What to know: This is the fun part — choosing paint colours, seeing your flooring go down, and watching the space come to life.
Week 12+
Snagging & Handover
Final inspection walk-through with your project manager
Any snagging items identified and addressed
Building Control final inspection and completion certificate issued
All certificates, warranties, and documentation handed over
Keys to any new locks provided
Your extension is complete — enjoy your new space
What to know: We don't disappear after handover. If anything needs attention in the weeks and months ahead, we're always a phone call away.
How We Keep You Informed
Throughout the build, your dedicated project manager keeps you updated at every stage. We provide:
A detailed programme of works before we start
Regular progress updates — in person, by phone, or via WhatsApp
Advance notice of any noisy or disruptive stages
Clear communication about material deliveries and access requirements
Immediate discussion of any changes or unexpected issues
What About Double Storey Extensions?
A double storey extension follows the same sequence but adds extra stages — first floor joists, upper storey walls, a more complex roof structure, and additional internal finishing. Expect 14–22 weeks depending on size and specification. We provide a detailed programme specific to your project before work begins.
Ready to Plan Your Extension?
We'll give you a realistic timeline and detailed quote — no surprises, no hidden costs.
