What Actually Happens During The Build? — The Home Extension Build Process Explained
- Grant Redfern
- Dec 10, 2025
- 3 min read
THE HOME EXTENSION SERIES — PART 4
Your step-by-step guide to getting it right from day one.
🧱 Understanding the Home Extension Build Process
A step-by-step look at how your extension comes to life once boots hit the ground.
When you're planning an extension, it’s natural to wonder what the home extension build process actually involves. At GCR Construction, we follow a structured, transparent approach so clients always know what’s happening on site and what comes next.
🧱 1. Site Set-Up & Groundworks
This is where everything kicks off. We secure the site, set out the footprint, bring in machinery and start excavating ready for foundations.
Groundworks are messy, noisy and absolutely essential — they create the structural base that carries everything above it.
🔩 2. Foundations & Drainage Installation
Depending on soil conditions and the structural design, this could be strip footings, trench fill, or mini-piles if the ground is poor.
Once dug and passed by Building Control, we pour concrete foundations and install/alter drainage to suit the new layout.
🧱 3. Building the Masonry Shell
Your extension finally starts to take shape.
We build the external and internal walls, install cavity insulation, fit lintels and create all new openings.
This is the point where you can actually “see” the size and feel the new space.
🪚 4. Structural Steels & Opening Up the Existing House
To merge old and new seamlessly, we install the structural steelwork designed by the engineer.
This is one of the biggest milestones — we break through into the existing property (carefully!) and open the space up exactly as the plans show.
🏠 5. Roof Structure & Covering
Whether it’s a flat roof, pitched roof or a combination, the structure goes on next.
We fit timbers, insulation, membranes and the final covering.
This is also where rooflights or lanterns get measured/installed.
🔌 6. First Fix Electrics & Plumbing
Once the shell is watertight, first fix begins:
– Wiring for sockets, lights, switches, media, alarms etc.
– Plumbing for hot/cold feeds, underfloor heating, radiators and waste runs.
Everything is positioned now before the walls get closed up.
🚪 7. Windows, Bi-folds & External Doors
Your glazing is installed to lock the building up.
This step massively improves the feel of the space and helps us control temperature and security so trades can crack on inside.
🧱 8. Insulation, Plasterboard & Plastering
Internal walls are insulated and boarded.
Plasterers skim everything, transforming the place from “building site” to an actual room.
This is when clients start getting excited — it suddenly feels real.
🛠️ 9. Second Fix Carpentry, Electrics & Plumbing
The finishing details go in:
– Skirting, architraves, internal doors
– Final sockets, switches, lighting
– Radiators, sanitaryware, kitchen connections
It’s all the visible parts that make the space feel finished and refined.
🎨 10. Decorating, Flooring & Finishing Touches
Walls are painted, flooring is laid and all final cosmetic details are completed.
Kitchens are fitted at this stage too if they form part of the build.
This is where the extension truly comes alive.
🧼 11. Snagging, Cleaning & Final Checks
We walk the job with you, list any minor snags and get them resolved.
The site is deep-cleaned ready for you to enjoy your new space.
Building Control sign everything off, and you get your completion documents.
Every project follows the same core stages of the home extension build process, even though each build is unique. Understanding these steps helps you feel more in control, better prepared, and confident about what’s coming.
👉 NEXT WEEK:
Part 5 — How To Prepare Your Home Before Work Begins.
A step-by-step look at the construction process from start to finish..
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