Table of Contents
In our experience, home extension delays rarely come from the building work itself. They tend to stem from factors that could have been addressed earlier in the process:
• Late design decisions
• Planning objections or delays
• Poor ground conditions
• Time taken to order materials in advance.
• Party Wall Act matters
• Weather
Here are estimated timelines of how long the different stages of the actual build takes.
Groundworks and Foundations
Every project is different. Before we can give you a reliable timeline, we need to understand the full picture: what you’re building, where, and whether planning permission applies.
That said, the construction industry does follow fairly predictable patterns, and after more than three decades of delivering extensions across Kent and the South East, we can speak with confidence about what realistic timelines look like at every stage.
Structural Frame, Walls, and Roof
Once the slab or oversite is complete, the structure goes up. The external walls (brick, block, or timber frame), first-floor joists if double-storey, and the roof structure. This phase typically takes three to six weeks, depending on scale.
First Fix: Electrics, Plumbing, and Carpentry
Electricians run cables, plumbers install pipework, and carpenters fit studwork partitions, door linings, and staircase elements. This phase requires careful coordination between trades; it’s where a builder with a strong network and good project management really earns their fee. First fix typically takes two to four weeks.
Plastering and Second Fix
Once first fix is complete and inspected by building control, the plasterers move in. Wet plaster needs adequate drying time before second fix begins, usually two to three weeks for the plaster to achieve suitable moisture content. Second fix brings everything to life: skirting boards, architraves, kitchen or bathroom fitting, electrical sockets and switches, and sanitaryware. A further two to four weeks is typical.
Decorating and Final Touches
The final stage — painting, tiling, flooring, and the installation of appliances — brings the extension to a finished standard. Allow two to four weeks, and bear in mind that bespoke or specialist finishes may add time.
Make as many finish and fixture decisions as possible before work starts. A pre-start meeting with your builder to confirm every material and specification is one of the most valuable hours you’ll spend on the whole project.
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Living at Home During a House Extension
The majority of homeowners we work with choose to remain in their properties throughout the build, and in most cases that’s entirely manageable, particularly for rear extensions. The most disruptive period is usually when the existing house is opened up to connect the new extension, which typically involves forming new structural openings and temporary propping of the structure above.
A well-managed project minimises this disruption. We work with hoardings, dust sheets, and temporary provisions to keep the rest of the property habitable, and we plan the sequence of works so that the connected phase is as brief as possible. Clear communication throughout makes a significant difference to how the experience feels from inside the house.
Getting a Realistic Timeline for Your Project
The figures throughout this guide are based on real-world experience across hundreds of projects in Kent and the wider South East. But every plot, every property, and every brief is different. The best way to understand your specific timeline and to avoid being caught out by any site-specific factors is to have an experienced builder walk your property and give you an honest assessment.
At Hargrave Construction & Renovations, that’s exactly what we offer. We’ll visit, ask the right questions, and give you a programme and a quote that reflects the genuine scope of your project, not an optimistic estimate designed to win the work.
Frequently Asked Questions
Key factors include the size and complexity of the extension, whether planning permission is required, ground conditions and foundation type, the weather (particularly for groundworks), the availability of materials and specialist trades, and how many decisions are still outstanding at the start of the build.
Yes. Virtually all house extensions require Building Regulations approval, regardless of whether planning permission was needed. Building control inspections happen at key stages throughout the build and a completion certificate is issued at the end. This is important for future property sales.
From your first conversation with a builder through to moving into your new space, the total timeline is typically 6–12 months. This includes design and drawings (4–8 weeks), planning permission if required (8–10 weeks), pre-start preparations (2–4 weeks), and the build itself (8–24 weeks depending on scale).
The Party Wall etc. Act 1996 applies when you’re building on or near a boundary shared with a neighbouring property. You must serve formal notice on affected neighbours before work begins. If they appoint their own surveyor, the process can add 6–8 weeks to your programme.
Winter can affect groundworks and external works due to frost and wet weather, but it doesn’t stop construction altogether. Many projects progress perfectly well through winter once the structure is weathertight. An experienced builder will plan around seasonal conditions.
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