How Long Does a House Extension Take from Start to Finish?
- Robert Bartlett
- Jul 16
- 7 min read
Planning a house extension is an exciting step toward transforming your home into a more functional, spacious, and valuable property. But one of the most common questions we get asked at RGB Construction is: "How long does a house extension take from start to finish?"
The short answer is: it depends.
Every extension project is unique, and timelines can vary depending on several factors, including the size and type of extension, the complexity of the build, planning permissions, availability of materials, and even the weather.
In this guide, we’ll walk you through a realistic house extension timeline in the UK, outlining each stage of the process so you know what to expect. We’ll also highlight the factors that could influence the schedule and give you tips on how to keep things on track.
Typical House Extension Timeline UK (General Overview)
Here’s a rough breakdown of a standard single-storey rear extension timeline:
Total estimated time: 4 to 8 months (depending on complexity)
Please note: These timeframes are general guidelines. For a more accurate timeline specific to your project, we always recommend getting in touch with our experienced team.
Step-by-Step: How Long Each Stage Takes
Now, let's dig a little deeper into those stages to give you a better idea of what to expect.
1. Initial Consultation, Design & Planning (2-4 weeks)
This is where your extension journey begins. During this stage, we discuss your goals, survey the property, and begin developing concept designs.
Site visits and measurements
Architectural drawings
Budget discussions
Feasibility study
If you already have clear ideas and your decision-making process is quick, this stage can be completed in as little as two weeks.
2. Planning Permission (8-12 weeks, if required)
Not every extension needs planning permission. Some projects fall under permitted development rights, which can significantly reduce delays. However, if your extension exceeds certain limits or you’re in a conservation area, full planning permission may be needed.
Preparing and submitting planning application
Waiting for local authority review (typically 8 weeks)
Possible revisions and resubmission (can extend timeline)
You can check if you might need planning permission via the UK Government's Planning Portal.
Tip: Speed up this stage by working with a builder like RGB Construction who understands local council requirements across Cardiff, Newport, and South Wales.
3. Building Regulations Approval (2-4 weeks)
Whether or not planning permission is required, building regulations approval is essential for nearly all extensions.
You can choose between:
Full Plans Application - where detailed plans are submitted in advance.
Building Notice - faster, but less suited for complex projects.
We usually recommend the Full Plans route for greater clarity and fewer surprises during construction.
4. Pre-Construction Preparations (1-2 weeks)
Before breaking ground, there are still a few important steps:
Finalising contracts
Scheduling materials and trades
Health & safety assessments
Notifying neighbours (especially under the Party Wall Act, if relevant)
This preparation ensures everything is lined up for a smooth start.
5. Construction Phase (10-16 weeks)
This is the most visible part of your project - when the transformation truly begins.
The length of time depends on the size and complexity of your extension:
Approximate construction timelines:
Single-storey rear extension: 10-14 weeks
Double-storey extension: 14-20 weeks
Wrap-around or large-scale extension: 16-24+ weeks
What’s involved:
Groundworks and foundations
Building the walls and roof
Windows, doors, and structural works
First fix electrics and plumbing
Insulation and plastering
Throughout this phase, inspections by building control ensure compliance with regulations.
6. Finishing, Fixtures & Snagging (1-3 weeks)
This final stretch includes:
Painting and decorating
Flooring installation
Kitchen or bathroom fitting (if included)
Final electrics and plumbing (second fix)
Final inspection and snagging
A good builder will walk through everything with you and address any minor issues before sign-off.
Factors That Affect Your House Extension Timeline
✅ Size and Complexity
A small rear extension is naturally quicker than a double-storey wraparound with internal reconfiguration.
✅ Planning Delays
If you need to revise and resubmit plans, this can add several weeks to your project.
✅ Weather Conditions
Heavy rain, frost, or storms can delay groundwork or roofing.
✅ Access Issues
Tight spaces, shared driveways, or limited parking can slow down deliveries and trades.
✅ Material Lead Times
Specialised or imported materials may take longer to arrive, especially during high-demand periods.
✅ Changes During the Build
Client-led changes or additions during construction can shift the schedule, so it’s best to finalise decisions early.
Tips to Keep Your Extension Project on Schedule
Choose an experienced builder: Like RGB Construction - we manage everything from design to build.
Plan thoroughly upfront: Rushed decisions early on often lead to costly delays.
Stick to agreed specs: Last-minute changes can have a knock-on effect.
Stay in communication: Regular updates and transparency keep expectations realistic.
So… How Long Does a House Extension Really Take?
In general, most domestic extensions in the UK take between 4 and 8 months from concept to completion - but that depends heavily on your circumstances.
At RGB Construction, we understand that time is of the essence - whether you're extending to accommodate a growing family, add value to your home, or create your dream kitchen-diner. We pride ourselves on delivering high-quality work within agreed timeframes and helping our clients across Cardiff, Newport, and the wider South Wales area plan with confidence.
Ready to Start Planning Your Extension?
Let us help you understand the possibilities and timelines specific to your home.
Whether it’s a kitchen extension, a double-storey build, or something more bespoke - we’re here to guide you every step of the way.
Get in touch with the RGB Construction team today for a free consultation and personalised timeline estimate.
FAQs
How long does a single-storey extension take in the UK?
A typical single-storey rear extension takes between 10 and 14 weeks for construction, plus additional time for planning, design, and approvals. End-to-end, expect a timeline of 4 to 6 months on average.
What is the average time for a house extension from planning to completion?
On average, a full house extension project in the UK takes around 4 to 8 months, depending on complexity, size, permissions, and weather conditions.
Do I need planning permission for a house extension?
Not always. Some extensions fall under permitted development rights. However, if your design exceeds size limits or affects neighbouring properties, you may need full planning permission.
How long does planning permission take for an extension?
Planning permission decisions typically take 8 weeks from submission, although it can take longer if revisions are needed or if your property is in a conservation area.
Can a house extension be completed in 3 months?
It’s possible for a small, straightforward extension with no planning delays or design complexity. However, most projects take longer - typically 4 to 6 months from start to finish.
What can delay a house extension?
Common delays include planning permission issues, poor weather, material shortages, changes to the design, and unforeseen site conditions.
How long does building regulations approval take?
Building regs approval usually takes 2 to 4 weeks, depending on whether you opt for a Full Plans Application or a Building Notice.
When is the best time of year to build a house extension in the UK?
Spring and summer are popular due to better weather conditions, but experienced builders like RGB Construction work year-round, with proper planning in place for winter builds.
How long does it take to get started after planning approval?
Once planning is granted, you’ll need 2 to 4 weeks to finalise details, schedule trades, and begin construction, depending on availability.
How long does it take to build a double-storey extension?
A double-storey extension typically takes 14 to 20 weeks for construction alone, not including design and approvals. The total timeline is usually 6 to 9 months.
How long does the design phase of an extension take?
The design and consultation stage usually takes 2 to 4 weeks, but can be shorter or longer depending on how quickly decisions are made.
Can I stay in my house during the extension build?
In most cases, yes - especially with rear or side extensions. However, there may be some disruption, and temporary arrangements might be needed for certain phases like plumbing or electrics.
Do kitchen extensions take longer?
Kitchen extensions may require additional plumbing, gas, and electrical work, so they can add 1-2 weeks to a standard build. Allow for 12 to 16 weeks depending on the design.
What are the stages of a house extension project?
The main stages are:
Initial consultation and design
Planning permission (if required)
Building regulations approval
Pre-construction prep
Construction
Finishing, fixtures and snagging
How long does the finishing stage take?
The final stage - including painting, flooring, kitchen/bathroom installs, and snagging - typically takes 1 to 3 weeks, depending on the complexity of the finish.
How long does a wraparound extension take?
A wraparound extension usually takes 16 to 24+ weeks to build due to its scale and complexity. The full project timeline can exceed 8 months.
Is it quicker to use permitted development for my extension?
Yes - using permitted development rights means you can avoid the 8-12 week planning permission stage, which can significantly reduce the overall timeline.
How soon can RGB Construction start my extension project?
This depends on our current schedule and your project’s readiness. Get in touch with our team for a personalised timeline - we’re happy to provide realistic lead times based on your location and requirements.
Can delays be avoided with a design & build company?
Absolutely. Using an experienced design and build contractor like RGB Construction streamlines the process, reduces communication issues, and helps keep the project on schedule.
How much notice do I need to give neighbours before work starts?
If your extension affects a shared wall or boundary, you may need to serve notice under the Party Wall Act - usually 2 months before work begins.