How Long Will Your Home Extension Take? Key Milestones Explained
A single-storey extension takes 10–16 weeks on site and a double storey 14–24 weeks, after three to five months of design and approvals. The milestones from feasibility to handover, and what delays them.
Home extensions are among the most popular ways to add space, functionality, and value to a property. Whether you’re planning to expand your kitchen, create a new living area, or add an extra bedroom, a home extension can significantly improve your quality of life and increase the appeal of your property. However, one of the most common questions homeowners ask is: How long will my home extension take?
Short answer (2026): a single-storey extension takes 10–16 weeks on site and a double storey 14–24 weeks, after three to five months of feasibility, design, planning (eight weeks if an application is needed), Building Regulations and party wall notices. From first meeting to finished room, seven to twelve months is typical.
The truth is, the answer depends on a range of factors—from the complexity of the design to the time it takes to secure planning permission. That said, having a clear idea of the typical milestones and the timeframes associated with each phase of an extension project can help you plan effectively, set realistic expectations, and avoid unnecessary delays.
In this article, we’ll walk through the key milestones of a typical home extension, breaking down what happens at each stage and how long you can expect each part of the process to take.
1. Initial Planning and Design (2 to 6 weeks)
Every successful home extension begins with detailed planning. This is the phase where you define what you want from the extension, consult an architect or designer, and get a rough idea of budget, materials, and layout.
Tasks include:
- Defining your requirements
- Meeting with architects or designers
- Receiving design concepts
- Refining your ideas
During this stage, you might also begin informal conversations with your local planning authority or a planning consultant, especially if your extension is not likely to fall under permitted development rights.
Estimated time:
2 to 6 weeks, depending on how quickly decisions are made and the availability of professionals.
2. Planning Permission or Permitted Development Confirmation (8 to 12 weeks)
Not all extensions require formal planning permission. Some fall under permitted development rights, particularly rear single-storey extensions, provided they meet specific size and height requirements. However, even if your project is permitted, obtaining a Lawful Development Certificate from your local authority is often recommended for legal clarity.
If full planning permission is needed, the process will typically involve:
- Preparing and submitting an application
- A public consultation period
- Local authority review and decision
Estimated time:
- Permitted development: 2 to 4 weeks (including certification)
- Planning permission: 8 to 12 weeks (can be longer if appeals or revisions are needed)
3. Technical Drawings and Building Regulations Approval (2 to 6 weeks)
Once you’ve received planning permission (or confirmation under permitted development), the next step is creating detailed technical drawings and submitting them for building regulations approval. These drawings will include structural details, energy efficiency measures, fire safety, and drainage systems.
Depending on your local authority, you can apply via:
- Full Plans Submission: Comprehensive and pre-checked by building control
- Building Notice: Faster but less detailed; better for simpler builds
In many cases, a structural engineer may be required to prepare calculations, especially if steel beams or complex foundations are involved.
Estimated time:
2 to 6 weeks, depending on complexity and response times.
4. Tendering and Appointing a Builder (2 to 4 weeks)
Before construction can begin, you’ll need to choose a contractor. This typically involves:
- Getting multiple quotes
- Checking references and reviews
- Reviewing previous work
- Signing a written contract
Avoid rushing this stage. Selecting the right builder is critical to avoiding delays, disputes, and extra costs later.
Estimated time:
2 to 4 weeks, depending on builder availability and your own decision-making speed.
5. Site Preparation and Groundworks (2 to 4 weeks)
With everything in place, the construction phase begins. The first task is site preparation, which includes:
- Clearing the area
- Setting up access
- Marking out foundations
This is followed by groundworks, which often involve:
- Excavation
- Pouring concrete foundations
- Installing initial drainage
Factors such as soil conditions, site access, and weather can all influence how long this stage takes.
Estimated time:
2 to 4 weeks for straightforward projects
6. Building the Superstructure (4 to 8 weeks)
The superstructure refers to the walls, roof, and external structure of your extension. This is where your vision begins to take physical form.
Tasks include:
- Building walls (block or brickwork)
- Installing lintels and windows
- Roof construction and weatherproofing
At this stage, your extension should become weather-tight, meaning it can withstand the elements, allowing interior work to begin.
Estimated time:
4 to 8 weeks, depending on size and design complexity
7. First Fix (2 to 3 weeks)
The first fix includes all the internal systems that go into the building before plastering begins. This includes:
- Electrical wiring
- Plumbing pipework
- Heating installation
- Stud wall framing and insulation
This phase needs to be coordinated with various trades, including electricians, plumbers, and heating engineers.
Estimated time:
2 to 3 weeks
8. Plastering and Drying (1 to 2 weeks + drying time)
Once the first fix is complete and building control has inspected the work, the walls and ceilings can be plastered. Drying time will vary depending on the season and ventilation, and no further finishing should be done until plaster is fully dry.
Estimated time:
- Plastering: 1 to 2 weeks
- Drying: 1 to 3 weeks
9. Second Fix (2 to 3 weeks)
This phase covers the finishing touches:
- Installing sockets, switches, and light fittings
- Connecting radiators and plumbing fixtures
- Fitting skirting boards, internal doors, and flooring
Second fix usually moves faster than first fix, but the quality of finish is critical at this stage.
Estimated time:
2 to 3 weeks
10. Snagging and Final Inspections (1 to 2 weeks)
Before the extension is fully complete, you’ll walk through the space with your builder to identify any snagging issues. These might include:
- Touch-ups to paintwork
- Realignment of doors
- Sealant finishing
You’ll also need a final inspection from building control to receive your completion certificate, which is essential for insurance and potential resale.
Estimated time:
1 to 2 weeks
A realistic programme
| Stage | Duration | Runs in parallel with |
|---|---|---|
| Site visit, feasibility, budget | 2–4 weeks | — |
| Concept and planning drawings | 3–5 weeks | — |
| Planning decision (householder application) | 8 weeks from validation | Technical design can start |
| Building Regulations drawings, structural calculations, specification, fixed price | 3–6 weeks | Party wall notices (1–2 months) |
| On site — single storey | 10–16 weeks | Kitchen lead time (6–10 weeks) ordered at contract |
| On site — double storey | 14–24 weeks | — |
| Snagging and handover | 1–2 weeks | — |
The three things that most often stretch a programme are late kitchen decisions, party wall notices served late, and ground conditions that change the foundation design after excavation. All three are avoidable with early decisions and a proper feasibility visit — see how we run a project.
Final thoughts
Building a home extension is a significant investment of time, money, and energy—but when carefully planned, the rewards can be substantial. Understanding the key milestones and the expected timelines at each stage can help you make informed decisions, manage your budget, and minimise disruption.
While every extension is unique, a realistic timeframe for a standard home extension ranges between 3.5 to 6 months, from concept to completion. By working with experienced professionals, keeping communication open, and preparing for each phase, you’ll be well on your way to a successful home upgrade.
If you're about to start your own extension project, remember: clear timelines, thorough planning, and attention to detail are just as important as bricks and mortar.
Frequently asked questions
Do I always need planning permission for a home extension?
Not necessarily. Many extensions fall under permitted development rights, especially smaller single-storey rear extensions. However, it’s wise to check with your local authority and obtain a lawful development certificate for peace of mind.
Can I live in my home during the extension works?
In most cases, yes—especially for single-storey extensions. However, expect noise, dust, and limited access to parts of your home. Some people choose to move out temporarily during the more disruptive phases.
What can delay my home extension project?
Common causes of delay include poor weather, planning permission complications, late material deliveries, changes to design mid-build, and lack of contractor availability. Good planning and communication are essential to stay on track.
How much notice do I need to give neighbours?
If your extension affects a party wall, you’ll need to serve a Party Wall Notice at least two months before work begins. General courtesy and early conversations with neighbours are always recommended, even if not legally required.
Can I extend during winter months?
Yes, but expect possible delays due to shorter daylight hours and adverse weather. Some stages, like groundwork or roof construction, are more weather-dependent and may be affected.
Do I need a completion certificate
Yes. Once the work is finished and signed off by building control, you’ll receive a completion certificate. It’s vital for future property sales, mortgage applications, and insurance purposes.
About this guide. Written by the Milkov & Son Construction team and reviewed by Stoyan Milkov, Director & Project Manager. Cost figures are North London market guides for the year stated and not quotations; planning and Building Regulations summaries are general and should be confirmed for your property. About the company.
