A home extension is a practical and cost-effective way to gain more space without moving house. It might give you a larger kitchen, a brighter dining area, a family room or a better connection to the garden. Before committing, though, most homeowners want to know one thing: how long does an extension take?
As a broad guide, many home extensions take around four to eight months from early design work to completion. The build itself is often shorter, but the full timeline also includes surveys, drawings, planning, building regulations, party wall matters and ordering materials.
So, how long does it take to build an extension? It depends on the size of the project, the property and how many approvals are needed. A simple single-storey rear extension will usually be quicker than a side return, wraparound extension or project with major structural work.
What Affects the Duration of an Extension?
No two homes are quite the same, especially in London. Victorian terraces, Edwardian houses, maisonettes and newer properties all bring different considerations. Your timeline may be affected by:
- The size and type of extension
- Whether planning permission is needed
- Building regulations approval
- Party wall notices or agreements
- Structural work, drainage and foundations
- Access to the property
- Lead times for glazing, steelwork, kitchens and finishes
- Weather during groundworks and roofing
Some extensions fall under permitted development rights, provided they meet set limits and conditions. Others need a householder planning application. If your home is listed, in a conservation area, or has already been extended, this can add time.
Building regulations are separate from planning permission. Even if your extension does not need full planning consent, it will usually still need to meet building regulations covering structure, insulation, ventilation, drainage, fire safety and electrics. You can read more in our guide to Building Regulations UK.
The Main Stages of Building an Extension
Understanding the stages of building an extension makes the process easier to plan. A well-managed project should move through each stage in a clear order, even if some parts overlap.
1. Design and Feasibility
This is where you decide what the new space needs to do. Do you want a bigger kitchen? More room for family life? Better natural light? A design and build team will look at your home, discuss your ideas and explain what is realistic.
This stage can take a few weeks, depending on how quickly the layout is agreed and how much design detail is needed.
2. Drawings, Planning and Approvals
Once the design is agreed, the technical work begins. This may include measured surveys, planning drawings, structural calculations and building regulations drawings.
If a householder planning application is required, councils are generally expected to make a decision within eight weeks once the application has been validated. This does not include the time needed to prepare the drawings before submission. Some councils may also ask for changes or extra information, which can extend the process.
For larger single-storey rear extensions, prior approval may apply instead of a full planning application. This includes a neighbour consultation process, so it still needs to be built into the programme.
3. Party Wall Matters
If your extension affects a shared wall, sits on or near a boundary, or involves excavation close to a neighbouring property, the Party Wall etc. Act 1996 may apply.
This does not automatically mean there will be a dispute, but it can add several weeks. Some neighbours agree quickly. Others may appoint surveyors. It is best to deal with party wall matters early, rather than leaving them until the build is ready to start.
4. Pre-build Preparation
Before work begins on site, your contractor will confirm the build schedule, order key materials and plan site logistics. In London, access can be a real consideration. Narrow side returns, terraced layouts, limited parking and controlled parking zones can all affect deliveries and waste removal.
This is also the time to plan daily life during the build. If your kitchen is being removed, you may need a temporary cooking area, extra storage and a plan for laundry, pets and working from home.
5. Groundworks and Structural Work
The first weeks on site usually involve demolition, foundations, drainage and structural preparation. This can feel disruptive because the house is being opened up and the site changes quickly.
Older drains, tree roots, poor ground conditions or nearby structures can add time. A good team will explain any issue clearly and adjust the schedule where needed.
6. Walls, Roof, Glazing and First Fix
Once the structure is in place, the extension starts to look like a room. Walls go up, steel beams are installed, the roof is formed, and windows or rooflights are fitted.
First fix work covers plumbing, electrics and other hidden services before plastering. Weather can matter during this stage, especially during external works. Heavy rain or very cold conditions may slow progress, although experienced builders will plan around common seasonal delays.
7. Plastering, Second Fix and Finishes
The final stage includes plastering, flooring, lighting, sockets, decoration, joinery and kitchen installation if your extension includes a new kitchen.
This is often the most exciting part, but it still needs careful scheduling. A delayed kitchen delivery, missing tiles or a late worktop template can affect the completion date.
Time Estimates for Different Types of Extensions
Every project needs its own schedule, but these rough guide times are useful when planning:
- A modest rear extension may take around 10 to 14 weeks on site.
- A side return extension may take around 12 to 16 weeks on site.
- A side and rear or wraparound extension may take around 16 to 24 weeks on site.
- A two-storey extension or more complex project may take six months or more from start on site.
The full timeline is longer once design, planning, building regulations and party wall matters are included. For many homeowners, a realistic start-to-finish period is around four to eight months, and sometimes longer for complex homes.
Do You Need to Move Out While Building an Extension?
In many cases, no. Plenty of homeowners stay in their property during an extension, especially if the work is mainly at the rear and the upper floors remain usable.
That said, living through building work can be disruptive. There is likely to be some dust, noise and regular activity from tradespeople, and certain areas of the ground floor may be unavailable at times. Some homeowners choose to move out temporarily, particularly if they have young children, work from home full-time, have health concerns or are replacing their only usable kitchen or bathroom.
When is the Best Time to Build an Extension in the UK?
Spring and summer are popular because there is more daylight and milder weather. This can help with groundworks, roofing and external finishes. The trade-off is that good builders often get booked early.
Autumn and winter can still work well, especially if drawings and approvals are already in place. Rain, shorter days and Christmas closures may need to be factored in, but a professional team will plan around this.
The best time to start is usually when the design, approvals, budget and build team are ready. Rushing onto site too early can cost more time later.
Planning Your Extension with Plus Rooms
A clear programme makes an extension much easier to manage. There may still be decisions, approvals and the occasional surprise, but the process feels far less daunting when one team is guiding the design, planning and construction.
Plus Rooms offers extension design and build services for homeowners who want a more joined-up way to plan and deliver their project. From early design ideas and planning guidance through to construction and finishing details, the team can help you understand what is possible, what permissions may be needed and how long your extension is likely to take.
If you are planning a home extension and would like clear advice on timescales, design options and next steps, contact Plus Rooms to discuss your project.
