How Long Does a House Extension Take to Build? | Gosport Builder’s Guide
One of the first questions people ask when they’re thinking about extending their Gosport home is how long the whole thing is going to take. It’s a fair question. An extension affects your daily life while it’s being built, and if you’re working around school terms, a new baby, or simply trying to plan when your kitchen will be out of action, you need a realistic idea of what you’re looking at.
The honest answer is that it depends — on the type and size of extension, whether you need planning permission, how complex the groundwork is, and how smoothly the project runs day to day. But there are typical timescales for each stage that give you a reliable framework. This guide breaks them down using the kind of projects we build across Gosport, from straightforward single storey rears to larger double storey and wrap-around extensions.
The Stages Before Building Starts
Before anyone picks up a shovel, there’s a period of design, approvals, and preparation that most people underestimate. Getting this stage right is what separates projects that run smoothly from those that stall halfway through.
The design phase typically takes two to four weeks. This involves an architect or designer visiting your property, drawing up plans, and working with you on the layout. For a straightforward rear extension on a semi in Privett or Elson, this might be quicker. For a more complex wrap-around on a detached property in Alverstoke or Lee-on-the-Solent, allow the full four weeks to get the design finalised properly.
If your extension falls within permitted development rights, you can skip the full planning application and move straight to Building Regulations approval, though a lawful development certificate is worth getting for your records. If you do need planning permission — which is common for double storey extensions, anything near a boundary, or properties in conservation areas — the local authority has eight weeks to make a decision from the date your application is validated. In practice, straightforward applications through Gosport Borough Council are often decided within this window, but allow ten to twelve weeks from submission to be safe, factoring in any time the council takes to validate your application and any minor amendments they request.
Building Regulations approval can run alongside the planning process or follow it, depending on your approach. A full plans application typically takes four to six weeks for approval. Some builders work under a building notice instead, which allows work to start sooner but means inspections happen as you go without pre-approved drawings.
Altogether, the pre-build phase takes anywhere from six weeks for a permitted development project with a quick design turnaround, up to four months or more where full planning permission is needed and the design goes through revisions. This is the stage where patience pays off. Rushing into construction without proper approvals and a detailed specification leads to delays, additional costs, and compromises later.
Single Storey Extension Build Times
A single storey rear extension is the most common type we build across Gosport, and also the most predictable in terms of timescale. For a typical three to four metre rear extension on a semi-detached or terraced property, expect a build time of roughly eight to twelve weeks from breaking ground to completion.
The first two weeks cover groundwork — excavating the foundations, pouring concrete, and building up to damp proof course level. This is the stage most affected by weather, and heavy rain can slow things down, particularly on Gosport’s clay-heavy ground where trenches can flood. Weeks three and four involve brickwork rising to wall plate height and the steel beams going in where internal walls are being removed. By weeks five and six, the roof structure is on and the extension becomes watertight, which is a significant milestone because internal trades can now work regardless of weather.
The remaining six weeks or so cover first fix electrics and plumbing, insulation, plastering, and then second fix work including kitchens, flooring, tiling, decoration, and finishing. This phase involves the most coordination between different trades, and a good builder keeps this running in sequence so nobody is waiting around for someone else to finish before they can start.
Larger single storey extensions — six to eight metres deep or wrap-around designs — add two to four weeks to these timescales because there’s simply more of everything. More groundwork, more brickwork, a larger roof structure, and more internal finishing.
Double Storey Extension Build Times
A double storey extension adds significant space but doesn’t take twice as long as a single storey because the foundations and much of the structural work serve both floors simultaneously. A typical double storey rear extension on a three or four bedroom property takes roughly twelve to sixteen weeks from foundations to completion.
The groundwork takes slightly longer than a single storey because the foundations need to be deeper to carry the additional load. Brickwork takes longer to reach full height across two storeys, and scaffolding adds a step at the front end of the build. The roof is more complex, often involving tying the new ridge into the existing roof line, which requires careful work to get weathertight. First floor joists, staircase modifications if applicable, and additional structural steels for the upper level all add time that a single storey doesn’t need.
Internal finishing on a double storey also takes longer simply because there are more rooms to plaster, wire, plumb, and decorate. If the upper floor includes a new bathroom or ensuite, the plumbing and tiling for that adds a week or more compared to bedrooms alone.
Properties across Gosport vary in construction and ground conditions, and both affect timescale. Older homes in the town centre and around Stoke Road may require more careful structural work where new walls meet existing ones. Newer builds in areas like Rowner and Bridgemary tend to be more straightforward but may have different foundation requirements depending on the ground.
What Can Delay an Extension?
Even well-planned projects encounter delays, and knowing the common causes helps you plan around them. Weather is the biggest factor during groundwork and brickwork. Extended wet spells in autumn and winter can add one to three weeks to these stages, though once the extension is watertight, weather has minimal impact on the remaining work.
Ground conditions are another variable. If the foundation trenches reveal unexpected issues — tree roots, filled ground, old drains, or clay that requires deeper foundations — additional work is needed before the build can progress. A good builder accounts for the most likely scenario in their timescale but cannot predict every underground surprise.
Material availability occasionally causes problems. Certain bricks, roof tiles, steels, and kitchen components can have lead times of several weeks, particularly if you’re matching existing materials on your property. Ordering these early, before they’re needed on site, prevents stalls. A builder who plans the programme properly will have critical materials ordered well before they’re required.
Changes to the specification during the build also add time. Deciding halfway through that you want a different kitchen layout, additional sockets, or a different flooring material means revisiting work that may already be partly done. The more decisions you finalise before construction starts, the smoother and faster the build progresses.
How to Keep Your Extension on Track
There are practical things you can do as a homeowner to help your project run to schedule. First, finalise all design decisions before building starts. That includes kitchen layout, bathroom specifications, socket and lighting positions, flooring, tiles, and decoration choices. Your builder needs this information to programme trades in the right order and order materials with sufficient lead time.
Second, respond to questions quickly. During a build, decisions and approvals crop up regularly, and a delay of a few days on your end can push a trade back by a week or more if they move to another job in the meantime. Being available and responsive keeps things moving.
Third, choose a builder who manages the programme properly. The biggest cause of extensions overrunning isn’t the build itself — it’s poor coordination. A builder who schedules trades in advance, orders materials ahead of time, and communicates clearly about what’s happening each week will deliver your extension faster and with less stress than one who works reactively.
Finally, be realistic about living with the build. Most families stay in their Gosport home during an extension. The first few weeks of groundwork and brickwork are largely external. The disruptive phase comes when internal walls are removed and the kitchen or living space is out of action. Your builder should give you a clear idea of when this will happen and how long it will last, so you can plan around it.
Planning Your Gosport Extension
Every extension is different, but as a rough guide you’re looking at three to four months for a single storey, four to five months for a double storey, and up to six months for larger or more complex projects — all measured from breaking ground. Add the design and approvals stage on top and the total from initial enquiry to moving the furniture in is typically six to nine months.
If you’re thinking about extending your Gosport property, the best starting point is a conversation with a builder who can visit, look at what you want to achieve, and give you an honest timescale alongside a detailed quote. We’re happy to do exactly that, free of charge and with no obligation. Get in touch and let’s talk about your project.