Most single storey extensions take between 10 and 16 weeks on site, and two storey extensions usually run to 16 to 24 weeks. The build itself is only part of the story, though. Once you add planning, drawings, structural calculations and the time it takes to book a good builder, a realistic start to finish figure is nearer six to twelve months, and this guide explains where that time goes.
The pre-construction stage is where most of the waiting happens, and it is the part homeowners tend to underestimate. If your extension needs full planning permission, East Devon District Council has a statutory eight week target for householder applications, but it is common for decisions to take 10 to 12 weeks once validation and any neighbour comments are factored in. Many single storey rear extensions fall under permitted development, which avoids planning altogether, but a Lawful Development Certificate is still worth having and typically takes around eight weeks.
Alongside planning you will need building regulation drawings and, for almost every extension, structural calculations for steel beams and foundations. Allow three to six weeks for an architect or technician to produce these. In Budleigh Salterton and the surrounding villages there are extra factors to check early: parts of the town sit within a Conservation Area, some properties are listed, and anything near the Otter estuary or the coast may need a flood or ecology check before the council will determine the application.
Once work starts on site, a typical single storey rear or side extension of around 20 to 30 square metres follows a fairly predictable sequence. Foundations and groundworks take one to two weeks, depending on ground conditions. Around Budleigh Salterton the ground varies from clay to the local pebble beds, and building control will inspect the trenches before concrete is poured, so a deeper dig can add days rather than weeks.
After that the walls go up over two to three weeks, the roof structure and covering take another two, and the property is made watertight. First fix plumbing and electrics, insulation and plastering then take three to four weeks, with plaster needing proper drying time before decoration. The final two to three weeks cover second fix, kitchen or bathroom fitting, flooring, decorating and snagging. Knocking through into the existing house is usually left until late in the programme to keep you living comfortably for as long as possible.
The single biggest cause of delay is late decisions. If the kitchen, windows, bifold doors or rooflights have not been chosen and ordered before the build starts, the site can sit idle while lead times of six to twelve weeks run down. Made to measure aluminium doors in particular are rarely quick to arrive.
Weather matters more in a coastal spot like East Devon than inland. Persistent rain during groundworks or before the roof is on can cost a week or two, which is one reason spring and early summer starts are popular and get booked up quickly. Unexpected ground conditions, old drains where the plans did not show them, and design changes mid-build are the other common culprits. A good builder will price and programme for a sensible amount of contingency, but changing your mind about the layout after the walls are up will always cost both time and money.
Get all your drawings, structural calculations and building control approval in place before you sign a contract, rather than hoping to sort them out while the build is underway. Choose your fixtures and finishes early and confirm lead times in writing. Ask your builder for a written programme with milestones, and agree how variations will be priced and how they will affect the finish date.
It also helps to be realistic about living arrangements. A single storey extension usually allows you to stay in the house, but there will be a period of several weeks with no rear wall, kitchen or utility access. Planning for that in advance means fewer stressful phone calls and fewer changes once the work is in full swing.
Typically 10 to 16 weeks on site for a straightforward rear or side extension. Including design, planning and building control approval beforehand, allow six to nine months from first conversation to finished room.
Many single storey rear extensions fall under permitted development, but Conservation Area status, listed buildings and previous extensions can change that. Always check with East Devon District Council or your designer before assuming, and consider a Lawful Development Certificate for peace of mind.
Usually yes for a single storey extension, as the knock through into the existing house is left until near the end. Two storey extensions and those involving the kitchen are more disruptive, and some households choose to move out for a few weeks at the final stage.
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