How long a house extension takes
A one-storey house extension takes 8 to 14 weeks to build and a two-storey one 14 to 24 weeks. Before that come 8 to 16 weeks of design and pricing, plus about 12 weeks for planning permission when the plan needs it. Converting a garage is the fastest way to a new room, because the walls and roof are already standing.
Every stage from the first drawing to moving into the new room, and what stretches it.
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- 8–16 weeksfor design, drawings and builders' prices
- 12 weeksplanning decision and appeal time, if needed
- 8–14 weeksbuilding one storey
- 14–24 weeksbuilding two storeys
Stage by stage
- Design and pricing: 8 to 16 weeks. A measured survey of the house, the drawings, the engineer's design, and builders pricing them.
- Planning permission, if your plan needs it: About 12 weeks. Notices first, then up to 8 weeks for the council to decide and 4 more for appeals. An exempt extension skips this stage.
- Commencement notice, if needed: 14 to 28 days before the start. Needed above 45 m², or where there's planning permission. Lodged online, €30.
- Groundworks: The first weeks of the build. Excavation, any drains diverted, foundations, and the insulated floor slab.
- The structure: The middle weeks. Walls in block or timber frame, the upper floor on a two-storey, the steel and the roof. By the end the new rooms are closed in against the weather.
- Windows, services, the break-through: Once it's closed in. Windows, doors and rooflights go in, the wiring and pipes are run, and the old walls are opened into the new rooms.
- Finishing: The final weeks. Plaster, screed and floors, the en-suite and any kitchen, second fix and decorating.
Once building starts the stages overlap. Together they come to 8 to 14 weeks for one storey and 14 to 24 for two.
Living in the house while it's built
You can usually stay. The new rooms are built outside the house first, and the old walls only come out once they are closed in, so the disruption inside lasts weeks, not the whole job. A two-storey extension is noisier for longer, because the upstairs opening is made through a bedroom or the landing.
Plan for no kitchen or no back door for a short spell near the end, dust in the rooms next to the opening, and a skip and deliveries at the front.
Plan your house extension
Four quick taps, and your plan fills in as you answer: what it costs, whether it needs planning permission and how long it takes. Contact details come last, and only if you want a builder to price it.
25 m² single-storey rear, mid-range finish: €52,000 to €65,000, including VAT and fees.
How the estimate is worked out
Every kind of extension has a build rate per m² for each region of Ireland, VAT at 13.5% included. A standard finish uses the lower half of that range and mid-range the upper half; high spec or a wall of glass moves the build to the glazed rate. Design, engineer and BER fees go on top, with anything you tick (an en-suite, a kitchen, a steel beam into the house) priced at your finish. A garage conversion gets one price for the whole job, since the walls and roof are already standing. Totals are rounded to the nearest €1,000. Use it to plan with. It isn't a quote: a builder prices your house after seeing it.
What slows a build down
- A drain or manhole where the new foundations go, which has to be diverted first.
- Windows, doors and rooflights are made to measure; order them late and the job stands still.
- Changing the design once work has started.
- Wet weather while the ground is open and before the roof goes on.
- A request for further information, or an appeal, on the planning application.
Prices in hand over the winter let you book a spring start while builders still have room in their diaries.
Questions before you build
How long does a house extension take in Ireland?
A one-storey house extension takes 8 to 14 weeks to build and a two-storey one 14 to 24 weeks. Before that come 8 to 16 weeks of design and pricing, plus about 12 weeks for planning permission when the plan needs it. Converting a garage is the fastest way to a new room, because the walls and roof are already standing.
How much time does planning permission add?
About 12 weeks: up to 8 for the council's decision, then 4 for appeals. A further information request or an appeal makes it longer.
How long does a two-storey extension take to build?
14 to 24 weeks of building, after design, pricing and, in most cases, planning permission.
Can we live at home during the build?
Usually. The new rooms are closed in before the old walls are opened, so the upheaval indoors lasts weeks, not months.
When should we start?
Get prices in the winter for a spring start, so the digging and the roof happen in drier weather.
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