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House extensions
More room at the back or the side of the house, built by one crew from the foundation to the last coat of paint, with a written price that does not move once we start.
in short
AltHome builds single and two storey house extensions across Kerry, Cork and Limerick, with one crew taking the job from foundation to the last coat of paint. The price is set in writing after a survey and does not move once work starts. A typical extension takes 10 to 16 weeks on site, and the house stays lived in because the old wall only comes out once the new roof is on.
what it costs
What makes one extension cost twice as much as another?
Size is the obvious answer and the least interesting one. Below the surface, four things do most of the damage to a budget. Groundwork comes first. A flat garden with firm ground and a shallow foundation is the cheap start. Made ground, a high water table, a slope, or a sewer running where your foundation wants to be all add digging, concrete and time before anything is visible. Ask about the drains early, because diverting a public sewer is a different project from building over a private one. Second, the shape of what you open up. Taking out a section of wall and dropping in a steel beam is routine. Taking out most of the back wall to make one open room means a bigger steel, sometimes padstones and a column, and a structural engineer to size it. That is money well spent, but it is money. Third, glazing. Sliding doors, roof lanterns and corner glass are where a plain extension turns into an expensive one. They are also what people remember, so it is worth deciding early rather than trimming them at the end. Fourth, what the new space asks of the old house. A kitchen means plumbing, electrics, ventilation and often moving the boiler. A room you only sit in asks for far less. Regulations sit over all of it. Building regulations apply to the work whatever the size, so insulation, ventilation, fire safety and structure are not optional. Planning is separate: a single storey extension to the rear can be exempt within limits on floor area and on how much garden is left, and those limits are smaller once the house has been extended before. Front extensions and most two storey work need permission. We check the house against the rules at the survey and tell you plainly which route you are on before you spend money on drawings.
How long will we be living on a building site?
Ten to sixteen weeks is the honest range for a single storey extension, longer if the glazing has a lead time. The house stays usable for most of it. The hard week is when the back wall comes out, and we plan that for when the new structure is already roofed and closed. We agree the dust screens, the route in and the toilet arrangement before day one, not after.
the work
What is included in a house extension?
- Survey the site, check the drains and set out the foundation.
- Dig and pour the foundations, build the rising walls and lay the insulated floor slab.
- Build the walls, fit the steel where the old wall opens up, and roof the new structure.
- Fit the windows and doors, then first fix the electrics and plumbing.
- Insulate, board, skim, tile and decorate.
- Connect the drains, make good the garden, leave the site clean and take the waste with us.
4 steps
How long does it take to build a house extension?
You get in touch
Ring, message or send the form with a photo. We answer the same day.
We come and look
A survey on site, then a written price that does not move once work starts.
We do the work
Materials come in at the side, the garden takes the mess and the house stays lived in. The old wall comes out only when the new roof is on.
You sign it off
We walk the job with you, clear the site and leave the guarantee in writing.
next door
The rest of the house
An extension only looks finished when the old half of the house matches it, and that is the part people forget to price.
asked
Extensions: common questions
Do I need planning permission?
Sometimes. A single storey rear extension can be exempt within limits on floor area and on the garden left behind it, and those limits shrink if the house was extended before. Front extensions and most two storey work need permission. We measure what is already there at the survey and tell you which side of the line you are on. Where it is close, we send you to the council with the numbers rather than guessing for you.
Can you work to a fixed price?
Yes, once we have seen the ground and the drawings. The price covers the work described in writing. The two things that can move it are what we find under the ground and changes you ask for later, and both are agreed with you in writing before the cost lands.
Do you do the drawings and the paperwork?
We build. We work alongside your architect or engineer, and if you do not have one we will point you at people we have worked with in Kerry, Cork and Limerick. You keep that contract directly, so nobody is marking up somebody else’s fee.
How much does an extension cost in Kerry?
Size is only part of it. Ground conditions and drains, how much of the existing wall is opened up, the glazing, and the kitchen or bathroom fitted inside make the biggest difference. We price from drawings or a survey, line by line, so you can see where the money goes.
What size extension can I build without planning permission?
In Ireland a rear extension to a house can be exempt up to 40 m² in total, including earlier extensions, as long as it meets limits on height, garden space left and distance from boundaries. Anything to the side or front, or larger, needs permission. Check your case with the council or your designer before committing.
quote
Get a fixed quote for an extension
Tell us the address and what you want done. We work across Kerry, Cork and Limerick. We ring you back within one working day. Add photos and the price we send you will be tighter.
085 220 1422 · info@althome.ie
Written by the AltHome crew. Last reviewed September 2026.