Basement conversion in Mayo

Converting a basement in Mayo costs €1,000 to €2,500 a m², and tanking €50 to €180 a m². Tell us the job and one basement company that covers Castlebar, Ballina and Westport and the rest of Co. Mayo rings you with a written price.

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17.6%of homes the EPA measured in Mayo were above the radon reference level
1,458 mmof rain a year at Castlebar
15%of Mayo homes were built before 1946
€1,000 to €2,500a m² to convert a basement

Basements and the work

A white terrace of period town houses with black railings and basement areas along a stone pavement — **Period houses.** Period town houses with basement areas behind the railings

Narrow steps leading down between black railings to a red basement door — **Basement flats.** Steps down to a basement door, below street level

Brick steps with a handrail leading down into a lit vaulted brick cellar — **Cellars.** Brick steps down into a vaulted cellar

Basements in Mayo

895Mayo homes measured above 200 Bq/m³

3,366Mayo homes built before 1919

1,458 mmrain a year at Castlebar, the wettest of three Mayo towns

281one-off houses finished in Mayo in 2025

Census 2022 counted 51,996 households in Mayo. 3,366 homes (7%) were built before 1919 and 15% before 1946: the period houses where most cellars and basement storeys are. 70% are detached, with room at the side or back for a light well.

281 one-off houses were finished in Mayo in 2025. A basement costs least when it's designed in before the house is built.

Radon in Mayo

Of the 5,076 homes the EPA has measured in Mayo, 895 (17.6%) were above the 200 Bq/m³ reference level, and 77 were above 800. The highest reading was 6,200 Bq/m³. That's the 5th highest share of the 26 counties, against 14.1% nationally.

That's high. In Mayo, put a radon barrier and a sump into any basement plan from the start, and test the room once it's in use.

Water and Mayo basements

Castlebar gets 1,458 mm of rain a year, Westport 1,447 mm and Ballina 1,222 mm.

That's wet ground for much of the year. Water pushes against basement walls in Mayo more often than in the east, so a drained membrane with a sump and a back-up pump is the safer system here.

Planning in Mayo

Converting an existing basement inside the house usually needs no permission. A new basement, a new front light well or a protected structure is a question for Mayo County Council. See planning permission.

What it costs for your size

Two taps: the job and roughly how big the basement is. The answer comes from our price guide.

The job

Convert an existing basementInto a finished roomWaterproof (tank) itDamp or water coming inDig a new basementOr lower the floor

Floor area, roughly

Typical range

€30,000 to €75,000

30 m² at €1,000 to €2,500 a m², the usual range to turn an existing basement into a finished room. Tanking with a membrane and a sump is often priced on top, at €3,000 to €12,000.

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How this is worked out

For a conversion or a dig-out, the floor area times our range a m² (€1,000 to €2,500 to convert, €3,000 to €6,000 to dig). For tanking, the typical price for a basement that size. It's a guide, never a quote: the company prices your basement after a look. Building work on a house is charged VAT at 13.5%. Ask whether the written price includes it.

Near Mayo

Basement conversion and waterproofing guides & price breakdowns

Straight answers to what people ask most: itemised costs, specifications, planning or grants, and what to check before you book.

Cost & Pricing GuideBasement conversion cost in IrelandBasement conversion cost in Ireland: €1,000 to €2,500 a m², €30,000 to €100,000 for most. Tanking €50 to €180 a m². Our price guide and one free quote.Read the guide →Specification GuideBasement sump pumpsBasement sump pumps in Ireland: €1,000 to €2,000 for a sump system. How a sump works, two pumps, battery back-up, alarms and servicing. One free quote.Read the guide →Comparison GuideTanking vs cavity drain membraneTanking vs cavity drain membrane for a basement in Ireland: how each works, which suits a wet basement, costs, sumps and guarantees. One free quote.Read the guide →Grants & RegulationsBuilding Regulations for a basementBuilding Regulations for a basement in Ireland: escape in a fire (Part B), radon and damp (Part C), ventilation (F), insulation (L), structure (A).Read the guide →Specification GuideRadon and basementsRadon in basements in Ireland: the 200 Bq/m³ reference level, High Radon Areas, radon sumps (€500 to €2,000) and testing. One free quote.Read the guide →Timeline & PreparationHow long a basement conversion takesHow long a basement conversion takes in Ireland: 6 to 12 weeks for most, waterproofing 1 to 2 weeks, finishing 2 to 3 weeks. Digging out takes longer.Read the guide →

More guides & resources: All guides & calculator hub · Technical & trade glossary · Frequently asked questions · All areas covered · About this site

Mayo questions

How much does a basement conversion cost in Mayo?

€1,000 to €2,500 a m² to convert an existing basement, or €30,000 to €100,000 for most. Tanking alone is €50 to €180 a m².

Is radon a problem in Mayo basements?

17.6% of the homes the EPA measured in Mayo were above the reference level. Seal the floor and fit a radon sump while the basement is open.

Do I need planning permission for a basement in Mayo?

Not usually inside an existing basement. A new basement or a protected structure is a question for Mayo County Council.

Do you cover all of Co. Mayo?

Yes. Requests from Castlebar, Ballina, Westport, Claremorris and Ballinrobe and everywhere else in Mayo go to one basement company that covers your county.

How long does a basement conversion take in Mayo?

6 to 12 weeks for most. Planning, where it's needed, comes first.

Basement conversion and waterproofing across all 26 counties

Requests from all 26 counties go to one vetted local specialist who covers your county — from Dublin, Cork, Galway and Limerick to Kildare, Meath, Wicklow, Waterford and Donegal. Pick your county below for local prices, specifications and advice. Compare all areas covered →

Get a free quote for your basement

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