Basement conversion & waterproofing FAQ

€1,000 to €2,500 a m² to turn an existing basement or cellar into a finished room, so €30,000 to €100,000 for most whole conversions. Waterproofing on its own is €50 to €180 a m². Digging a new basement is €3,000 to €6,000 a m². See the cost guide.

6 to 12 weeks for most conversions. The waterproofing itself is 1 to 2 weeks, then 2 to 3 weeks of finishing. Digging out takes longer, because the underpinning goes in stages. See how long it takes.

No. There's no national grant for converting or waterproofing a basement. Radon work isn't grant-aided either, but the EPA tests the house again for free after the work.

Some. Old plaster and floors come out first, so expect dust and a skip. Most waterproofing work stays inside the basement. Digging out means spoil leaving through a side passage or the house, so the company plans the route before they start.

Ask for the waterproofing guarantee in writing: who gives it, for how long and what it covers. A sump pump needs a yearly service to keep working, and often to keep the guarantee.

Not usually to convert an existing basement inside the house. A new basement dug under the house or garden, a light well at the front or a protected structure is a question for the council. See planning permission.

One basement company that covers your county. They look at the basement, check where water gets in and how high the radon risk is, and price it in writing. You deal with them directly.

Georgian, Victorian, and Edwardian brick walls move slightly with the seasons and hold decades of ground salts. Rigid cementitious tanking can crack if the masonry shifts or debond under hydrostatic pressure, whereas a studded Type C cavity drain membrane depressurises any moisture behind the wall and directs it harmlessly to a sump pump.

Every habitable Type C basement chamber is fitted with a primary mains pump, a secondary standby pump on an independent float switch, a non-return check valve on the rising main, and a battery backup inverter capable of cycling the backup pump hundreds of times while mains power is out.

To feel comfortable and accommodate a drained floor membrane, rigid floor insulation, screed, and a fire-rated ceiling below the ground-floor joists, a finished ceiling height of 2.2 m to 2.4 m is ideal. If your raw cellar is only 1.7 m to 1.9 m high, lowering the floor via structural underpinning adds the extra headroom.

Converting an existing internal cellar or lowering its floor strictly within the footprint of the house is often exempt from planning permission unless the property is a Protected Structure or sits in an Architectural Conservation Area, though adding a new front lightwell or external stair always requires planning permission.

Yes. Grey water from a washing machine or basin and foul waste from a basement toilet are piped into a sealed, odour-tight below-floor pumping station that lifts the waste up into the main house soil stack or external manhole via a 32 mm or 50 mm pressure pipe.

A basement sump chamber and perimeter drainage channels should be inspected and flushed once every 12 months. The annual service takes under an hour and cleans silt from the sump base, tests both float switches, checks the non-return valve, and load-tests the backup battery.