Basement waterproofing and tanking

Tanking a basement costs €50 to €180 a m². A small cellar is €2,000 to €10,000; a cavity drain membrane with a sump is €3,000 to €12,000; full waterproofing of a whole basement is €6,000 to €26,000.

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€50 to €180a m² for tanking or a membrane
€3,000 to €12,000a membrane system with a sump
€6,000 to €26,000full waterproofing of a basement
1 to 2 weeksfor the waterproofing itself

Cellars and basements

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

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

A long curved terrace of white period houses with balconies and black railings along the pavement — **Period houses.** A long terrace of period houses with basement areas behind railings

Three ways to keep water out

Waterproofing below ground is designed to BS 8102, the code of practice used in Ireland. It names three types, and a basement you'll live in often uses two together.

Type A, barrier (tanking). A cement-based slurry or a membrane bonded to the walls and floor. It holds the water back. Good on sound walls with little water.
Type B, structurally integral. Waterproof concrete. Mostly for new basements, built that way from the start.
Type C, drained protection. A dimpled cavity drain membrane on the walls and floor. Water that gets through the wall runs behind it to a channel and a sump, and is pumped out. It doesn't fight the water pressure, so it suits wet basements and old stone or brick.

A room you'll live in needs a dry, warm space with no damp patches: what BS 8102 calls Grade 3. That usually means Type C, or Type A over very sound walls, with ventilation to deal with the moisture in the air.

What goes wrong, and how it's avoided

Painting on a sealer. A coat of waterproof paint on a wet wall blisters and fails. Water pressure wins.
Skipping the survey. Water from a leaking drain, a broken gutter or a high water table needs a different fix. Find the source first.
No sump maintenance. A drained system is only as good as its pump. Plan a yearly service and a battery back-up or a second pump.
Fixing through the membrane. Shelves and radiators fixed through a membrane need sealed plugs, or the water comes with them.
No guarantee in writing. Ask who gives it, how long it lasts and whether it's backed by insurance.

Related guides

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 →

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Questions we get asked

How much does basement tanking cost in Ireland?

€50 to €180 a m². €2,000 to €5,000 for a 15 m² cellar, €4,000 to €10,000 for 20 m², and €4,000 to €10,000 or more for 30 m².

Is tanking or a membrane better?

For a wet basement, a cavity drain membrane with a sump is the safer choice, because it doesn't try to hold back the water pressure. Tanking suits sound walls with little water. See tanking vs cavity drain membrane.

Can I waterproof a basement from the inside?

Yes. Almost all basement waterproofing in existing Irish houses is done from the inside, because digging out the outside of the walls is rarely possible.

How long does basement waterproofing last?

A well-installed system lasts decades. The sump pump is the part that wears, so it needs a yearly service.

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