Technical condition and energy

Waterproofing (hydroizolace)

In Czech: Hydroizolace

Waterproofing (hydroizolace) is a layer or treatment that stops water and ground moisture getting into walls, floors, cellars and the roof. Where it is missing or worn out, you get damp, mould and crumbling plaster.

Also called: damp-proofing, damp-proof course, tanking, izolace proti vlhkosti

What it means

Waterproofing (hydroizolace) protects a building from water. Below ground it means insulating foundations, cellar walls and floors against ground moisture or water under pressure. Above, it is the roof covering and the waterproof layers of roofs, terraces and balconies; bathrooms have it under the tiles too.

Many older houses have no working waterproofing below ground, or it has reached the end of its life. Moisture then rises into the walls, ruins plaster and creates conditions for mould.

How it works in the Czech Republic

You usually cannot see the waterproofing itself, because it is in the ground, under the floor or in the roof. Its failure shows through the consequences: damp patches and salt deposits on ground-floor and cellar walls, blown plaster, a musty smell, stains on ceilings below the roof or a terrace. If in doubt, call a building surveyor who can measure moisture in the masonry.

The fix depends on the cause: retrofitted insulation in the masonry, digging out and sealing the foundations, drainage around the house or roof repairs. It is best to know the scope and cost before you buy. In a block of flats the roof and foundations are usually common parts, repaired through the owners' association (SVJ) or cooperative.

Damp that appears after purchase and could not be recognised at the viewing may be a hidden defect (skrytá vada). For a building firmly attached to the ground, the Civil Code says the buyer must claim it within five years of acquisition at the latest. If the seller knew or must have known about it, they cannot defend themselves by saying the claim came too late.

Practical example

For example, you view a family house on low ground near a river. The cellar is freshly painted, but the corners smell musty and the lower part of the wall is cold and darker. Ask when and how damp was dealt with, have the masonry moisture measured and check whether the plot lies in a flood zone (záplavové území). Reflect the result in your budget or offer.

What to watch out for

  • Inspect the cellar, ground floor and top-floor ceilings for damp patches, salt deposits and fallen plaster.
  • Be cautious with freshly painted cellars and covered plinths.
  • Ask about any history of leaks and for documents on repairs to the waterproofing or roof.
  • Check whether the plot lies in a flood zone.
  • For a flat under the roof or a terrace, ask the SVJ about their condition and planned repairs.

Frequently asked questions

How can I tell a house has no working waterproofing?

Typical signs are damp patches and salt deposits low on the walls, crumbling plaster and a musty smell. Measuring moisture in the masonry and a professional inspection give a more reliable picture.

Can waterproofing be added later?

Yes, there are several methods, from cutting in a new barrier or injection to sealing excavated foundations. A specialist will choose the method and estimate costs based on the cause.

Is damp a hidden defect?

It can be, if it was not noticeable at the viewing. For a building, the Civil Code requires the buyer to claim it within five years of acquisition; a lawyer can assess your case.

  • Latent defects (skryté vady)Latent defects (skryté vady) are faults in a property that could not normally be spotted at the viewing or handover, such as damp in the walls or damaged pipes. For buildings, the law links them to a five-year period from acquisition.
  • Structural stability (statika budovy)Structural stability (statika budovy) describes how a building's load-bearing parts, its foundations, walls, floors and roof frame, carry loads. Structural defects show up as cracks or sagging ceilings and are assessed by a structural engineer.
  • Flood zone (záplavové území)A flood zone (záplavové území) is an officially defined area that may be flooded in a flood. It is set by the regional authority through a general measure, and statutory restrictions apply in its active zone, for example to building.
  • Renovation (rekonstrukce)Renovation (rekonstrukce) means repairing or modernising a flat or house by renewing parts of it, such as wiring, plumbing, the bathroom, windows or roof. In Czech listings the word can cover anything from new floors to a full rebuild.
  • Family house (rodinný dům)A family house (rodinný dům) is a building intended mainly for one or a few households, either detached or attached to neighbouring houses. It is usually sold together with the land, of which the building is legally a part.

Sources

Laws and official pages this text is based on (in Czech).

This text is for information only and has not yet been checked by a legal or financial expert. It is not legal, tax or financial advice. Verify important details in the listed sources or with a professional.

Updated 25 October 2026

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