Is moisture damage always visible?

No. The most serious damage spreads inside the structure and is only confirmed by a moisture measurement or condition survey.

How long does waterproofing last?

Typically about 20–30 years. Before 1999 the membrane may be inadequate or missing.

Who is liable for moisture damage after the sale?

It depends on whether the defect was hidden and what the inspection found. Clarify liabilities before the deal.

Moisture damage: how to spot it and what to ask before buying

By Lumi · Updated: Jun 19, 2026, 12:00 AM

Moisture and mould damage is the most common hidden defect. Where it comes from, where it hides and how to verify the wet-room before buying an apartment.

Important: Moisture damage is the most common hidden and costly defect. Check the wet-room waterproofing and its age — buildings before 1999 often lack it. When in doubt, order a condition survey.

Moisture damage is the most common cause of disputes and surprise costs in apartment sales. It often develops slowly from a wet-room or pipe leak and is invisible on the surface. Here is how to assess the risk before making an offer.

Where moisture damage comes from

The usual causes are inadequate or aged wet-room waterproofing, a pipe leak and poor ventilation. The damage often spreads for years inside the structure before it shows.

Modern wet-room waterproofing has only been standard practice since around 1999. In older bathrooms the membrane may be inadequate or missing entirely.

Where it usually hides

The bathroom, sauna, the kitchen sink cabinet and the area around the floor drain are the most typical spots. External walls and the base floor can also be affected.

Smells, dark patches, bubbling paint or loose tiles are warning signs — but the most serious damage is not always visible on the surface.

How to verify the condition before buying

Ask the year of the wet-room renovation and whether the waterproofing was done properly. Check the renovations listed in the manager's certificate.

When in doubt, order a condition inspection or a more detailed condition survey — a moisture measurement from the structure is the only certain method.

What to ask the seller

Has the apartment had moisture damage or water leaks? When was the bathroom last renovated and is there documentation?

The building's age and the wet-room risk window are shown directly by address in the Lumi report.

Frequently asked questions

Is moisture damage always visible?: No. The most serious damage spreads inside the structure and is only confirmed by a moisture measurement or condition survey.
How long does waterproofing last?: Typically about 20–30 years. Before 1999 the membrane may be inadequate or missing.
Who is liable for moisture damage after the sale?: It depends on whether the defect was hidden and what the inspection found. Clarify liabilities before the deal.