Damp Cellar: Costs, Tips & Renovation (2026)

October 5, 2026

4 minutes

If your cellar is damp, you need to act quickly to prevent mould and structural damage. Often, the cause is not immediately apparent – ranging from incorrect ventilation to defective waterproofing. As of 2026, current guidelines show that while professional renovation is an investment, it preserves the value and safety of your property in the long term.

Key facts at a glance

The most important facts about damp cellars and their renovation at a glance:

Risk of summer condensation: Warm summer air condenses on cool cellar walls. Do not ventilate on hot days to avoid additional moisture.
Health risk of mould: Persistent moisture promotes mould, which can irritate the respiratory tract and cause massive damage to the building structure.
Investment in the building envelope: A complete external waterproofing is complex and represents a major investment, but it protects the house from ground moisture in the long term.
Costs of internal waterproofing: The injection method for internal waterproofing costs between 250 and 600 CHF per square metre, depending on the effort and condition of the masonry.
Optimal humidity: A healthy indoor climate in the cellar has a relative humidity of 50 to 60 percent.

These guidelines will help you better assess the situation and take the right measures.

Important technical terms explained simply

Summer condensation

Moisture formation that occurs when warm, humid outside air cools and condenses on cold cellar walls.

Horizontal damp-proof course

A structural barrier in the masonry that prevents ground moisture from rising through the walls via capillary action.

Vertical waterproofing

A surface waterproofing of the cellar walls from the outside that stops the penetration of lateral moisture from the ground.

Injection method

A method of internal waterproofing in which liquid sealants are pressed into the masonry to close pores.

Correctly distinguishing these terms will help you when communicating with specialist companies.

Cellar renovation methods compared

External waterproofing (vertical waterproofing)

When suitable

When lateral moisture from the ground penetrates the walls and a complete, long-term renovation of the building envelope is desired.

Costs & time

The costs for a detached house are between 15 000 and 30 000 CHF. The work usually takes several weeks.

Risks & disadvantages

Very complex and weather-dependent, as the soil around the house must be completely excavated. Gardens will be temporarily affected.

Who should do it

Must be done by a professional structural waterproofer or builder.

Internal waterproofing (injection method)

When suitable

For rising damp due to a missing or defective horizontal damp-proof course, or if external excavation is not possible.

Costs & time

The costs amount to 250 to 600 CHF per square metre. The procedure is significantly faster than external waterproofing.

Risks & disadvantages

The outer wall remains damp and uninsulated, which can lead to spalling in severe frost.

Who should do it

Specialist companies for cellar waterproofing.

Professional room dehumidification

When suitable

If there are no structural defects, but the moisture is caused by usage (e.g. drying clothes) or slight condensation.

Costs & time

A professional device including wall mounting costs around 1 000 to 1 600 CHF. The installation is completed in a few hours.

Risks & disadvantages

Only treats the symptom. If there is a structural defect, the masonry will continue to be damaged.

Who should do it

Can often be installed yourself or by an electrician (for the power connection).

Step-by-step: How to dry out your cellar

A damp cellar requires a structured approach to permanently resolve the cause. Follow these steps:

Determine the cause of the moisture

Check whether the dampness is caused by incorrect ventilation (condensation), a burst pipe, or defective outer walls. A hygrometer helps with the initial assessment.

Apply correct ventilation habits

In summer, only ventilate in the early morning or late evening hours when the outside air is cooler than the cellar air to avoid summer condensation.

Contact a specialist company for a site inspection

If the walls are permanently wet or mould forms, consult an expert (structural waterproofer or energy consultant). In the case of mould infestation, quick action is important for health reasons.

Determine the renovation method

Decide together with the professional whether external waterproofing, an internal injection, or the use of a building dryer is the best solution.

Compare quotes and check for subsidies

Obtain at least two comparative quotes. Clarify whether your canton or municipality offers subsidies for the renovation and insulation of the cellar.

Have the waterproofing work carried out

Have the structural measures implemented by the specialist company. After water damage, the cellar must also be professionally dried and disinfected.

Careful planning and cooperation with professionals guarantee that your cellar will remain permanently dry.

Frequently asked questions about damp cellars

Here you will find the most important answers regarding the dehumidification and renovation of cellar rooms.

Why is my cellar damp in summer?

This is usually due to so-called summer condensation. Warm outside air can hold a lot of moisture. If this flows into the cool cellar, it cools down and the excess water condenses on the cold walls.

How much does cellar waterproofing cost in Switzerland?

A complete external waterproofing for a detached house costs an average of 15 000 to 30 000 CHF. Internal waterproofing using the injection method is around 250 to 600 CHF per square metre.

Can I waterproof the cellar myself?

You can handle minor interior work or setting up a dehumidifier yourself. Complex work such as excavating the soil or installing a horizontal damp-proof course must be carried out by professionals.

What measures are necessary after water damage?

Quick action is required after water damage. Specialist companies use powerful condensation dryers for drying out. In the event of sewage flooding, professional disinfection is also absolutely necessary.

Are there subsidies for cellar renovation?

Yes, many cantons and municipalities offer subsidy programmes, especially if the waterproofing is combined with an energy-efficient renovation (perimeter insulation). Specialist companies can advise you on this.

Do not hesitate to consult a building expert in the event of persistent moisture to avoid expensive consequential damage.