Solving moisture and mould problems in historic churches

When employees at the small, medieval Heldum Church in the most western part of Denmark, started complaining about health problems, it became clear to the parish council that something needed to be done.

Humidity levels were often above 80%, which had implications not only for the condition and preservation of the building itself, but also for the health of the employees. Several employees reported symptoms that could be linked to poor indoor air quality, and it became clear to the church council that action was needed.

Causes of high air humidity and mould in the church space

Several factors contributed to the moisture problem in the church:

A generally wetter climate combined with harsh wind conditions in the West Jutland landscape and insufficient natural ventilation meant that moisture often accumulated, providing optimal conditions for mould to grow.

To reduce energy costs, the temperature is lowered when the church is not in use, which is most of the time. The low temperatures and stagnant air further contributed to the problem.

Conservation restrictions also made it difficult to implement permanent changes such as a built-in ventilation system.

A simple dehumidifier solved the problem

The parish council was advised by their architect to try a mobile dehumidifier that could work effectively without requiring permanent changes to the building structure. The parish council's building manager, Kristen Sørensen, and cemetery manager, Anders Clausen, then contacted Dantherm in Skive, and after professional advice, a dehumidifier with remote monitoring was installed in early 2023. The dehumidifier was placed in the centre of the church room and can easily be moved out when the church is used for services and events.

To accurately monitor the humidity problem, three sensors were placed at key points where there had previously been problems with high humidity levels. The dehumidifier activates itself when the humidity level rises and the humidity level is now stable at 60-65% - a level that protects against mould without damaging the church's woodwork. The air must not become too dry either.

Kristen Sørensen and Anders Clausen confirm that the indoor climate has improved and that the dehumidifier is very easy to work with. If problems arise, Dantherm is always easy to get in touch with and their contact person is very good at suggesting solutions.

Remote monitoring and documentation for the future

With the remote monitoring and the associated programme, they can both easily track temperature and humidity levels on the computer and keep track of whether the equipment is running optimally and if, for example, the dehumidifier is switched off by mistake. The sensor solution stores data and documents the conditions in the church, which can be useful if there is a need to apply for further permits in the future, or if more extensive solutions are required.

The dehumidifier is a more effective solution than simply heating the church, as heating alone lowers the relative humidity without removing the moisture (as warm air can contain more moisture than cold air). Heating could even risk creating additional condensation when the warm air meets the cold church walls.

Kristen Sørensen from the parish council concludes: "We are considering whether the dehumidifier should be a permanent solution. It's difficult to install ventilation in an old building, and manual solutions such as leaving an employee in charge of ventilation can easily lead to errors and irregularities.

The next step is for us to evaluate the solution together with the architect and assess what will happen in the future and how we can incorporate climate control in a future renovation of the church."

Results and perspectives

Since installation in early 2023, the dehumidifier has removed a minimum of 10 litres of water per day and consumed approximately 1700 kWh in 20 months. Heldum Church's moisture problems are under control and the employees' health problems have disappeared. The mobile dehumidifier has provided the parish council with a valuable solution that protects the historic building, improves the working environment and is very cost efficient.

To find out more about Dantherm Group's complete range of dehumidification solutions, contact our team via the form below.