Optimal indoor climate in churches: guidance from the Diocese of Lund

In our historic churches, where history and spirituality meet, maintaining a favorable indoor climate is not only a matter of preservation but also of well-being for visitors and staff. The Diocese of Lund has therefore developed detailed recommendations to determine the optimal relative humidity (RH) in the diocese's church buildings—guidelines aimed at protecting the churches' structure, furnishings, and interior design.

Background to the recommendations

Recognizing that every church building is unique, the guidelines emphasize the need to establish an indoor climate tailored to the specific conditions of each structure. The downloadable document replaces the previous requirement for specialized consulting when installing dehumidifiers, providing general yet customized guidance.

Relative humidity is a key parameter in these recommendations. RH indicates how much moisture the air contains relative to the maximum amount it can hold without condensation forming. Understanding and controlling this metric is essential to prevent condensation and the issues associated with both excessively high and low RH levels.

Challenges and Solutions

High or low RH levels can lead to a range of problems, from mold growth and organic damage to cracking in woodwork. The document therefore stresses the importance of maintaining RH levels within specific ranges to mitigate these challenges. Pipe organs, in particular, require stable humidity and temperature conditions to preserve their quality and functionality.

Mold and its prevention

Mold is a common challenge in church buildings, and the recommendations highlight the importance of keeping RH below 70-75% to prevent mold growth. This is particularly crucial since mold proliferation can not only damage the building and its artifacts but also pose health risks.

Salts and Lime Paintings

Another key aspect addressed in the document is the management of salts in masonry. These salts, which can damage plaster and paintwork by dissolving and subsequently crystallizing at varying RH levels, must be managed by maintaining a relatively stable RH.

Concluding Remarks and Recommendations

Ultimately, the goal of the recommendations is to provide guidance that enables the best possible protection and preservation of the church buildings within the Diocese of Lund. By following these guidelines, one can ensure that the church interiors maintain an RH level of 56–68%, which is optimal for preventing the most common indoor climate-related issues.