Interrupting the ventilation of buildings has a significant impact on indoor air quality and moisture and mold problems. However, periodic use or reduction of general ventilation is very common due to its high energy consumption.
A study has recently been published on the subject, according to which buildings become under-pressurized when the general ventilation is off. In practice, this causes the microbial concentrations and humidity in the indoor air to increase when the flushing effect of the replacement air is removed.
Negative pressure can also lead to the migration of microbes through structures, for example from the crawl space of buildings into the indoor air. On the other hand, using ventilation at 20–30% partial power generally seems to keep the pressure differences sufficiently small, and the microbial and moisture concentrations in the indoor air do not increase as much as in situations where the ventilation is stopped completely.
For non-residential buildings, there is a guideline in the Finnish Building Regulations that the ventilation coefficient should be at least 0,2 l/h outside of operating hours. This can be done by keeping only the ventilation of the hygiene facilities running continuously and by intermittent ventilation of the rest of the building. The general recommendation is that before starting the periodic use of general ventilation, the pressure differences in the building should be carefully studied in order to find out the possible risks and effects on both the quality of the indoor air and the functionality of the structures.
Finland's repair debt is currently around 50 billion euros. The amount clearly shows that the condition of the buildings is not at the required level. About one in four public buildings suffers from moisture and mold damage that requires repair measures and evacuation facilities. If the buildings that are still in good condition are to be kept operable in the future as well, attention must be paid to use and maintenance, and actions must be taken in accordance with the care and repair plan made and maintained in advance. Regular, preventive measures extend the life cycle of the entire building and are especially cost-effective in the long term, when expensive repairs can be avoided with them.
Already three years ago, the Parliamentary Audit Committee's publication (1/2012) "Dampness and mold problems in buildings" stated that, despite the requirements of machine maintenance instructions, only 5-10% of ventilation systems are maintained and cleaned flawlessly. The measurement and balancing of air flows, which are extremely important measures, are also quite often not done. If the ventilation systems are not taken care of, the effects of stopping them cannot be known.
Jani Kemppainen
Agent
Building Construction Industry Association
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