Airtight structures are rarely the cause of indoor air problems

Energy efficiency is not a threat to good indoor air as long as buildings are built correctly.

Airtight and energy-efficient buildings are often criticised for having indoor air problems. However, an airtight structure is not always the cause of the problems.

“The use of plastic vapour barrier sheets, for example, is often considered the cause of mould growth, but studies have shown that they do not cause moisture damage. The problems are often caused by the fact that when they began to use plastic as a vapour barrier, they forgot to add ventilation systems to the buildings,” says Juhani Pirinen, head of a business unit at FCG, who has studied indoor air problems for a long time.

According to Pirinen, overly airtight buildings often have no supply air systems or the ventilation system draws supply air through the structures.

“And when there is no ventilation, problems will appear. These problems can, however, be avoided. It makes sense to build an airtight building and bring air in with ventilation equipment or clean ducts passing through walls. Then an airtight structure will not be a problem.”

Non-airtight structures allow impurities to enter indoor air

Pirinen points out that a mechanical ventilation system should not be installed until the building structures are definitely airtight.

“Supply air usually comes from underground where microbes grow. If the structure is not airtight and microbes enter the indoor air, there will be problems. At least the biggest holes must be eliminated first. Even minor air leaks can make life more difficult if the residents have become sensitised to poor indoor air.

According to Pirinen, more attention should be paid to the airtightness of sheathing structures. “If the sheathing structure is not airtight, dust will accumulate in the thermal insulation and over time it will become moist and mouldy, especially if ventilation behind the facade structure is insufficient.”

There is a lot of lively debate over indoor air issues. It’s no wonder as many municipalities are feverishly looking for solutions to the challenges caused by indoor air problems. Indoor air, moisture problems, energy efficiency and, for example, the choice of materials involve a lot of data based on measurements and studies, but there are also many perceptions, assumptions and open questions related to the issue. Petri Heljo, head of R&D from Kiilto’s construction unit, compiled several statements and prevailing views on indoor air problems. Experienced and respected indoor air specialist Juhani Pirinen then commented on them and we were able to create an interesting series of articles that will be published during the autumn of 2018.