The aim of improving air tightness of structures is to prevent the uncontrolled air leakages through structures. Built environments contain microbes, particulate and gaseous impurities but removing them is not always necessary. For example, an ageing building envelope commonly contains microbial impurities even when there is no obvious moisture damage. Air leaks convey impurities to indoors where they can lead to poor indoor air quality and associated health problems. Air leaks have also negative impact to energy efficiency and living comfort.
An air tight building envelope prevents air leaks through the envelope structure. Common air leakage places are the joints of structures, i.e. the joint of ground slab and external wall and untight inlets of the envelope. The joints of the structures are typically not air tight without detailed planning. In Finland an air tight building envelope is taken into account in the building regulations and therefore airtightness is relatively good in the new construction. In the existing buildings improving airtightness of structures is a relatively new concept. It can be used in a combination with other renovation methods to solve indoor air quality problems in buildings. In Finland several techniques have been implemented in order to prevent uncontrolled air flux through the structures since 1980’s. In practise the air tightness renovation method has been successful in indoor air quality problems in buildings.
The main principle of moisture or microbial damage renovation is that before installing new building materials all moisture or microbially damaged materials are removed and the source of the problem is identified and fixed. However, in practise it is often impossible to remove all impurities and therefore improving airtightness of the new structure has an important role in completing a successful renovation. Improving of airtightness must be applied on to the whole building envelope. Air tightening renovation is never a single renovation action but always a part of other action. The air tightening material must be elastic, safe and long lasting and tested for its purpose. Improving airtightness requires planning, accurate execution on the construction site and supervision. Quality control measurements are in a key role to success. Quality control measurements are done visually and with the trace-gas leak test. It is very important always adjust the ventilation system to match the changed pressure difference.
In Finland there are no guidelines for planning, execution or supervising air tightness renovation method. It is planned to start certification training and publish first guideline in 2014.