In this study, durability of building airtightness was assessed by means of repeated airtightness testing of the studied houses. This approach generally involves the following issues which complicate the comparison of the test results:
- a lack of knowledge about the modifications of the air barrier system between two tests
- differences in building preparation
- differences in testing procedure and equipment if the tests are performed by different technicians
- different conditions during each test
In this study, all the tests were performed by the same technician using the same equipment. The technician always prepared the building in the same way and followed the same measuring procedure. The majority of the tests were carried out in the same period of year under similar climatic conditions. Therefore, the differences between the test results should reflect namely the impact of ageing and the impact of the air barrier system modifications. Information concerning interventions to the building envelope was collected from the building users or the caretaker. Therefore, the impact of such interventions on the building airtightness is traceable.
The studied buildings were built in 2007 using the same construction system with an emphasis on the quality of execution of the air barrier system. They have a very similar size, the same timber structure and the same air barrier system (PE foil, butyl tapes). Building A and D are an inhabited single family houses. Building B is a showhouse of the construction company and the building C serves as training centre and conference room. This allows a comparison of the potential impact of different users’ behaviour on the airtightness durability. The buildings A and B were tested at the commissioning, 3 years after and then each 2 years or even each year. The buildings C and D were tested only twice, at the commissioning and 11 years later.
In all the buildings, airtightness has deteriorated over 11 years. The n50 of buildings A and B increased from 0.5 h-1 to 0.7 h-1. The n50 of building C and D increased more significantly from 0.5 h-1 to 1.3 h-1 and from 0.7 h-1 to 1.4 h-1 respectively (due to improper repair works after a failure of the sewage water system and due to a refurbishment carried out with little concern about airtightness). The results show that a good airtightness durability (relatively small increase of the n50 value) can be achieved if:
- the air barrier system is designed and executed carefully
- the users respect some basic restrictions concerning the modifications of the building envelope which aim to protect the air barrier system
- all interventions into the air barrier system that can occur e.g. during refurbishment or repair works are properly repaired (inversely, improper interventions can significantly deteriorate the airtightness)
The results confirm that the airtightness decreases namely during the first years of the building service (e.g. in building B, the n50 increased from 0.5 h-1 to 0.65 h-1 during the first 3 years and from 0.65 h-1 to 0.7 h-1 during the next 7 years).