What do we know about the durability of building airtightness?

Airtightness durability is a growing issue in Europe and the US. In the long-term, it seems that some specific sealing products have durable performances but on-site studies have shown that many factors can deteriorate the airtightness durability of wall assemblies such as the association of incompatible products, poor implementation conditions, extreme wind loading or external interventions into the building envelope. As a result the global building airtightness seems to not be robust, and to deteriorate mostly in the first years after the construction.

Durability is investigated through laboratory and on-site studies. On site studies have shown that changes in building airtightness over time are very variable: for each study results differ considerably between the tested houses, with almost always at least one presenting an improved airtightness (by up to 40%) and almost always at least one presenting a very deteriorated airtightness (by up to 580%) compared to the initial airtightness test result.

Airtightness durability is a growing issue in Europe and the US. Various studies have been ongoing for the past 15 years as well as major projects (i.e. DURABILIT’AIR).

Some studies focus on laboratory tests to evaluate the durability of sealing products, in particular tapes with mechanical tests performed before and after artificial ageing. In Germany, a standard to test the durability of airtightness products in laboratory, DIN 4108-11, has been published at the end of 2018 and may be introduced as a project to CEN (European Committee for Standardization) to the T.C. (Technical Committee) 89.

Results of such laboratory tests give indication on the product performance. It is however not a guarantee that the building airtightness relying on these products will be durable as:

there is no obvious correlation between the durability of the product alone and the assembly airtightness [1];
laboratory conditions differ from on-site building conditions so that the measured performance may differ in practice from test results;
natural ageing, with various load types (temperature, humidity, wind, UV, rain, etc.) occurring sometime simultaneously cannot be accurately reproduced with artificial ageing and is specific for each building;
the product performance is usually measured through mechanical tests (peel and shear resistance measurement for example) such as in DIN 4108-11, which is not a direct air permeability measurement, and results may differ significantly [2].

On-site studies have also been carried out in the past decades to evaluate the buildings airtightness durability ([3]-[15]). Pressurization tests are performed both shortly after construction and some years later (from 1 to 25). The comparison between these airtightness measurements allow us to draw, for now, the following conclusions:

Airtightness is not robust: Significant changes in air permeability with time are observed for at least part of the tested houses in all studies (except one study [10]). This is the case whatever the initial airtightness level, building age and building sample size.
Airtightness tends to deteriorate after completion: The mean change in air permeability is positive for all studies.
Changes in airtightness are very variable: For each study results differ considerably between the tested houses, with almost always at least one presenting an improved airtightness (by up to 40%) and almost always at least one presenting a very deteriorated airtightness (by up to 580%).
Changes in airtightness occur quickly after construction: the mean change in measured air permeability does not seem to clearly increase with the building age, which would mean that changes occur mostly within the first (1 or 2) year(s) of the building use. This is suggested in the study with the largest sample size [8] and confirmed by a study with buildings tested regularly where air permeability increased mainly in the first years [6].
Changes in airtightness in absolute terms seem correlated to the initial air permeability level: Changes in absolute terms are bigger for initially more permeable buildings. In other words, an initially very airtight building tends to have rather small additional air flow rates (in absolute term) compared to an initially leaky building.
Changes in airtightness does not seem to strongly depend on the main construction material: both wooden and concrete constructions were sometimes found to have a durable airtightness and other times a strongly deteriorated airtightness.

These studies also point out various possible key factors of airtightness decrease over time:

Building’s natural “movements”: Heating houses for the first time may induce the shrinkage of mastics and structure movements
External interventions: Drilling hole into the envelope deteriorating the air barrier system; Installation of cables or ductwork after the completion of the building
Specific building materials and construction types:
- Houses generally became leakier than the flats in [13]
- 2-storey houses seem to deteriorate more than 1-storey [8].
- Airtightness of houses with exposed wood frame roofs seems to deteriorate more than other roofs [8].
- Airtightness unchanged for houses with polyethene air barriers, but slightly degraded for houses built with the drywall approach in [5].
- Plasterboard-lining as an internal finish can result in very high leakage according to [16]
Poor workmanship
Unsuitable implementation conditions for adhesives and mastic such as cold and/or dusty conditions [17].
Airtightness measurement conditions: building preparation and measurement uncertainty [3]. Especially if the two tests are not performed by the same people.

To conclude, in the long-term, it seems that some specific sealing products have durable performances but on-site studies have shown that many factors can deteriorate the airtightness durability of wall assemblies such as the association of incompatible products, poor implementation conditions or external interventions into the building envelope. As a result the global building airtightness seems to not be robust, and to deteriorate mostly in the first years after the construction.

References

[1] P. Ylmén, M. Hansén & J. Romild, "Durability of air tightness solutions for buildings", 35th AIVC Conference "Ventilation and airtightness in transforming the building stock to high performance", Poznań, Poland, 2014, p. 268‑278.

[2] E. B. Møller & T. V. Rasmussen, "Testing Joints of Air and Vapour Barriers, Do We Use Relevant Testing Methods?", XV International Conference on Durability of Building Materials and Components (DBMC 2020), Barcelona, Spain, 2020.

[3] W. Bracke, J. Laverge, N. Van Den Bossche & A. Janssens, "Durability and Measurement Uncertainty of Airtightness in Extremely Airtight Dwellings", International Journal of Ventilation, vol. 14, no 4, p. 383‑393, 2016, doi: 10.1080/14733315.2016.11684095.

[4] S. Verbeke & A. Audenaert, "A prospective Study on the Evolution of Airtightness in 41 low energy Dwellings", 12th Nordic Symposium on Building Physics (NSB 2020), E3S Web Conf., vol. 172, p. 05005, 2020, doi: 10.1051/e3sconf/202017205005.

[5] G. Proskiw, "The variation of airtightness of wood-frame houses over an 11-year period", Thermal performance of the exterior envelopes of buildings VII Conference, Clearwater Beach, Florida, 1998, p. 745-751\r874.

[6] J. Novák, "Assessment of durability of airtightness by means of repeated testing of 4 passive houses", 39th AIVC Conference "Smart Ventilation for Buildings", Antibes Juan-Les-Pins, France, 2018.

[7] ADEME, "Quelle pérennité de la perméabilité à l'air des maisons individuelles BBC en Normandie?", 2016.

[8] B. Moujalled, V. Leprince, S. Berthault, A. Litvak & N. Hurel, "Mid-term and long-term changes in building airtightness: A field study on low-energy houses", Energy and Buildings, vol. 250, p. 111257, nov. 2021, doi: 10.1016/j.enbuild.2021.111257.

[9] W. Feist, W. Ebel, S. Peper, W. Hasper, R. Pfluger & M. Kirchmair, "25 Jahre Passivhaus Darmstadt Kranichstein", Darmstadt, 2016.

[10] S. Peper, O. Kah & W. Feist, "Long-time durability of passive house building airtightness", 38th AIVC Conference "Ventilating healthy low-energy buildings", Nottingham, UK, 2017, p. 13-14.

[11] H. Erhorn-Kluttig, H. Erhorn, H. Lahmidi & R. Anderson, "Airtightness requirements for high performance building envelopes", 30th AIVC Conference "Trends in High Performance Buildings and the Role of Ventilation", Berlin, Germany, 2009.

[12] M. Hansén & P. Ylmén, "Changes in air tightness for 6 single family houses after 10-20 years", TightVent- AIVC International workshop: "Achieving relevant and durable airtightness levels: status, options and progress needed", Brussels, Belgium, 2012, p. 67‑76.

[13] T. Philips, P. Rogers & N. Smith, "Ageing and airtightness: how dwelling air permeability changes over time (NF24)", NHBC Foundation, 2011.

[14] J. Wingfield, M. Bell, D. Miles-Shenton, T. South & B. Lowe, "Evaluating the Impact of an Enhanced Energy Performance Standard on Load-Bearing Masonry Domestic Construction", Department for Communities and Local Government , 2011.

[15] W. R. Chan, I. S. Walker & M. H. Sherman, "Durable Airtightness in Single-Family Dwellings-Field Measurements and Analysis", International Journal of Ventilation, vol. 14, no 1, p. 27‑38, 2015.

[16] D. Johnston & R. Lowe, "Improving the airtightness of existing plasterboard-lined load-bearing masonry dwellings", Building Services Engineering Research and Technology, vol. 27, no 1, p. 1‑10, February 2006, doi: 10.1191/0143624406bt135oa.

[17] U. Antonsson, Utveckling av metodik för verifiering av beständighet hos system för lufttäthet, etapp 1, SP Technical Research Institute of Sweden, 2015.

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