Building airtightness (also called envelope airtightness)  is a general descriptive term expressing the resistance to inward or outward air leakage through unintentional leakage points or areas in the building envelope. This air leakage is driven by differential pressures across the building envelope due to the combined effects of stack, external wind and mechanical ventilation systems [1]. The smaller the air leakage rate at a given pressure difference across a building envelope, the greater the airtightness [2].

In standards [3] as well as publications for non-experts, building airtightness is also called air permeability of buildings.The terms however are not synonymous: the more airtight the envelope, the less permeable it is.

References

[1] G. Guyot, F. R. Carrié and P. Schild, “Project ASIEPI – Stimulation of good building and ductwork airtightness through EPBD,” 2010.

[2] AIVC Technical Note 36. Air Infiltration and Ventilation Glossary. 1992.

[3] ISO 9972:2015 Thermal performance of buildings – Determination of air permeability of buildings – Fan pressurization method

Detecting the location of leakages in the building envelope is useful in order to reduce the leakage area of the envelope and/or to estimate the leakage distribution of buildings [2]. Blower doors are very useful to find leaks [1]. 

The usual procedure consists of creating with the blower door an underpressure from approximately 50 Pa and checking the complete building envelope. This is done for example by walking around from room to room in the house while the blower door is running and feeling the incoming air with a hand. Sometimes it is useful to use a wet hand, because evaporative cooling makes it more sensitive. It is possible to open and close single interior doors in order to get an idea of the leakage from individual rooms. The worst rooms are usually the ones that have plumbing or those with connections to attics, crawl spaces and garages.

Several methods are possible for leak detection, listed below from gross to fine:

• Visual inspection of specific parts of the constructions like wall-roof connections. 
• Inspection of the building envelope while the blower door creates 50 Pa negative pressure in the building and locate leaks with your hand. 
• Thermal-Anemometry is a very reliable tool to locate air flows at 50 Pa negative pressure. It can be held against places of the building envelope or devices where one might suspect leakages. If the instrument shows an air velocity, it is an indication of leakage [2].
• During 50 Pa leakage test (depressurization), a thermal camera can be used to localize air infiltration as long as there is a temperature difference between indoor and outdoor. The infrared image shows the heating or cooling of the surface near the leakage caused by the incoming air flow. Sometimes this kind of temperature change on surfaces can also be observed due to the natural pressure difference caused by wind or stack effect.
• Smoke from a smoke generator in combination with a blower door creating a pressurization or depressurization can help to find leaks. The smoke is generated to visualize the airflow through the envelope, devices, etc. and to detect the location of the leakage. In some cases it is also possible to find the way – the leak path – how the air moves through the envelope.
• There are systems available that use ultrasonic sound to get detailed qualitative information on leaks around windows, doors, walls/roof connections. Some research has been done to also use ultrasonic sound to quantify leakages [3]

References

[1] Allison A. Bailes III, PhD, "A House Needs to Breathe … Or Does It? An introduction to Building Science" (page 111: “Using a Blower Door to Find Leaks”), Bright Communications, October 2022.

[2] International Organization for Standardization, "ISO 9972:2015. Thermal performance of buildings — Determination of air permeability of buildings — Fan pressurization method", 2015

[3] Benedikt Kölsch et al., "Quantification of air leakage paths: a comparison of airflow and acoustic measurements", International Journal of Ventilation 22(6), August 2021.

See also:

• Designing Buildings, "Draughts in buildings" , Retrieved 30 June 2023
• Designing Buildings, "Leaks in buildings", Retrieved 30 June 2023

Existing methods to estimate building airtightness include: 

• Fan pressurization, multi point test
• Fan pressurization, single point test
• Pulse test
• Tracer gas test

Fan pressurization, multi point [1],[2]

From a multi point pressurization test the airflow through the leakages in the building envelope is measured at different building pressures differences. A blower door uses a fan to depressurize or pressurize the building envelope. Both a multi point and a single point test can be carried out with the blower door. From the multipoint test a leakage graph with flow coefficient and leakage exponent can be generated in order to calculate air leakage rates at different building pressure differences (e.g. at 50 Pa, 4 Pa etc.) to determine for example the air change rate of a building. This measurement method is described in ISO 9972:2015.

With a single point test it is possible to get a rough estimation of the airflow at a certain building pressure difference. The fan is adjusted to the target pressure and the air flow is read to determine a value of interest (e.g. the air change rate at 50 Pa). The blower door method is extensively described in the FAQ "What is a blower door?".

1-point measurement using the home's ventilation system [3]

A method developed in the Netherlands uses the ventilation system to pressurize the building.The instrument consists of a reference vessel fitted with a valve and a differential pressure meter. Before the start of the measurement the valve is open and the ventilation system is off. At the start of the measurement the valve closes. While the ventilation system is switched on and off several times, the pressure difference between the building and the reference vessel is measured. From this pressure difference in combination with the ventilation volume flow, the air permeability is determined. The time required for the 1-point measurement is limited (approximately 10 minutes). The preparations and conditions of the building or building section to be tested are the same as for the determination with a blower door. As mentioned already, for a single point measurement the flow exponent must be chosen.

The Pulse test [4], [5]

The pulse test was developed in the UK. The measuring principle of the pulse test (Jens Couckuyt, 2018) is: "The device contains an air tank with a certain capacity, e.g 60 liters. The vessel must be charged by a compressor. During the measurement a known volume of air is sent out for one and a half seconds. This causes a short rise (pulse) in the air pressure. This pressure rise provides airflow through the air leaks. Over time the pressure difference will be stabilized again. The pressure difference, during two seconds before and after the air pressure pulse, is also recorded by the device. The container must be refilled after the test. The measurement result is calculated at a pressure difference of 4 Pa. The pressure range that is achieved is not the same for every test. It depends on the pressure in the air tank, the air leakage and the volume of the building".

Tracer gas test [6], [7]

This test method entails introducing a small amount of tracer gas into a structure, thoroughly mixing it, and measuring the rate of change (decay) in tracer concentration. The air change rate can be estimated from the decay rate of tracer concentration with respect to time. Onsite meteorological conditions are measured concurrently. In the on-site monitor variant, tracer concentrations as a function of time are measured on site as air samples are obtained. In the container sample variant, after the tracer gas has thoroughly mixed, an initial air sample container is filled. The tracer gas is allowed to decay for a period of several hours during which a second and perhaps third sample container is filled. The air change rate can be determined from the decay in tracer concentrations.

References

[1] International Organization for Standardization, "ISO 9972:2015. Thermal performance of buildings — Determination of air permeability of buildings — Fan pressurization method", 2015

[2] David Keefe, "Introduction to Blower Doors", Home Energy. January/February 1994.

[3] T. Lanooy, W. Kornaat, N-J. Bink , W.  Borsboom, "A new method to measure building airtightness", 39^th AIVC Conference "Smart Ventilation for Buildings", Antibes Juan-Les-Pins, France, 18-19 September 2018.

[4] Jens Couckuyt, "Experimenteel onderzoek bij luchtdichtheidsmetingen: vergelijkende studie tussen traditionele Blowerdoor en vernieuwende Pulse test". Ghent University, 2018.

[5] E. Cooper, X. Zheng, C. Wood, M. Gillot, D. Tetlow, S. Riffat, L. De Simon, "Field trialling of a new airtightness tester in a range of UK homes", 36^th AIVC Conference " Effective ventilation in high performance buildings", Madrid, Spain, 23-24 September 2015.

[6] ASTM, "Standard test method for determining air leakage rate by tracer dilution", ASTM Designation E 741-83, August 1987.

[7] M.H. Sherman, "Tracer-gas techniques for measuring ventilation in a single zone", Building and Environment, Vol 25, No 4, pp 365-374,1990.

[8] A. Vega Pasos , X. Zheng, V. Sougkakis , M. Gillott , J. Meulemans , O. Samin , F. Alzetto , L. Smith , S. Jackson , C. J. Wood, "Experimental study on the measurement of Building Infiltration and Air Leakage rates (at 4 and 50 Pa) by means of Tracer Gas methods, Blower Door and the novel Pulse technique in a Detached UK Home", 39^th AIVC Conference "Smart Ventilation for Buildings", Antibes Juan-Les-Pins, France, 18-19 September 2018.

[9] M.J. Limb, "TN 55: A Review of International Ventilation, Airtightness, Thermal Insulation and Indoor Air Quality Criteria", AIVC Technical Note 55, 2001

​See also

• Corbett Lunsford, "Tracer Gas Test", Home performance, YouTube, 2018

Infiltration/exfiltration is the uncontrolled inward/outward leakage of outdoor/indoor air through air permeable materials, joints, cracks, interstices and other unintentional openings of a building envelope, caused by the pressure effects of wind, the stack effect or operation of HVAC-systems [1]. Infiltration/exfiltration causes convective heat and moisture transfer, resulting in excessive heat loss and potential moisture problems in the building envelope. The building airtightness measurement aims at finding, quantifying and reducing those unintentional cracks and openings in order to get the intended airtightness of the building.

References

[1] Limb. M.,1992. “Technical note AIVC 36- Air Infiltration and Ventilation Glossary” International Energy Agency energy conservation in buildings and community systems programme, 1992.

See also

• How is the building airtightness quantified?

The airtightness of a building is quantified by means of the measured air leakage rate through the building’s envelope in m³/h at a given reference pressure difference, often 50 Pa. The building airtightness may be expressed by other quantities, derived from the air leakage rate at a reference pressure difference, and normalised using, for example, one of the following measures for the size of the building:

• Internal building volume V. At 50 Pa, the associated indicator is called air change rate at 50 Pa and noted n₅₀ [unit h^-1].
• Envelope area A_E. At 50 Pa, the associated indicator is called air permeability at 50 Pa and noted q_E50 (former: q₅₀ in EN 13829) [unit m³/(h.m²⁾[.
• Net floor area A_F. At 50 Pa, the associated indicator is called specific leakage rate and noted q_F50, (former: w₅₀ in EN 13829) [unit m³/(h.m²)].

Other indicators of airtightness exist in national regulations.

Air penetrates through porous building materials and through joints in the building structure, therefore, airtight construction techniques must focus on these aspects. Different construction materials exhibit different leakage characteristics. Irrespective of construction material, a modern building is normally of double skin construction in which the inner and outer leaves are separated by a layer of insulation. Air-tightness is dependent on good sealing of the inner leaf by means of an air barrier system. [1]

With air barrier systems in place, key air infiltration paths to address are the interfaces between building components, most importantly interfaces between windows and walls, and between walls and roof or floors. [2]

Common leakage sites are listed in Figure 1 below. Figure 2 gives the classification of these sites in 4 categories [3]:

Figure 1: Vertical section of a typical building with identification of potential leakage junctions (Source: CEREMA – Pôle QERA)

1. Junction lower floor / vertical wall
2. Junction window sill / vertical wall
3. Junction window lintel / vertical wall
4. Junction window reveal / vertical wall (horizontal view)
5. Vertical wall (Cross section)
6. Perforation vertical wall
7. Junction top floor / vertical wall
8. Penetration of top floor
9. Junction French window / vertical wall
10. Junction inclined roof / vertical wall
11. Penetration inclined roof
12. Junction inclined roof / roof ridge
13. Junction inclined roof / window
14. Junction rolling blind / vertical wall
15. Junction intermediate floor / vertical wall
16. Junction exterior door lintel / vertical wall
17. Junction exterior door sill / sill
18. Penetration lower floor / crawlspace or basement
19. Junction service shaft / access door
20. Junction internal wall / intermediate floor

Figure 2: Common leakage sites classified in 4 categories (Source: CEREMA – Pôle QERA)

---

References

[1] Liddament M., 1996. Guide to energy efficient ventilation. AIVC, 1996.

[2] Van Den Bossche N., et al. 2011. Airtightness of the window-wall interface in cavity brick walls. Energy and Buildings. DOI: 10.1016/j.enbuild.2011.10.022

[3] Carrié F.R., Jobert R., and Leprince V., “Contributed Report 14- Methods and techniques for airtight buildings” AIVC, 2012.

The text and images of this webpage is available for modification and reuse under the terms of the Creative Commons Attribution-Sharealike 3.0 Unported License and the GNU Free Documentation License (unversioned, with no invariant sections, front-cover texts, or back-cover texts).

Poor building airtightness results in excessive air infiltration and resultant uncontrolled energy loss. The energy use increase is dependent on the infiltration flow rate and the amount of conditioning of the air that is necessary to achieve thermal comfort. The infiltration flow rate depends on the building airtightness and natural driving forces by wind and stack effect. For the same building airtightness, the energy impact is larger when the building is more exposed to high wind speeds and large temperature differences, and when the building is higher.

As an approximation, an increase of the air permeability of the building envelope with 1 m³/(h.m²)@50Pa has a similar energy impact as an increase of the average building envelope thermal transmittance (U-value) with 0.02 W/(m²K).

Overall most of products are tested according to EN12114 (air permeability of building components) or EN 1026 (airtightness of windows) either internally or externally.

The most known way of certifying products is through Passive House Institute in Germany [1], the product, including installation manual, is sent to PHI Darmstadt, where THEY apply the product and assess it on its airtightness properties. A yearly fee has to be paid to maintain the certificate.

Another possibility would be to get a Komo certificate for the Dutch market (thus rather limited to Holland) or to go for quality stamps such as a Sintef approval (with some authority outside of Norway too).

There is also the MO01, a German directive written by IFT (Institut für Fenstertechnik) which enables to assess airtightness of perimeter joints around a window before and after ageing. The ageing is based on pressure, temperature and mechanical load.

References

[1] Passive House Institute. Components Database. Airtightness systems. 

Calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of known accuracy, a device generating the quantity to be measured such as a voltage, a sound tone, or a physical artifact, such as a meter ruler. 

A calibration laboratory establishes whether the value given by a measuring instrument is correct in relation to the international unit of measurement. An ISO-17025 accreditation offers the best guarantee that this is indeed the case. Accreditation is granted for a specific area of work based on a specific, defined method. In accreditation, this is called the 'scope'.  

Each European country has its own accrediting body. These organisations have a so-called Mutual Recognition Agreement (MRA) with each other, in Europe, and often beyond. In Europe there is an umbrella organisation called the European Cooperation for Accreditation (EA). This organisation ensures that accreditation is dealt with in the same way in all countries and that the same requirements apply everywhere. Certificates issued under accreditation in all these countries are therefore fully recognized and accepted in countries that have signed the MRA.

A guarantee of flawless work can never be given. Accreditation guarantees that "work is performed with the highest possible reliability". In order to continue to test this reliability, audits are carried out, with some regularity internal audits and at least once a year an external, independent audit is carried out by the accrediting body. Accredited laboratories are obliged to participate in proficiency testing, studies in which the test results of different laboratories are compared with each other. 

The calibration of a blower door consists of 2 parts: a pressure calibration and a flow calibration. It is always recommended to make sure how these calibrations are performed. What kind of measurement setup is used and what are the measurement points? The scope (measured quantities, measuring method, ranges and uncertainties) of accredited labs can be found on the internet.

Links

• Directory of EA Members and MLA signatories – European Accreditation

• International Organization for Standardization,"ISO/IEC 17025: 2017. General requirements for the competence of testing and calibration laboratories", 2017.

See also

• What are the requirements for a calibration in terms of traceability and quality?

A calibration should be carried out by an ISO/IEC 17025 accredited lab. Sometimes in some specific context it is allowed to have the calibration done by:

1. a lab that has standards traceable to ISO/IEC 17025 accredited calibrations
2. the manufacturer
3. the user of the instrument

There are no general requirements, each country has its own regulations and the extent to which it is an advice, recommendation or obligation also varies from country to country. The calibration must, at the very least, demonstrate compliance with the factory specifications of the device.

References

• International Organization for Standardization,"ISO/IEC 17025: 2017. General requirements for the competence of testing and calibration laboratories", 2017.

See also

• What is calibration?

The recommended calibration for building airtightness measuring devices should follow the manufacturers recommendation as well as the governing body or standard being adhered to.

The recommended calibration for building airtightness measuring devices depends on the manufacturer's specifications. It is typically recommended to follow the calibration interval specified by the manufacturer, which is usually every 5 years. In addition, annual field calibration checks should be performed following the guidelines outlined in the manufacturer's blower door manual. The fan should retain its calibration as long as it has not been physically damaged, such as being dropped or fallen over. Manufacturers' manuals also provide guidance on checking the placement of the flow sensor or nacelle in the fan to ensure that it has not been moved since its original manufacture.

In some instances local, regional or national standards bodies will have differing recommendations to adhere to. This should be taken into consideration for calibration timelines.

In addition to the fan, it is also essential to consider the calibration of the digital pressure gauge. Typically, these devices should also follow the manufacturer's recommended calibration interval, which can vary from every 1, 3, or 5 years, depending on the device. It is important to reference the calibration requirements of the standard you are testing, in order to ensure accuracy. Field checks of the device should also be conducted by following the guidelines in the manufacturer's manual. Cross-checking the device with another recently calibrated gauge is also a recommended practice to ensure accuracy. 

Furthermore, it is crucial to verify that the calibration facility holds the proper accredited scope to perform the calibration work. An ISO-17025 accredited lab is normal for calibrations in the air-tightness industry. This ensures that the calibration is performed to the highest standards and that the results are reliable and accurate.

Yes. The Building Research Establishment in the UK has published an experimental study showing energy savings achievable with improved airtightness [1,2].

[1] R. Coxon, “Research into the effect of improving airtightness in a typical UK dwelling,” The REHVA European HVAC Journal-Special issue on airtightness, vol. 50, no. 1, pp. 24-27, 2013.

[2] D. Butler and A. Perry, “Co-heating Tests on BRE Test Houses Before and After Remedial Air Sealing,” Building Research Establishment.

Yes, provided that the building is equipped with an appropriate ventilation system (whether natural, mechanical or hybrid). A French study mentioned in the AIVC newsletter n°2 shows that better building airtightness converges with better indoor air quality because the ventilation system operates more efficiently. Building leaks cause uncontrolled airflows and potentially poorly ventilated rooms although the total building air exchange rate may be sufficient [1].

[1] L. Mouradian and X. Boulanger, “QUAD-BBC, Indoor Air Quality and ventilation systems in low energy buildings,” AIVC Newsletter No2, June 2012.

Wind creates a heterogeneous pressure distribution around the building and induces a pressure difference between indoor and outdoor even when the fan is turned off. The impact of wind can be partly compensated by measuring and subtracting this zero-flow pressure and by making the average between pressurization and depressurization test.

When we test a building for air tightness, a two-channel manometer is used to measure both the fan pressure on the blower door system and the pressure difference between indoor and outdoor.  The building is either pressurized or depressurized by the blower door fan to create a measurable pressure differential that generates air flow through building’s leaks. This pressure differential is measured in units of Pascals (Pa).The impact of wind can be observed with the two-channel manometer and can sometimes make it difficult to get a stable, reliable reading since the wind causes the conditions outside to constantly fluctuate.

On windy days, leaks located downwind and upwind won’t have the same pressure difference. Therefore the flowrate through each leak will depend on its location on the building envelope: the impact of some leaks will be overestimated and some others will be underestimated. 

Performing the test both in pressurization and depressurisation helps to limit the impact of wind on the result of the airtightness test.

Additionally, to account for windy conditions, a bias pressure (zero-flow pressure) is collected before the airtightness test. This is where the two-channel manometer collects a sample reading of the outdoor conditions for a given amount of time, usually 60 seconds. Some test standards require an additional bias pressure to be collected at the end of the test as well. The average pressure differential is then applied to the blower door results to remove the measured impact of wind, similar to the way we zero a scale before we weigh an object. Nevertheless, as the relation between flowrate and pressure is not linear, this subtraction is not sufficient to cancel the error.

Other recommendations exist but as stressed in [1] depend on standards, for example some texts recommend to smooth windy conditions with mechanical wind dampening where the outdoor reference tubing is branched into multiple sections with 90 degree turns.

This subject has been discussed in [1] and has been the subject of much research.

References

[1] Hurel N. & Leprince V., 2021. VIP 41: Impact of wind on the airtightness test results. AIVC, 2021

See also

• Bailly Mélois A. et al., 2019. Designing a model-scale experiment to evaluate the impact of steady wind on building air leakage measurements. 40th AIVC Conference “From Energy crisis to sustainable indoor climate – 40 years of AIVC", Ghent, Belgium, 15-16 October 2019
• Delmotte C., 2019. Airtightness of buildings – Considerations regarding place and nature of pressure taps. 40th AIVC Conference “From Energy crisis to sustainable indoor climate – 40 years of AIVC", Ghent, Belgium, 15-16 October 2019
• Bailly Mélois A. et al., 2018. Wind speed in building airtightness test protocols: a review. 39th AIVC Conference "Smart Ventilation for Buildings", Antibes Juan-Les-Pins, France, 18-19 September 2018.
• Leprince V., & Carrié F.R., 2017. On the contribution of steady wind to uncertainties in building pressurisation tests. 38th AIVC Conference "Ventilating healthy low-energy buildings", Nottingham, UK, 13-14 September 2017
• Peper S., & Schnieders J., 2019. Measurement of airtightness in high-rise structures. 11th International BUILDAIR Symposium, 24- 25 May 2019, Hannover, Germany
• Hsu Y-S.m 2019. Insights into the impact of wind on the Pulse airtightness test in a UK dwelling. 40th AIVC Conference “From Energy crisis to sustainable indoor climate – 40 years of AIVC", Ghent, Belgium, 15-16 October 2019
• Prignon M., Dawans A., & van Moeseke G., 2019. Quantification of uncertainty in zero-flow pressure approximation due to short-term wind fluctuations. 40th AIVC Conference “From Energy crisis to sustainable indoor climate – 40 years of AIVC", Ghent, Belgium, 15-16 October 2019

There are various kind of airtightness tester organizations. Some organizations are led by the qualification scheme in the country for example the British ATTMA and iATS and the Belgian BCCA. In France Qualibat is in charge of the qualification process with about 1000 qualified testers and Syneole is the trade union for airtightness testers. Among other things, Syneole represents airtightness testers in standardization and regulation working groups and is part of the commission for tester qualification.

In Germany the association FLIB, more than 300 members, helps to improve both the implementation of airtightness and the measurement protocol by editing guidelines and contributing in standardization committee (such as for ISO 9972’s national annex). 

There are also smaller associations of testers, such as the Association Blower Door CZ (A.BD_CZ) in the Czech Republic, gathering 21 members in 2022, which represents about half of the testers operating in the country. Its objective is also to improve measurement practice by performing round-robin tests with its members.

Since September 2012, TightVent hosts an airtightness associations committee (TAAC) with representatives of national/local associations or groups including, Syneole, A.BD_CZ, FLiB, iATS and ATTMA.

In Europe, there are various quality frameworks to qualify building airtightness testers ^1,2,3,4, including:

There are also many other countries in Europe that do not have a quality framework for airtightness testers (e.g. Spain, Poland or Estonia) but some testers choose to get a certification from one of the above listed quality frameworks. For example in Latvia it is estimated that there are approximately 8 persons qualified by the manufacturer programme Retrotec; 1 person qualified by FLiB (German Association for Airtightness) and  2 persons qualified by the Air Tightness Testing & Measurement Association (ATTMA). 

References

[1] Carrié F.R, Wouters P., "AIVC TN 67: Building airtightness: a critical review of testing, reporting and quality schemes in 10 countries", AIVC, 2012

[2] Leprince V., Carrié F.R., Kapsalaki M., "Building and ductwork airtightness requirements in Europe – Comparison of 10 European countries", AIVC, 2017.

[3] Kalamees T., Hallik J., Mikola A., "AIVC VIP 45.1: Trends in building and ductwork airtightness in Estonia", AIVC, 2022.

[4] Hoek T., Poza-Casado I., Melgosa S., "AIVC VIP 45.2: Trends in building and ductwork airtightness in Spain", AIVC, 2022.

[5] De Strycker M., Van Gelder, L. Leprince V., "Quality framework for airtightness testing in the Flemish Region of Belgium – feedback after three years of experience", AIVC, 2018

[6] Leprince V., Carrié F.R., Olivier M., "The quality framework for Air-tightness measurers in France: assessment after 3 years of operation", AIVC, 2011

[7] Solcher O., "Quality system for airtightness measurement of buildings", AIVC, 2011

Duct tester systems designed to conduct air tightness tests on duct systems can sometimes be used to test building air tightness. The fans used in these systems have a much lower flow capacity than a standard blower door system, which means the building would have to be tight enough to accommodate the fan. This typically requires deliberate planning for air tightness and proper installation of air sealing materials. There are blower door kits available that use a duct tester fan that include a cloth with a smaller hole to accommodate that type of fan.

France, Belgium (Flemish Region) & the United Kingdom have national databases that gather most of measurements performed by qualified testers in their countries. Other initiatives also exist in Spain, Germany, Czech Republic, Estonia, Canada and the US ([1], [2], [3]).

• Spain (from the University of Valladolid): 400 tests data collected as a one-time effort for the INFILES Project, which represents a minor share of the total measured data.
• Germany (from The Association for Air Tightness in Buildings: FLiB e.V.)
• Czech Republic (from the Association Blower Door CZ: A.BD_CZ): 100 records per year which represents less than 6 % of the total amount of tests performed by the members
• Estonia (from the Tallinn University of Technology): There is no constantly updated database, the university has however collected and published measurement data several times
• Canada (Natural Resources Canada)
• the US (Lawrence Berkeley National Laboratory)

The table below is a summary of the main databases characteristics in Europe and North America ([3])

More information can be found in AIRBASE, the Bibliographic Database of the AIVC (e.g. search on “database”), as well as the Proceedings of AIVC & TightVent Joint conferences and workshops.

References

[1] V. Leprince, F. R. Carrié and M. Kapsalaki, “Building and ductwork airtightness requirements in Europe – Comparison of 10 European countries” in 38th AIVC Conference “Ventilating healthy low-energy buildings”, Nottingham, UK, 13-14 September 2017, Nottingham, 2017.

[2] V. Leprince, M. Kapsalaki, F. R. Carrié, “VIP 37: Impact of Energy Policies on Building and Ductwork Airtightness” AIVC, 2017.

[3] I. Poza-Casado, V.E.M. Cardoso, R.M.S.F. Almeida, A. Meiss, N.M.M. Ramos, M.Á. Padilla-Marcos, “Residential buildings airtightness frameworks: A review on the main databases and setups in Europe and North America”, Build. Environ. 183 (2020) 107221. https://doi.org/10.1016/j.buildenv.2020.107221.

TightVent Europe has published a list of applicable standards for building and ductwork airtightness. The detailed list can be found here.

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.

See also 

AIVC Technical Note 71. Durability of building airtightness. 2022.

The relationship between the air flow rate (Q) and the pressure difference (ΔP) is often modeled by a power low:

Q = C Pⁿ

The air flows from the higher to the lower pressure.

For air to flow through the building envelope there must be:

• An open pathway (leakage)
• A pressure difference at the pathway

For the same pathway, a higher pressure difference results in more air flow.

Whether found by extrapolation, interpolation or direct measurement, the principle metric used to quantify air tightness is the air leakage flow rate, the air flow through the envelope at a specific reference pressure. The most common reference pressures are 50 Pa and 4 Pa, but 1 Pa, 10 Pa, 25 Pa, and 75 Pa are used as well. The air flow is often denoted with the reference pressure as a subscript (e.g. Q₅₀ or Q₂₅) [1].

Regardless of the flow regime the air leakage flow rate Q can be calculated from the pressure difference ΔP using the power law description: 

Q = C Pⁿ

where C is the flow coefficient and n is the pressure exponent. The fluid flow regime ranges from fully laminar (n=1) to a fully turbulent flow (n=0.5) so 0.5 <= n <=1. The pressure exponent is normally found in the vicinity of 0.65 [2]. 

The power law is broadly accepted in air tightness measurement standards. 

An alternative is the so-called quadratic form that 

P=AQ+BQ²

based on a combination of the pressure flow relationships for laminar flow (Q=K₁P) and turbulent flow (Q=K₂P^1/2)

Walker et al. [3] compared both formulations and concluded that, based on theoretical considerations and field and laboratory measurements, the power law is valid for low pressure (<100 Pa) building envelope leakage. More on this can be found in Sherman and Rengie [1].

References

[1] Sherman, M., & Chan, R. (2004). "Building airtightness: Research and practice". James & James. Lawrence Berkeley National Laboratory. LBNL Report #: LBNL-53356. Retrieved from https://escholarship.org/uc/item/5jb277km

[2] Orme M., Liddament M., Wilson A., "AIVC TN 44: Numerical Data for Air Infiltration and Natural Ventilation Calculations (replaced by Guide GU05)", AIVC, 1994

[3] Iain S. Walker, David J. Wilson Max H. Sherman, "A comparison of the power law to quadratic formulations for air infiltration calculations" Energy and Buildings, Volume 27, Issue 3, June 1998

Good building airtightness is achieved in 3 steps: Plan – Build – Check.

The building airtightness requirement is defined in the design phase of the building. The air barrier  is then drawn in design and execution plans, and materials and details are worked out. Based on the plans and descriptions, the craftsman can select suitable airtight materials and install the air barrier and connections in a professionally airtight manner. A quality check of the air barrier at 50 Pa negative pressure before its cladding, e.g. with gypsum board, enables a quick and cost-effective improvement if necessary. At the end of the construction process, an air tightness measurement is carried out in accordance with the standard (e.g. ISO 9972) to verify the requirement.

Building Airtightness requirement

It is necessary to define the airtightness of the building during the planning phase. A Passive House for example must reach a better air permeability than “normal” buildings. Designer, planer, craftsmen etc. must know this in order to take care of it.

Air Tightness Concept

Even in the planning phase the required air barrier should be considered when choosing the type of construction. Similar to the thermal building envelope this protection layer, the air barrier, has to continuously enclose the entire heated volume. To plan the air barrier the building interior is marked with a red pen in one uninterrupted, continuous line.

Illustration of the principle of the airtight and continuous “air barrier” [1]

The red line forms the later air barrier. This procedure should be repeated for all floor plans and sections. For each exterior building component it has to be determined which layer of the building element will provide air tightness.

From Outline to Detail

The outline is followed by detail drawings of points of change in building components, material, or directions. Also mark the run of the air barrier in these detailed representations. Finally, plan where the airtight building component layers are lastingly connected airtight at their transitions.

Example of a detail including the air barrier [1]

Avoiding Penetrations

The number of necessary penetrations of the air barrier (wiring, pipes, electrical outlets in the external walls) should be kept to a minimum.

 Air barrier: materials and installation methods

Based on the planning and the execution plans, craftsmen can install the air barrier. During implementation, the manufacturer's instructions on the airtightness of the materials and their way of installation must be observed, such as a dry and dust-free substrate when using adhesive tapes, etc. 

Checking for leaks at 50 Pascal induced pressure

When the air barrier is completed, create a pressure difference between inside and outside of the building of ca. 50 Pa negative pressure with the test equipment (blower door).  To check for leaks at building components use your hand, a thermoanemometer, a fog generator or an infrared camera. Create a leakage report and / or mark the leakages so that they easily can be found and sealed by the craftsmen.

Final measurement

At the end of the construction process, the air tightness measurement is performed according to the relevant standards (e.g. ISO 9972 in Europe). This measurement serves to verify whether the air tightness of the building envelope defined at the beginning is achieved and meets the desired requirements.

Many countries have developed guidelines to build airtight, some of them are listed in [2].

References

[1] Carrié F.R., Jobert R., Leprince V., "AIVC Contributed Report 14: Methods and techniques for airtight buildings", AIVC, 2012

[2] Leprince V., Kapsalaki M., Carrié F.R., "AIVC Ventilation Information Paper (VIP) 37: Impact of Energy Policies on Building and Ductwork Airtightness", AIVC, 2017

A combination of materials within wall and roof assemblies which establish a continuous plane of airtightness in the building envelope. Its most important function is moisture control, but it also plays a significant role in energy efficiency, rain control and external noise protection. The system has to meet four requirements: a sufficiently low air permeance, continuity at all joints and intersections, strength against peak wind pressures, and the ability to meet these functions over the service life of the system (durability). These criteria apply to all air barrier components: boards, films, fasteners, gaskets, sealants, etc. Additional points to be considered in the design and assembly of air barrier systems are the accessibility for maintenance and the certification of specialised trades, in order to ensure that air barrier systems are installed at a consistent quality in practice [1].

References

[1] NRC, 1997. Air barrier systems for walls of low-rise buildings: performance and assessment. Canadian Construction Materials Centre, National Research Council Canada, Ottawa, Ontario.

See also

• What is the way to get a good airtightness of the building (from contractor to craftsman)?

Requirements depend on the country and the context of the measurement. Most EU countries include in their regulations either required or recommended minimum airtightness levels with or without mandatory testing. There are several countries (e.g.United Kingdom, France, Belgium, Ireland) where, by regulation, airtightness testing is mandatory for certain building types or in the case of specific programmes [1].

References

[1] Leprince V., Kapsalaki M., & Carrié F., R., “VIP 37: Impact of Energy Policies on Building and Ductwork Airtightness”. AIVC, 2017.

In most European countries the building preparation is based on ISO 9972 requirements. However, the interpretation of these requirements may differ from one country to another, and based on different building preparation rules.

Building preparation errors are probably the dominant source of uncertainty in an airtightness test. The reference testing protocol in Europe is described in ISO 9972, in the USA in ASTM 779-19, and in Canada in CGSB 149.10-2019. Nevertheless, ISO 9972 proposes 3 different methods (with different preparation requirements):

• Method 1: Test of the building in use
• Method 2: Test of the building envelope
• Method 3: Test of the building for a specific purpose according to a standard or policy in each country

Many countries have developed specific guidelines to detail or adapt to the ISO 9972 requirements.

A study has been performed to compare building preparation rules for airtightness testing in 11 European countries [1]. Information has been collected through a questionnaire sent to TAAC (TightVent Airtightness Associations Committee) members [2]. It has been found that building preparation differs significantly from one country to another and that methods 1 and 2 described in the standard are either too detailed or insufficiently described to fit the specificities of each country. This has supported the creation of “method 3” in ISO 9972:2015 (which is one of the major changes compared to former EN 13829:2000). "Method 3" needs to be defined at the national level which allows to adapt the measured extent and the building preparation to the purpose and context of the test. More specifically, it allows each country:

• to describe more precisely the basic principles of the preparation to avoid ambiguities; and
• to have some flexibility to specify rules consistent with their energy performance calculation method.

The main obstacles to harmonize pressurization test methods between countries are:

• In each country the test method shall be consistent with the energy performance calculation method. But there are significant differences in calculation methods between countries in the way airflow rates are taken into account.
• There are specific devices and construction traditions in each country that may require tailored rules.

Therefore, it is clear that building airtightness should not be compared between countries unless precaution is taken in the sample analyzed and in the interpretation of the results.

The figure below shows how 6 openings categorized as "other" in the standard are prepared in the countries asked in the above-mentioned study. It shows, for example, that in some countries the air exhaust of a clothes dryer will be left open while in others it will be sealed.

References

[1] Leprince V. & Carrié F.R, "Comparison of building preparation rules for airtightness testing in 11 European countries", 35th AIVC Conference "Ventilation and airtightness in transforming the building stock to high performance", Poznań, Poland, 2014

[2] TightVent Airtightness Associations Committee (TAAC), "TAAC Deliverables", Retrieved on April 6, 2022

A blower door is a device used to measure the airtightness of buildings. 

It can also be used to measure air leakage between building zones, to locate leaks in ductwork and to help physically locate air leakage sites in the building envelope.

There are three primary components to a blower door:

1. a calibrated, variable-speed blower or fan, capable of inducing a range of airflows sufficient to pressurize and depressurize a variety of building sizes,
2. a pressure measurement instrument, called a manometer, to simultaneously measure the pressure differential induced across the face of the fan and across the building envelope, as a result of fan airflow, and
3. a mounting system, used to mount the fan in a building opening, such as a door or a window.

Source: BlowerDoor GmbH

References

[1] M. Limb, “Technical note AIVC 36- Air Infiltration and Ventilation Glossary,” International Energy Agency energy conservation in buildings and community systems programme, 1992.

[2] "Blower Door Tests | Department of Energy". Energy.gov. 2012-04-02

A method of quantifying how much air leaks into or out of an enclosure. EN 13829 gives a standard test method for buildings. Several standards apply to ductwork systems (see also “How is the ductwork airtightness quantified?“).

Building airtightness levels can be measured by using a fan, temporarily installed in the building envelope (a blower door) to pressurize the building. Air flow through the fan creates an internal, uniform, static pressure within the building. The aim of this type of measurement is to relate the pressure differential across the envelope to the air flow rate required to produce it. Generally, the higher the flow rate required to produce a given pressure difference, the less airtight the building [1].

[1] M. Limb, “Technical note AIVC 36- Air Infiltration and Ventilation Glossary,” International Energy Agency energy conservation in buildings and community systems programme, 1992.

n₅₀ is a number used to quantify building airtightness. It gives the air change rate occurring as a result of air leakage through the building envelope when an air pressure difference of 50 Pa exists between inside and outside. This air change rate is the leakage volume airflow rate in m³/h measured at 50 Pa pressure difference divided by the buildings’ internal volume. It is expressed in h^-1.

Air infiltration adds to the quantity of air entering the building but may also distort the intended ventilation air flow pattern to the detriment of overall indoor air quality and comfort. The consequences are inferior performance, excessive energy consumption, and inability to provide adequate heating (or cooling) [1].

Because air infiltration is uncontrolled, poor envelope airtightness may affect:

• Indoor air quality: Some rooms may be largely under-ventilated while other are over-ventilated as a consequence of distorted air flow patterns. Also the air circulating in the wall may bring inside pollutants from outside and from building product emissions.
• Energy use: Air leakage may inadequately increase the total ventilation airflow rate; or it may decrease the relative impact of heat recovery (in case of systems with heat recovery devices, the unit will only recover heat on the airflow passing through it).
• Moisture performance: air leaking through the envelope from a warm, humid environment to a cold environment, may cause condensation damage as it flows along materials with a temperature below its dew point. In cold climates condensation damage may occur in materials at the outside of the thermal insulation when air exfiltrates, while in warm climates damage may occur at the inside of the insulation when air infiltrates.
• Acoustic performance: airborne sound may propagate through leakages. It is found that sound transmission loss can be degraded by up to 15 dB under field conditions, mainly because of sound leaks.

References

[1] Liddament M.W., 1996. A Guide to Energy Efficient Ventilation. AIVC, 1996.

See Definitions of tightening products.

TAAC  is the TightVent Airtightness Associations Committee, launched in September 2012 by the TightVent Europe platform, with the primary goal to bring together national associations and experts in order to promote reliable testing/inspection and reporting procedures.

The scope of TAAC includes various aspects such as: building & ductwork airtightness requirements in the countries involved; competent tester schemes in the countries involved; applicable standards and guidelines for testing; inspection of ventilation systems; collection of relevant guidance and training documents; share of knowledge and experience; and information on ongoing research work in the field of building and ductwork airtightness.

At present the participants are from Belgium, Czech Republic, Estonia, France, Germany, Hungary, Ireland, Latvia, Netherlands, Poland, Portugal, Spain, Sweden, Switzerland, UK and the US.

In case you are interested to join this initiative, please write an email to: info@tightvent.eu.

Links:

For more information please see:

• About TAAC: https://tightvent.eu/taac
• TAAC participants: https://tightvent.eu/taac/taac-participants
• TAAC deliverables (publications, webinars etc.): https://tightvent.eu/taac/deliverables
• Becoming a Tightvent partner (for companies): https://tightvent.eu/contact
• Becoming a TAAC member: https://tightvent.eu/taac/contact-join