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OVERVIEW | Right and Tight: What’s New in Ductwork and Building Airtightness?

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Blower Door Test/ © Cerema / Romuald Jobert

by Valérie Leprince (PLEIAQ), Maria Kapsalaki (INIVE), François Rémi Carrié (INIVE)


In the last decade, building airtightness testing has gradually become mandatory in Denmark, France, Ireland, Portugal and the United Kingdom. Many other European countries are currently considering mandatory airtightness testing because of the increasing appreciation of the impact of air leakage on the overall energy performance of low-energy buildings. This overview article summarises airtightness requirements in European countries, developments of relevant competent testers’ schemes, databases, networks, as well as relevant incentives in the field. 


The impact of the EPBD on building and ductwork airtightness


The Energy Performance of Buildings Directive 2010/31/EU (EPBD) sets targets for Europe to implement Nearly Zero-Energy Buildings (NZEB). Building airtightness has proven to be a major contributor towards reaching low and very low levels of energy consumption. An ever-increasing number of airtightness tests is being carried out in European countries, either to demonstrate compliance with energy performance regulations and specific energy (subsidy) programmes, or simply as a result of the goodwill of building owners. At present, over 200,000 tests are performed every year in Europe.


Hold Tett (Hold tight) campaign, Lavenergi Programmet, Norway



Most energy regulations in Europe include the impact of building airtightness in their overall energy performance calculations. Some countries, such as Belgium and France, include also ductwork airtightness in the calculations. The examples that follow include measures taken for building and/or ductwork airtightness with respect to requirements and energy performance calculation methods, as well as steps to encourage market transformation.


Figure 1: Does regulatory energy performance (EP) calculation depend on building airtightness? (Source: TightVent Airtightness Association Committee-TAAC, 2017)



Airtightness requirements in European countries


An increasing number of countries (e.g. the Czech Republic, Denmark, Estonia, France, Germany, Ireland, the Netherlands, Norway, Portugal and the United Kingdom) include in their regulations either required or recommended minimum airtightness levels, with or without mandatory testing. Furthermore, mandatory testing has gradually come into force in Denmark, France, Ireland, Italy, Portugal and the United Kingdom.


Figure 2: Do minimum building airtightness requirements exist in EP regulations? (Source: TightVent Airtightness Association Committee-TAAC, 2017)



In Denmark, with the BR 2015 regulation, the local council is required to demand airtightness measurement at completion in at least 10% of all new construction projects. Airtightness testing is also required for the low-energy standard ‘Building class 2020’ which anticipates 2020 regulatory requirements. Moreover, pressurisation testing must be carried out by an impartial, qualified building tester.


In France, the building thermal regulation explicitly requires justified building airtightness levels for residential buildings either by testing or by applying a certified quality approach. The latest update of the French energy performance regulation (RT 2012), limits the airtightness value of a single-family house to 0.6 m3/(h.m2) at 4 Pa (i.e., 3.2 m3/h.m2 at 50 Pa) and for other residential buildings the limit is 1 m3/h.m2 at 4 Pa (i.e., 5.4 m3/h.m2 at 50 Pa).


In Ireland, Technical Guidance Document L- Conservation of Fuel and Energy – Dwellings (2017) subjects new residential buildings to a pressurisation test in order to measure and confirm their air permeability prior to completion. Acceptable measured air permeability should not be higher than the limit value of 7 m3/(h.m2) at a reference pressure of 50 Pa.


In Italy, there are no national requirements on airtightness, but some regional requirements exist. On 1 March 2010, the Province of Bolzano introduced mandatory blower door tests (according to EN 13829) in case of energy certification of new residential buildings. In other regions (e.g., in the province of Trento), a blower door test is often requested for the certification of buildings with a higher energy class.


In Portugal, mandatory requirements for ductwork airtightness have been included in the regulation since 2006, as part of the implementation of the EPBD. Requirements for new HVAC systems include a set of mandatory tests that must be carried out during commissioning, before the building receives its permit of occupation; these requirements apply to buildings larger than 1,000 m2. To pass the airtightness test, ductwork leakage may not exceed 1.5 l/s.m2 under a static pressure of 400 Pa.


In the United Kingdom, Approved Document L1A "Conservation of fuel and power in new dwellings of the Building Regulations 2010" subjects new residential buildings to a pressurisation test in order to measure and confirm their airtightness upon completion. Acceptable measured air permeability should not be higher than the limit value of 10 m3/(h.m2) at a reference pressure of 50 Pa (the same applies to non-residential buildings above 500 m2). Ductwork leakage testing should also be carried out, where required by and in accordance with the procedures set out in technical guidance B & ES DW/143 and B & ES DW/144, on systems served by fans with a design flow rate greater than 1 m3/s.


Financial and other incentives


Most European countries have certain financial low-energy programmes whereby a good airtightness has to be showcased to receive a subsidy. Various examples can be cited, e.g., Effinergie+ in France, NF15 and NF40 in Poland, Passiefhuis in Belgium, etc.


In France, an alternative to testing involves airtightness being justified through the "approved quality approach". Since 2006, it is possible for builders to fill in an application and have their quality approach for airtightness testing approved by the state (this is mostly used by single-family house builders). Successful applicants can avoid systematic airtightness testing of their buildings. The quality approach necessarily includes training of craftsmen, thereby promoting good practice. A similar concept is operational in Japan.


Airtightness testing can either be required by regulation or be supported by default values that highly penalise the result of the energy performance calculation (e.g., in Belgium, 30-50% of buildings are tested while testing is not mandatory).


Development of competent tester schemes


The development of competent tester schemes represents an opportunity for improving the reliability of the building airtightness tests including monitoring the application of policies in practice. The schemes described below are based on ISO 9972:2015: Thermal performance of buildings — Determination of air permeability of buildings — Fan pressurization method which provides guidance for testing with good repeatability and reproducibility, and includes additional specifications - e.g. for testing large or multi-family buildings, or for reporting in a database. Such schemes are operational in Belgium (BCCA, Kwaliteitskader Luchtdichtheid), Denmark (Foreningen Klimaskærm), Finland (Rateko), France (QUALIBAT, Qualification 8711,8721), Germany (FLiB), Ireland (National Standards Authority of Ireland- NSAI, Irish National Accreditation Board - INAB), Japan, the United Kingdom (Air Tightness Testing & Measurement Associations –ATTMA, the Independent Airtightness Testing Scheme – iATS), USA (RESNET) and Sweden (Diplomerad lufttäthetsprovare -diplomaed airtightnestester). Note that the certification framework in Japan was successfully developed since the early 1990s, with about 3,800 testers registered in 2011. The Czech Republic has no tester scheme in place but there is an association of testers that follows an ethical code.


Development of airtightness networks


Many European countries have developed or are considering the development of frameworks to increase the reliability of building airtightness testing and reporting for regulatory or voluntary airtightness compliance check purposes. Airtightness networks are often a central place to discuss these issues. Among the best known networks are the German FLiB, the British ATTMA and iATS, and the French trade union Syneole. Since September 2012, TightVent hosts an airtightness committee with representatives of national associations from 21 countries (TAAC).


Database developments


The development of databases confirms the growth in the number of tests performed in Europe. It gives valuable statistical data to better understand the impact of building characteristics on airtightness. It is also an important tool to estimate the impact of regulations and energy performance programmes (for new and retrofit buildings) on building airtightness. It is also used to help policy development.   


The French database managed by Cerema gathers over 65,000 measurement data. In the United States, the Lawrence Berkeley National Laboratory’s (LBNL) Residential Diagnostics Database contains more than 130,000 relevant data points.


In the United Kingdom, ATTMA and iATS introduced in 2015 and 2016 mandatory registration of all tests performed by their members, representing over 540 test engineers across the country. ATTMA has worked with the manufacturers of the fans that are most commonly used in the Unit Kingdom to support the development of their testing software to be able to record tests from within the software. For ATTMA, on average, this system includes around 550 tests per working day.



Summing up


This overview paper follows up a review conducted in 2013 in the field of building and ductwork airtightness. Since then, much has changed in the EU as regards building airtightness. Awareness has grown and new energy performance regulations and programmes have been developed, taking into account the level of airtightness. This has led to an increase in the number of tests performed every year and the number of qualified testers has doubled since 2013. While energy performance remains the main driver, further work on this topic is necessary to better quantify the impact of airtightness on energy use.


Figure 3: Number of qualified testers in Europe as of January 2017 (Source: TightVent Airtightness Association Committee-TAAC, 2017)



In relation to ductwork airtightness, progress has been slower than for the building fabric. In most European countries ductwork airtightness is still not a factor that is considered in regulations and energy performance programmes. There is a need for more fieldwork to better understand the impact of ductwork airtightness on energy use (fans, cooling and heating) and indoor air quality.


NOTE: This article is a fully updated version of which was originally posted in February 2013.