Significant progress has been made over the past 5 years to improve building airtightness, but there remain challenges to consider long term performance or to contain risks of inappropriate ventilation. As for ductwork airtightness, except for Scandinavian countries, we are still at a stage where awareness raising is sorely needed.

Building and ductwork airtightness are key factors for achieving nearly zero-energy buildings. Looking 5 years behind, it is clear that significant progress has been made in several European countries with regard to building airtightness. On the other hand, this concern is still lagging behind in many regions and/or building sectors, although relevant in terms of energy savings and indoor environmental quality. In addition, very few European countries have taken steps to foster airtight ductworks.

To address these concerns, TightVent Europe, the AIVC and QUALICHeCK supported the organisation of a 90-minute workshop during the Clima 2016 conference. Discussion was based on the analysis of answers to prepared questions asked to the audience, preceded by a series of short presentations to introduce those questions. Answers were collected instantaneously with a voting system and are briefly summarised below.

Building airtightness

The motivations for considering building airtightness include the energy use impacts, IAQ, building damage and safety. Energy remains the main driver, but the voting results confirmed increasing concerns for effective implementation of adequate ventilation provisions where additional research is needed.

Significant policy changes with regulations or programmes requiring building airtightness testing or strongly pushing better building airtightness were highlighted, stressing the need for competent testers, clear calibration rules, robust test methods in windy conditions or for multi-zone buildings, etc.

Also, participants recognized that durability of products and assemblies should be better considered to secure airtightness levels in the long term, but it was unclear from the discussion which methods should be prioritised to address this problem. This subject had been a key research area in the 80s, but without clear results in terms of methods to characterize or improve building airtightness durability. Since about 2010, there seems to be a revived interest for this topic, which is good, since there is no standardised method to assess or specify building airtightness long term performance. While the audience preferred characterization based on complete assemblies, it is unclear how this can be done in practice given the numerous combinations of product/structure/workmanship that should be tested. Also, while a combination of stress cycles based on field observations and unfavourable humidity and temperature conditions seem preferable to assess the degradation of product performance, testing costs need to be carefully evaluated.

Ductwork airtightness

On the topic of ductwork airtightness, the participants recognized that field data is sparse. The SAVE-DUCT project remains a reference for the ground status although the data is now over 15 years old. There was a clear consensus on the need to gather and consolidate more field data, building on the increasing number of tests performed in several countries. The workshop participants also clearly agreed on the fact that, although a number of studies demonstrate the large energy implications of duct leakage, the methods used to quantify these implications need to be evaluated as a first step towards a standardised method, building upon FprEN 16798-5-1.

Reduction of airflow rates at ATDs, contaminant transfer from dusty areas, increase of dust accumulation in filters, heat exchangers, ducts, etc. were all considered as priority research areas in terms of IAQ impacts of duct leakage.

The market incentives towards better airtightness seem weak in most countries, with few exceptions, for instance: Scandinavian countries where requirements have been commonly used and met for several decades; or more recently, UK and France, where airtightness testing is required for specific systems (UK) or when applying for Effinergie+ label in France.

The participants acknowledged industry efforts to improve ductwork airtightness, for instance with the development of duct-mounting without screws, factory-fitted seals for rectangular ducts, or semi-rigid ducts with joint-fitted components. On the other hand, there is a clear need for solutions for existing ductwork—only one technology is commercially-available specifically to seal existing ductwork.

Conclusions and perspectives

In summary, looking 5 years behind, there is a striking contrast in the evolution of the regulatory landscape and field practice between building and ductwork airtightness. On envelope issues, some countries have experienced a radical change, in particular when airtightness testing has been encouraged. Still, there remain many challenges to consider of long-term performance, to contain risks of inappropriate ventilation provisions, or to monitor the implementation of policies with field data. On ductwork issues, we should be concerned with stable poor performance observed in the field despite the availability of high-performing products and methods for new installations. Research is clearly needed to address this problem which should involve consolidation and analysis of field data, standardised methods for impact assessments, development and evaluation of policy scenarios, and development of methods to reduce leakage of existing ductwork systems.

Presentations and voting results of this session are available on the REHVA website.