An airtight building doesn’t sound all that appealing – how are you meant to get fresh air? How does the building ‘breathe’ (whatever that means)? What about the children!? It’s an undercurrent that rages in the Passivhaus vs ‘standard’ construction realm, and questions that reveal a chasm of misunderstanding of the concept always comes up at speaking engagements. There is often an ‘us’ and ‘them’ dichotomy: those who understand that efficiency can only be gained with control of air and energy flows, and those who – for whatever the reason might be – don’t.
As part of efforts to analyse the most easily quantifiable impacts of infiltration, i.e. energy use, our team has pulled together an exercise to the establish the demonstrable effects of building sealing.
Our results are presented here for consideration; with clear outcomes. We believe the case is clear – for energy efficiency, building durability, resilience, indoor air quality and, not least, occupant health and safety.
Airtight buildings are cited to be more energy efficient and are evidenced by construction practices all around the world. Passivhaus buildings are distinctly characterised by their airtight envelopes, with this measure a significant factor in delivering the optimised, affordable and efficient performance.
There are side issues to note; airtightness is much more than an energy issue. Building quality and durability, indoor air quality and safety of occupants are just as relevant, if not more so. The energy side of the argument is but one part; if it was the be-all, then we could simply put renewables on every building to deliver efficiency, no? But correct building sealing can remove concerns around condensation; it is this reason that the 2019 NCC draft includes both requirements for quantified building sealing and condensation risk abatement measures. The new testing requirements are locally ambitious, and fantastic for asking the industry to address issues relating to demonstrated performance as well as associated build quality.
Energy modelling is often cited as a relatively useless exercise, not least because of the frustrating irrelevance the model typically holds to the completed product. The large discrepancy between modelled and realised building performance can partly be attributed to the gap between assumptions and designed reality, but then also to the large void in performance testing and verification. One issue we see in code compliance modelling (JV3) is the assumption of a reasonable level of airtightness, while the reality is far from it and likely never considered in the design process at all. Data from the public database of airtightness tests reveals a shocking range of 2 to 35 m3/h.m2 in 25 commercial building tests. Something no streamlined modelling protocol could capture.
It should follow, then, that building performance be not just estimated more closely, but verified with airtightness testing on all buildings. At present, over 200,000 tests are performed annually in Europe, and we will see this take off locally, should the Australian building code measures be implemented. The minimum compliance levels they are looking for seem ambitious, but it can be achieved with both locally available construction practices and products.
Mandatory building airtightness testing has come gradually into force in many parts of the world, including the United Kingdom, France, Ireland and Denmark. It is also considered in many other European countries, either as regulatory or programme requirements, mostly because of the proportionally increasing influence of building leakage on the overall energy performance of low-energy buildings. We expect to see hiccups as the local industry moves to improve construction practices but also deliver the testing, with a huge increase in the number of accredited testers required.