Ecological disappointed at ‘unambitious’ Part L
This article was originally published in issue 41 of Passive House Plus magazine. Want immediate access to all back issues and exclusive extra content? Click here to subscribe for as little as €10, or click here to receive the next issue free of charge
The update is designed to provide an interim framework prior to the proposed Future Homes standard, which is to be issued in 2025. The aim of the 2022 interim standard is to achieve a 31 per cent reduction in energy use for new dwellings.
The air permeability backstop has been tightened from 10 m3/hr/m2 to 8 m3 hr/m2 – this is 3 m3/hr/m2 higher than the original draft proposal of 5 m3/hr/m2. “Whilst there are some positives to glean in the new Part L document, such as the elimination of sample testing [every building now needs to be tested], this essentially still means that England has the worst regulative backstop airtightness in Europe,” said Ecological’s UK technical manager, Neil Turner.
“Setting a target of 8 m3/hr/m2 is barely better than previous legal limit of 10 m3/ hr/m2 which was set in 2002. Surely the industry has moved on since then? In fact, a figure of 8 m3/hr/m2 is still behind the now obsolete equivalent standard for Ireland in 2011, which was set at 7 m3/hr/m2! In reality, since the Irish TGD Part L introduced its latest NZEB standard, airtightness levels are now averaging 2.55 m3/hr/m2 in new dwellings.
“Setting such an unambitious backstop gives a clear signal to industry to carry on as usual. As airtightness is one of the most cost-effective means of reducing fabric heat loss, and can be cost effectively carried out at the building stage, it makes this meagre improvement even more baffling.”
“The benefits of attaining an airtight building envelope are widely known ranging from reduced heat losses, reduced risk of interstitial condensation, improved acoustic performance and improvements in thermal comfort to name a few.”
Turner said that a reduction in uncontrolled air infiltration into the building also allows for a more constant ambient temperature. This, in turn, improves the efficiency of air source heat pumps, which are going to be the main source of heating in the future. “Some people believe that an airtight building will result in poor indoor air quality.
This is not the case, as airtightness should also be combined with adequate controlled ventilation such as MVHR. The guiding principle is to ‘build tight and ventilate right’,” he said.
“There is a perception that airtightness is expensive. However, tested and certified airtightness tapes, membranes, and penetration seals are a tiny fraction of the overall cost of construction and result in a very short payback for the homeowner. Substituting fit for purpose airtightness products with items such as basic silicone caulk and basic tapes merely results in a building not being airtight within a reltively short timeframe after occupation.
“Airtightness technology has evolved over the last two decades. Solutions such as Pro Clima airtightness grommets, Aerosana Visconn airtightness paints and other solutions have led to a simplification of executing airtightness effectively on site. This makes attaining much higher levels of airtightness on site even more possible.”