Simple measures to improve airtightness
Much of Australia’s home building stock is below par for building performance, but a few simple measures can be employed to improve airtightness and home owner comfort. Angus Kell explains.
There is little doubt that on the surface Australian houses appear to be built to some of the highest standards of anywhere in the world; but, look beneath the beautifully ﬁnished outer lining and unfortunately you will ﬁnd another storey.
This is reinforced by a survey undertaken by CSR in 2015 where the company posed a question to more than 100 European and North American ex-pats living in Australia on what they thought of local housing, and they commented as follows:
– 70% love the look of Australian homes compared to ‘back home’
– 75% thought building performance was relatively poor
Probably the single greatest inﬂuence on the performance of our housing, and therefore the subsequent comfort of its occupants, is the small cracks and gaps that lie beneath the inner and outer linings of the external walls. By allowing these cracks and gaps in our construction we fail as an industry to provide the standard of housing achieved in countries including Europe, Canada and the US.
A signiﬁcant proportion of housing in Australia is still constructed with stick-built framing, put together by trades on trades, leading to the potential for signiﬁcant variation of work practises by a labour source of great skill variation. In addition, our focus on delivering what we recognise as aﬀordable housing through the minimisation of expensive labour and the selection of materials based on lowest price, is likely contributing to the poor standard of construction. This is at the expense of the ongoing operational performance of the house.
A study undertaken by the CSIRO in 2012 into the airtightness of Australian housing found that when tested for airtightness using the blower door pressurisation test method, our housing measured an average air leakage of 19.9ACH@50Pa (air change rate at pressure), which equates to replacing all the internal air within the total volume of the house every hour through uncontrolled cracks and gaps. By comparison, building codes in the US and Europe typically require airtightness at approximately 2-3ACH@50Pa and the standard for PassivHaus (a recognised voluntary international standard for energy eﬃcient building) is 0.6ACH@50Pa.
A recent study undertaken by the BC Housing Research Centre titled Much Illustrated Guide, Achieving Airtight Buildings considers why airtightness is important and comments: “The restriction of air movement by the air barrier system in one of the most important functions of the building enclosure and, in some cases, the interior partitions. Air is a transport mechanism for water, vapour, heat energy and airborne contaminants. As a result, uncontrolled air leakage can lead to moisture issues from condensation and bulk water ingress, excessive heat loss that leads to discomfort and energy waste, as well as poor indoor air quality that aﬀects occupant health and comfort”.
While this article is written based on the experiences of the northern hemisphere, it can be extrapolated as representative of Australian conditions, noting that the eﬀect on loss of heat or cool air is dependent upon the climatic zone and season. The eﬀect on energy consumption is the same if we replace all the heated and/or cooled air and have to heat and/or cool the air to ensure an acceptable level of comfort through conditioning the air.
Another signiﬁcant reason to limit the gaps and cracks is to prevent moisture transfer through the building enclosure. In such cases air movement is probably the most common transfer mechanism: whether it be forcing external rainwater from entering the house; or driving water vapour through the building enclosure where it may condensate inside the cavity.
Similarly, acoustics are also greatly aﬀected by gaps and cracks in the building enclosure. To the extent that a hole of 0.01% of the total external wall area can lead to the loss of acoustic performance of the wall from Rw60 to Rw40, and this seemingly small breakdown of the building enclosure could lead to a detrimental eﬀect on the amenity of the occupants through failure to protect them from sources of external noise.
And ﬁnally it is obvious that gaps and cracks will aﬀect the ﬁre performance of a ﬁre-rated wall as it allows the penetration of both smoke and ﬁre through the building enclosure. A failure of this magnitude is an immediate threat to the life of the occupants.
Some simple measures to improve airtightness in our homes include:
– Ensure air barriers in the external wall are installed correctly, including taping joints, sealing the perimeter and folding and taping the barriers into window and door openings.
– Source exhaust fans and vents with installed dampers to minimise the uncontrolled passage of air from the outside to inside of the house.
– Select good quality windows with built-in thermal breaks and high performing perimeter seals.
– Ensure lining and ﬁnishing trades are educated to achieve tight ﬁtting linings with sealed perimeters.
– Seal around window frames, architraves, skirtings and cornices.
– Minimise penetrations through the external walls.
– Add seals to external doors, including doors between conditioned and unconditioned internal spaces.
– Ensure the door between the garage and main house has seals to limit the contamination of the internal air with heavily polluted air.
Obviously, the best way to ensure an airtight building is to undertake airtightness testing using the blower door pressurisation test method prior to handover to the home owner. From this testing evaluation can be made of your existing construction methods, and improvements can be made to future projects with the aim of providing home owner with the type of housing they expect, and more importantly deserve.