Condensation in Buildings - Australian Building Codes Board
Condensation in Buildings - Australian Building Codes Board
Condensation in Buildings - Australian Building Codes Board
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Information Handbook: <strong>Condensation</strong> <strong>in</strong> Build<strong>in</strong>gs<br />
North American and European experience has revealed potential difficulties with exterior<br />
cladd<strong>in</strong>gs with high water storage capacity. In this context, they are termed reservoir cladd<strong>in</strong>gs.<br />
Saturated after heavy ra<strong>in</strong>fall and heated by the sun, they release water vapour which will<br />
migrate towards a cool air conditioned <strong>in</strong>terior. In the 1990s, <strong>in</strong>stallation of polyethylene vapour<br />
barriers suited to very cold climates became widespread <strong>in</strong> milder American and European<br />
locations to deal with lower w<strong>in</strong>tertime condensation risks. The unexpected consequence was<br />
that these barriers, located on the <strong>in</strong>terior face of wall <strong>in</strong>sulation beh<strong>in</strong>d the l<strong>in</strong><strong>in</strong>g became the<br />
site of condensation <strong>in</strong> summer from moisture driven out of brick veneer and similar cladd<strong>in</strong>gs<br />
(Lstiburek 2001). S<strong>in</strong>ce such practices were not applied <strong>in</strong> Australia, the issue is little known<br />
here but may serve as a cautionary example of fail<strong>in</strong>g to recognise the year round effects of<br />
strategies to manage water vapour risks.<br />
3.8 Consequences of <strong>Condensation</strong><br />
Once relative humidity of water vapour at a surface has reached 100% and dew po<strong>in</strong>t, it will<br />
revert to liquid water or frost. Figure 3.13 illustrates a number of risks that may follow.<br />
Figure 3.13 – Some risks from condensation <strong>in</strong> the occupied and <strong>in</strong>terstitial space of a build<strong>in</strong>g<br />
Slippery films<br />
on hard floors<br />
Dripp<strong>in</strong>g from<br />
cooler <strong>in</strong>door<br />
surfaces<br />
Dripp<strong>in</strong>g from<br />
underside of roof<strong>in</strong>g<br />
Track<strong>in</strong>g along<br />
roof fram<strong>in</strong>g<br />
Pond<strong>in</strong>g<br />
on eaves<br />
l<strong>in</strong><strong>in</strong>g<br />
Stream<strong>in</strong>g on glass<br />
and frames<br />
Wett<strong>in</strong>g of<br />
<strong>in</strong>sulation<br />
Pond<strong>in</strong>g at base<br />
of wall frames<br />
DRAFT HANDBOOK<br />
Liquid water responds to gravity to accumulate, run, drip and pond, possibly caus<strong>in</strong>g nuisance<br />
or damage <strong>in</strong> places away from the first po<strong>in</strong>t of condensation. When water appears where it is<br />
not wanted <strong>in</strong> a build<strong>in</strong>g, it is often taken as evidence of a leak and a search for the cause<br />
beg<strong>in</strong>s <strong>in</strong> the wrong places. The “leak” might not be due to a weather event but to periodic<br />
condensation which outpaces any <strong>in</strong>termittent dry<strong>in</strong>g. Condensate form<strong>in</strong>g as a persistent<br />
surface film under a cold roof, for example, can develop over time <strong>in</strong>to droplets and streams<br />
<strong>Australian</strong> Build<strong>in</strong>g <strong>Codes</strong> <strong>Board</strong> Page 27