The problem of condensation on the underside of a metal roof – is due to heat escaping the home to the roofspace, this heat loss permeates the ceiling and insulation to rise to the underside of the metal roof. As the top of the metal roof covering is much colder than the underside, the heated air that rises to come in contact with the underside holds a percentage of water vapour, at this point of contact called the Dew Point. The heated air will condense and the moisture within will disperse and become water, it could be raining in your roof.
As well as any protusions through the ceiling will be dumping more heated air into the roofspace for example – exhaust fans from cooking (range hoods) showers and baths from the bathroom downlights, the laundry etc etc. The fans should be ducted to the outside atmosphere.
So you see there could be quite a lot of factors contributing to condensation on the underside of metal roofs. Then you have the problem of bad building practice, any sort of low pitched roof is a recipe for disaster.
Condensation and Sick Building Syndrome (SBS) are more evident in Australian homes today than ever before, this is mainly due to over insulation and some bad building practices. A metal roof without effective roofspace ventilation can be compared to playing Russian roulette with a full magazine.
Other bad building practice –
- No vapour barrier under the metal roof.
- Vapour barrier that has been stretched tightly across the rafters, bringing the vapour barrier into contact with the roof sheet – you may as well have no vapour barrier at all.
- Not taping the laps of the vapour barrier.
- Last but not least metal battens, these work like a wick for condensation. When timber battens are used this is not a problem.
See BLOG on this site “Message to Victorian Builders” this will give some indication of good building practice with metal roofs.
When you are looking to alleviate the problem of condensation problems in your metal roof, Universal Tile Ventilators have the solution to allow the ambient temperature to circulate your roofspace and quite possibly solve your problem.
Universal Tile Ventilator System for concrete and terracotta tiled roofs and the Smoothline Ventilator System for corrugated colourbond roofs.
ANYTHING ELSE IS A COMPROMISE
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