# Why Double Strapping Prevents Condensation Forming beneath Metal Roofs



## Metal Roof Ottawa (Aug 16, 2017)

Will a double strapped metal roof lead to condensation forming beneath my metal panels? Great question.​

​The inherent flaws of single strapped metal roofing are well documented and have given self ventilating metal roofs built on double strapping an unwarranted reputation of trapping moisture beneath the steel roof panels. Condensation occurs because warm, moist air collects in an air space which has contact with a cooler metal roof surface. Whenever temperatures drop, the temperature of metal roofing drops simultaneously . If warm, moist air contacts this cool metal roof surface, its “dewpoint” is reached and condensation develops. 

There are no exceptions to this rule, condensation forms beneath both metal shingles and continuous sheet steel panels.

Metal shingles have no way of dealing with this condensation other than the protection of the vapor barrier system applied beneath the shingles. 

While single strapped and double strapped roofs both provide ventilation, only a double strapped roof provides both the drainage and ventilation needed to deal with condensation build up behind metal roofing.

THE CONDENSATION RISKS ASSOCIATED WITH SINGLE STRAPPED METAL ROOFS

Condensation naturally forms behind all steel roofing. Single strapped metal roof systems provide no drainage which can eventually rot out both the wood strapping and the sheathing deck that holds the strapping and metal roof panels in place.

Roof failure caused by single strapping is more common with interlocking metal shingles because they allow small amounts of wind driven water to collect behind the single strapped roof. This happens because the strapping is only mounted horizontally directly to the roof deck.

http://www.metalroofottawa.com/metal_roof_condensation_prevention.html


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