# Condensation problem with flat "warm deck" roof.



## strangebrew (Dec 27, 2010)

This problem is actually on the flat roof of my own commercial shop. It has a 20 year old EPDM roof, mechanical fasteners, warm deck method. Surprisingly, the roof is in very good condition for it's age. I maintain it regularly and it has no leaks. The problem I'm having, (and have always had since I've owned the building for the past five years) is that during the winter when there is snow on the roof, condensation droplets form on the underside of the decking, BUT only in a few areas. The roof is installed exactly the same from the front to the back, so it is really stumping me as to why this condensation problem is occurring in only a few areas. Also, none of the areas in question have any protrusions. I also do not heat the building as it never gets below 50 degrees inside because I am insulated well by the buildings on both sides.


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## O'Donnell Roofing & Solar (Jan 17, 2011)

Thats a real good one,
Is the deck steel or wood?
Is the insulation tapered?
Same insulatiom R value maintained over the entire area?
What's in the room, under the area with the moisture?


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## Grumpy (Oct 29, 2008)

If it's steel it's not unusual. What can be done now? 

A vapor barrier can be installed beneath the insulation but over the metal deck but the roof and insulation would need to be removed.

Perhaps spray in place foam on the bottom of the metal deck, but that's just a guess as I have not experimented with this application, though in theory it should do the job.


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## [email protected] (Mar 26, 2011)

The insulation may be wet/damp in the location of the condensation. This would change the insulations R-value and affect the dew point calculations. Verify insulation condition before proceeding with any other remediation. DO NOT spray foam the bottom of the deck.


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