Cerebrus and others, Carlisle TPO Venting Question?

A Private Message Question I received regarding a Carlisle roof on a hospital.

I was hoping that Cerebrus and others with with a better flat roof ventilation knowledge could chime in.



*"We have a roofing problem on a hospital roof. It is a Carlisle 6 year old TPO membrane system. The fasteners let loose in a partical area of about 3000sf of a 21,000sf roof. It is adjacent to an open field at a 3rd story level.

The mfg. did core testing multiple times (different seasons) and also infrared camera to determine moisture levels. The mfr. is willing to correct the problem but maintains that the fasteners corroded due to moisture coming from within the bldg. not from a leak.

The core samples revealed moisture in the top layer of insul (polyiso) but not the lowere layer. At other times when the exterior conditions were warmer the core samples showed no moisture in the insul. This supports their condensation of moisture theory.

My question is does anyone have experience with the use of one-way vents in a flat commercial roof application?

The hospital maintains a 50 percent humidity level and claims that the condensation theory is invalid.

A roofing consultant says the one-way vents only service 1 square foot. Any ideas or suggestions?"*

I’m not Cerebrus, but maybe I can help. :mrgreen:

First of all, one-way vents are fairly ineffective, though I don’t know that I would limit their effective range as only being 1 square foot. However, if you asked me if I would put them on the hospital roof in question and believe they would solve the problem? My answer is indubitably, NO!

Before I get further into my answer, I would like to know how old the roof is and if you had anything to do with the installation? If so, was the insulation board stored on the roof only in the factory shrink wrap, or was it properly tarped and elevated above the ground? Did any of the insulation get laid out and rained upon before the new roofing was installed?

The reason I ask, is they obviously have a vapor-drive issue with that roof. The moisture typically will be driven into the roof board insulation during the night, but will condensate on the bottom of the membrane during the day depending on interior and exterior temperatures and humidity. If the building is fairly new, the excess moisture may eventually dissipate and roofing components moisture content will near equilibrium.

You say the hospital keeps the humidity at 50%, but I don’t know if that is high for your area. If it is high, then a vapor-barrier should have been installed with the roofing. Chances are, this is not the case unless the hospital has some walk-in coolers or something like that beneath the roof that is experiencing moisture problems.

Also, are we talking about a metal roof deck, concrete or did they install insulation over lightweight concrete?

Too many questions for me to give you a good answer right now. Give me some more background information and I may be able to help you better.

Opps, just went back and saw where you said the roof is 6 years old. So, it sounds like there are some other issues. Once again, what kind of roof deck do you have? Are there any roof leaks that you know of, or were there any? That moisture is entering the system some how.

Did the roofing consultant take cores and have gravimetric testing performed, or how did they determine there was an elevated moisture content?

Are you sure the fasteners failed due to corrosion, or could it have been a failure related to wind uplift?

Let me know some more, and maybe I can help.

When all is said and done though, I’m going to put my money on them having a problem with the dew-point falling within the top layer of insulation. If I’m right, and the project was a re-roof of an existing building, then the problem may have been caused by an increase in the roof insulation value. Sometimes just adding more and more insulation to a roof is not a good thing.

Thank you, “Cerberus”

Too bad the other guy hasn’t responded yet.

This is not my roof, nor anyone I know.

It was a Private Message I received on www.DIYchatroom.com where I am one of the Moderators.

The party who PM’d me has no previous posting history background for me to delve further, so I must wait for their response for more information.

Thank You.

Credit will be given to the proper respondents for their collective thoughts and possible solutions.