# EPDM rubber venting questions



## moveinmaryland (Dec 17, 2012)

Hey everyone,I'm a GC and I don't do much roofing, mainly because I'm not comfortable with all of the techniques yet. I wanted to get opinions from some more experienced professionals in the roofing field. I am doing a roofing project on my own house, so I'm working through it in my free time and I've run into a point of contention
Situation:
I have a 12x23 flat roof over a sunroom on the back of my house, and it runs into a pitched roof over the main structure. The roof rises about 6" over a span of 12'. I have installed a Firestone EPDM rubber roof without any problems. The roof is adhered to 1/2" of insulation, which is over two layers of decking (3/4" and 1/2"). The way the roof is structured, I have an opportunity to put install a soffit vent, install baffles in between each of the rafters, and run the baffles continuously into the attic of the main roof structure (which already has ridge vents) for continuous air flow. I live in Maryland, where the winters can get down to and hover below freezing during the winter, and the summers usually stay in the upper 90's with 80-100 percent humidity for a few months. I have had conflicting answers from everyone that I have talked to so far. Including the Firestone roofing hotline giving me a "no comment". I'm trying to decide if I should vent and insulate, or seal the cavities and insulate. Moisture and heat are my main concerns. 
Q1. If i seal the roof and insulate with no venting, will possible moisture created through temperature differences cause problems
Q2. If I vent the roof and insulate, will that just be letting moisture in through the soffit and causing problems?
Q3. Is the shallow span of the roof enough to provide airflow even if I do vent it?
Q4. If moisture is an issue, should I be installing a vapor barrier over the insulationbefore I put up sheetrock on the ceiling?
Q5. Can you think of anything I might be overlooking? Or have any suggestions?
I would greatly appreciate any help and suggestions. I want to get this thing finished up before my wife pops out our firstborn this spring.


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## shazapple (Dec 3, 2010)

A lot of flat roofing systems are designed so the vapour barrier is on one side of the insulation, and the roofing membrane is on the other with no air spaces. This gives a fairly large temp differential, but I think most membranes can handle this (shingles are another matter...) 

THAT SAID, I've worked with a lot of ventilated flat roofs, and they flatout beat the pants off a system I described above. I figure there is less thermal stress on the membrane, and any water that may get into the system has a chance to evaporate. They just tend to be a lot more forgiving.

1) possible, depends on how well the roof and vapour barrier have been sealed.
2) No more than you'd see in your attic
3) Low slope roofs typically require 1:150 vent area (vs a typical shingle roof needs 1:300)
4) Depends on what is typical in your area. Around here a vapour barrier is the norm.


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## Pie in the Sky (Dec 21, 2011)

Not alot of info in your post... I started roofing in Philadelphia and we were right on the edge of where a VR was recommended. Your Vapor drive in MD is most likely out to in. If you posted some pics we may be able to give more advice, if not Shaz covered it.


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