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A contractor installed a 3″ of Rmax polyiso rigid insulation on my roof

Dennis DeCant | Posted in General Questions on

A contractor installed a 3″ of Rmax polyiso rigid insulation, 3 ” air gap, and foil-back sheating. I have installed ridge and eave venting. What amount of venting is required for a 3″ deep air space?

I currently am having water dripping into my house when the outside temperature is 28 degrees. I currently meet the air flow requirement for sq footage of [ventilation] for an attic which has much higher volume.

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  1. Aj Builder, Upstate NY Zone 6a | | #1

    Post much more detail Dennis.

    How are you getting half the job and someone else getting half the job?

    Run away but before you do take your business card back.

  2. Dennis DeCant | | #2

    when the outside temp reaches 28 deg. My contractor did the job but put in no eve ventelation. the first time it was dripping water in the house he had me install 3" eve vents. it dripped again this year. I did the research and have been to trying to solve the problem on my house. My contractor is my friend and it is creating problems.

  3. Aj Builder, Upstate NY Zone 6a | | #3

    Your buddy buys all beer from now on and for that matter for the rest of your life.

    As to your drips, you need to describe the layers of your roof better. And where is this, what climate, city?

  4. Dennis DeCant | | #4

    The roof of the living space is 4/8 sheets of t/g pine with a paper back. Open beam sealing with a 4/12 roof. the next layer is 3" rmax rigid insulation. then 2 2/4's on side to create 3" air space. 2/4's are bolted to the beams every 4 feet and the pine between 4' dpans. The roof is finished with aluminum back sheeting and 30 yr asphalt shingle. ridge vent is 12.6 nfa and the 2 4" eve vents per 2' bay create a 60/40 balance on air flow. Dripping comes between the 4/8 pine sheets in the center of the roof area.

  5. Aj Builder, Upstate NY Zone 6a | | #5

    Dennis, never heard of such a roof assembly. I would have to see the problems in person to help you. Sorry guy.

  6. TJ Elder | | #6

    Dennis, it's possible that your dripping is from metal fasteners coming through the rigid insulation, causing condensation somewhere in the ceiling. At 28° outside temp obviously water should be frozen on the cold side of the foam, but drips could come from warm indoor air reaching a cold surface. Maybe there are some screws making cold spots on the ceiling.

    If that's not the issue, then it may be your heated air escaping into the 3" vent space and condensing against the foil backed sheathing. That could result from poorly sealed joints between sheets of foam insulation. Better venting might help carry away that moisture, but it's really an issue with how the insulation was installed and the chosen thickness (3" is really not much and probably well below your code minimum).

  7. Aj Builder, Upstate NY Zone 6a | | #7

    Thomas, foam joints leak. The pros offset two layers taped well and fitted well because of the leaks. Amateurs learn the hard way. Of course the pros did too but improved their methods over time.

  8. Jack Saw | | #8

    Well Dennis, there are a number of factors that are going in your stated situation, and for me to quantify this for you I would need of multitude of details to give you an answer you can run with. When I look at a job like this my conscious mind is process things while my subconscious is mind is processes things. So, when I look at things you are really getting 2 people on a project. And, because this is my mind, there is no inhibitions of machismos going on that would keep out any pertinent information. Though I can 't say definitively whether my sub is being forthright, I can say that I would be. I would be happy to come out and assess your situation for an hourly rate of $65 an hour plus expenses. And I won't charge for my subconscious. I have checked air fair and car rental, lodging, and food for this project and my expenses will run around $2500. Plus I charge an 8-hour minimum. So, are we a go?

  9. GBA Editor
    Martin Holladay | | #9

    What's your climate or your location?

    Warm, humid interior air is apparently contacting cold surfaces on the underside of your roof, leading to condensation and drips. Without a site inspection, it's impossible to tell whether the condensation is happening on the ends of protruding screws or on the underside of one of your layers of foam.

    A couple of observations:
    1. Three inches of polyiso gives you an R-value of R-21 -- less than the minimum code requirement in all parts of the country that experience 28 degrees and lower outdoor temperatures. So you don't have enough insulation.

    2. An insulated roof like the one you describe will only work if each layer is airtight. If there are any cracks in your ceiling, interior air will find its way between the sheets of your polyiso until it encounters a cold surface, leading to condentation.

    The solution probably includes air sealing work and the installation of thicker insulation.

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