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  1. #1
    Join Date
    Oct 2008
    Location
    Chapel Hill NC
    Posts
    15

    Default Misconceptions about metal roofing condensation

    I know that this topic has been thoroughly discussed with me and I appreciate all of your thoughtful answers but unfortunately I continue to run into this problem and the answers that I have been providing to my customers have been met with dissatisfaction and alienation. In the 80's in this area it was quite common to build cathedral roof assemblies on straight purlins, no roofing deck, no drainage plain. Thus I have responded to a number of "leaks" that have occurred on roofs with no valleys, transitions, occurring infrequently, with a variety of different methods of assembly, where the roof appears to be sound. I have had several contractors come in behind me and contradict me straight out, often losing my customer on the way.

    My understanding is that with metal roofing you absolutely HAVE to have a drainage plain. This would mean a plywood deck with some sort of building paper to handle the inevitable condensation that forms on the underside of the roofing. Am I wrong to insist on this? Any help with this issue would be very appreciated.
    TIA, TIM

  2. #2
    Join Date
    Jun 2004
    Location
    Des Moines, Iowa
    Posts
    3,846

    Default Re: Misconceptions about metal roofing condensation

    Tim
    Draw a cut of a couple of these and post them.

    How are these ceilings insulated?
    Mark Parlee
    BESI(building envelope science institute) Envelope Inspector
    EDI Certified EIFS Inspector/Moisture Analyst/Quality Control/Building Envelope II
    Level one thermagrapher (Snell Training)
    www.thebuildingconsultant.com
    www.parleebuilders.com
    You build to code, code is the minimum to pass this test. Congratulations your grade is a D-

  3. #3
    Join Date
    Jun 2004
    Location
    Northern Vermont
    Posts
    1,381

    Default Re: Misconceptions about metal roofing condensation

    CH Custom,
    I agree with you. There are two good reasons for installing roof sheathing and roofing underlayment under metal roofing:
    1. To provide an air barrier at the top of the insulation
    2. To handle condensation.

    The (possible) exception: if the roof has two layers of rigid foam, installed with staggered seams, on top of the roof sheathing.

  4. #4
    Join Date
    Dec 2005
    Location
    Michigan
    Posts
    7,535

    Default Re: Misconceptions about metal roofing condensation

    Martin, with all due respect:

    He hasn't said how he's insulating or even IF there's any insulation anywhere in there. So your answer is extremely presumptive at best.

    Provide an air barrier at the top of the insulation? You're kidding, right? Let's see, assuming there IS insulation at the roof level, the reason you need sheathing is for an air barrier? What if his insulation is spray PU foam? That's an air barrier. So now he doesn't need sheathing according to your answer?

    What if this is a vented attic and there is no insulation at the roof deck level?

    CH, if you want help you need to give all the pertinent info.

  5. #5
    Join Date
    Jun 2004
    Location
    Northern Vermont
    Posts
    1,381

    Default Re: Misconceptions about metal roofing condensation

    DG Builder,
    The original poster wrote, "In the 80's in this area it was quite common to build cathedral roof assemblies on straight purlins, no roofing deck, no drainage plane."

    I responded to his description of the roof assembly under consideration: a cathedral roof (that is, an insulated sloped roof.)

    If the steel roofing is installed on purlins without any OSB or plywood roof sheathing, then your suggestion that the insulation might be spray foam seems to me to argue in favor of what I wrote: you still need continuous sheathing under the steel roofing. Installing spray foam insulation on the underside of the steel roofing, around purlins, would be a mistake. Replacing the roofing in 40 years would be a nightmare.

  6. #6
    Join Date
    Jul 2008
    Location
    Suburbia (Washington, DC area)
    Posts
    1,938

    Default Re: Misconceptions about metal roofing condensation

    Just heard Joe Lstiburek last month saying "all metal roofs leak some", and I also agree with the condensation concern.
    We usually do full, HT (High Temp) ice & water over sheathing. Grace or Carlyle.
    Typically the roof is ventilated so the decking is not an air barrier over the insulation though. Nowadays if we have the budget we would install vent channels, some spray foam (or all depending) then spyder or cellulose to finish out.
    I'm intrigued with the foamboard-on-the-deck method and we may give that a shot one of these days. We don't see a lot of condensation-based moisture problems in our climate though, so that may be more horse than we need for the race, around here. Very similar climate to Chapel Hill.

  7. #7
    Join Date
    Jun 2011
    Location
    Alaska
    Posts
    1

    Default Re: Misconceptions about metal roofing condensation

    Hi....I made a outhouse last year,and due to rain the roof of my outhouse damages very badly, Can anybody please suggest me Is metal roofing safe? Should I use metal roofing for my outhouse?How much will be the cost of metal roofing?
    ______________________________________
    You can know more about roofing Austin or Austin roofers.

  8. #8
    Join Date
    Jun 2004
    Location
    Northern Vermont
    Posts
    1,381

    Default Re: Misconceptions about metal roofing condensation

    Hetty,
    No, metal roofing is not safe. If you cut a panel with metal shears, the sharp edges will cut your fingers.

  9. #9
    Join Date
    Jun 2004
    Location
    Des Moines, Iowa
    Posts
    3,846

    Default Re: Misconceptions about metal roofing condensation

    Hetty
    make sure you get all of those metal slivers cleaned off of the seat as well
    Mark Parlee
    BESI(building envelope science institute) Envelope Inspector
    EDI Certified EIFS Inspector/Moisture Analyst/Quality Control/Building Envelope II
    Level one thermagrapher (Snell Training)
    www.thebuildingconsultant.com
    www.parleebuilders.com
    You build to code, code is the minimum to pass this test. Congratulations your grade is a D-

  10. #10
    Join Date
    Jun 2004
    Location
    Friday Harbor, San Juan Island, Washington
    Posts
    13,029

    Default Re: Misconceptions about metal roofing condensation

    Metal roofing is definitely not safe. As soon as you install the last piece it's too slippery to walk back down to your ladder, so you're stuck up there.
    Bailer Hill Construction, Inc. - Friday Harbor, WA
    Website - Facebook

  11. #11
    Join Date
    Jun 2004
    Location
    Houston & Washington Texas
    Posts
    12,201

    Default Re: Misconceptions about metal roofing condensation

    Quote Originally Posted by David Meiland View Post
    Metal roofing is definitely not safe. As soon as you install the last piece it's too slippery to walk back down to your ladder, so you're stuck up there.
    I am doing my first metal roof in a few years, we used high heat I&WS with Sharkskin over it. I posted some videos on my You Tube channel. We are putting same metal (Galvalume) as facia and soffit.
    ============================================

    Twitter

    Houzz

  12. #12
    Join Date
    Jun 2004
    Location
    Friday Harbor, San Juan Island, Washington
    Posts
    13,029

    Default Re: Misconceptions about metal roofing condensation

    Truthfully, I love metal roofing. It can be really hard to work on it, though, if it's steeper than about 6:12 it's like a playground slide. I am having a welder make me a permanent roof hook so I can get on top of my shop to clean the chimney and the skylights.
    Bailer Hill Construction, Inc. - Friday Harbor, WA
    Website - Facebook

  13. #13
    Join Date
    Jun 2004
    Location
    Northern Vermont
    Posts
    1,381

    Default Re: Misconceptions about metal roofing condensation


  14. #14
    Join Date
    Jun 2004
    Location
    Friday Harbor, San Juan Island, Washington
    Posts
    13,029

    Default Re: Misconceptions about metal roofing condensation

    Martin, what I'm doing is having a hook made that will be permanently attached to the roof, just below the ridge. I have a 20' section of lightweight aluminum ladder that is used only for climbing roofs, and in this case I will be able to slide it up the roof, drop it over the hook, and climb. I also have a couple fo sets of Qual-craft roof hooks that attach to ladders but those don't feel secure over a metal ridge cap, and they can mangle the metal too, so I mostly use them on comp roofs that are 8:12 or steeper.
    Bailer Hill Construction, Inc. - Friday Harbor, WA
    Website - Facebook

  15. #15
    Join Date
    Jun 2004
    Location
    Greenville,S.C.
    Posts
    377

    Default Re: Misconceptions about metal roofing condensation

    I've worked on quite a few metal roofs some with 70' panels on big churches. Often it was a leak around a vent stack or other penetration. I found anything over a 5" pitch and I was constantly "peddling" with my shoes to stay in place, kinda like my Schnauzer when you tickle him behind the ears.
    After constantly juggling tools and materials and burning my rear end I came up with an answer. I made up a "sled" with carpet on the bottom, padded on the top, that has a place for tool & materal storage.It clamps to the standing seams. It took about an hour to make but was well worth it if the fix was time consuming.

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