Whats the right way to do a metal roof?

Discussion in 'Homesteading Questions' started by SouthernThunder, Sep 5, 2007.

  1. SouthernThunder

    SouthernThunder Well-Known Member

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    I am wanting to put a new metal roof up starting from scratch (trusses will be here next week) and have got a different opinion on how to install it from everyone I ask. I understand there are two main issuses that need to be prevented. That is the fastners pulling out and sweating.

    This is what has been suggested the most. 3/4 plywood. tar paper. foil faced bubble wrap. furring strips. metal panel.

    There seems to be some disagreement about where the foil bubble wrap goes and also whether or not to use the furring strips.

    Does anyone have any usefull info here? Who has a roof that has been installed for a long time without issues and how was it done?
     
  2. DavidUnderwood

    DavidUnderwood Well-Known Member

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    I do metal roofs for a living. Been to
    workshops sponsored by the manufacturers.
    Q and A sessions cover most topics at these.
    On new work, in our climate(central NC) it
    is common practise to put 2X4's on the trusses
    to attache the metal. With free air circulation
    all around, it will not sweat. If you use solid
    plywood decking, use felt(tar paper) or red
    rosin paper. No plastic, no where. Plastic will
    cause sweat(condensation) dang near ANYWHERE
    you use it. If painted metal is delivered to a job
    site, especially in hot weather, try to keep it dry.
    Water between sheets nested tight will cause
    the paint to come off. Do NOT cover it with plastic.
    That will cause sweating, and will also make the
    paint peel. If you use solid plywood and felt, there
    is no reason for furring strips. Elevating the metal
    on strips will leave an air space, thereby allowing
    the metal to sweat. And never apply metal to treated
    wood. It is extremely corrosive. In 25 years Ive learned
    from my mistakes. Yet and still, someone now and
    then wants me to do something that I know is wrong,
    insisting that a friend told him how it should be done.
    I reccomend he hires this "friend" to roof his house.
     

  3. SouthernThunder

    SouthernThunder Well-Known Member

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    Hey David, thanks for the reply and good information. What spacing would you suggest for the 2x4s on the trusses (which are 16oc)? Is there anything that can be done for rain noise reduction if it is just the metal roof on 2x4s?

    Which method would you say is the longest lasting and toughest, plywood/tarpaper or the 2x4?
     
  4. rambler

    rambler Well-Known Member Supporter

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    Is this a storage building (heated or not), a livestock building, or a dwelling for humans? Not sure what you are building, makes a huge difference on the amount of moisture & how to construct it.....

    --->Paul
     
  5. SouthernThunder

    SouthernThunder Well-Known Member

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    sorry, forgot to mention, this is a 2 story house in oklahoma.
     
  6. Beeman

    Beeman Well-Known Member

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    www.metalroofing.com has a forum and a list of manufacturers that will answer your questions.

    I don't know it I'd use the furring strips, just deck it, seal it and then put the metal. I used foil/foam/foil insulation instead of bubble. it's made by environmentally safe products called low-E insulation.
     
  7. Up North

    Up North KS dairy farmers

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    We have a dairy barn with Asphalt shingles. I would like to cover it with white
    roofing steel. Furring strips or no?
     
  8. Ramblin Wreck

    Ramblin Wreck Well-Known Member Supporter

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    That's how we did it on my house and garage (and several other family member projects too), and I've (we've) had no problems with sweating. We're in the South, so it might be a different issue in other climates with snow loads.

    One other comment/suggestion: Regardless of what underlayment/structure you go with, make it as square as you can. It makes for a much quicker, easier install.

    Good luck.
     
  9. fantasymaker

    fantasymaker Well-Known Member

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    The metal is going to sweat.
    The 2 X4s under it will give space for air circulation to help dry the sweating.
    if you must insulate near the metal use Spray foam insulation sprayed directly on the metal.
    That will put the condensation point inside the foam where the air cant get to and thus no condensation,
    If your not doing that reread DavidUnderwood's post.
     
  10. TedH71

    TedH71 Well-Known Member Supporter

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    When I helped build houses for Americorps..we installed metal roofs. Was told to put 2 by 4s then put vapor barrier (forgot what type) over it then the roof over that and it was all screwed in. No furring strips, etc. Main reason for metal roofs is that it will reflect heat off the house and not need replacing in for 50 years compared to 20 years on your standard shingle roof.
     
  11. Farmerwilly2

    Farmerwilly2 Well-Known Member

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    All of the buildings I've put up to date on the place are uninsulated. I use 2x4 nailed to the rafters and then the steel. I've not had any condensation to date. The shed has a gravel floor, damp when it rains. The poultry house has a wooden floor, but birds that poop and breathe. No condensation at all. Hoping David writes back, I will be replacing the roof on the house when the time comes with metal roofing. I'd like to know what the manufacturers regarding fiberglass batts and a vapor barrier beneath the rafters.
     
  12. sugarbush

    sugarbush Bees and Tree specialty

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    And I always thought that the biggest debate in metal roofing was whether to screw it on the ridges or plains!
     
  13. Farmerwilly2

    Farmerwilly2 Well-Known Member

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    I'm a 'nail it through the ridge' kind of guy. I've had to tear off screwed down roofing. I'd rather rub down a bobcat with a handful of broken glass.
     
  14. SouthernThunder

    SouthernThunder Well-Known Member

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    When people say a metal roof is good for 50 years what exactly goes bad after 50 years? Does it start to rust out or need to be re-fastened or just repainted? My problem is there is chance I might still be alive in 50 years but probably will not be able to re-roof this joint.
     
  15. sugarbush

    sugarbush Bees and Tree specialty

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    Well providing that it comes painted and you don't get scratches in the paint while putting it down or hail/wind damage it should last forever......it will need to be maintained just like anything else.
     
  16. ET1 SS

    ET1 SS zone 5 - riverfrontage Supporter

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    I sprayed foam onto the underside of our roof, we are very happy with it.
     
  17. Farmerwilly2

    Farmerwilly2 Well-Known Member

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    Could you give a little more detail. As I recall you set up a metal building to live in. Is this sprayed foam the only roof insulation? Did you rent or buy a sprayer? How do you handle moisture levels in your home?
     
  18. ET1 SS

    ET1 SS zone 5 - riverfrontage Supporter

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    Yes I built a steel building. 60foot by 40foot and 12foot eaves.

    I sprayed foam onto the interior roof and walls, about 1.5 inch thick. It solidified the sheet metal. It sound deadened it. I then hung R-30 fiberglass batting against that foam, and held it in place with wood paneling.

    The foam that I used comes in a pack of two pressurized bottles. The two components mix in the nozzle as it is sprayed out. The foam is an epoxy that sticks to everything it touches. It heats itself to 200 degrees as it expands and hardens. It is hard within about 30 seconds. It is pressurized with nitrogen, as it expands it out-gasses mostly nitrogen. You can spray it with only a paper mask over your face.

    We have a propane water heater that sucks make-up air from the house and vents it outside, this lowers the inside humidity some.

    And we have a stove that burns wood / peat / coal. The stove also removes humidity from the house.
     
  19. Farmerwilly2

    Farmerwilly2 Well-Known Member

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    I think that's the foam I saw from Northern Tool? Any problem keeping the spray at a consistent thickness? I wonder if it's like the 'instapak' foam I used in a shiping dept. years ago. Thanks for the answers.
     
  20. artificer

    artificer Well-Known Member

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    For the best quality job, which lasts the longest, use furring strips. If you don't, the paint/coating on the bottom can be abraded by the the stones in the shingles. If you get any moisture in there, then it will rot out from the bottom. Granted... it'll take years/decades to do so, but for the small cost and additional time, it makes sense. Its also easier to screw/nail the sheets down, since you now have a know good fastening surface.

    Michael