Question on Installing Metal Roof

Discussion in 'Shop Talk' started by ThreeCreeks, Feb 28, 2005.

  1. ThreeCreeks

    ThreeCreeks Member

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    I want to put a metal roof (the plain, wavy, 8' x 26" panels) on a cabin which right now has a shingle roof. The existing roof has a couple of leaks. I plan to nail the panels right over the shingles. The roof is exactly 8' from the high point at the top down to the eaves.
    Questions:

    The nails that I plan to use are 1 3/4" ring shank neoprene washer hot galvanized roofing nails. Are these good?

    How much overlap between panels do I need?

    They make rolls of putty-like stuff that is supposed to go between the panels. Do I need this?

    If I do it right, will the roof not leak when I'm done?

    Are there any questions that I should be asking that I'm not?

    Answers to any or all questions, or any other information, greatly appreciated.
     
  2. agmantoo

    agmantoo agmantoo Supporter

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    If I were installing the metal I would nail lathing strips, placed on 16 inch centers, through the shingles and into the rafters using ring or spiral shank nails. Then I would use screws with the neoprene washers to install the metal to the lathes. The caulking you referenced would be used on each sheet of metal the full length. As for the exposure, most of the metal is designed for X amount of exposure. Measure the width and determine what the exposed amount would be with it lapped. Usually this will be a fixed even number and no fractions. Something like 24 or 36 inches. You will want the laps to be placed to where the prevailing winds will not try to lift the lap joint. As for leaking, you did not give the pitch dimension but doing the above should eliminate leaking. You are aware that you will need a ridge cap?
     

  3. ThreeCreeks

    ThreeCreeks Member

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    Yes, I knew about the ridge cap. The lathe strips sound like a good idea. Wouldn't they want to go wherever I plan to overlap the panels, though, so each overlapping point is screwed down?
     
  4. mikell

    mikell Well-Known Member

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    You can also shim the furring strips to make the roof look square again.

    mikell
     
  5. agmantoo

    agmantoo agmantoo Supporter

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    3creeks, The lathing strips run perdendicular to the metal. This will provide a strong connection every 16 inches at the lap joints. The top lathing strips should be placed at the ridge to accomodate both the ridge cap and the roofing metal fasteners. The screws will permit proper snugging of the material without distortion which occurs with misplaced or heavy hammer blows. You can get by with less screws and that will offset some of the additional costs of the screws over nails.
     
  6. ThreeCreeks

    ThreeCreeks Member

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    OK, now I understand about the lathe strips. Good idea. So I do need to use the putty? Do I need it along the lengths of the ridge cap?
    Good idea about the shims, too.
     
  7. agmantoo

    agmantoo agmantoo Supporter

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    Yes, the "putty" (roll caulking) is cheap insurance against rain overwhelming the corrugations and flooding via running under the lap joint. You need a continuous caulked joint at each lap running from the ridge cap to the eve.

    You never stated the exact type of metal you are planning on using. Maybe you have already purchased it. If not, I strongly suggest the galvalume finish on steel. If you use the metal with corrugations that is so common to newer steel buildings, the screws go in the flats? On metal when using nails, the l fasteners go in the top of the Vs.
     
  8. rambler

    rambler Well-Known Member Supporter

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    I've never heard of sealing the vertical seams of a tim roof, but that doesn't mean it's not done.

    You must be using simple corrigated tin; the typical roof tin around here has 3 or 5 ribs per sheet & you simply overlap the outer rib, there are special lips & angles bent in the tin for a good seal to make them leak proof. I would pay attention to the roof cap, there are special seals to keep water from pushing up under there.

    If this building is heated, I would consider condensation, it will not be good to let warm or damp air hit the back side of that roof, it will be 'raining' every day! I'm not qualified to tell you how to avoid it, but I do know it can be a problem. Perhaps your roof is already well insulated & vapor barriored already.

    --->Paul
     
  9. comfortablynumb

    comfortablynumb Well-Known Member

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    I used black wet/dry tar in a calk tube and made a thick bead on the overlaps...

    and yea use coated deck screws, they will hold better too...
    and put a blob pf goo on each head to seal it doubleplusgood.
    I didnt use furring strips I screwed it right to my old shingles,so i wouldnt have any gap for the winds to grab...
     
  10. Neville Aponte

    Neville Aponte Active Member

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  11. ThreeCreeks

    ThreeCreeks Member

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    Thanks for all the good advice. I think that I will be able to do a good job and avoid some problems now.
     
  12. mink

    mink Well-Known Member

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    only thing to remember is when lapping the side with the lil quarter inch lip goes on top.......nothing needed on the seams and screw in the flats if using screws with the neoprene washers.