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Doubling metal roof panels?

BilljustBill | Posted in Construction Techniques on April 25, 2008 10:44am

I have two buildings that have metal roofs with shallow, but a high density of golf ball size dents.  One is R-panel and the other is U-panel.  The white paint color is in great shape.

When I have the roofing replaced, is there any disadvantage to letting the old panels stay in place and after the old screws are removed, lay the new metal over the top?  Should there be a sealant placed in between metal sheets to keep moisture from wicking up from the bottom or from the ridge down?

  Thanks for your experience and information!!

  Bill

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  1. Piffin | Apr 26, 2008 12:59am | #1

    I'm thinking that just finding someone willing to do that and warrantee it would be a problem

     

     

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    CapnMac | Apr 26, 2008 01:52am | #2

    One is R-panel and the other is U-panel.  The white paint color is in great shape.

    I want to remember that MBCI used to carry an "overlay" R panel for roof repairs. it was pressed to allow you to set them over a thin repair membrane or in a mastic bed of some kind.

    When we patche the roofs over in Lee County though, the contractors told us that the panels are out of stock, unless you need a full run of 10,000 of them.  Turns out it is easier to reroof than to overlay generally.

    If your paint is unbroken, I'd likely call it even and live with it.  Kynar 500 is the way to go with new panels, but it's not cheap (except over the panel lifetime); so an un-damaged panel with unbroken finish is much cheaper to you over unstiching the panel screws and replacing with new.

    But, that's my opinion; others' differ.

    Occupational hazard of my occupation not being around (sorry Bubba)
    1. BilljustBill | Jun 26, 2008 07:27am | #5

      Could you help me by describing that 'inlay' panel between the two metal roof layers?

      All I can find to attach one r-panel roof over another is something called a metal furring strip ( called a "hat top") that screws to the tops of each of the panels ribs.  The cost about $3.50 per ten ft. section and is double screwed to each rib.  It is said that there is about a 7/8" space between the old roof panel and the new one; just enough space for a thermal break to let the old white roof become somewhat of a radiant barrier.  Plus with the free airflow up to a ridge vent, it should stay cooler and moisture vapor free...

      For time and money, something like you are describing would really help me keep down the R-panel costs.  Here in Texas, R-panel metal roofing  cost $500 a square to replace.

        Thanks for you help and time,

        Bill

      Edited 6/26/2008 12:34 am ET by BilljustBill

      1. User avater
        CapnMac | Jun 26, 2008 08:31am | #6

        All I can find to attach one r-panel roof over another

        That is all the present catalogs show, unless. like my old boss you keep your 1993 catalogs to spec from.

        That was the problem at Lee County back in 2006.  We had a spec for the snap-over repair panel.  Contractor calls up and they will press the panel to order, but it's 10,000 panels, or several thousand square's worth minimum run.

        If I remember the detail right, the flat roof to metal roof joint was originally to have mastic , then whicheever single-ply roof the contractor selected laid in th emastic, then more mastic, with the snap-on R panel set over that, when then got rib screws to normal R panel spec.

        I do not remember what they changed to after the panel sanfubar, I ws neck-deep in a clinic project.Occupational hazard of my occupation not being around (sorry Bubba)

  3. Marson | Apr 26, 2008 01:41pm | #3

    OK, I don't do a lot of steel roofing, but I would pretty much guarantee that there is about thirty issues you haven't even thought of in putting a second layer of steel over the first. I would think you would be money ahead in the long run just peeling the original steel first. Heck, you wouldn't even have to pay to get rid of it, except for the hauling.

    I hope it is a shallow pitch because the guys would have to walk safely on the old roof to put on the new roof. And picture it in practice. They spend the time to back out the screws. Put on the new panel. Oops, forgot a screw. Take off the new panel. etc. Also, how would the eve look? How would panel laps work?

  4. BilljustBill | Apr 26, 2008 06:06pm | #4

    Thank you.  All of you so far have given me information to ponder!!

    What got me to thinking about double layering instead of removal and replacement was in the small addition I added about 2 years ago.  The roof was extended and where the white 14 year old R-panel stopped I unscrewed it and slid the new metal underneath it for about 12" to help blend any visual "bump".  Where the the golf ball hail hit in that transition area, there are no dents seen from underneath the roof....

      The ends of the roof are hidden by the wide gutter that projects about 2" higher than the roof.  The gable ends have 10" wide brown metal trim overlapping the roof and down the end walls.  It would never show.

       Any more thoughts or experience is surely welcomed.

      Bill

     

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