Metal roofing, leave the old shingles?

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  • LinuxRandal
    Veteran Member
    • Feb 2005
    • 4889
    • Independence, MO, USA.
    • bt3100

    Metal roofing, leave the old shingles?

    I just paid the last house payment yesterday, and now it is time for a new roof. I have done shingles before (helped a couple neighbors) but am looking at metal roofing as well (several neighbors had this installed in the last year or two).

    I know I need to scan the old posts (headed out to work), but I also want to half celebrate the last house payment.
    For those that have used metal, do you have a big noise difference between the metal directly on the top, verses over a layer of shingles? (I have one layer)

    thanks
    She couldn't tell the difference between the escape pod, and the bathroom. We had to go back for her.........................Twice.
  • Mr__Bill
    Veteran Member
    • May 2007
    • 2096
    • Tacoma, WA
    • BT3000

    #2
    I don't know anything about metal over existing shingles, so no help there. I did live several years in a house with a copper roof. The snow slid off with great wooshing sounds in the middle of the night, first time scared the heck out of us, after that it was rather a neat sound to listen for. In heavy rain the sounds put the kids right to sleep at night, very soothing.

    I knew two people who installed their own metal roof. The kind with that looks like a baked on enamel finish with standing ridge seams. They said it was real easy to do themselves. Neither house had any valleys. One thing said was that you had to have the tool for making up the joints. This was a few years ago so things may have changed.

    Bill
    over here at the other end of the Oregon Trail

    Comment

    • capncarl
      Veteran Member
      • Jan 2007
      • 3564
      • Leesburg Georgia USA
      • SawStop CTS

      #3
      Don't succumb to the stupid side and take the good ole boys recomendation of just putting some wood slats over the existing shingles and screwing down the sheet metal. Do your research. Believe what it says and install the sheet metal over insulation / vapor barrier like the it is suppose to be. If not you will have moisture under the metal roof to rust off the fasteners and rot out the slats. This is a worse situation than having an old shingle roof.

      capncarl

      Comment

      • pelligrini
        Veteran Member
        • Apr 2007
        • 4217
        • Fort Worth, TX
        • Craftsman 21829

        #4
        Take a look at the manufacturers installation instructions for whatever product you are going to use. Most will advise as to what is acceptable. There are some systems that can be installed on a layer of composite shingles.

        In any case, there will be moisture under the metal roof at times due to condensation.
        Erik

        Comment

        • chopnhack
          Veteran Member
          • Oct 2006
          • 3779
          • Florida
          • Ryobi BT3100

          #5
          I'd advise against it. Why install one of the more expensive roofing options over a worn out system? Down here the recommendations are to strip down and install manufacturer specific secondary water barriers and underlayment. i.e. "peel and seal" at minimum over all plywood joints (in case you loose your roofing material in storms, the taped joints are water tight.) Some of the underlayments are designed specifically to stand up to the heat of being installed under a metal roof. And plus plus to what others have said, with insulation it should be quieter than what you have now. Another thing to think about is how long will you be in the house.
          I think in straight lines, but dream in curves

          Comment

          • Pappy
            The Full Monte
            • Dec 2002
            • 10453
            • San Marcos, TX, USA.
            • BT3000 (x2)

            #6
            I have R Panel roofing that my son and I installed. I did a lot of research before starting, including asome extensive conversations with the owner of a commercial roofing company on my route. Every thing I found and was told was that you can put metal over shingles by adding 1x4 stringers but it was a bad idea for several reasons. First is the gap for condesation build up that capncarl mentioned. Reason 2 is the additional weight on the roof structure. Finally, there is the noise level. The gap created by the 1x4 stringers turns your roof into a drum head. Potential hail damage is reduced by the solid backing under the metal roof.

            What I did, on the advice of the pros, was:

            1. Strip down the roof to the sheathing (Rent a dumpster)
            2. Eliminate all of the roof vents and patch the holes in the sheathing where they were
            3. Lay 30# felt with a 6" overlap and double layers on the valleys (I don't have to worry about ice build up)
            4. Screw the R panels directly to the sheathing, following the mfg recommended pattern
            5. Add a continuous ridge vent on both the main ridge and the one gable

            Additionally, I ask my contractor neighbor about the reason/need for 6 plumbing vents in the roof. The reason is that it is easier and faster to plumb in 6 straight vents than to connect the ones close to each other in the attic and put fewer pipes through the roof. I now have 2 vent pipes, one for the baths in the bedroom end of the house and another for the kithen/laundry/small bath at the other end, both on the back side of the roof and not visible from the street. If you go this route, make sure the pipes run uphill to the roof vent to avoid trapping gasses. Another advantage is only 2 vent boots to worry about sealing.

            Installing R panel isn't hard. Pay attention to the alignment/square of the panels as you install them. Use a drill driver with a clutch to avoid stripping any screws. Stand several panels against the roof and drag them up into final position as you are ready for them. DO NOT try to work before the morning dew has evaporated or too late into the night. Metal roofing is slick when wet! (DAMHIKT)

            Another note on noise. I have the same roofing over my porch that was done first. The panels are attached to the joists and there is a bead board ceiling with no insulation. The noise level in a hard rain is deafening! In the house the same rain can barely be heard.

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            Don, aka Pappy,

            Wise men talk because they have something to say,
            Fools because they have to say something.
            Plato

            Comment

            • LinuxRandal
              Veteran Member
              • Feb 2005
              • 4889
              • Independence, MO, USA.
              • bt3100

              #7
              Thanks all.

              First, I don't plan on moving (its paid for)! Maybe I will buy some property, so I can eventually build, but I am not planning that anytime soon.

              Second, Pappy, you mentioned vents. Let me ask you about a different type of vent! Did you have, or have to do anything to increase the ventilation of the attic? (gable fan, etc)
              She couldn't tell the difference between the escape pod, and the bathroom. We had to go back for her.........................Twice.

              Comment

              • Pappy
                The Full Monte
                • Dec 2002
                • 10453
                • San Marcos, TX, USA.
                • BT3000 (x2)

                #8
                The only thing I did was to change the soffit to Hardy so I have constant venting the length of the eaves. I haven't checked it but it is a lot cooler in the attic in the summer. The air exchange from the full length soffit vents and out through the ridge vent coupled with the reflective property of the light colored metal roof made a big difference.
                Don, aka Pappy,

                Wise men talk because they have something to say,
                Fools because they have to say something.
                Plato

                Comment

                • pelligrini
                  Veteran Member
                  • Apr 2007
                  • 4217
                  • Fort Worth, TX
                  • Craftsman 21829

                  #9
                  Originally posted by LinuxRandal
                  Second, Pappy, you mentioned vents. Let me ask you about a different type of vent! Did you have, or have to do anything to increase the ventilation of the attic? (gable fan, etc)
                  Ridge vents work a lot better than turbine or other ventilation solutions. I don't know too much about powered venting. The higher you can get a portion of the roof venting the better, especially using a ridge vent. This is a portion of the 2003 IRC (International Residential Code) on attic venting.

                  R806.2 Minimum area. The total net free ventilating area
                  shall not be less than 1 to 150 of the area of the space ventilated
                  except that the total area is permitted to be reduced to 1 to 300,
                  provided at least 50 percent and not more than 80 percent of the
                  required ventilating area is provided by ventilators located in
                  the upper portion of the space to be ventilated at least 3 feet (914
                  mm) above eave or cornice vents with the balance of the re-
                  quired ventilation provided by eave or cornice vents. As an al-
                  ternative, the net free cross-ventilation area may be reduced to
                  1 to 300when a vapor barrier having a transmission rate not ex-
                  ceeding 1 perm (57.4 mg/s · m2 · Pa) is installed on the warm
                  side of the ceiling.

                  R806.3 Vent clearance. Where eave or cornice vents are
                  installed, insulation shall not block the free flow of air. Amini-
                  mum of a 1-inch (25.4 mm) space shall be provided between
                  the insulation and the roof sheathing at the location of the vent.
                  Erik

                  Comment

                  • dbhost
                    Slow and steady
                    • Apr 2008
                    • 9209
                    • League City, Texas
                    • Ryobi BT3100

                    #10
                    First off, major congrats. LOML and I are busting our tails trying to get out of debt... Sick of being a slave for the banks... Now if only we can get the yolk of the tax man off of us...

                    I don't know much of anything on metal roofing in residential applications. I have noted however, at least in several commercial buildings with metal roofing that I have worked in, that they seemed to me to be awfully leak prone... But then again those were some seriously old buildings that had been through hurricanes...
                    Please like and subscribe to my YouTube channel. Please check out and subscribe to my Workshop Blog.

                    Comment

                    • cabinetman
                      Gone but not Forgotten RIP
                      • Jun 2006
                      • 15218
                      • So. Florida
                      • Delta

                      #11
                      I don't hqave much input on metal roofing other than the research I did for a roof for a shed I built. I wound up using roofing panels 49"x79" from Lowes called Ondura. I've got to say it was easy to install, very inexpensive, and light weight. You might want to just take a look.

                      .

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