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  • Holes in Roof?

    Hi all! Working though the many choices involved in solar installation. Super happy to be getting ready to join the Sun Power Club!

    The company with the most to offer for the money has informed me that they can install the panels onto a metal standing seam roof. However, they do not use a clamping system, but rather drill holes through the roof to drop lag bolts into the rafters. This metal roof is 5 years old and should last for decades. While the panels have a long term warranty I have been told that the installation via this method comes with a 10 year leak guarantee. I am a little concerned about executing an install w/a 10 year "no-leak" policy on a roof that should last over 3 decades.

    Can anyone please speak to the durability of the flashing/sealant on this method of install? Anyone with experience? Pros/Cons?

    Thanks in advance for your help!!
    Q

  • #2
    Your average corrugated roofs do very well with hundreds and hundreds of screw holes just protected by little gaskets under the screws. Not as good as a standing seam with no holes, but it works. We do both standing seam clamps and screwed mounting feet and also are confident of the simple, less expensive screw method, but leave it up to the customer's comfort level to make the decision of which way to go. Think of the screws as forming a compression seal, very much like the compression seal on your head gaskets. Roof sealant out in the open, just globbed on will fail over time, but under a mounting foot with pressure squeezing it down - will last the lifetime of your roof.
    Last edited by solarix; 10-06-2021, 04:59 PM.
    BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed

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    • #3
      I agree with Solarix, although he's a pro with many installs under his belt and I've only done two. The thing that surprised me the most when doing the load calculations was how much more the predicted wind uplift forces were than the downward loads due to the weight of the panels. I'd sleep a lot better at night during windstorms knowing that the mounts were lagged into the rafters.

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      • #4
        If the roof was installed with an underlying layer of high temp ice and water shield which is current practice in my area (due to the difficulty of chasing down leaks) I would not be really worried as the ice and water shield acts as the actual waterproof membrane, the steel roof is really just acting as UV shield for the ice and water shield. Fasteners that are drilled through Ice and water shield self heal almost instantly.

        In my experience no matter what the brand sealant just does not last. Its tough application and a steel roof is going to expand and contract from night to day. Go with a high end sealan, like a Sika product and touch it up every 10 years and it will last a long time. A flashing boot with pour in sealant seems to be far more reliable.

        Look at most commercial roof guarantees and there is usually a required inspection by the installer every 5 or 10 years to keep the guarantee in force. Most owners ignore it. It they do the inspection the installer usually has a caulking gun in hand and touches up penetrations and flashing.

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        • #5
          Originally posted by sdold View Post
          I agree with Solarix, although he's a pro with many installs under his belt and I've only done two. The thing that surprised me the most when doing the load calculations was how much more the predicted wind uplift forces were than the downward loads due to the weight of the panels. I'd sleep a lot better at night during windstorms knowing that the mounts were lagged into the rafters.

          For relatively lightweight loads with high wind profiles such as is usually the case with solar arrays, uplift (or downward for that matter) usually exceed the dead or weight loading.

          What's often overlooked in such calcs is the potential pullout load that the screws or lags exert on the rafters, which is different than the rafter loading alone.

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          • #6
            Standing seam clamps rely on the roofing nails or screws to now hold down the array as well as the steel roofing. If you go by the ASME wind loading calcs, the uplift forces can be huge. Our building dept requires us to prove that extra fasteners were used under the array portion of the roof. And if you read the fine print on S5! standing seam clamps, they want you to put a clamp on every seam. Gets real expensive.
            BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed

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            • #7
              Originally posted by solarix View Post
              Standing seam clamps rely on the roofing nails or screws to now hold down the array as well as the steel roofing. If you go by the ASME wind loading calcs, the uplift forces can be huge. Our building dept requires us to prove that extra fasteners were used under the array portion of the roof. And if you read the fine print on S5! standing seam clamps, they want you to put a clamp on every seam. Gets real expensive.
              At the risk of sounding too pricky, I'd assume you mean the ASCE (American Society of Civil Engineers) not the ASME (American Society of Mechanical Engineers). The ASCE is responsible for standards to calculate loadings on structures including wind loads.

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              • #8
                I stand corrected. (and my dad was in the ASCE)
                BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed

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                • #9
                  Originally posted by solarix View Post
                  I stand corrected. (and my dad was in the ASCE)
                  I'm a retired member of the ASME but needed to be quite familiar w/ASCE standards for structural design work.

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