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Installers: Attaching standoffs on flat spray foam roof?

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  • #16
    Originally posted by SunEagle View Post

    I agree that the ballasted systems are not very safe in high wind areas and can overload a roof if there is a lot of rain or snow.

    Better to attach the panel framework to the roof beams and find a way to seal up the holes.
    in some regions you have to have some attachment points for earthquake stabilization and need stamped plans to show that the structure is capable of holding the added weight.

    With the foam insulation, there could be compression as well.


    It would seem that littleharbor solution of measuring from the inside through the window to the outside wall and transferring that measurement to the roof should be fairly trivial.
    OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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    • #17
      Originally posted by ButchDeal View Post

      in some regions you have to have some attachment points for earthquake stabilization and need stamped plans to show that the structure is capable of holding the added weight.

      With the foam insulation, there could be compression as well.


      It would seem that littleharbor solution of measuring from the inside through the window to the outside wall and transferring that measurement to the roof should be fairly trivial.
      As you write, seismic stabilization points can be used, but the design and the load combinations on such attachment points will most likely need recalc'ing for the new situation of new (additional) loadings being added to those stabilization points.

      Also, it better be assumed the bolted connection doesn't compress any foam or non rigid material. If it does, that bolted connection needs to be calculated similar to the way a gasketed joint is calculated, which is not the same as a simple bolted connection. I'd not design or seal a design that relied on a compressed foam joint for this type of application. I strongly suspect the required stress needed in the bolt to develop the joint strength necessary for the design loading would crush the foam and loosen the joint (making the developed joint strength unstable or at least unreliable over time). That's why standoffs (moats. pusspockets, etc.) filled with tar are used.

      Any way it's done, putting stuff on an existing flat roof is a PITA. Back in the day when I designed equipment for a living, we tried to avoid it as much as possible.

      BTW, I think I had the first post that mentioned the inside measurement method , but no matter. I'm sure I'm not the first to use it, and if it works, who cares.
      Last edited by J.P.M.; 02-09-2017, 05:38 PM.

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      • #18
        Originally posted by J.P.M. View Post

        As you write, seismic stabilization points can be used, but the design and the load combinations on such attachment points will most likely need recalc'ing for the new situation of new (additional) loadings being added to those stabilization points.

        Also, it better be assumed the bolted connection doesn't compress any foam or non rigid material. If it does, that bolted connection needs to be calculated similar to the way a gasketed joint is calculated, which is not the same as a simple bolted connection. I'd not design or seal a design that relied on a compressed foam joint for this type of application. I strongly suspect the required stress needed in the bolt to develop the joint strength necessary for the design loading would crush the foam and loosen the joint (making the developed joint strength unstable or at least unreliable over time). That's why standoffs (moats. pusspockets, etc.) filled with tar are used.

        Any way it's done, putting stuff on an existing flat roof is a PITA. Back in the day when I designed equipment for a living, we tried to avoid it as much as possible.

        BTW, I think I had the first post that mentioned the inside measurement method , but no matter. I'm sure I'm not the first to use it, and if it works, who cares.
        I was saying that balasted would compress. With the standoffs, the foam should be removed, install the standoff and reapply sealand and insulation.

        didn't mean to take credit away from you on the measurement. It would be the first choice and in this home should be pretty simple.
        OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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        • #19
          Originally posted by ButchDeal View Post

          I was saying that balasted would compress. With the standoffs, the foam should be removed, install the standoff and reapply sealand and insulation.

          didn't mean to take credit away from you on the measurement. It would be the first choice and in this home should be pretty simple.
          Understood. Thank you.

          Depending on the per ft.^2 loading of the foam by the ballast, and the compressive modulus of the foam, the foam might mot compress all that much.

          Still, and IMO only, with all the hassle and extra work that comes with ballasted systems (if they're done correctly and safely) bolting still seems an all round better way.

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          • #20
            Got any space for a ground mount or a pole mount ?
            Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
            || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
            || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

            solar: http://tinyurl.com/LMR-Solar
            gen: http://tinyurl.com/LMR-Lister

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            • #21
              I have owned home with a flat foam roof for 25 years. When I installed solar hot water panels I had the same issue being discussed here about mounting. In my case, I purchased a sheet of three-quarter inch marine grade plywood. I cut the plywood into 12" x 12" squares. I stacked the squares to make a mounting base that was always taller than the surrounding foam that I would embed them in. Using the squares as a template I cut around them into the foam. I dug out the foam completely down to the roof deck so that I could drop in the 12" x 12" mounting bases. Everything was glued and screwed with construction adhesive and long wood screws through the mounting bases into the existing roof deck and joists.

              Using a polyester roofing membrane and a bucket of elastomeric roof sealant I completely sealed over the new mounting bases about 8 to 10 inches further than any cutting I had done into the foam. After that was dried, I then applied another layer of polyester membrane 45 degrees to the first layer. After one more coat of roof sealant I let everything cure. This left me with large, thick, solid bases that were slightly higher than the surrounding roof so that water would not puddle around the brackets I was getting ready to mount. When it came time to mount the brackets it was no longer so critical to hit a joist below due to the large thick plywood base. I always tried to hit a joist with an extra-long lag bolt if I could. Once everything was lagged down and final I used more elastomeric roof sealant on the brackets and legs.

              That install was over 20 years ago. The 4 x 8 panels stand nearly vertical and I've never had an issue even with our summer monsoon storms. With the brackets above the deck I still have access to the hardware and water does not puddle around them.
              Last edited by azdave; 02-10-2017, 10:15 AM.
              Dave W. Gilbert AZ
              6.63kW grid-tie owner

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              • #22
                Originally posted by azdave View Post
                I have owned home with a flat foam roof for 25 years. When I installed solar hot water panels I had the same issue being discussed here about mounting. In my case, I purchased a sheet of three-quarter inch marine grade plywood. I cut the plywood into 12" x 12" squares. I stacked the squares to make a mounting base that was always taller than the surrounding foam that I would embed them in. Using the squares as a template I cut around them into the foam. I dug out the foam completely down to the roof deck so that I could drop in the 12" x 12" mounting bases. Everything was glued and screwed with construction adhesive and long wood screws through the mounting bases into the existing roof deck and joists.

                Using a polyester roofing membrane and a bucket of elastomeric roof sealant I completely sealed over the new mounting bases about 8 to 10 inches further than any cutting I had done into the foam. After that was dried, I then applied another layer of polyester membrane 45 degrees to the first layer. After one more coat of roof sealant I let everything cure. This left me with large, thick, solid bases that were slightly higher than the surrounding roof so that water would not puddle around the brackets I was getting ready to mount. When it came time to mount the brackets it was no longer so critical to hit a joist below due to the large thick plywood base. I always tried to hit a joist with an extra-long lag bolt if I could. Once everything was lagged down and final I used more elastomeric roof sealant on the brackets and legs.

                That install was over 20 years ago. The 4 x 8 panels stand nearly vertical and I've never had an issue even with our summer monsoon storms. With the brackets above the deck I still have access to the hardware and water does not puddle around them.
                Your method, as you describe it seems mostly sound and practical. One concern I'd have is that it sounds like there's some lack of assurance that all, or maybe even most - no way to tell - how many the attachments hit roof joists or something else that's a bit more substantial than decking. Was the method reviewed/signed off ?

                As for the so far so good method of proofing a design, perhaps design conditions haven't been seen yet. I've done seismic and wind designs and always hope they're never tested to design conditions. Hasn't failed yet doesn't usually too well as a logical argument .

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                • #23
                  Originally posted by azdave View Post
                  I have owned home with a flat foam roof for 25 years. When I installed solar hot water panels I had the same issue being discussed here about mounting. In my case, I purchased a sheet of three-quarter inch marine grade plywood. I cut the plywood into 12" x 12" squares. I stacked the squares to make a mounting base that was always taller than the surrounding foam that I would embed them in. Using the squares as a template I cut around them into the foam. I dug out the foam completely down to the roof deck so that I could drop in the 12" x 12" mounting bases. Everything was glued and screwed with construction adhesive and long wood screws through the mounting bases into the existing roof deck and joists.

                  Using a polyester roofing membrane and a bucket of elastomeric roof sealant I completely sealed over the new mounting bases about 8 to 10 inches further than any cutting I had done into the foam. After that was dried, I then applied another layer of polyester membrane 45 degrees to the first layer. After one more coat of roof sealant I let everything cure. This left me with large, thick, solid bases that were slightly higher than the surrounding roof so that water would not puddle around the brackets I was getting ready to mount. When it came time to mount the brackets it was no longer so critical to hit a joist below due to the large thick plywood base. I always tried to hit a joist with an extra-long lag bolt if I could. Once everything was lagged down and final I used more elastomeric roof sealant on the brackets and legs.

                  That install was over 20 years ago. The 4 x 8 panels stand nearly vertical and I've never had an issue even with our summer monsoon storms. With the brackets above the deck I still have access to the hardware and water does not puddle around them.
                  Azdave, you're in Gilbert with a PV system too - how was that mounted?

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                  • #24
                    Yes, I've done several roofs like this.

                    I wager that there is an insulated space above your ceiling with sleeper framing on 24" centers and decking above. Compare your outside wall height to the inside wall height to find out for sure. For the foam - yes, you need to bore 4" dia holes in the foam and anchor the solar mounts to the joists with 2 screws. (We like the nifty 1/4" Spax brand screws that Chalet Depot sells as they are engineered to not need pilot holes and are much less likely to split your lumber than the usual BF crummy steel 5/16" lag bolt). Look for clues in the roof apparatus as to where the joists are. Skylights, roof vents etc are often framed in next to the joists. Once you find one, you can measure over to the rest. All you need to do is be accurate to within an inch as the solar mount will cover any misses that are close. Use 14ga bare copper wire to probe around through a hole that misses to find the framing.

                    Then purchase a system called "ChemCurb" by the Chemlink company to fill the foam hole and create a raised pad that will keeping standing water away from your damage. Or you can make them yourself with PVC pipe and elastomeric roof sealer. Or you can bring in a local foam roof installer to do a guaranteed job.
                    BSEE, R11, NABCEP, >1200kW installed

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                    • #25
                      Originally posted by J.P.M. View Post
                      As for the so far so good method of proofing a design, perhaps design conditions haven't been seen yet. I've done seismic and wind designs and always hope they're never tested to design conditions. Hasn't failed yet doesn't usually too well as a logical argument .
                      Sorry for the delayed reply. I just now noticed there were questions.

                      After 25 years with no issues and after having a portion of my adjacent shingled roof lifted, my garage door collapsed and a pine tree snapped in two in a micro-burst 11 years ago, think I can argue my homeowner panel mounting survived better than the engineered and inspected home structure. I know some people still won't like that answer. Since the pine tree shade is long gone I could mount the panels horizontally but why bother now?


                      Originally posted by Spektre View Post
                      Azdave, you're in Gilbert with a PV system too - how was that mounted?
                      I still own the home discussed here but I put PV on my new home just down the road in Gilbert. It is a tile roof and was installed by Harmon Solar with the full blessings of my HOA, the Town of Gilbert and SRP utility.
                      Dave W. Gilbert AZ
                      6.63kW grid-tie owner

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