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Installers: Attaching standoffs on flat spray foam roof?

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  • Installers: Attaching standoffs on flat spray foam roof?

    I'm thinking Solarix has had to do this more than once, and hopefully some other installers can chime in too.

    My house is Santa Fe/Frontier style with parapet walls and a spray foam roof. I've all but given up on ballasted racks for my install, and am focusing on penetrating mounts. I'm thinking about Ironridge XR100 at about 25 degrees of tilt.

    My question is:

    When installing the Ironridge standoffs, do you cut a plug through the foam down to the deck plate and attach with 4 lag bolts to the deck plate only? Or do you have to hit a joist?

    I see that there are plenty of standoffs with a single lag, but to my knowledge there's no stud finder in the world that's going to allow you to pinpoint a joist through the multiple inches of foam and decking plywood without a bunch of exploration holes.

    A follow-up question:

    Do you simply re-foam around the standoff like you would any other roof penetration on a flat roof, or do you use some other piece with the standoff in addition to foaming?

    Thanks in advance for your help!

  • #2
    What product are you talking about from Ironridge? The flashfoot 2?
    http://www.ironridge.com/pitched-roof-mounting/features

    finding the joist is easy if you can get into the attic, drill up through one.
    OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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    • #3
      Originally posted by ButchDeal View Post
      What product are you talking about from Ironridge? The flashfoot 2?
      http://www.ironridge.com/pitched-roof-mounting/features

      finding the joist is easy if you can get into the attic, drill up through one.
      Unfortunately (as I indicated in my post, I hope) a house with a flat spray foam roof does not have an attic.

      I'm speaking of the IronRidge XR Rail 7" standoff:
      Iron Ridge Standoff.JPG

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      • #4
        Originally posted by Spektre View Post

        Unfortunately (as I indicated in my post, I hope) a house with a flat spray foam roof does not have an attic.

        I'm speaking of the IronRidge XR Rail 7" standoff:
        Iron Ridge Standoff.JPG
        you should have two holes lines up with the joist and lag bolts.

        you still may be able to find the joist easier from the inside with a traditional stud finder, drill up through one and measure for the rest from it.
        minor ceiling repair of the hole on the inside.
        OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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        • #5
          Originally posted by ButchDeal View Post
          ............you still may be able to find the joist easier from the inside with a traditional stud finder, drill up through one and measure for the rest from it.
          minor ceiling repair of the hole on the inside.
          I'd play it safe, while the ladder is up inside, mark ALL the joists, near both ridge and eves. I've seen lousy spacing, and warped/twisted lumber. drill the ones that are non-standard.
          Then chalkline the shingles on the top. Otherwise, you rely on the installers $8 helper to notice the lack of torque on the electric driver putting the bolt into the foam next to the rafter.

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          • #6
            Originally posted by Mike90250 View Post
            I'd play it safe, while the ladder is up inside, mark ALL the joists, near both ridge and eves. I've seen lousy spacing, and warped/twisted lumber. drill the ones that are non-standard.
            Then chalkline the shingles on the top. Otherwise, you rely on the installers $8 helper to notice the lack of torque on the electric driver putting the bolt into the foam next to the rafter.
            FWIW, I'd add that for long spans or irregularities of construction, some joists/rafters may be overlapped. That will change the joist location by one joist width to one side of the joist or the other from where you think it may be located as you move along the member. I've got one roofing member like that.

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            • #7
              My thanks to those of you who've taken the time to answer, but I fear that either I was unclear, or reading comprehension is a lost art.

              To clarify:
              • My roof is flat
              • It has no shingles, ridges or eaves
              It looks like this:
              roof view.JPG

              and to further clarify, this is the interior ceiling:
              interior ceiling.jpg

              That's all wood, so drilling holes is kind of a non-starter.

              Is there anyone oh here who's actually installed these type of standoffs on this type of roof?

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              • #8
                Originally posted by J.P.M. View Post

                FWIW, I'd add that for long spans or irregularities of construction, some joists/rafters may be overlapped. That will change the joist location by one joist width to one side of the joist or the other from where you think it may be located as you move along the member. I've got one roofing member like that.
                I've seen that in a floor before too - the builder must've decided to add a bay window, so they cut the rim joist and scabbed on a bunch of extensions without any sort of lateral support or blocking where they removed the rim joist.

                When I pulled the subfloor up it was pretty horrifying to see how much the entire system had twisted and heaved, not to mention the wildlife that had decided to invade the space thanks to the opening where the rim joist had been.

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                • #9
                  Most installations that I have seen on flat roofs require a framework that just sits on it and is weighted down with a ballast of some kind.

                  The installation still needs to meet all building codes for the area, like the wind load (uplift calculations) as well as the dead weight limit for the roof.

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                  • #10
                    Discretely placed and minimal drilling just to locate the first joist should work and be undetectable. If you go to the far side of the first rafter at either end you should be able to create unnoticeable and easily filled holes. There are small diameter bell hanger bits or super long specialty bits will allow you to drill right alongside and perfectly in line with the side of your Joist. Once you have a positive location then careful measuring will get you to the center of the remaining joist. Carpenters creed; Measure twice, cut once. In this case, measure as many times as it takes you to be positive of where you are. I would take a dowel and run it through the hole leaving it protruding above the roof. this will give you a positive point to pull your measurements from. I would snap out the entire joist/rafter layout , (both sides of the joist) with a chalkline on the roof to verify all rafter locations. then measure and check again and again until you are positive you are right.
                    Last edited by littleharbor; 02-09-2017, 03:44 PM.
                    2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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                    • #11
                      Originally posted by Spektre View Post
                      My thanks to those of you who've taken the time to answer, but I fear that either I was unclear, or reading comprehension is a lost art.

                      To clarify:
                      • My roof is flat
                      • It has no shingles, ridges or eaves
                      It looks like this:
                      roof view.JPG

                      and to further clarify, this is the interior ceiling:
                      interior ceiling.jpg

                      That's all wood, so drilling holes is kind of a non-starter.

                      Is there anyone oh here who's actually installed these type of standoffs on this type of roof?
                      I have not. But I did successfully chase a leak and roof side locate interior exposed support beams under a flat roof in a sant

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                      • #12
                        My response got eaten.

                        See what Littleharbor wrote, or measure from the inside,add a wall thickness and measure off the sum from the outside wall surface. I used that method to successfully locate exposed interior roof beams relative to outside when chasing a roof leak on a home very similar to what you are showing. Lots of ways to get creative.

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                        • #13
                          Looks like 6x, but possibly 8x rafters, This should be a piece of cake given their width.
                          2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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                          • #14
                            Originally posted by SunEagle View Post
                            Most installations that I have seen on flat roofs require a framework that just sits on it and is weighted down with a ballast of some kind.

                            The installation still needs to meet all building codes for the area, like the wind load (uplift calculations) as well as the dead weight limit for the roof.
                            Putting enough ballast on a flat roof to hold what can act as a very effective sail is often a fool's errand. The longer and unsupported flat spans are usually not designed for such dead, concentrated loads (ballast weight) and also wind induced variable/vibratory loads. Nor are after design ballasted systems usually frimly enough fixed to avoid movement/creep without some fixation to the structure they sit on. Such fixation often requires roof penetration. With roof penetrations often/usually among, or the sole reason for ballasting in the first place, that seems counterproductive.

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                            • #15
                              Originally posted by J.P.M. View Post

                              Putting enough ballast on a flat roof to hold what can act as a very effective sail is often a fool's errand. The longer and unsupported flat spans are usually not designed for such dead, concentrated loads (ballast weight) and also wind induced variable/vibratory loads. Nor are after design ballasted systems usually frimly enough fixed to avoid movement/creep without some fixation to the structure they sit on. Such fixation often requires roof penetration. With roof penetrations often/usually among, or the sole reason for ballasting in the first place, that seems counterproductive.
                              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.

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