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Thickness of roof?

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  • Thickness of roof?

    Gearing up to purchase and install solar panels. Hoping to replicate this: https://www.youtube.com/watch?v=UY98...-wKFXY7UMATNOk

    Anyway - How thick is the roof? OR perhaps more importantly, how thick / what size are the ceiling rafters / studs?
    2020 Imagine 2400BH
    2014 Ford F150 FX4 4x4 Supercrew 3.5 Ecoboost and tow package (not max tow)

  • #2
    I'm planning the same thing. I bought the renogy tilts which are only rated for their panels up to 100W. I ordered 6 sets for my 4 200 watt renogy panels, and plan to use three rails per panel instead of just the two. Probably overkill, but they're pretty cheap tilts.

    openrangeowners (Mark) used the strut system with his setup (without tilts), and it looks good and sturdy on his rig.

    I had asked about roof thickness for my Reflection 150 260RD in another thread. I'm a bit worried about the screws getting a decent bite in the underlayer. I've looked at situations where people adhered rails with 3M VHB, but my roof appears to have an outer layer over the roof (rubber?). There are a couple of spots where there is a slightly raised crease/roll. I'd be worried that this layer may not be adhered well enough to the roof.
    John & Karen, RV Newbies
    2020 Relection 150, 260RD
    GMC Sierra Denali 2500

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    • #3
      Originally posted by bellis View Post
      Gearing up to purchase and install solar panels. Hoping to replicate this: https://www.youtube.com/watch?v=UY98...-wKFXY7UMATNOk

      Anyway - How thick is the roof? OR perhaps more importantly, how thick / what size are the ceiling rafters / studs?
      I just pulled the drawing on the 2400BH. The roof deck is 3/8. I don't know the exact thickness of the ceiling rafters, but they are spaced at 16" on center, starting 9-1/8" from the back. So there is a rafter at 0", 9-1/8", 25-1/8", 41-1/8", 57-1/8", and every 16" beyond that going forward. Based on my memory, the rafter's are 1-1/2" wide, but I'm not 100% positive of that.

      Jim
      The moderators for this site are not GDRV employees, but we do own GDRV products.

      Jim and Ginnie
      2017 Reflection 297RSTS

      Comment


      • #4
        Originally posted by TucsonJim View Post

        I just pulled the drawing on the 2400BH. The roof deck is 3/8. I don't know the exact thickness of the ceiling rafters, but they are spaced at 16" on center, starting 9-1/8" from the back. So there is a rafter at 0", 9-1/8", 25-1/8", 41-1/8", 57-1/8", and every 16" beyond that going forward. Based on my memory, the rafter's are 1-1/2" wide, but I'm not 100% positive of that.

        Jim
        Any idea how deep they are below the surface? Are they directly below the roof deck, or are they below a layer of insulation? I'm guessing they would be difficult to locate with a studfinder, given the 3/8 plywood layer.
        John & Karen, RV Newbies
        2020 Relection 150, 260RD
        GMC Sierra Denali 2500

        Comment


        • #5
          Originally posted by JohnD View Post

          Any idea how deep they are below the surface? Are they directly below the roof deck, or are they below a layer of insulation? I'm guessing they would be difficult to locate with a studfinder, given the 3/8 plywood layer.
          The plywood is directly attached to them. So the roof deck is in direct contact with the rafters. As for locating them. When you carefully examine your roof, you should see a ripple running across the roofing material every 48". This indicates the edges of the plywood. This will give you a very good idea of where every third rafter is. Just measure 16" from those seams and you'll locate the next one.

          BTW, I've seen hundreds of solar installs over the last few years, and well over 95% of the mounts are just screwed to the plywood decking, and not the rafters.

          Jim
          The moderators for this site are not GDRV employees, but we do own GDRV products.

          Jim and Ginnie
          2017 Reflection 297RSTS

          Comment


          • #6
            Originally posted by TucsonJim View Post

            The plywood is directly attached to them. So the roof deck is in direct contact with the rafters. As for locating them. When you carefully examine your roof, you should see a ripple running across the roofing material every 48". This indicates the edges of the plywood. This will give you a very good idea of where every third rafter is. Just measure 16" from those seams and you'll locate the next one.

            BTW, I've seen hundreds of solar installs over the last few years, and well over 95% of the mounts are just screwed to the plywood decking, and not the rafters.

            Jim
            Thanks Jim, you have been extremely helpful.
            John & Karen, RV Newbies
            2020 Relection 150, 260RD
            GMC Sierra Denali 2500

            Comment


            • #7
              That is extremely helpful. I would still prefer to hit the rafter (like the adage - it's always better to hit a stud). What screw size would you use? OR do you have a particular recommendation for what to use?
              2020 Imagine 2400BH
              2014 Ford F150 FX4 4x4 Supercrew 3.5 Ecoboost and tow package (not max tow)

              Comment


              • #8
                Originally posted by bellis View Post
                That is extremely helpful. I would still prefer to hit the rafter (like the adage - it's always better to hit a stud). What screw size would you use? OR do you have a particular recommendation for what to use?
                Be careful--there is wiring and air conditioning conduit under the plywood in various locations. If you miss a rafter (while driving a long screw) there could be unintended (bad) consequences.

                FYI, I also installed my solar to the plywood in the roof--no issues to date over many thousands of miles. I regularly inspect the roof and solar panels. Everything is still solid.
                Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.

                Howard, 2017 Ford F-350 DRW, '19 315RLTSPlus

                Comment


                • #9
                  The upper part of the rafters (that the plywood attaches to) are arched pieces of "1 x 2". Actually about 1 1/2" wide x 3/4" thick. I wouldn't be too concerned about finding these rather that fastening just to the plywood as others have done. Per Howard's caution . . . use screws that extend only a little past the plywood to avoid hitting wires and ductwork inside the roof space. The screws should go in far enough that you get past the tapered end of the screw and have the straight shank fully engaged in the plywood. Drill a small pilot hole first and use a coarse thread screw. Stainless steel sheet metal screws would be a good choice.

                  Rob
                  Cate & Rob
                  (with Border Collies Molly & Angel and their kitty Gracie)
                  2015 Reflection 303RLS
                  2014 Ecoboost F150 with Heavy Duty Payload Package
                  Bayham, Ontario, Canada

                  Comment


                  • #10
                    This has been interesting. I am installing tilt brackets on strut channels as shown in the youtube link in the OP. I installed two 10' strut channels, using Howard's advice about finding plywood seams (which are very obvious on my roof) and measuring 16" centers from there. Each rail has 8 anchors, and I drilled pilot holes for each. Only 1 of the 8 holes in the first rail (4" from the outside edge of the roof) felt like it went into a legitimate stud. All others went through roughly 3/8 hard material, followed by 1/2" empty space (styrofoam?), and then more wood (not sure how deep, because I was only drilling about 1 1/4"). In the second rail (2 feet in from the other rail), I encountered the same thing, with the exception that where I anticipated the legitimate stud as experienced on the other rail, the bit deflected off what felt like metal just below 3/8 inches. I decided not to use that hole for fear of penetrating something unfortunate. I moved two inches over, and got 3/8 inches of hard material and pulled out pink insulation. So, the interesting thing is that there do seem to be some locations that have wood support directly below the plywood, most (at 16" centers) that have a gap before hitting more hard support, and the one spot I chose that was not a 16" center, no support below the plywood. While going through this process, I talked to Mark ( openrangeowners ), and he said he encountered roughly the same in his solitude.

                    I am actually confident that the rails are secure the way they are mounted, but the roof structure does not seem to be as has been described above.

                    Unfortunately, I am now trying to install two pairs of 5' strut channels for my other two panels (Winegard and vent interrupting the contiguous run). The inside rail on one, and the outside rail on the other both have high points or bulges in the roof such that I cannot get the channels to mount flat. One of them is such that the center bulge causes one end to be 1" off the roof if the other is touching, or both ends 1/2" up if I even it out. I'm trying to decide if I should 1) just bolt it down with a bend, or 2) place a few layers of 3M VHB below the two ends and just screw it down with a bit of a bend, or 3) cut some hard spacers to place under the ends. FYI, If I place these rails on the other side of the RV (same symetrical location), they lie flat. One of them is actually directly opposite the 10' rails I have already successfully installed without this issue.

                    I guess the moral of the story is that nothing is ever easy.


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                    John & Karen, RV Newbies
                    2020 Relection 150, 260RD
                    GMC Sierra Denali 2500

                    Comment


                    • #11
                      JohnD

                      Your description of fastening the rail along the edge of the roof makes sense because the upper arch of the roof truss does not go all the way to the edge of the roof. Rather than tapering the 1x2, it ends about 4" from the edge of the roof. The screws that you installed, likely missed the end of the upper part of the truss but went into the lower part which is the same width but thicker. On the inner rail, you likely hit one of the screws that hold the truss upper beam to the vertical supports.

                      Rob
                      Cate & Rob
                      (with Border Collies Molly & Angel and their kitty Gracie)
                      2015 Reflection 303RLS
                      2014 Ecoboost F150 with Heavy Duty Payload Package
                      Bayham, Ontario, Canada

                      Comment


                      • #12
                        What was your screw length that you used?

                        I think I am going to do as advised and just try to get barely through the plywood. 3/8" plywood + unknown roofing material thickness + 1/16" to barely clear the plywood = ???
                        2020 Imagine 2400BH
                        2014 Ford F150 FX4 4x4 Supercrew 3.5 Ecoboost and tow package (not max tow)

                        Comment


                        • #13
                          Unless you are sure you are screwing into a rafter/truss, there is no reason to go longer than 3/4" which will account for the bracket thickness as well as the roof membrane and 3/8" roofing plywood with about a 1/16" to spare. I have had good luck with Z brackets and have never had one come loose yet.
                          Jeff and Debbie
                          2021 Imagine 2250RK
                          2015 Ram 2500 6.7 CTD Crew Cab Short Bed Factory Air-Ride Auto Level
                          USMC Veteran

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                          • #14
                            Originally posted by Heavysledz View Post
                            Unless you are sure you are screwing into a rafter/truss, there is no reason to go longer than 3/4" which will account for the bracket thickness as well as the roof membrane and 3/8" roofing plywood with about a 1/16" to spare. I have had good luck with Z brackets and have never had one come loose yet.
                            That means 3/4" screw or 0.75" would be consumed by 3/8" roof plywood or 0.375", 1/16 through plywood or .0625, and maybe 1/8" or 0.125 for the bracket - that leaves 0.1875 for roof thickness. That's only 3/16". Surely the roof is thicket than that? Or is my math off?

                            Again, Most helpful - thank you.
                            2020 Imagine 2400BH
                            2014 Ford F150 FX4 4x4 Supercrew 3.5 Ecoboost and tow package (not max tow)

                            Comment

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