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rack footing options for elastomeric coated built up roof in Tucson

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  • rack footing options for elastomeric coated built up roof in Tucson


    I'm hoping that some other Arizona folks can help me better understand my feet/mount options suitable for my roof.

    My roof, very typical in the region from what I can tell, is a built up tar & paper roof with a 1:12 slope. The top surface is a mopped-on, white elastomeric coating which requires re-coting every 5-12 years.

    Is there a "typical" method for footings on this type of roof? I intend to use Iron Ridge racking, and they have a flat roof mount (imagine a flanged dome of aluminum) which is one option. Mechanically it is straightforward: two lags carefully centered into the underlying rafter. But the sealing/flashing is less obvious. Iron RIdge makes several membrane options which install over the top of the mount, but these are specific to certain single-membrain roof types (PVC, TPO, EDPM, etc) and don't include any versions suited to the tar + elastomeric roof of mine.

    The flashing products I see online are very large aluminum squares (like 18" x 18") with cones in their center. The cone makes sense to me, but I don't see the need for such a large base for my type of roof.

    I've considered using the Iron RIdge flat roof mounts and then seal them with layered build up of elastomeric repair sealant and polyester "tex" cloth, but I'd like to get some confirmation that this is acceptable. Also, these mounts seem expensive at $28-ish each + $12 for mebrane seal.

    Surely there are commonly used solutions for this application. Can anyone enlighten me?
    Last edited by TucsonMCM; 07-31-2020, 02:37 PM.

  • #2
    Sorry, I don't know. Have you phoned IronRidge? When I had a question, they were very helpful and knowledgable.

    Whenever possible, we want to use parts and materials that have been tested and approved for our exact situation.

    Side point: I did an installation last weekend on a low-cost metal-roofed barn. I think it was simply galvanized sheeting with folds for strength. we used a small flat footing that bolted to the sheathing under the metal sheet and sealed to the metal sheet with a rubber layer under the footing. I can't recall the part number, but if you need it I can find out. I don't see it in the IronRidge catalog and don't know if it is right for your roof.
    7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV


    • #3
      I have talked to IronRidge. I agree that they are helpul, or at least are happy to try and help. Unfortuntely, they had no clue what sort of roof I was describing, nor were they particularly familiar with their various membranes/covers for sealing their flat roof mount to single-membrane roofs. I'm surprised they don't have a flashing product for "generic" built-up tar/elastomeric roofs . . . it seems like a very common roof type.


      • #4
        Originally posted by TucsonMCM View Post
        I have talked to IronRidge. ......... I'm surprised they don't have a flashing product for "generic" built-up tar/elastomeric roofs . . . it seems like a very common roof type.
        I think that may be a geographic observation, In my neighborhood in Northern California most of the roofs are composition shingle. I have a rental home in Southern California that had a TPO roof and the flashing was provided by the roofer from the same material as the membrane. They cost me $50 each for the roofer to install. In your case, elastomeric is a coating and my guess is a stand off could be sealed and coated with the elastomeric coating as they were being installed. The product you described sounds similar to the boot used on my TPO membrane. The size probably related to the surface area for adhesion. All of this is going to be below the panels so long term the cost of removing the panels to recoat may be more expensive that the boot which may have a longer life.

        @nwdiver is from the flat roof part of the Southwest, maybe he has some insight.
        Last edited by Ampster; 08-01-2020, 02:09 PM.
        9 kW solar. Driving EVs since 2012


        • #5
          IronRidge does have hardware for flat roofs, they just don't have flashings for elastomeric roof coatings. Oddly it is under the section for tilt mount, but scroll down. There is another section for ballast mount for flat roofs.

          I know that elastomeric coatings recommend recoating every few years but I wonder if that might be extended for the section under solar panels since that section does not see the direct rays of the sun. That is pure speculation on my part.
          9 kW solar. Driving EVs since 2012


          • #6
            @Ampster, the Ironridge mount you mention is exactly what I mentioned in my original post. Its p/n FRA-BASE-01-M1 if anyone wants to see what they look like. As far as the re-coating goes, roofers (or myself, in my DIY case) can mop the coating around the panels without removing them. The higher your panels, the easier it is. In my case, the south legs will be ~7" and the north legs at least 15", so getting a roller underneath in 5-8 years won't be particularly difficult.

            My question specifically regards the best practice for sealing a mount like the FRA-BASE-01-M1 on an elastomeric coated built-up flat roof. Ideally from someone who has done it, or had it done.


            • #7
              I've owned flat roof homes in Mesa and Gilbert for over 30 years. Both had roll roofing as a base and then white elastomeric sealers were applied several times over the years as required. If there has ever been a need to seal a penetration of a pipe, conduit, roof junction, drain, scupper or a seam, I have always embed roofing fabric into the coating in those areas. I have never had this extra level of protection fail me but many times I've had seams pop open if only a layer of sealer was applied in the past. Applying the fabric as you seal the penetrations is a requirement in my book. The best fabric I have found is a polyester woven cloth that accepts the sealer quite well and lays down nicely. Some of the fiberglass cloth products are hard to work with. I would put overlapping pieces of cloth around the mounts and seal it all down before any panels go up. Future re-seals would go right over the same.

              Check out Henry #195 polyester fabric at Home Depot. It contours pretty well over uneven areas.

              My current home is a blend of standard cement tile and flat roof. My panels are mounted on the angled tile portion so I have no PV standoffs on the flat roof that I can show you.
              Dave W. Gilbert AZ
              6.63kW grid-tie owner


              • #8
                Thanks @azdave, that's helpful. I've used the polyester fabric for some small repairs on my roof, and it seems to work pretty well. That was my default presumption for sealing mounts on my roof, but its good to hear some positive feedback on that approach from someone familiar with it.


                • #9
                  Originally posted by TucsonMCM View Post
                  @Ampster, the Ironridge mount you mention is exactly what I mentioned in my original post. ......
                  Sorry, I skipped right over that paragraph.
                  I see AZ Dave gave you some advice that reminded me of a couple skylights I installed on a flat torch down tar roof. I also used that fabric and sealed it with elastomeric. Both products were by Henry's. I had a 1 in 12 pitch roof and slipped the uphill side of the skylight flashing under a layer of the tarpaper and then used several layers of that fabric to cover the nails and seal the flashing all around.
                  I will try to ping @nwdiver again and see if he has any ideas.

                  Last edited by Ampster; 08-04-2020, 07:49 AM.
                  9 kW solar. Driving EVs since 2012


                  • #10
                    I got some coating from Revetement Agro back in the day. Probably a little too far away from you, though.


                    • #11
                      Our go to method for sealing flat roof mounts is Chemcurbs. You can make your own with some sort of curb ring filled with elastomeric coating.
                      BSEE, R11, NABCEP, Chevy BoltEV, >2500kW installed