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Taping down flex panels to a TPO Roof

Jchance

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Dec 14, 2020
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Has anyone taped down flexible panels to a TPO roof? I’ve watched a few videos of a method of adding a corrugated plastic sheet to an RV roof as a barrier to prevent some heat transfer, then mounting the panels to the sheet with carriage bolts, so the panels are easily removeabel. However, I’m finding mixed reviews whether or not to use this method on a TPO roof? I don’t want to drill into my roof. The trusses are not where I want the panels to be, and I already purchased the flexible SunPower panels.

John
 
I would be OK with taping down flex panels to a rubber roof. The caveat is that you have to ensure that there is no way the panels can produce any lift while driving. Anything that can cause a rubber roof to lift (delaminate) from the subsurface is bad.

I think your referring to the RV With Tito video. I watched Brian's videos and have no problem with his approach. Putting a heat generating panel directly on a rubber roof is not something I would do. The Coroplast is a good way to implement a thermal barrier, although I'm not sure it can be called a thermal barrier. Keep in mind that Coroplast comes in a variety of sized.
 
Thanks HRTKD,

Home Depot stocks the 1/8” board, would you suggest I try and see if I can get it in 1/4”? Or is 1/8” good enough?

john
 
Actually HD has 24”x36” sheets in 5/32” thickness. I might just go with this?
 
Actually HD has 24”x36” sheets in 5/32” thickness. I might just go with this?

You can order thicker sheets from HD. However, the last time I did that, there was a five sheet minimum.

I don't know if the thicker Coroplast is necessary. Thicker equals more ventilation. Since I already have the thicker Coroplast, I would use that if I were installing flex panels.
 
Any sign shops in your area? They use a lot of it, also can try art shops....
You could try a strip of Eternabond across the front as well for a "fairing"
 
When mounting flex panels on the roof of any vehicle, I would (and always do) use 3M VHB tape. In strips around the perimeter, and with intentional gaps of about 1" between 6" long strips. The gaps can let a bit of driven rain IN, but they also let water and water vapor OUT. Some of my installs are > 5 years old.
 
I originally used 1/4” Lexan Thermoclear but it was too ridged, and in one day of rain and strong florida sun, with no solar panels attached, it started cupping and pulling away from the double side eternabond tape I used. My thinking was to leave the corrugated edges open, to act as a heat sink, epic fail! So I think the coroplast is a bit more flexible. I’m just concerned about pulling the TPO up, but I guess if I put a fairing on the front edge it will prevent lift.

Perhaps I can try same method with coroplast & VHB tape, leaving the edges open for ventilation?

back to the drawing board & bank account!
 
When mounting flex panels on the roof of any vehicle, I would (and always do) use 3M VHB tape. In strips around the perimeter, and with intentional gaps of about 1" between 6" long strips. The gaps can let a bit of driven rain IN, but they also let water and water vapor OUT. Some of my installs are > 5 years old.
Thanks Rickst29, do you also use coroplast as a minting/heat reducing surface?
 
I haven't tried VHB with Coroplast. Gorilla Glue Tape works OK. I have this combination on the bottom of my RV trailer to encapsulate the DIY insulation around my fresh water tank. The tape is there just to seal the edges, not to hold the Coroplast on. Coroplast is notorious for not working well with a lot of adhesives. So be sure to secure the solar panel to the roof, not the Coroplast to the roof and the solar panel to the Coroplast.

FreshWaterTankCoroplastFront.jpg

Note: While the Gorilla Glue Tape work "OK" on the bottom of the trailer, I would not use it on the roof for such a critical use case as holding down solar panels. I provided the Gorilla Glue Tape example to show that such a sticky, heavy duty tape only works "OK" with Coroplast. It's not permanent, I'll be replacing the tape every few years. Maybe I'll find a better solution that doesn't require periodic replacement.
 
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Thanks for asking (above). I strongly recommend AGAINST using Coroplast as an intermediate layer. It would create two bonding surfaces, each of which must drain away any water (or water vapor) which gets underneath, and VHB tape by itself provides all the stretch-handling which you need. Although my current installs are all with semi-fexible "shingled" panels, I have also had great results with using VHB tape on the underside of Z-bars. (Avoiding screw piercings in the RV roofs.) I have always used an extra z-bar or two, along each long side of "solid" aluminum-framed panels which I have mounted in the past.

The BIG advantage with VHB tape is the flexing foam layer in the middle. The steel, aluminum, or rubber roof substrate will not expand and contract at the same rate as the panels above, even when they are at the same temperatures (and the panels generally get much hotter than the RV/Trailer roof.) The two adhesive surfaces must remain remain firmly attached, while the foam layer handles the push-and-pull of panel above and mouting surface below.

Either go with 'solid panels' on Z-bars, providing air underneath, or let the roof take the heat from the panels. With aluminum or steel RV roofs, panel heat goes through the and gets spread pretty quickly from underneath, radiating back off from uncovered sections of the RV roof. With fiberglass or carbon fiber, the panels get hotter - but the tape handles it just fine. In all of my installs, no one has EVER reported failure or peeling of VHB tape back to me.

In two instances of removing failed panels from painted aluminum and painted steel respectively (after 2 and 5 years), I've had a very challenging time weakening and peeling VHB away the substrate bond. Depending on the fexibility of the RV roof, structure, I prefer the thickness which used to be called "RP-25" on the stiffest of Roofs (Class-B Conversion van steel), and "RP-32" on super-flexible Carbon Fiber or intermediate-flexing fiberglass and aluminum. But again - the most important concept is to attach only around the perimeter, with just a couple of smaller 5"x 1" segments across the middle of the panel (well separated from each other). Around the panel, I always use 5-6" strips separated by 1" gaps. Water can get forced in, but it is also free to exit underneath - and to simply dry off as water vapor, when panels again bocome warm under sunlight.

I have used VHB tape with Z-bars in mounting a few "solid panels" as well, although I have always added some extra Z-bars along the long sides of those panels. As with the flex panels, the roof-to-z-bar bottom tape has NEVER loosened or given way. But I have taken care, in those two installations, to strip the pain completely of from the metal substrate, sanding for extra adhesion strength (P400 wet, equivalent to about 300 grit in ANSI and painting exposed metal afterwards. When finally removing those two panels and replacing them semi-fexible "shingled" panels, the VHB underneath each Z-bar took almost 15 minutes to fully remove.

These installations have all travelled at greater-than 70 MPH speeds for many hours at a time, plus prevailing winds. No panel mount has ever given the slightest hint of sliding or peeling loose.
 
Thanks for asking (above). I strongly recommend AGAINST using Coroplast as an intermediate layer. It would create two bonding surfaces, each of which must drain away any water (or water vapor) which gets underneath, and VHB tape by itself provides all the stretch-handling which you need. Although my current installs are all with semi-fexible "shingled" panels, I have also had great results with using VHB tape on the underside of Z-bars. (Avoiding screw piercings in the RV roofs.) I have always used an extra z-bar or two, along each long side of "solid" aluminum-framed panels which I have mounted in the past.

The BIG advantage with VHB tape is the flexing foam layer in the middle. The steel, aluminum, or rubber roof substrate will not expand and contract at the same rate as the panels above, even when they are at the same temperatures (and the panels generally get much hotter than the RV/Trailer roof.) The two adhesive surfaces must remain remain firmly attached, while the foam layer handles the push-and-pull of panel above and mouting surface below.

Either go with 'solid panels' on Z-bars, providing air underneath, or let the roof take the heat from the panels. With aluminum or steel RV roofs, panel heat goes through the and gets spread pretty quickly from underneath, radiating back off from uncovered sections of the RV roof. With fiberglass or carbon fiber, the panels get hotter - but the tape handles it just fine. In all of my installs, no one has EVER reported failure or peeling of VHB tape back to me.

In two instances of removing failed panels from painted aluminum and painted steel respectively (after 2 and 5 years), I've had a very challenging time weakening and peeling VHB away the substrate bond. Depending on the fexibility of the RV roof, structure, I prefer the thickness which used to be called "RP-25" on the stiffest of Roofs (Class-B Conversion van steel), and "RP-32" on super-flexible Carbon Fiber or intermediate-flexing fiberglass and aluminum. But again - the most important concept is to attach only around the perimeter, with just a couple of smaller 5"x 1" segments across the middle of the panel (well separated from each other). Around the panel, I always use 5-6" strips separated by 1" gaps. Water can get forced in, but it is also free to exit underneath - and to simply dry off as water vapor, when panels again bocome warm under sunlight.

I have used VHB tape with Z-bars in mounting a few "solid panels" as well, although I have always added some extra Z-bars along the long sides of those panels. As with the flex panels, the roof-to-z-bar bottom tape has NEVER loosened or given way. But I have taken care, in those two installations, to strip the pain completely of from the metal substrate, sanding for extra adhesion strength (P400 wet, equivalent to about 300 grit in ANSI and painting exposed metal afterwards. When finally removing those two panels and replacing them semi-fexible "shingled" panels, the VHB underneath each Z-bar took almost 15 minutes to fully remove.

These installations have all travelled at greater-than 70 MPH speeds for many hours at a time, plus prevailing winds. No panel mount has ever given the slightest hint of sliding or peeling loose.
Wow! Good info, thank you!
 
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