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Old 12-07-2022, 06:06 PM   #1
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Thor roof, how sturdy, how thick?

We have a 2016 24SR on which I am preparing to do a solar install using a Renology 400 watt kit.
  • How long a screw can I use without poking through?
  • What backs up the fiberglass roof?
My question relates to attaching the solar panels to the roof. How thick is the fiberglass, and what's below it? Obviously, I don't want screws poking through into the passenger compartment, and I also don't want solar panels flying off as I cruise down the highway at 75 mph.

If the fiberglass is either strong enough itself, or backed with wood or other backing, I feel I should be able to screw the Renology brackets to it directly.

If the backing isn't strong enough, it looks like I'll have to use some sort of an adhesive mount instead of the supplied brackets. There are some corner mounts available which have more square inches and can be securely adhesed to the outside of the roof without any screw holes.

Either way, I'm going to create a safety cable with some thin stainless wire just in case a panel decides to come loose while I'm driving down the road.

Thanks,
JB

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Old 12-07-2022, 06:58 PM   #2
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Go to the Thor owners resource page and download the roof structural drawings for your rig. That will answer your questions
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Old 12-07-2022, 07:20 PM   #3
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Quote:
Originally Posted by unsichtbarre View Post
We have a 2016 24SR on which I am preparing to do a solar install using a Renology 400 watt kit.
  • How long a screw can I use without poking through?
  • What backs up the fiberglass roof?
My question relates to attaching the solar panels to the roof. How thick is the fiberglass, and what's below it? Obviously, I don't want screws poking through into the passenger compartment, and I also don't want solar panels flying off as I cruise down the highway at 75 mph.

If the fiberglass is either strong enough itself, or backed with wood or other backing, I feel I should be able to screw the Renology brackets to it directly.

If the backing isn't strong enough, it looks like I'll have to use some sort of an adhesive mount instead of the supplied brackets. There are some corner mounts available which have more square inches and can be securely adhesed to the outside of the roof without any screw holes.

Either way, I'm going to create a safety cable with some thin stainless wire just in case a panel decides to come loose while I'm driving down the road.

Thanks,
JB
I suggest getting in touch with Thor. They should be able to send you a schematic showing the whole coach framing layout. Just tell them you need to make some repairs. If you mention that you are making a modification, you will get the canned response, "Thor cannot advise on modifications". However, I believe every roof penetration is fully "framed" with aluminum tubing that runs across the width of the coach body. Thor will be able to tell you how big the framing members are. I would use a high-end stud finder to locate the framing. As long as you keep the screws shorter than the dimension of the framing you won't go through. If you screw into the framing, you should not need additional safety cables. Frankly if you chain the panel down like as you suggest, you will likely do a lot more damage to the roof than just having the panel just fly off. In either case the panel will likely be toast anyway so, IMHO do what you can to minimize the damage. Use Lock Tight Blue to keep the screws from working lose and be sure to seal the mounting brackets using the appropriate sealer, use the same stuff used around the skylights and other roof attachments.
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Old 12-07-2022, 07:22 PM   #4
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I thought that Thor roofs use a wooden truss covered with a sheet of very thin (< 1/4”) plywood with a rubber TPO covering.

David
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Old 12-07-2022, 07:44 PM   #5
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I will look again, I've spent quite a bit of time there and hadn't actually found structural drawings of the roof.
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Old 12-07-2022, 07:45 PM   #6
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Good idea: "I've experienced damage and I would like to repair it"
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Old 12-07-2022, 07:45 PM   #7
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My roof is definitely fiberglass. It appears to be pretty sturdy. I'll get a stud finder.
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Old 12-07-2022, 08:27 PM   #8
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Originally Posted by DavidEM View Post
I thought that Thor roofs use a wooden truss covered with a sheet of very thin (< 1/4”) plywood with a rubber TPO covering.

David
Yes, some older RV were indeed made that way. However, more modern RV, have an aluminum or steel frame for the coach body. An aluminum frame is probably lighter and stronger than a wooden frame. I believe I saw something somewhere that Thor uses an aluminum coach frame. Also, my 2018 ACE defiantly has a flat fiberglass roof.
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Old 12-07-2022, 08:52 PM   #9
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Quote:
Originally Posted by DavidEM View Post
I thought that Thor roofs use a wooden truss covered with a sheet of very thin (< 1/4”) plywood with a rubber TPO covering.

David
It's not even plywood.... its the same crappy paneling they use for the inside walls behind the wall paper.
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Old 12-08-2022, 12:23 AM   #10
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It wasn’t a Thor product, but when I installed solar panels on my roof I used an ordinary stud finder to locate the roof “trusses”. In my case they are stamped aluminum and I was able to use stainless steel screws into these structural elements. Super strong.
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Old 12-08-2022, 01:54 AM   #11
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I'll check for studs with a stud finder, but all of a sudden I'm reconsidering going the adhesive route and using some of those wider plastic bases you can get on Amazon.
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Old 12-08-2022, 09:24 AM   #12
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Mounting Solar Panels

Brian at RV with Tito has a great no-hole method for mounting panels to his roof:
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Old 12-08-2022, 10:46 AM   #13
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I opted for lighter weight flexible solar panels mounted to corrugated plastic panels and then attached to the roof with EternaBond Tape.
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Old 12-08-2022, 05:32 PM   #14
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Quote:
Originally Posted by DavidEM View Post
I thought that Thor roofs use a wooden truss covered with a sheet of very thin (< 1/4”) plywood with a rubber TPO covering.

David
TPO is not rubber. It's a plastic based material.
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Old 12-08-2022, 05:41 PM   #15
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I opted for lighter weight flexible solar panels mounted to corrugated plastic panels and then attached to the roof with EternaBond Tape.
Yeah, I thought long and hard about the flexible route, but for both economic and lifespan reasons I opted for the Renology panels.
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Old 12-08-2022, 05:43 PM   #16
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TPO is not rubber. It's a plastic based material.

Yes, it is. It is “Thermoplastic polyolefin, or TPO for short, is a type of single-ply roofing material that is heat-reflective and energy-efficient. In laymen’s terms, TPO roofing belongs to the broader category of “rubber roofing” materials. It contains a blend of rubbers and other elements (fillers) that add to its durability and flexibility.”

https://improveitmd.com/what-is-tpo-roofing/
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Old 12-08-2022, 05:58 PM   #17
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Yes, it is. It is “Thermoplastic polyolefin, or TPO for short, is a type of single-ply roofing material that is heat-reflective and energy-efficient. In laymen’s terms, TPO roofing belongs to the broader category of “rubber roofing” materials. It contains a blend of rubbers and other elements (fillers) that add to its durability and flexibility.”

https://improveitmd.com/what-is-tpo-roofing/
While the "source" material is a blend which includes a rubber material, TPO roofing should not be confused with traditional RV rubber roofs made with EPDM.

Normally RV roofs are classified as either TPO, rubber, or fiberglass. Calling TPO rubber just confuses the issue.
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Old 12-08-2022, 06:30 PM   #18
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It's not even plywood.... its the same crappy paneling they use for the inside walls behind the wall paper.
Wow! The industry standard had been 1/8" ply wood not 1/4" over the foam insulation. Then TPO, EDPM, or fiberglass. Then there is the Aluminum ones. I am shocked that that pressed paper fiber could hold any weight at all. Even pressed and glued wood chips are not strong enough to walk on with 1/8" thickness. Things have really gone cheep. I have plywood and know because of the front AC replacement this year, but mine is a 2013.
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Old 12-08-2022, 07:49 PM   #19
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Originally Posted by unsichtbarre View Post
My roof is definitely fiberglass. It appears to be pretty sturdy. I'll get a stud finder.
According to the specs the 2016 24SR roof is TPO and not fiberglass.
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Old 12-08-2022, 08:33 PM   #20
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The panel mounts on my TPO roof are fastened by SikaFlex adhesive only
To date, since installing 3+ years ago, holding firm
I have thought abt adding 1 screw in each of the 6 front facing mounts, but have not so far.
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