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Old 04-01-2021, 05:23 PM   #1
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What's size of the screws should I use for Motorhome roof to mount the solar panel

Hello everyone,

Any one know the size of the screws that I can use for the Thor Motorhome roof to mount the solar panel brackets? I don't know how thick the roof of the motorhome, and don't want use the screw too long to drive through the roof, also don't want use screws too short and can't holding down the panel well.

Thanks.
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Old 04-01-2021, 05:33 PM   #2
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Originally Posted by Shawn View Post
Hello everyone,

Any one know the size of the screws that I can use for the Thor Motorhome roof to mount the solar panel brackets? I don't know how thick the roof of the motorhome, and don't want use the screw too long to drive through the roof, also don't want use screws too short and can't holding down the panel well.

Thanks.
If you are still under warranty and you jack with roof, you kill your coverage. Have to have authorized shop install them to not void your warranty.

This is what I used when I had panels installed.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
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Old 04-01-2021, 05:35 PM   #3
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Originally Posted by Shawn View Post
Hello everyone,



Any one know the size of the screws that I can use for the Thor Motorhome roof to mount the solar panel brackets? I don't know how thick the roof of the motorhome, and don't want use the screw too long to drive through the roof, also don't want use screws too short and can't holding down the panel well.



Thanks.


On mine I used one inch stainless steel sheet metal screws. Probably #8 but I don’t actually remember. I expect 3/4 inch would be fine. My roof (SOB) is only about 1/4 - 3/8 inch thick and the rafters I fastened into are stamped aluminum so added almost no thickness. But the ceiling has a good two inches of insulation so there was no particular risk associated with using longer .
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Old 04-01-2021, 06:50 PM   #4
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Liquid Nails works wonders. I wouldn't trust screws...too much flexing underway to trust them staying tight. Most water leaks are found one day to late.
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Old 04-01-2021, 07:29 PM   #5
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my service center same thing under warranty let them do it
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Old 04-01-2021, 10:50 PM   #6
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Originally Posted by Shawn View Post
Hello everyone,

Any one know the size of the screws that I can use for the Thor Motorhome roof to mount the solar panel brackets? I don't know how thick the roof of the motorhome, and don't want use the screw too long to drive through the roof, also don't want use screws too short and can't holding down the panel well.

Thanks.
You might want to read Tom's blog on the ultimate solar setup. He is a degreed electrical engineer with a lot of idea and actual facts.
<https://mortonsonthemove.com/ultimate-off-grid-rv-solar-power-system-build/>
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Old 04-01-2021, 11:38 PM   #7
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Thank you for the reply, my RV is 2019 model, it is out of warranty already.
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Old 04-01-2021, 11:45 PM   #8
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For a Thor, with its TPO roof, I would not rely on just adhesives to attach your solar panels. For fibeglass or aluminum roofs, yes.

But there is a layer of 1/8" or so plywood underneath the TPO that will hold reasonable loads with a wood screw. Macdaddy's Amazon reference above shows #8 or #10 self tapping sheet metal scews tha should work fine. As noted above you only need 3/4-1" length.

Do use a good blob of Dicor or similar sealant above and below the screws.

David
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Old 04-02-2021, 01:28 AM   #9
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For a Thor, with its TPO roof, I would not rely on just adhesives to attach your solar panels. For fibeglass or aluminum roofs, yes.

But there is a layer of 1/8" or so plywood underneath the TPO that will hold reasonable loads with a wood screw. Macdaddy's Amazon reference above shows #8 or #10 self tapping sheet metal scews tha should work fine. As noted above you only need 3/4-1" length.

Do use a good blob of Dicor or similar sealant above and below the screws.

David


I located the rafters with a stud finder, predrilled for the screws, injected Dicor into the holes, puddled a good bit of the stuff to bed the brackets and then flooded the brackets and screws when everything was in place. Super strong and zero risk of a leak.
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Old 04-02-2021, 03:27 AM   #10
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Thank you very much.
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Old 04-02-2021, 02:21 PM   #11
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I used well nuts. The expansion of the rubber creates a tight fit and it also provides a waterproof connection. I added lap sealant a an additional protection against moisture. The panels are not going anywhere.
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Old 04-07-2021, 06:48 PM   #12
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I have had the glue down mounts on my AXIS since the first part of 2017, I get on the roof every year with the Dicor to check all joints, the glue Renogy wanted me to use is called Sikaflex an I had to find a special primer from a local construction supply dealer, we get the Santa Ann winds in Southern California and they can take an awning off a rig going through the mountains in a heart beat, if ever they loosen up I will have the option to just add some screws but they assured me if installed correctly they will never come off, I have 4 of the 100 watt panels and they use 6 mounts per panel
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Old 04-07-2021, 10:11 PM   #13
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I also live in South Cal, with Santa Ana Winds, and freeway speeds.

I have flexible solar panels, and for those I glued them down, glue on the backside and then a bead around the edge. Left some gap on the edge to allow water to escape.

But it depends on your roof, your solar panels, and your own conditions.

Rybie
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Old 04-08-2021, 12:05 AM   #14
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My suggestion : If you want to try drilless mountings, you could install "Renogy Solar Panel Roof Drill-Free Corner Bracket Mount' with Sika Flex (SIKA flex, Multi-Purpose Industrial Grade Polyurethane Sealant & Adhesive) : look on Amazon for details.
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Old 04-08-2021, 01:14 AM   #15
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FWIW, at highway speeds the panels don't actually experience a lot of high velocity air movement. The air gets pushed up over the roof forming a bubble. If you've seen a boat's wake, it's the same thing, but extended vertically up and over the roof. The actual air movement within the couple inches of the roof where the panels are is pretty low. Most of the forces the mounts need to handle are related to the RV bouncing on rough roads.
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Old 04-08-2021, 01:19 AM   #16
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My tech guy Kurt has installed 400 solar panels and only
1 has hale damage..he said dicor the hole and dicor
The screws and dicor top of screws
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Old 04-08-2021, 01:59 AM   #17
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I used 1” self tapping #10 stainless, and Dicored everything. All good.
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Old 04-08-2021, 02:08 PM   #18
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Originally Posted by atreis View Post
FWIW, at highway speeds the panels don't actually experience a lot of high velocity air movement. The air gets pushed up over the roof forming a bubble. If you've seen a boat's wake, it's the same thing, but extended vertically up and over the roof. The actual air movement within the couple inches of the roof where the panels are is pretty low. Most of the forces the mounts need to handle are related to the RV bouncing on rough roads.


Not sure how you could know that but my anxiety came from considering the unpredictable gusts from passing an oncoming semi on a two lane with closing speeds that could be 140mph or more. Obviously glued mounts work but I feel safer with screws into structure and figure a few more screws well sealed won’t significantly to the leak of risks given that there’s already 100 or more screws up there.
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Old 04-08-2021, 04:30 PM   #19
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They don't generally model these things for RVs, but do for semis, trucks and buses. RVs aren't that different though.

Box truck:
Truck Aerodynamics - What & Why? - Aerodyne

The yellow and red are higher wind velocity areas, green is relatively low, blue is very low. You can also see the vacuum at the back of the box from this too.

This paper discusses the aerodynamics of several different configurations of bus:
https://iopscience.iop.org/article/1...2/1/012002/pdf

In several of them, the low velocity area over the roof is pretty clearly visible (esp. Figures 2, 4, and 6).
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Old 04-08-2021, 04:49 PM   #20
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Originally Posted by atreis View Post
They don't generally model these things for RVs, but do for semis, trucks and buses. RVs aren't that different though.

Box truck:
Truck Aerodynamics - What & Why? - Aerodyne

The yellow and red are higher wind velocity areas, green is relatively low, blue is very low. You can also see the vacuum at the back of the box from this too.

This paper discusses the aerodynamics of several different configurations of bus:
https://iopscience.iop.org/article/1...2/1/012002/pdf

In several of them, the low velocity area over the roof is pretty clearly visible (esp. Figures 2, 4, and 6).


Interesting stuff. Thanks for posting it. Still glad I used screws tho!
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