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Old 01-04-2019, 05:36 PM   #1
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solar panel screw length

I'm in NY and am told it's too cold now for 3m vhb tape ..I'm mounting 3 solar panels .should i be concerned hitting something below the skin of the roof with the solar panel mounting screws ? .. there are flush mount lights ,speakers. and the a/c duct-work ..and using geocel rv sealant .thanks i have a 2014 cambria,aspect class c
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Old 01-04-2019, 05:49 PM   #2
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I'm in NY and am told it's too cold now for 3m vhb tape ..I'm mounting 3 solar panels .should i be concerned hitting something below the skin of the roof with the solar panel mounting screws ? .. there are flush mount lights ,speakers. and the a/c duct-work ..and using geocel rv sealant .thanks i have a 2014 cambria,aspect class c
You might want to check with the factory to find out how thick the roof is and what it is made of. I did that for my Winnebago Fuse and found out how thick the plywood under the fiberglass is, and thus how long the screws should be. they told me that all of the wires were in the foam insulation under the plywood so as long as the screw stays in the plywood I would be OK.

I have no idea if the roof of the Fuse is anything like the roof of the Cambria, but the factory can probably tell you.
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Old 01-04-2019, 07:28 PM   #3
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If it's anything like most Winnebago MHs, the plywood is only about 1/8" thick over a 2" - 3" (approx) layer of foam. Therefore there's no need for screws longer than what's necessary to penetrate mounting feet and the plywood plus maybe a 1/4" or so safety margin to minimize the risk of pull-out. Additionally, larger diameter screws with relatively coarse threads will hold better than smaller, fine thread screws. And try install the screws in one "shot" each. Removing and re-installing a screw will reduce the holding power.
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Old 01-04-2019, 08:06 PM   #4
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What might you hit? There are some wiring channels in the roof with low voltage wire bundles laying in them. There is some 120 Volt Romex in some channels too. You can look at diagrams on the WinnebagoInd.com web site for your specific RV and get some idea, but not their exact location. I have mounted solar panels on my Vista, using 24 fasteners, and have not had any issues with hitting anything and impacting any electric circuits.

The above roof "Z" bracket is only about 1/16" thick. The roof is fiberglass panel over plywood, about 1/4" thick. Personally I use 3/4" long #10 stainless screws. So, your 3/4" screw is only going down slightly less than 1/2" into the syrofoam insulation under the roof panel. I drill pilot holes with a 1/3" depth stop on the drill bit. You could even probe the pilot hole with a drill bit and see if you can feel anything in that 3/4" depth space, but personally I have never done that.

Good luck.
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Old 01-04-2019, 08:31 PM   #5
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For my computer network projects I have a signal generator/sensor that will pinpoint the location of cable within a wall or ceiling to a inch or so. Can also setup to trace low voltage and 120v cables if needed. Makes this type of work simple. Otherwise a factory wiring diagram is a good bet, most are online.
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Old 01-04-2019, 10:45 PM   #6
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Renogy recommends well nuts, AKA expansion nuts, to mount their panels. Whatever you do, make sure that you use some sort of sealant between the roof and the flange to seal the screw shank and roof against water seepage. I use 1/8" butyl tape. And use stainless screws. The satellite dish mount on our preowned '14 Sunstar was not done this way, and most of the zinc plated screw shanks had half corroded away.
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Old 01-05-2019, 04:29 AM   #7
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thank you all...excellent ideas...I worked for the phone company and never liked drilling into areas i could'nt see behind, there are lights and speakers behind the front skylight and in the rear i got all lights,speakers and a/c ductwork ,i will call the factory and get transferred to someone that can help. 3/4" #12 stainless screws, i would guess will be the correct size ,renogy sent me 1 1/4 long ones with the mounts ,geocell cures down to 0*F 3m 4951 vhb low temp tape cures down to 32*F..im in NY and nights will be chilli through march..i'm heading down south next month and the solar would be nice with the shorter days...,
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Old 01-05-2019, 05:32 AM   #8
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I can not speak about the thickness of the roof of any of the other RVs, but the tech guy at the factory told me that the plywood on my roof was 1" thick, not 1/8" thick, and that as long as my screw was less than 1 inch long I was good to go because all of the wiring was in the foam under the plywood. I can walk on my roof and I would not think that I could safely walk on any roof that had only 1/8" thick plywood.

I would suggest calling Winnebago and asking. Give him your VIN and he can look up your specific model and tell me pretty much everything about it. In case you need it the Winnebago number is 800-537-1885 and that is the Owner Service number so it is intended for owners who have technical questions.
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Old 01-05-2019, 01:28 PM   #9
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A simple way to determine for sure how your roof is made is to pull the four corner screws that hold up the plastic trim around any of the 14 x 14" vents/fans and you can see all of the layers and there thickness, at least at that point on the roof. Some roofs maybe tapered or rolled somewhat and thus insulation thickness may vary some.

A 1" plywood roof on an RV, really?? I've never more than 1/2" plywood used. But all things are possible.
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Old 01-05-2019, 01:35 PM   #10
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rarebear's suggestion is right on. I can't imagine that there's 1" of plywood in your roof, the tech guy may have misunderstood and was only advising you on the screw length.

It's not the 1/8" ply that supports the weight it's the entire "sandwich" of a top and bottom layer of 1/8" ply with foam in between. It's incredibly strong and is how my Suncruiser is built.
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Old 01-05-2019, 01:52 PM   #11
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Perhaps you are right, but what he told me was very clear. He said that I should use a wood screw no longer than 1" long because the plywood under the fiberglass was 1" thick and anything longer would poke into the foam under the plywood and possibly run into the wiring.

As I said, I do not know myself, but I do know what he said. Perhaps he was wrong, and I will call again on Monday and ask again, but that is what he told me.
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Old 01-05-2019, 04:07 PM   #12
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Let us know what they say. We should start a pool. I'm still going with 1/8" plywood.

I think the issue is that anything longer than 1" might penetrate a wire which is going to be in a channel running through the foam.

In any case, 1" screws will be safe per what Winnebago has told you.
Everything I've dealt with on mine, skylight, vents etc. has been secured with 1" screws and I know, for a fact, that my plywood is only 1/8" thick.

Make sure you use stainless steel screws and if you drill pilot holes (not necessary with thin plywood), make sure you mark your drill bit with tape so you don't go too deep.

And put sealant on the bottom of the brackets before mounting them. Check out the sealant call-out sheet for what to use:

https://winnebagoind.com/diagram/Sealant.htm

Also put sealant around the screws underneath their heads before you drive them in to ensure the screw hole is well sealed. Clean up the excess for a nice clean installation. There's no need to goop it on 1/4" thick all over the bracket and edges. It's what's under the bracket and in the holes that counts. On a well kept boat you'll hardly ever notice that any sealant was used. As a long-time boat owner, I was shocked when I saw how sloppily the roof of my first RV had been sealed.
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Old 01-07-2019, 07:47 AM   #13
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Let us know what they say. We should start a pool. I'm still going with 1/8" plywood.
You win.

I called again this morning and got someone different. When I asked him about the thickness of the plywood he said 1/8", but gave me the same information on screw length - 3/4 to 1" and no longer.

I am sure that I had been told that the plywood was 1" thick by the previous guy, but apparently that information is wrong. I do wonder if the roof is safe for someone to walk on if the plywood is only 1/8" thick.

Quote:
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Make sure you use stainless steel screws and if you drill pilot holes (not necessary with thin plywood), make sure you mark your drill bit with tape so you don't go too deep.
Yes, I did know about marking the drill bit.

Quote:
Originally Posted by BobC View Post
And put sealant on the bottom of the brackets before mounting them. Check out the sealant call-out sheet for what to use:

https://winnebagoind.com/diagram/Sealant.htm

Also put sealant around the screws underneath their heads before you drive them in to ensure the screw hole is well sealed. Clean up the excess for a nice clean installation. There's no need to goop it on 1/4" thick all over the bracket and edges. It's what's under the bracket and in the holes that counts. On a well kept boat you'll hardly ever notice that any sealant was used. As a long-time boat owner, I was shocked when I saw how sloppily the roof of my first RV had been sealed.
This is a flexible panel so there are no brackets. I was planning to use butyl tape under the panel to seal the connection and to use sealant to cover the screws. I already ordered NUCO 311 from Winnebago to use as the sealant but the interesting thing is that the existing panels, installed by the factory, do not have any sealant on them. A bit of putty under the panels, a washer and screw to hold them down and that is it. Nothing to seal them, so I suppose I should add some sealant when I am doing the new panel.
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Old 01-07-2019, 08:59 AM   #14
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[QUOTE=AJMike;3831847] I do wonder if the roof is safe for someone to walk on if the plywood is only 1/8" thick.

Walking on the roof isn't a problem. The roof structure is a foam "sandwich" and is incredibly strong, so don't worry about it.
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Old 01-07-2019, 09:49 AM   #15
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I do wonder if the roof is safe for someone to walk on if the plywood is only 1/8" thick.

I'm 220 lbs and I walk around on our Sunstar a lot. You shoudn't have any problems.
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Old 01-13-2019, 04:51 PM   #16
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Solar Panel Screw Length

Is there any worry about the solar panels sailing? I owned cruiser boats for over 16 years and we never used screws unless it was impossible to use bolts with self locking nuts. Boats typically vibrate too much for screws. I'm new to RVs and it appears it is impossible to bolt these panels on the roof?

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Old 01-13-2019, 07:41 PM   #17
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Is there any worry about the solar panels sailing? I owned cruiser boats for over 16 years and we never used screws unless it was impossible to use bolts with self locking nuts. Boats typically vibrate too much for screws. I'm new to RVs and it appears it is impossible to bolt these panels on the roof?

Thanks,
Bob
From what I've read both here and on IRV2, people haven't had the problem of solar panels sailing off. My plan, however, is to use both 3M VHB tape and screws.

I'm a former sailboat owner and know what you mean about screws vs. thru bolting. Thru bolting on a Winnebago roof is possible as long as 1) you know that you're avoiding a wire chase and 2) use backing plates or fender washers and 3) don't over tighten so as to compress the foam core, but it doesn't seem to be necessary for most of the things mounted on our roofs. in contrast, most of our boating fixtures have some sort of load or stress applied to them such as railings, cleats, chocks, fairleads, etc. The stresses on our motorhome fixtures are minimal, the only real exception being ladders.

As a former boat owner I suspect that you, like me, were shocked to see how RV manufacturers and owners slap on gobs of caulking with very little regard for removing old caulking before applying new caulking.
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Old 01-14-2019, 08:54 AM   #18
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I installed 3-160W panels a couple of years ago on my '08 Sightseer 29R. Winnebago will send you a roof diagram with your VIN no. Yes, there are electrical runs and structural supports that run through the roof. I used 1-1/2" X 1/2" expansion (rubber) nuts with stainless steel machine screws. Simply drill a hole only deep enough to break through the fiberglass skin (no deeper), fill hole with Dicor non-sag, insert expansion nut and screw in the bracket (enough to 'mushroom' the expansion nut), cover top of screw cap with Dicor. Should you ever need to modify the point of attaching, remove the expansion nut, fill the hole again with Dicor and insert a cap plug.
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Old 01-14-2019, 09:26 AM   #19
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fill the hole again with Dicor and insert a cap plug.
Perhaps it would be better to use the Winnebago sealant NUCO 311. I have seen online videos warning against using Dicor on a fiberglass roof.
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Old 01-14-2019, 11:11 AM   #20
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From what I've read both here and on IRV2, people haven't had the problem of solar panels sailing off. My plan, however, is to use both 3M VHB tape and screws.

I'm a former sailboat owner and know what you mean about screws vs. thru bolting. Thru bolting on a Winnebago roof is possible as long as 1) you know that you're avoiding a wire chase and 2) use backing plates or fender washers and 3) don't over tighten so as to compress the foam core, but it doesn't seem to be necessary for most of the things mounted on our roofs. in contrast, most of our boating fixtures have some sort of load or stress applied to them such as railings, cleats, chocks, fairleads, etc. The stresses on our motorhome fixtures are minimal, the only real exception being ladders.

As a former boat owner I suspect that you, like me, were shocked to see how RV manufacturers and owners slap on gobs of caulking with very little regard for removing old caulking before applying new caulking.

Yes, shocked would be the word.
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