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Roof construction

corn18

Village Idiot
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Sep 9, 2021
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I took the inside cover off my maxaire vent in the bathroom to see if I could determine my roof construction. The image is what I found. Looks like 1/2" plywood covered by EPDM. I have ducted a/c so there is quite a bit of space between the upper roof and inside ceiling. It is a crowned roof.

I am using aluminum strut track spaced @ 17" for each panel. I tried to find cross members on the roof with a stud finder but it just beeped the whole time. I think I was causing it to detect stud all the time.

Based on what I am seeing with 1/2" plywood as the upper surface, I am just going to use 1" wood lag screws to fasten the strut track every 16". Each track is 10ft long. I am only mounting 1 panel per side for now.

Is there anything else I can do to verify roof construction? Does this match what others have found on a Forest River product (2021 Salem Hemisphere 290RL 5er)?

Screen Shot 2021-09-24 at 08.19.43.pngIMG_4940.jpg

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I have seen professional installers use double sided tape. Scares me a bit honestly.

But I don’t think you need to hit the studs with a 1/2” ply decking. There isn’t much lift on those panels.

I’ve not worked on a roof like yours but because everything on an RV roof eventually leaks a little, I would use stainless lag screws with sikaflex 221 in the holes and under the rails with eternabond tape run up the sides of the rails for added measure.
 
I have seen professional installers use double sided tape. Scares me a bit honestly.

But I don’t think you need to hit the studs with a 1/2” ply decking. There isn’t much lift on those panels.

I’ve not worked on a roof like yours but because everything on an RV roof eventually leaks a little, I would use stainless lag screws with sikaflex 221 in the holes and under the rails with eternabond tape run up the sides of the rails for added measure.
Good call on stainless.

I am not using LHB tape because my roof is EPDM and there are many spots where it is not securely fastened to the plywood. I cannot imagine how it could possibly hold the strut channel on. The strut channel would be securely fastened to the rubber membrane as it was ripping off the underlayment, flying through the air @ 70 mph and smashing into some old lady's windshield. Her comment: "Wow! That LHB tape really works well."

I am going to put Dicor non-self leveling in the screw holes and around them under the strut channel. Then more on top of the screws. Hadn't thought of Eternabond up the side of the rails. I like it.
 
Regarding the stud-finder, make sure to use them 100% as indicated in the manual. Many of those finders get tossed because people think they don't work right, but in reality they made mistakes when operating them.

In my case I have to push the finder against a wall (or floor), make sure I'm in an area that has no stud around, THEN push the button to turn it on. Then start moving SLOWLY and you should find the studs easily. It needs to be reset this way with every single push against the wall / floor. Don't keep the button pushed, lift the finder and try somewhere else. Don't push the button over a stud. Don't push the button before hitting the wall / floor.

Once you find the studs, attach the strut channels with long stainless steel wood screws. Use washers. Use thick double sided butyl tape between the roof and the channels (first water barrier), add sikaflex 221 around the screw holes AND cover the screws entirely once tightened.

Should look like this:

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PS: don't waste your time and space with those small 200 watt panels. Heck I have 460 watts on my minivan camper. Paid 220 bucks locally.


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I don’t think the roof is actually plywood, but pressboard.

After installing my panels I found a couple of ways besides a stud finder.

1) Early morning dew or frost. Either makes the beans obvious or pools away. Not all the time, but occasionally.

2) The beams become apparent when walking and I can feel where the beam is. When I do, I can run my habnd along this and find a seam.

3) Inside the RV, looks like there’s some brown trimming running left to right across the ceiling, which lines up with where I think the beans are. I think when constructed, the ceiling panels are secured along the beams with nails or staples, and then this trim is installed to pretty it up.
 
Thanks everyone! I hadn't noticed but someone pointed out to me that you can see the cross members in my picture of the roof. I'll be darned, it looks like you can. I'm sitting by the campfire right now, otherwise I would be up on the roof installing strut channel. After how much we drank last night, I'm not sure that would be a good idea anyway.
 
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