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Old 12-01-2021, 09:09 PM   #1
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Filon Roof?

I have a roof on our RV that as far as I can tell is a "Filon" roof. It looks like a textured fiberglass. I'm trying to figure out how to take care of it and if I can put holes in it. I've found lots of references that say you should never put holes in fiberglass.

The reason I ask is I have a solar panel on the roof. I've glued the brackets down pretty well. I go up and check it every once in a while to make sure the roof isn't separating from whatever is underneath it. But, I really don't like it. I would feel much more comfortable if I could screw them down so that the wind while driving doesn't pull up the "filon" roof.

So, the question is, can I drill holes in a filon roof? Will that cause any problems with cracks or anything else? I've searched but not found any good information.

Thanks for any advice you can give.
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Old 12-01-2021, 09:20 PM   #2
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I have solar on my thin layer fiber roof, clued tabs and added a stainless screw 1" long

no issues
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Old 12-02-2021, 08:25 AM   #3
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Hi CyrusL,

I am not familiar with the term Filon, but your description of "textured sheet fiberglass" is the roofing material used for the Phoenix Cruiser. Here is a picture of our PC's roof.


Phoenix Cruisers with solar panels, the panels are attached by drilling and screwing into the metal roof rafters. "PRE-drilling" the holes in the thin fiberglass sheathing makes clean holes that won't encourage cracking. I advise to first drill a small pilot hole, then enlarge it to the proper diameter for the mounting screws to pass through the fiberglass sheathing to avoid making contact with it.

I would most definitely locate the roof rafters and screw down your solar panels to it. If you can't hit a rafter for each of the 4 feet, relocate the feet on the panel so that they do. Once finished, remove each screw, inject caulk in the screw hole (be generous), then re-screw and let the caulk ooze out, wipe clean and it's good.

What you did simply gluing the solar panel brackets to the fiberglass sheathing sounds very scary to me. Some manufactures do NOT 100% glue down the fiberglass sheet, but rather limitedly in "floating" fashion like sheet vinyl floor covering. So keep this in-mind.
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Old 12-02-2021, 09:50 AM   #4
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Quote:
Originally Posted by Ron Dittmer View Post
Hi CyrusL,

I am not familiar with the term Filon, but your description of "textured sheet fiberglass" is the roofing material used for the Phoenix Cruiser. Here is a picture of our PC's roof.


Phoenix Cruisers with solar panels, the panels are attached by drilling and screwing into the metal roof rafters. "PRE-drilling" the holes in the thin fiberglass sheathing makes clean holes that won't encourage cracking. I advise to first drill a small pilot hole, then enlarge it to the proper diameter for the mounting screws to pass through the fiberglass sheathing to avoid making contact with it.

...
Ron,

Yep, that looks like the stuff. I was thinking about something similar to your pre-drill idea. That sounds great. It hadn't occurred to me to find the rafters. I'll see if I can do that. Hopefully a standard stud finder will work for that.

Like I mentioned, I do go up every once in a while and check to see how solidly it's attached. So far I can shake the whole RV by shoving and lifting the panels. I'm just concerned that one day that stuff will separate from the roof with enough constant wind from driving.

Thanks for your insight.
Cyrus
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Old 12-03-2021, 01:08 AM   #5
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The trick to mounting anything on roof is find enough wood (or metal?) structure to screw into; adhesive/ tapes on solar panels will never hold in highway speeds, if truly Filon (-1/16" fiberglass glued to 1/8" Lauan plywood (*or AZDEL) and 1" foam, then 1/8" plywood / interior finish/ paneling. TECHNICALLY, Filon NOT Much tougher than poster board as far as strength; the strength is in the ASSEMBLY, TO INCLUDE both sides of the sandwich. STRUCTURE for SCREWING to in these panels is usually 1x1-inch metal tubing or wood inserted for attachments. HOPE this helps
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Old 12-04-2021, 05:01 AM   #6
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finding the metal or wood cage that is laminated into some of the roof systems is tough.. many times they are not standard spacing like a home, yes a few are..
In my case it was a pipe dream and placing the solar panel in a logical fashion to fit and e wired was the greater concern.

I would not use doucle sided tape as an only fastener. I have used good adhesives made for metal to the roof materiel.. A rubber roof will need proper adhesive or if roof was coated use a compatible adhesive.

I use some adhesives in automotive that bond panels in place of fasteners and welds... both metal, plastics and molded composites (like many RV roofs)..

Just make a plan.. research
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Old 12-04-2021, 07:01 AM   #7
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Quote:
Originally Posted by CyrusL View Post
I have a roof on our RV that as far as I can tell is a "Filon" roof. It looks like a textured fiberglass. I'm trying to figure out how to take care of it and if I can put holes in it. I've found lots of references that say you should never put holes in fiberglass.

The reason I ask is I have a solar panel on the roof. I've glued the brackets down pretty well. I go up and check it every once in a while to make sure the roof isn't separating from whatever is underneath it. But, I really don't like it. I would feel much more comfortable if I could screw them down so that the wind while driving doesn't pull up the "filon" roof.

So, the question is, can I drill holes in a filon roof? Will that cause any problems with cracks or anything else? I've searched but not found any good information.

Thanks for any advice you can give.
Not Filon. The newer FR Forester say fiberglass roof over luan and aluminum trusses. The fiberglass is thin as will be the luan. Finding the aluminum truss support should be doable with a stud finder. You absolutely need to use more than double sided tape. It's unlikely the spacing of the panels and roof support will line up so I suggest getting the front panel mounts into a support cross member and screws into the roof also for the rear mounts. If predrilled, fill holes with caulk/lap sealant before the screws are installed. and thoroughly cover the screws and brackets with the appropriate lap sealant. Some would suggest a strip of eternabond tape over each mount then the sealant too. Periodically, annually at a minimum, check the mounts and all other roof sealants. With eternabond and lap sealants, follow the manufacturers instructions. If in 2017 it was a rubber roof, check to see if TPO or EPDM and use compatible sealants.
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Old 12-04-2021, 10:20 AM   #8
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The problem relying exclusively on an adhesive (tape or glue) is that even if the adhesive holds, the finish layer of the roofing material can separate.
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Old 12-05-2021, 06:35 PM   #9
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Been traveling almost 8000 miles with my panels mounted with screws through Filon roofing. Filon is a textured fiberglass - reminds me of FRP that we used on restroom walls at work.

I mounted four solar panels on my rig several years ago with SS screws and a bead of Dicor sealant as an adhesive and sealant. No problems since. One thing that can cause cracking with fiberglass is over tightening the screws.

One trick that can reduce cracking when drilling is use a bit made for plastic. Regular drill bits are too aggressive and the cracking comes from when the bit bites and pulls itself into the work instead of shaving away a chip(s). This causes the flute to act like a wedge. One type of bit that won't dig is a step drill because it doesn't have a spiral flute. You can help reduce the tendency of a spiral bit to dig by using very light pressure.

You can also modify the twist bit to reduce it's tendency to dig by changing the tip profile from a cutting tip to a scraping tip. Drilling and Proper Handling and Maintenance of Acrylic Sheet: Plastic Distributor & Fabricator

I just drilled mine with a step drill. You'll be putting the screw through a bracket which will spread the clamping load reducing the chance of cracking, then covering the screws with sealant.

Don't worry too much about it. If it was that fragile, manufacturers wouldn't be cutting through it to mount accessories, air conditioners, or to attach ladders.
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