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Almot's avatar
Almot
Explorer III
Dec 05, 2013

TT roof questiion, any caprenters here?

Installing aluminum brackets for solar panels. Big heavy panels, 1/4" thick angles for brackets. Driving #10 wood screws into the roof, with roof sealant under the brackets. Like others before me. Nothing unusual.

Roof structure: EPDM on 3/8" particle board, with 1.1/2 wood studs, each stud 1.1/8" thick according to manufacturer's drawing that they emailed me (thickness of the particle board I found myself when removing TV antenna).

What is unusual:
When drilling pilot holes, I found that there was a gap between the stud and particle board, ~1/8" or 1/4". This in itself is not unusual - guys arched the stud at the crown, drove the screws close to the side walls but no screws at the crown, so it's arched and created a gap at the crown more then at the side walls.

Now, THIS is odd for somebody who is not a carpenter. Driving my #10 screws in, to attach the brackets. Tightened the screws until it stopped, one by one. The last screw is in, I go to the 1st one - and can tighten it some more. And then - other 2, and then again and again. Eventually I've managed to tighten the stud screws another 2-3 rounds after they were "tight". Screws have slotted hex heads, with the hex socket you can tighten it a lot more than with a flat screwdriver. I didn't use a wrench, just a screwdriver with assorted bits, so there was no lever.

This did NOT happen where there was no stud underneath (I drove a few screws into particle board next to the stud as well).

I think what happened was that I pulled the particle board closer to the stud, closing the gap. #10 screws are 2.5" long so they go through the stud completely.

Now, my question: should I be doing this? I mean, tightening it THAT much. Pulling the stud and plywood together and closing the gap, I've created a pressure that is trying to pry the stud and plywood apart, and potentially - pull #10 screw out of the stud a little. Screw went ~1/4" below the stud before I closed the gap, now without the gap it's 1/2" below the stud, so it won't pull out completely. The bracket sits now very tight, but I'm having doubts.

Promise to post all the pics after I'm done. I'm not home, internet in this location is a problem.

Oh yeah, and forget the stud finders if you do this. They don't see wood studs under 3/8" particle board.

9 Replies

  • Almot's avatar
    Almot
    Explorer III
    Dec 08, 2013
    Thanks, Westend.

    I've checked those gaps again - when drilling for another bracket - the gap is less than 1/8". So I will go with your suggestion, 1.5" screws, this will give me 3/4" grip in the stud alone, plus 1/2" grip in the particle board. So the screw will not go the last 1/4" or so in the stud.

    The pilot hole will still penetrate the 1.1/8" stud completely. It's difficult to calculate precisely the length of the pilot hole required, when the gap is known only approximately.
  • westend's avatar
    westend
    Explorer
    Dec 08, 2013
    No worries, just don't torque them down as far as you can, i.e. so much that you're deforming the surface.
    If you're using an impact driver or drill, tighten until contact and 1/4 turn of the fastener. If you experience some deformity in the progression of fastening, go back and only tighten the first fasteners until the head of the fastener contacts the angle bracket. With your screw schedule and use of sealant underneath, a bit of a gap isn't going to be a problem.

    Hope you get the picture posting figured out, it would be cool to see your work. Good luck!
  • Almot's avatar
    Almot
    Explorer III
    Dec 07, 2013
    Dammit, the picture disappeared. Forgot to tell, it's a sheet metal screw, not wood screw. Wood screws are partially threaded which I don,t like, and don't have slotted hex heads.
  • Almot's avatar
    Almot
    Explorer III
    Dec 07, 2013
    The manufacturer only sent me a drawing with 1.1/8 studs thickness, 1.1/2 width, and their approximate location. I call them "studs" because this is the top part of the rafter, it is arched, and the bottom part of the rafter is flat (where interior ceiling panels are attached).

    2.5" screws I chose based on the fact that total thickness of metal bracket foot + particle board + stud = 1.3/4". Also, the bracket foot is flat but the roof is arched upwards, so there were small gaps between the bracket foot and the roof. Though, these gaps under the bracket foot had disappeared when I tightened the screws in studs and flattened the particle board under the bracket. The screw go all the way through 1.1/4" stud, so I guess it doesn't matter whether they
    are 1.3/4" or 2.5".

    Yes, I pre-drilled 3/32" pilot holes all the way through the stud as recommended for "softwood", which is a particle board. For a "hardwood" it's recommended 7/64" pilot, but I don't know how "hard" is the stud. Could be just a regular pine board. The root of #10 tapping screw is 1/8", and in the woodworking blogs the opinion is not to drill any pilots when the root is less than 1/8".

    Since the screw goes through the stud anyway, it doesn't matter how long it is. Photo - sorry, don't know how to resize it on Skydrive.

    The bracket is 6" long, parallel to the back of the trailer. 3 screws in the stud and 2 just in particle board (those are 1/2" long).

  • pianotuna's avatar
    pianotuna
    Nomad III
    Dec 06, 2013
    Hi Almot,

    I hope the pilot holes were sized to the screws. If they were it is unlikely that the rafters have split.

    Is 2.5 inches #10 what the maker of the RV suggested?
  • loulou57's avatar
    loulou57
    Explorer
    Dec 05, 2013
    1st....you should not screw through the EPDM.

    2nd... You have tightened the particle board to the rafter therefore when the pressure releases the particle board will split, fall apart and drive up around the bracket ripping the EPDM.

    3rd...the #10 ...2 1/2 inch screw likely has cracked the rafter also.
  • westend's avatar
    westend
    Explorer
    Dec 05, 2013
    In my rig the roof sheet was slightly above the rafters in certain locations. Fiberglass batt had been inserted in those areas, between the rafter top surface and the roof sheet. I can only think this was done to maybe eliminate squeaks or to afford a thermal break. I wouldn't reef down on the screws more than necessary. If you have a 1/4" metal piece, a 3/8" wood sheet, and a 2 1/2" screw, you are getting nearly 13/4" of thread into the rafter, considering the gap. That should be plenty if you are using enough screws and are also using an adhesive sealant underneath the metal.
  • monkey44's avatar
    monkey44
    Nomad II
    Dec 05, 2013
    Not sure I understand ... is the roof sheeting arcing up, or is the stud bowing down (actually a rafter, if I understand your post correctly) ...

    In either event, it will more than likely increase the structural integrity if the 3/8 sheeting is screwed into the stud (rafter) tight ... Unless the arc / bow in strong enough that the screws pull through the sheeting. Photos would be great.

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