MCI rooftop layout

windtrader · July 06, 2021, 01:18:36 PM

I'm mounting unisstrut on the roof and want to screw into the strongest place. It seems the areas between the rows of rivets lie above structural cross-members. If so that seems to be the area to mount the unistrut.

One length seems overlapped, can one assume there are two sheets of roofing there?

Any suggestion on types of screws to fasten the struts? Is the cross beam solid or has holes so a screw may not get into the cross-beam?

dtcerrato · July 06, 2021, 01:51:52 PM

I can't comment on MCI construction but will make an informed recommendation to stay with stainless steel fasteners. SS self tapping screws will self tap fine in aluminum but if any part of the structure being fastened to is steel or ferrous - the SS self tappers will not do well. In that case I would recommend drilling, tapping, then using SS machine screws. Further more I used mechanical sealing SS neoprene bonded washers and stayed away from any kind of caulking. 2ndary means of sealing (below the SS neoprene bonded washer) could be a superior gasket making product called "The Right Stuff" used on the threads but would bet moisture won't get that far... My 2 cents & time-road tested...

Dave5Cs · July 06, 2021, 02:04:02 PM

Might try riv-nuts, where you drill a hole incert the riv-nut and use the riv-nut gun to fasten and it anchors it behind whatever panel you put it in. Much like an expansion anchor then just bolt it down to that.

windtrader · July 06, 2021, 03:03:35 PM

Good ideas. The existing rivets only guide you through solid sheating but not necessarily into the solid cross member. . I like Dave's idea but unless you know there is sufficient backing material then it may not grip into the cross-member.

SS machine screws are the call for sure. I'm still considering using 3M 5200 to secure the unistrut to the exterior roofing in addition to the screws. Grinding both surfaces this time should ensure full bonding and waterproofing around holes as well.

Any suggestions on machine screw size, spacing, and pattern? This is a forever-mounted set of brackets. LOL

dtcerrato · July 06, 2021, 03:18:13 PM

Don said
"Any suggestions on machine screw size, spacing, and pattern? This is a forever-mounted set of brackets. LOL"
IMO 1/4" hardware is stronger than required.
Riv-nuts are great for sheet metal as in body panels but shooting for structural frame under the body panel tapping should yield enough thread thickness.

ol713 · July 06, 2021, 03:59:40 PM

If you have a manual, the whole structure is shown along with body panels.
Merle

Dave5Cs · July 07, 2021, 07:29:24 AM

Don I wouldn't lay it on the roof. It should be up on at least 1/4" standoffs so water can pass under it.

chessie4905 · July 07, 2021, 08:19:16 AM

You are going to use aluminum Unistrut?

hogi6123 · July 07, 2021, 08:39:05 AM

In the 1994 MCI we are demolishing, the structure was as shown in the attached cross section picture. I think the lengthwise structural members also had another plate between the roof panels and inner structural member, I don't remember for certain.

Roof panels are aluminum.
Tar between the pieces.
Inner structural members are steel.

dtcerrato · July 07, 2021, 09:17:18 AM

Quote from: hogi6123 on July 07, 2021, 08:39:05 AM
In the 1994 MCI we are demolishing, the structure was as shown in the attached cross section picture. I think the lengthwise structural members also had another plate between the roof panels and inner structural member, I don't remember for certain.
Roof panels are aluminum.
Tar between the pieces.
Inner structural members are steel.

With steel in the works I'd shy away from penetrating a lapped joint (as you may create issues unrelated to trying to firmly hold the panels - dissimilar metals) and shoot for just body roof panel with what Dave mentioned: riv-nuts making certain they are all aluminum with SS hardware.
With all due respect, I was cringing to your original diy of adhesive only attachment to the roof. We have successfully used oversized (to what the solar panel mfger supplied in ferrous) SS self tapping screws into the roof panels only. These buses are robust when it comes to roof panel aluminum guage. Got some freeway milage on the panels and they are doing fine. If we see any reason for concern we will change out the self tappers for aluminum riv-nuts but currently confident of the install. Fwiw.

windtrader · July 07, 2021, 11:36:56 AM

Thanks for the ideas and the diagram of the panels secured to the cross-member.

I see two options then. 1) Riv-nuts penetrating the double sheeting. 2) remove original rivet that is through both sheets and the cross-member. Replace with SS machine screw or Riv-nut.

The uni-strut I'm looking at is steel and if placed on standoffs, then no adhesive bonding would be used. All the strength comes via the Riv-nut or machine screws.

I'm still convinced that if I had ground the surface coating off the galvanized brackets it would have held up. But this setup ain't going anywhere. lol

I'm planning on running the unistrut the full length if ever anything needed to be secured up top the railing is all there.

Dave5Cs · July 07, 2021, 02:00:31 PM

Where will you attach the TAILS?

chessie4905 · July 07, 2021, 02:41:46 PM

how about Huck rivets? they really hold, but you need long handled tool to set them.

6805eagleguy · July 07, 2021, 03:15:06 PM

Quote from: hogi6123 on July 07, 2021, 08:39:05 AM
In the 1994 MCI we are demolishing, the structure was as shown in the attached cross section picture. I think the lengthwise structural members also had another plate between the roof panels and inner structural member, I don't remember for certain.

Roof panels are aluminum.
Tar between the pieces.
Inner structural members are steel.

Eagles have that same support structure

Utahclaimjumper · July 07, 2021, 06:07:13 PM

If you decide to use Rivnuts,, then be sure to measure thru the drilled holes to determine the TOTAL THICKNES OF ALL PANELS.. A rivnut has to have the correct "gip length" to hold properly..>>>Dan