Bus conversion: roof sag

[Thorbuslife]

Hey evereyone, first post here!

I know this is an RV forum, but I am doing a bus conversion. I joined this forum as the body of my bus is made completely of fiberglass, and I am about to start my journy of deleting multiple windows and openings to turn it into my own custom space.

I think I have a good handle on deleting the openings, I am a woodworker and have done a bunch of research on fiberglass installation, youtube is a wealth of knowledge!

The problem i am seeking advice on is the roof sag on one side of the bus cieling.

The original structural composition consist of 1/8th thick fiberglass covered in a gell coat on the exterior, bonded to about 1 inch of that corrogated cardboard material you would see on the inside of a crappy interior house door, the cardboard is then bonded to a second layer of 1/8th thick fiberglass on the interior, it is quite strong, but there is no steel substructure. There is a ridge in the center of the roofline to create a very shallow slope on the roof to the outside.
There are strips of plywood and 1/6th steel in different places of the cieling underneath the inside layer.

I have a considerable sag on one side of my cieling section, spanning about 12 ft long, going from where the wall meets the cieling, to the center ridge of the roof. I want to fix this problem so that i have a flat surface to frame to for my insulation.

The solution i have come up with is to take 1 inch square steel tubing and run it perpendicular to the sag in the roof, jack it up till it is flat and tight, drill holes through both layers of fiberglass and the first layer of steel tubing, pull the tubing down, tap the holes in the tubing so the bolts can thread in, put the tubing back up and install the bolts from the roof side, with as wide of washers as i can find so as to disperse the pressure outwards on the fiberglass reducing the chance of damage. I would water seal the bolts with butyl tape before installion. The only concern is that by doing this i will be transferring some of this tension to the ridge of the roof, i hope this will not cause the ridge to collapse.

Can anyone give some insight on this issue? Is my technique that i am thinking about trying an approach that will hold up over time?

[TZBrown]

What you are describing will have a pull effect on small points of the roof structure around the washers. It may work, or lead to further cracking of the fiberglass.

I would consider making ribs for the inside with the curve of the roof you want, laminate plywood. if you may mount solar or a rack of some kind keep that in mind when you consider the strength you need. Consider wall to wall length for both sides with about a 4 inch height. Add a rib to floor brace at each end for strength.

In a 12 foot length 3 or 4 should do. place them where they can be used for other inside mounted walls or cabinets.

Good luck on your build

[Thorbuslife]

Thank you, this sounds like a much better option, and will increase the stength of the cieling as well.

[chernoboler]

Do you know what caused the sag in the first place? This is going to sound funny, but is there an issue with the under frame on the diagonally opposite corner (kitty corner)?

[Bill Robison]

Originally Posted by TZBrown

I would consider making ribs for the inside with the curve of the roof you want, laminate plywood. if you may mount solar or a rack of some kind keep that in mind when you consider the strength you need. Consider wall to wall length for both sides with about a 4 inch height. Add a rib to floor brace at each end for strength.

In a 12 foot length 3 or 4 should do. place them where they can be used for other inside mounted walls or cabinets.

I agree with TZBrown's solution. A pic would be handy?

What year buses have fiberglass construction?

Interesting project!

Bill

[John in Santa Cruz]

Originally Posted by Bill Robison

I agree with TZBrown's solution. A pic would be handy?

What year buses have fiberglass construction?

Interesting project!

Bill

An 'aerotech' seems to be a bus like this (modern version but I'm sure they've been around awhile with different generation van chassis).

[FRED SMAILES]

I would reconsider holes in the roof.
The steel tube could have a slight curve to force the roof up securing the tube ends to the walls to stop them from spreading out.
Then use fiberglass to laminate the tube to the roof structure. A wooden truss would laminate better but you would need to sacrifice ceiling height for truss height.
Hope you post pics of your reno journey in the bus.

[John in Santa Cruz]

FWIW, i don't think any of the molded fiberglass trailers use any sort of internal framing. On some, the cabinetry provides some internal support for the top, and contributes to the overall stiffness.

[Donna D.]

I'm thinking the OP would probably get better suggestions if on a forum for that kind of vehicle. While it may be all fiberglass, the way it's put together is not the same as an all-molded travel trailer.


I respectfully suggest: Skoolie.net https://www.skoolie.net/forums/


While at the site, I found this: https://www.skoolie.net/forums/f6/20...ion-40123.html

[Bill Robison]

Originally Posted by John in Santa Cruz

FWIW, i don't think any of the molded fiberglass trailers use any sort of internal framing. On some, the cabinetry provides some internal support for the top, and contributes to the overall stiffness.

Thx John for your feedback regarding the bus.

I had another idea for the roof/ceiling repair to consider...

To minimize use of interior headroom with a lam truss - what about possibility of using multi-layers of 1/4" or 3/8" ply? Using the 'jack idea' to return ceiling to the original height (not knowing actual ceiling configuration). Then, apply the layers of plywood secured with a construction adhesive? Minimal loss of ceiling height and even a gentle arch config with construction adhesive should yield strong support? Feedback appreciated, since initially I was thinking of a standard school bus type roof...