How do you attach a roof rack to a fibre glass roof?

AHH well.
that dpends on how it is constructed and if it is an all fiberglass construction or not.

I have two utes with fiberglass canopies....they have metal braces that come from the reinforced fiberglass door frames and the racks bolt thru the roof sheet onto these braces.

There has to be some structure somewhere.

cheers

Stuart, I would make a proper full metal roof over the fibreglass one like a tropical Landrover model, then screw to that.
Like Bantam said, there has to be a framework somewhere in there, so look for that (electronic stud finder, rivets present, obvious position when fibreglass pressed down, etc) . . . then work out where the best place is to mount a frame, then a skin of galv sheet or similar, stuck down with a modern coach and body sealer.

Remember, they will be permanently up high then, in the dust, so you'll have to ensure they get a regular wash down to maintain efficiency.
Also the extra risk of breakage from stones, falling branches etc.

You won't have the choice about orientating to the sun for the best results either.

What about those other type flexible panels as in this thread ?
Comment: Solar Power
Yeah you'd be up for purchasing them, but might be a lot cheaper long run rather than all the work altering the roof.

Keep in mind anything you do to the roof will increase risk of leaks too.

Hi Stuart,

There may be some metal bows moulded into the roof to support it. This is the method used in the brothers motorhome.

Using a cheap nail finder go along the roof and find each one of the bows, if they exist.

If they exist, mark each one with a pencil line and work out where the legs of your "roof rack" will sit. Mark each leg positions screw holes, then drill into each of the bows, using a small drill, in those positions.

Using a self drill metal thread screw (if the bows are metal) or a wood type TEK screw, screw the roof rack down to the roof. Make sure you use plenty of Sikaflex under each leg to ensure you get a good seal. Do not set the panels too high off the roof as they will only become an air brake if you do. Fifty millimetres is sufficient for air flow, 75 is a bit better I guess.

What I did was to do one side at a time using the other side partially screwed down as a location guide. When I had finished the first side, the last side had to be on target.
This is to ensure you do not get the Sikaflex everywhere as there is nothing worse than trying to find the screw holes when they are hidden under a fresh coat of Sikaflex.

This same method applies to a roof with wooden bows.

Note that you may have to relocate some legs on your "roof rack" in order for them to align with the roof bows.

To effect the passage of the cables through the roof I used a Clipsal Adaptable Box approx 100 X 100mm and Sikaflexed that onto the roof in the correct position. This correct position was obtained by working out where I was going to locate the regulator inside the van (or motorhome) and then drilling a hole through the roof from the underside in the appropriate location. (use an 8mm drill first for location purposes) I then centred the adaptable box over the hole outside on the roof and then screwed it down on a good bed of Sikaflex. I then used a 25mm hole saw to enlarge the pilot hole I had made through the roof to locate the adaptable box. Note also that you can get waterproof inlets or entries for these boxes that take the grey corrugated electricians conduit which can be used to further ensure the integrity of the roof and box from leaks.

Cheers, Bruce.

Have you considered changing to the lightweight flexible solar panels and you can glue them straight to the fibreglass like they do on boats

They are pretty cheap now days and only about 20% of the weight

The art of attaching stuff to fiberglass roofs is to place the load over a very large surface area.

You could always polyurethane a large sheet of aluminium onto the fiberglass and then thatch your panels using fasteners through the aluminium and fiberglass.

Sika make a range of bonding polyurethanes in a tube that may be of use.

You should first find out what type of fiberglass motor home it is
Eg; is it a foam sandwich panel, is it a glass sheet bonded to a alloy/timber/steel frame, etc etc
then & only then you will be able to correctly add anything to the roof

The Tvans have a fibreglass roof and the solar panel is simply bolted through the fibreglass with panel washers behind. I fitted my own, and fitted captured nuts to the panel, so fitting just requires the 4 bolts from below.
Sure it's ideal to have air flow underneath the panel, so the panel doesn't heat up too much, but I find the difference in output is not great. You could also space the panels up a bit by mounting them on 2 sides with aluminium angle.

Stuart,

Check out the link for Jaycar below. There's a couple of items there that will work better than a roof rack on your vehicle. They will spread the weight of the panels on the fibreglass roof, and reduce likelihood of any damage. Or go with Phil's suggestion, using aluminium angle........cheap, and gives you plenty of gluing and screwing options. Don't think I'll go any further with that one at the moment!!!

http://www.jaycar.com.au/productResults.asp?MID=12&SUBCATID=1004&CATID=84&keyform=CAT2#12

Also that front slope on roof is an ideal spot for a couple of panels, as you can park the 'van facing north, and get better insolation.

I feel the roof rack option will create more problems than it will solve.

Bob