Teardrops n Tiny Travel Trailers

Hi all,
I am working on my first build and am almost done. Question for you: what is your opinion about the roof substrate. I had originally planned to use 3 mm birch ply as the sub roof (glued and screwed to sidewall edge and spars) with aluminum over. But now I am thinking about just installing the aluminum. Note: I have 30 inch high front and rear bulk head walls at the front and rear exterior that are 3/4 ply, roof spars that are spaced every 7 inches up the side and over the front and rear curve, and then spars spaced every 11 inches ( except at the fan where the two 2x2s are 14 apart). The aluminum is .040 and bendy but firm I think it is 5052. there is hard foam insulation between spars up to the roof line.
I'd like to save the weight and extra step of installing the ply sub roof, what do you think?
Many thanks in advance,
Mariann

I like the idea of sealing and painting a solid box. Then the aluminum. Very little cost and time for extra piece of mind

I would install the plywood. If nothing else, it will help avoid dents and dings in your skin.

Thanks you all, sounds like the sub layer of ply I the way to go. Another question what is the best adhesive for the aluminum on to the ply?

Have 1/8 inch plywood under mine.Most people "float" the aluminum on top with no adhesive and use the trim to hold in place.I did use some caulk on the edges to keep water out and a few small nails on edges to hold in place before the trim molding was put on.

Thanks Steve. I'd rather have some adhesive is anything recommended in this case?

Yea,float the aluminum trim will hold it!

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mariannf, It's been some years since I built my trailer, but I think that I used a Carpet adhesive to attach my aluminum sides and top. Note, that if a adhesive is used, be it contact adhesive of carpet glue, it will most likely let go in the first high heat. At that point it will be floating and held in place by the trim and screws. My roof aluminum has about 1/8 to 1/4 inch air space between the ally and ply, to where if I push it with my thumb, it flexes in until it contacts the ply below. BTW, I did use 1/8" ply under the roof as a substrate. Like someone said before, it reduces denting, and increases overall rigidity and strength. I would highly recommend the ply substrate. Glueing the aluminum is optional, but may help in fitting and trimming of the aluminum. I seem to remember my sides went on first with the carpet glue and a couple of narrow crown staples which I placed under the trim, then I used shears, snips, & files to trim the ally to the trailer. Then I put on the top and again trimmed it at the edges. Then came the trim all bedded in RV putty tape, followed by a Urethane caulk. I had better luck with urethane sealant like Sika Flex vs. silicons or acrylic caulk. Most of the sealing is done by the RV putty, and caulk helps with corner where trim butts together or where water may puddle. Hope that helps.

Jerry Bleeg wrote:mariannf, It's been some years since I built my trailer, but I think that I used a Carpet adhesive to attach my aluminum sides and top. Note, that if a adhesive is used, be it contact adhesive of carpet glue, it will most likely let go in the first high heat. At that point it will be floating and held in place by the trim and screws. My roof aluminum has about 1/8 to 1/4 inch air space between the ally and ply, to where if I push it with my thumb, it flexes in until it contacts the ply below. BTW, I did use 1/8" ply under the roof as a substrate. Like someone said before, it reduces denting, and increases overall rigidity and strength. I would highly recommend the ply substrate. Glueing the aluminum is optional, but may help in fitting and trimming of the aluminum. I seem to remember my sides went on first with the carpet glue and a couple of narrow crown staples which I placed under the trim, then I used shears, snips, & files to trim the ally to the trailer. Then I put on the top and again trimmed it at the edges. Then came the trim all bedded in RV putty tape, followed by a Urethane caulk. I had better luck with urethane sealant like Sika Flex vs. silicons or acrylic caulk. Most of the sealing is done by the RV putty, and caulk helps with corner where trim butts together or where water may puddle. Hope that helps.

Thanks Jerry! I will go with floating the aluminum as many have suggested. It looks many have also used a flexible caulk or sealant along the underlying perimeters between ply and aluminum as well as at the joined points of the trim and in the screw holes. Question: when joining edge trim should I first underlay it with Rv putty and then once down apply some caulk or sealant at the joint?
Many thanks!

Yes, use the butyl/ rv tape under all the trim, screw it down tight enough to have some squeeze out, trim off the excess with and then you can add a little urethane caulk anyplace water may puddle and get in. when the trim gets hot, you will probably have more squeeze out of the rv putty. So don't go crazy with the caulk. Let the putty run its coarse for the first year.