On top of the roof we will be putting solar panels, so we will want a rigid attachment point for security reasons. Solar panels also perform up to 60% better if they can stay cool, so raising them up off of the roof is a smart move. Making them less noticeable is a good idea as well. The best way to mount them is on a ladder rack.
Rather than buy a roof rack, I salvaged some galvanized superstrut type B steel struts from a local junkyard, cut them into uprights and crossbars and then painted them white. They were fitted with end plugs and bolted onto the trapeze before putting on the roof. The solar panels will be bolted to superstrut stringers that rest on the ladder rack and are bolted there. We will go into more detail on the solar electrical system later, but it's important to understand the need to bolt on the ladder rack uprights before fitting the roof.
A watertight roof is critical to the trailer's longevity, safety and comfort. There are hundreds of amp-hours worth of batteries in here, clothes and bedding, and a propane heater. Basically a tiny house trailer is a big pile of kindling and accelerators, all in one, so keeping it dry is a large part of keeping it safe.
Wood also loses strength quickly when wet and rots, which is a common trailer killer.
For our build, I made a double layer of the skinned 2" foam, giving us a 4" R-27 roof. Each layer was attached with heavy duty liquid nails, each joint staggered/lapped to improve the strength and water resistance of the foam even before I applied waterproofing.
At that point I had two options, liquid EDPM compound, or a cold-process roof, both of which tend to be pricey and a little complicated. Alternatives to traditional cold-process roofing exist. To save money, I used returned 60-mil PVC shower pan liners. These are available in 5- and 6-foot widths, and when returned as wrong lengths to the store they are typically sold at about half price. I was able to cover the roof for about $70 with the stuff, bought over a few weeks time, which eased the purchase.
Pan liner is very tough, so wear gloves and cut it with a box knife with a hook blade. I cut and ran a 8" band around the edge of the roof and folded it over onto the roof. This formed a watertight drip edge. Then I laid the top panels onto the roof and lapped them from back to front. This allows water driven along the roof when driving to not be driven into the roof joints. We then overlapped the panel sides down onto the edge band and glued it there, giving me a strong seal. If you are penetrating the roofing with a ladder rack or skylight, I strongly suggest pushing the penetrating material upward through a smaller hole than needed and adding an overpatch for strength. This will give you a tight seal and help roll water away from the joint formed. High quality full silicone caulk will stick to this stuff, and I pumped it under all of the joints in the roofing before gluing any panel down.
Errors:
I made more mistakes on the roof than everywhere else.
The pan liner joints need to be wide, and well glued. I was stingy with glue in a few spots on the deck, and let the glue dry too much before rolling the joints. As a result, I had several dry joints that failed after a good hard rain. The foam panels limited the damage to a few drips. Re-gluing the joints fixed the problem, but I should have checked the joints after a day or two, and I didn't. Laziness can cost you.
My second error was I set the window too low into the roof, flush with the first layer of foam. This meant that in order to avoid a lake on top of the window, I had to run a drain for the top of the window tothe side. After some cussing about getting a watertight drain in place, I said screw it and further covered the triple pane window well with a Lexan sheet laid flat to the top of the roof. I found the sheet for $7 in a hardware store and laid it into a fat bead of full-silicone caulk. 3''x4' Lexan sheets are usually $70, so that was probably the deal of the week. Lexan will protect the window from bad things like hail, and water now runs off of the flush mounted panel instead of accumulating on the window to look for a leak before draining out the pipe I put there.
I do see some minor condensation under the Lexan in cold weather, but nothing major.
I'll post some pics of this later.
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