Housewrap for skin?

[KCStudly]

Aah, that is different. You may have an advantage of scale when buying material in bulk.

Consider a low crown roof instead of peaked.

[wagondude]

Do you have any drawings of your design? If I get to build anything, it will have to be in the 14-16 foot range in order to convince the wife to use it. I'm really having trouble deciding on a layout. I'm looking at production units to get ideas, but when she looks at them, she gets the wrong ideas.

[Mojave Bob]

I am considering a low-crown roof, but so far haven't decided. A crown is inherently stronger, but in using foam, I have to put a lot of kerfs in it that have to be re-glued. Either that or laminate up multiple thin sheets of foam, and risk not having full-surface contact for adhesion. I'm not sure if the resultant structure would be as strong/fracture-resistant as a peak, which has only the ridge-seam. What are the thoughts of the experienced on this? The roof will be spanning 6.5', and I am shooting for roughly a 6" rise at the peak. I will also need a flat spot to mount a fan/vent, but with foam, I can shape that in for either roof style.

On the topic of fan/vents, I know that Lil Snoozy mounts a fantastic fan in the bathroom end-wall. It seems to me that the fan is really designed for roof mount, and mounting it vertically negates the water-shedding design of the vent cover. This leaves the piano hinge exposed to the top surface, and is more dependent on the foam seal to keep things dry. I don't think there is a big risk of water coming into the camper, but it seems the motor may be exposed to more moisture that way. Has anybody had any experience with these fans mounted vertically?

[lthomas987]

Most everyone here has kerfed their roofs or walls at some point or another. I personally was very worried about the soft flexibility of the foam sheets after kerfing. The process of gluing them to the sides stiffened them up a bunch and I was happier but still nervous. I was STUNNED by how much stiffer everything got after I covered it with fabric. it is VERY rigid. Now I don't have a ton of extra kerfs. Most of my kerfs close up tight on the inside edge.

The answer is of course the foamy way TESTING!

I would buy a sheet of foam even 1" foam and kerf it about 3/4 the way through and make yourself a test curve. You can also use part of it for fabric testing with housewrap, and assorted glues.

[KCStudly]

Re: the crown roof, I have a 520 inch radius crown front to back on my Benroy-esque roof profile (5 x 9'-8"). I found that I needed spars (a mixture of cedar and poplar 1x2's on edge with 2x2's around the vent fan) just to keep the inner 5mm plywood panel from sagging during assembly (the ceiling panel with spars already attached went in first and the foam will follow soon). My original plan was to only rely on the cabinet face frames and bulkhead, thinking that the crown would be enough to stiffen the ply while assembling; but it was not enough. Once I had the spars on and the inner ceiling skin glued to the walls, there didn't seem to be any reason to remove the spars, so I will be filling between them with 2 layers of 3/4 inch foam. Seems like I might be able to form the foam to the low arch and will only need kerfs at my tightest radii. I compensated for the curvature under the fan by installing a couple of tapered shim pieces (about 1/8 inch difference front and rear vs. the tangent point).

I'm of the mind that filling and gluing each and every kerf is not needed. The foam core is the compression member that's sole purpose is to hold the inner and outer skins apart. The skins handle the applied loads.

If you want to try it without spars, you could maybe build your composite roof on a fixture, then install it in one or two sections, or (something that I considered) install temporary supports inside to support the ceiling while building. In the end, for me, adding the spars and leaving them was the most expedient solution from both a cost and time standpoint; weight not being as big of a deciding factor for me.

Another option would be to use low arch open truss spars with concentric chords, built up from bent 1x chords and ply; or possibly just glue thin 5 mm ply ribs (cut to the arch profile) imbedded between the foam sections, taking the place of spars. Would have to think about assembly sequence some more on the later.

The logic behind side wall mounting the vent fan can be twofold. Some people want absolutely no penetrations in their roof membrane. For some the opportunity for leaks at the fixings (screws and caulk) outweighs the chance of leakage past the fan lid.

Others want to keep their build heights low enough to be garage kept, and locating the fan off of the roof can save a few precious inches under their garage door headers.

[Mojave Bob]

Wagondude -- As of right now, I don't have any drawings that are fleshed out enough for posting. Just a couple of quick sketches. I tend to do most of my pre-engineering in my head, and put in on paper shortly before build, or if I have close tolerances to calculate. But, as a quick description, it is to be a rear-entry trailer. Immediately on entry, the bathroom is on the left, and a small coat/broom closet is on the right. Just forward of those, the galley is on the left, and a "living/dining room" on the right - basically an open floor space with a fold-down table and two comfortable REAL chairs. Forward of that space on the right is a wardrobe closet, and then a walk-around bed is in the front, with storage underneath. There are to be upper cabinets spanning the distance between the two closets on the right.