Installing Flat stuff on a curved roof

[Diemjoe]

I have a 9"x48" sky light and a fantastic fan that I am starting to fit between the roof spars. I am wondering if there are any considerations and tricks around their placement so that they lay flush against the curved ceiling, both inside and out.

I would also like to put in cross members between Spars for added structural strength and mounting screw points. The spars are at odd angles to each other so I am looking for some quick carpentry tricks on how to get them to fit nicely. The other problem with the cross-members is that they would be flat against a curved ceiling, Do I need to cut them to the profile curve too?

[KCStudly]

You may find the method I used for leveling my roof vent fan to be useful, assuming that your window is in a low crowned portion of your roof.

My roof has a gentle arc to the profile over the main part of it where the roof fan is and I wanted to make sure that the vent flange had a flat area to land on. I made the flat top/curved bottom side framing for it in this post.

Later on, halfway thru this post, I added some tapered shims to the front and rear spars to level out the rest of the flange.

I am covering with canvas and paint (… maybe epoxy instead) in the Foamie fashion, so I will be able to fair this slight difference in easily with some filler prior to covering, but if you are skinning with aluminum and your offsets are more severe, you could add some more framing around the outside of your flat, a ledge that matches the roof profile; let your roof skin land on this outer edge then form a sheet metal cap (like a top hat) that covers the level area and overlaps the roof skin. Consider having the flat area be a little larger than the window flange all the way around to have a bit of a reveal.

[Diemjoe]

Thanks, I will give it a try

[dales133]

Only other way witch I was considering on a curved roof or similar is to frame the fan hole out 1"1/2 bigger all round than required then add 3/4 x 2 " or whatever ends up flush with the ceiling sits about 1/2 inch higher the the finished roof hight all the way around and mount your fan to that

[KCStudly]

Kind of like a recess skylight or light well. Would only have to be tall enough to "celebrate" the difference and make it easier to trim, rather than impossible to blend.

I figured I would just use some foam weather strip on the inside trim flange of my vent when the time comes, sense my roof arc is so slight (520 inch radius on the inside surface of the ceiling), but on the outside where the weather needs to be sealed out I wanted to go to the extra trouble of making it flat.

For a window trim clamp ring that secures the window in the hole, you probably do want to make both inner and outer surfaces flat, especially if the curve is greater than what RV putty and sealer will accommodate in a proper tidy fashion.

[Nobody]

Unless your arc radius is very short, it shouldn't make a lot of difference whether it the framework is flat or curved, unless your skylight will 'run' lengthwise' of your profile. If the skylight is running crosswise, a 9" flat frame shouldn't make any difference in your profile & should be near invisible on the finished trailer. My TD cabin is 60" wide by 114" total length with a fairly long radius at front, a much longer radius on top, & a short radius at the rear of the hatch. My spars (& fantastic vent framework) were cut (ripped) from 2x4 spruce making them about 1.5x1.5" (give or take a little). I did 'curve' the lengthwise pieces slightly (to match the curve of my profile), primarily so the interior ceiling would be the same throughout its length. The 'flange' of the fantastic vent is some kind of plastic or vinyl, & with a good bead of RV putty tape it conformed easily to the very slight curve. My TD was completed in 2006, & almost 9yrs & 25K+ miles later there have been absolutely NO leaks around the vent/fan... As KCS said, you may want to add some tapered/beveled shims on the outside to have an absolutely 'level' surface for the 'flanges' to set but in my experience that is probably an unnecessary addition.

[Kaz]

I find myself with the same dilemma, I'm hoping to take the heat gun to the fan flange and massage it to fit the roof.

[dales133]

I find myself with the same dilemma, I'm hoping to take the heat gun to the fan flange and massage it to fit the roof.

I'd resist the urge to do that because it could warp the entire thing and cause bigger problems.
It realy is pretty si.ple to build the area around the fan up a small amount with will eliminate potential damage to the fan cover seal or frame/seal to roof of the fan.
They arnt that cheap if you break it

[KCStudly]

I was thinking the same thing and some plastics are real touchy with heat; I can see a nice white (and expensive) trim ring all blistered and charred from too much heat.

For my MaxxAir vent (which I assume is similar to a Fantastic Fan) has a sealing flange for the outside. This sits on and is sealed to the flat surface of the roof. The fan assembly sits down inside of this and seals on the vertical wall with a shrouded gasket. The inner trim ring is just that, a trim ring. The height gets trimmed to suit the thickness of the roof and it inserts up into the well formed by the fan assembly.

The plastic that all of these parts are made of is pretty thick and sturdy with stiffening ribs molded into the faces of the flanges (these presumably help to bed into the RV putty tape, as well).

Like I said, for my inner trim I think just a soft black foam gasket would fill the slight gap on the sides and form a shadow line that would look better than a gap. For a tighter arched profile that needs a little something more, you wouldn't have to build in anything, you could just make a wooden trim ring (or even just two side shims) and sandwich it/them between the ceiling and plastic fan trim. In fact I haven't ruled that out for my build since it would give me the opportunity to match the other Maple trims throughout my build.

Hope this gives options and ideas on how one might do a window, too.

[Diemjoe]

Thanks for all the responses. I got the ceiling in yesterday so I am hoping it won't be long before I can tackle this one with all of your suggestions. Except melting the plastic. ;-)