sloped roof

[Mako_Kupo]

hey guys a few of you may know I'm rebuilding a '79 ford coachman class c , 20 footer. so far I have the floor and all walls built, but need to do the roof next. a few questions:

its a 20 foot roof, should I build it on the ground and raise it up, or should I build it on the walls while they are mounted? I have step ladders.

do I need to pitch the roof? it came factory with a very, very small slope on the roof and while I taught myself a lot so far, I cannot figure out how to measure/cut these sloped pieces. I'm talking about the beams that run like a ribcage down the roof of the whole rv, from side to side. they have a very slight arch, probably just enough to let water run off. my questions is this:
do I need to slope it? if so, is there a cheat method so that I don't have to Individually tracer and cut all of these? thank you! its getting cold lol.

[Mako_Kupo]

I went to the store and got a new circular saw blade for framing, and holy ****. the difference is astounding, I had an old blade on there used for various projects and it cut fine but the laser wasn't accurate and you couldn't use the sights. now, with the new blade, the laser is 100% perfect. the first piece I did is a 100% accurate, perfect roof beam that is 1.5" at the ends, and 2.5" in the middle, an 89" stretch. there is 20.5"In the middle that is flat, to accommodate for the AC that is huge(15k upper limit Coleman). I think its a good slope, the only place there is stuff in the middle is the AC, so water won't be pooling anyway.

there is one 14" fan over the main bed, but that is on a different slope with different wood so for that, I can do different cuts anyway with a full slope on the whole piece. do you think this is a good idea? I think its best for the AC since its completely flat bottomed and wide as heck.

[Mako_Kupo]

haha the closest thing to a bandsaw I have is my jigsaw. I tried to circa saw, and messed up two pieces in a row. tried the jigsaw and while not perfect, it actually is accurate(~5%). I figure I can do all of them, then C clamp them together and sand them all at once to make them identical. as long as they are the same relative to each other, and there is some slope, its all good. PITA. over 200 hours into this so far, and am now just about to put walls on haha. big, big job...

[72cougarxr7]

A band saw would work nice, a sawzall would probably do the job as well.

[DrewE]

Mako Kupo wrote:
well I do have a few beams intact from before, but overtime I try to cut them, I bend my jigsaw blade and it messes the expensive wood up. a circular saw would actually work too? I'm concerned about being able to turn it, but I suppose it doesn't have to turn much does it. ill give it a try, thank you so so so much!

You can't really turn a curve with a circular saw. Instead, cut a series of tangents that approximates the curve you want. If you're particular about the finished product, a bit of finishing up with a belt sander and a coarse belt would smooth out the bumps left. That's probably not necessary in this case.

[Mako_Kupo]

well I do have a few beams intact from before, but overtime I try to cut them, I bend my jigsaw blade and it messes the expensive wood up. a circular saw would actually work too? I'm concerned about being able to turn it, but I suppose it doesn't have to turn much does it. ill give it a try, thank you so so so much!

[byronlj]

I saw a seller on Ebay that sells rv stuff. He has a bunch of aluminum or wood trusses in various sizes. You could try searching there.
Dave

[DrewE]

CJW8 wrote:
Keep it simple. Take a 2X4 long enough to span the walls. Lay it in it's side and draw an arch, starting on one end 2" from the bottom and ending on the other end 2" from the bottom where the top of the arch is the top of the 2X4 or 3.5". If you want more insulation or need room for duct work use a 2X6 and arch it so that it is 3" on the ends and 5.5" at the center. Cut the first one and use it as a pattern for the rest. Always use the same one as a pattern. The arch will be gradual enough you should be able to make the cuts with a skill saw.

This is a good plan, and very similar to what I was thinking of with plywood. Substitute "plywood" for "2x4" and that's about it. Probably the 2x would be easier to attach the roof sheathing to in a sturdy fashion. Plywood might be a little bit stiffer, but I would not bet much money on it.

If you have access to a bandsaw (and a friend or two to help), the cuts would be a bit easier. A circular saw would be practical, as suggested.

[CJW8]

Keep it simple. Take a 2X4 long enough to span the walls. Lay it in it's side and draw an arch, starting on one end 2" from the bottom and ending on the other end 2" from the bottom where the top of the arch is the top of the 2X4 or 3.5". If you want more insulation or need room for duct work use a 2X6 and arch it so that it is 3" on the ends and 5.5" at the center. Cut the first one and use it as a pattern for the rest. Always use the same one as a pattern. The arch will be gradual enough you should be able to make the cuts with a skill saw.

[MEXICOWANDERER]

Been There Done That Dept...

Build scaffolding then run cross pieces to stand on. Ladders are tiring. I laid down a mattress padding from a chaise lounge and laying flat I could work for hours. I couldn't believe how easy it was to sell the scaffolding after I was finished. Something like this is in high demand. It ended up costing me labor time. An RV dealer purchased it!

[theoldwizard1]

If you have good solid walls in place, build the roof on top of that. Check the rafters on the Jayco Magnum roof.

Time/weather (temprature) are against you, but if I was doing the job, after I got the rafters installed (16" on center spacing) I would sheet the roof with 3/8" plywood and then cover that with epoxy and 22 oz. triaxial fiber glass. You could use 1/4" plywood (not luan) if you did 2 layers of triaxial fiberglass. The only thing more durable than fiberglass is aluminum.

There are 2 big problems with roof systems

• Finishing over the edge and on to the exterior wall. This is a CRITICAL joint to prevent water intrusion into the wall. Sorry, no good suggestions.
  
• Sealing any place were something comes through the roof. With a pitched roof, so not make any holes along the center line. I think I would use butyl tape on the inside and a good caulk on the outside, plus some type of plastic/aluminum flashing. With flashing, the fewer the joints the better and they should be on the "downhill" side if possible. You might consider 'glassing the flashing down.

[Mako_Kupo]

the last option sounds interesting, and doable. I've taught myself to use a speed square, and can now cut decent angles. I don't want to cut any corners(like being cheap/skipping crucial steps, as ill be living in this for several years minimum), but don't have too much time left to learn ya know? can you give me a few more details of this method please? I don't mind taking a whole day to cut the pieces, I have an Ebay shop and am literally done at 10-10:30 each morning so I have time(daytime, but winter is near).

[DrewE]

An arched roof is much preferred to a flat one. The flat one will nearly always sag slightly and then have a constant puddle.

My '98 coachmen uses simple welded aluminum trusses to get this bow shape. I think the rise in the middle is about an inch or two above the ends. I suspect you could build up simple wooden bow trusses without overly much effort. One approach would be to build up the bottom and top chords from two pieces of wood, glued together to form a T cross section, and then have a few thin plywood members in between them attached onto the vertical part of the T. You'd basically just need graduated heights of plywood bits. The top one should be glued together in a bent shape (use shims when clamping it) or it will be far too stiff to bend well afterwards (and the whole will be under considerable stress if you do get it bent).

You could also just use heavier plywood pieces cut in a segment shape, sketching the rounded top with a string and a pencil adjusted to give an appropriate outline. That is a lot of individual cutting; with e.g. a bandsaw it could be simplified by laying one out and pad-sawing a few at a time by stacking several strips of plywood and cutting them simultaneously.

[newman_fulltime]

if front to back set all the rafters in their spots run a tight string down the sides of them at the wanted slope then mark where the string touches and cut each stringer.

[ScottG]

It's always best to have some slope so water doesn't just sit but either way will work.