New roof checklist (reframe) this weekend

[Thenoob]

Got a helper lined up, reframing the roof on the 73 d19 dodge.  Plan is to arch as per the tutorials on here, finishing with a new rubber or pvc membrane.


The check list:


New section is approx 16.4 feet. Planning as follows:


1. 2x4 arched trusses x 12 - 24" off centre doubling up at vents (have 2) cut to 3/4" at sides arching to full height at centre.  Glued and screwed at sides w stainless screws along sides of coach.


2. Below that running new sheets of frp x 4.


3.  Insulation plans - pink board insulation ? Looking for opinions on thickness/R rating.


4.  Top layer - looking for input for thickness, was originally planning on 1/4 or 1/2" marine grade plywood? Recommended Seam sealer?


My questions...


1.  The front nose cap metal. Should that simply be screwed into the top layer marine plywood? Before or after membrane? I'm imagining running the membrane underneath the front nose just slightly and screwing down on top and running dicor? Am I totally wrong?


2.  My top layer thickness... too thick and the ladder will have a hard time screwing back down?


3.  Don't really have plans for Solar but just in case should I run some cable up there to the exsisting panel just to have there? If ran to the roof, best way to "leave it up there? " or best place to run it too? I'm guessing back towards the rear as the panel is closer to the rear,...or the closet?? Looking for input. 


Lots of questions, but I want to pre-plan as we are planning to do the job on Monday.


Pics of the current roof:




http://i46.photobucket.com/albums/f117/bigruudz/Mobile%20Uploads/87C5128A-F85A-4E4D-80A5-DB23896AD56F.jpg


http://i46.photobucket.com/albums/f117/bigruudz/Mobile%20Uploads/7F7C0353-28C9-4F7F-8577-FAF12E2D2A92.jpg


http://i46.photobucket.com/albums/f117/bigruudz/Mobile%20Uploads/88A3580D-281D-4734-8878-DA5F3D67303A.jpg

[TerryH]

A few comments, all are my opinions only:
Check List #1.  Why do you want to double up on the trusses at the vents? Double the weight and not required for a 14" x 14" hole. 24" on centre means 22 1/2" between trusses, so only 8 1/2" overall between the vent and trusses. If the cutout is for an A/C unit, add cross braces.
                #4.   To me 1/2" would be both overkill and over weight. Given that you are putting a positive arch on the trusses 1/4" is more than adequate.
Seam sealer - consider 3" Eternabond tape. Fast and easy to apply, very effective, no wait for curing, no mess and, dependant on your final roof sealant, no compatibility issues.

Questions #2  If your concern is that the new roof will raise the ladder overall, your photo appears to show sliding escutcheons that fasten to the roof. If so you can cut the required amount (taking into account the flaring required) from the ladder tubes and effectively lower the ladder. Plates between the escutcheons and roof would be a good idea. Should have been there on all RV's originally.

             #3  Common practice dependant on access is to run the wiring down either the stink pipe or the fridge vent and the pick it up inside.

Not an expert, just offering suggestions.

[brians1969]

1. Since you are going to be cutting the 2x4 to get the arch, they will be much lighter weight (and less strength). If you have an a/c up there (or planning), definitely double up both sides.  Doing the vents may be overkill, you will be framing in for the 14"x14" anyways. You can decide when you're up there.

3. I used fiberglass insulation. Because of the arch, I couldn't conceive of how i would fill the cavity completely with rigid styrofoam. I thought it would not be good to have empty spaces. I'm sure you'll find opinions that fiberglass shouldn't be used in a camper.  Someone was telling recently about a new product called Roxul. It's a mineral wool insulation that won't attract vermin, doesn't absorb moisture, and I was told that it doesn't need a vapor barrier.  Maybe talk to an expert about it? I haven't done any research on it.

4. It looks like from your pictures that there was a capability for storage on the roof. I wouldn't recommend putting anything up there.  As far as the 1/4 or 1/2 inch....once you get a few of the rafters up, throw a piece of 1/4 inch plywood on them and try crawling on it. You decide. Even though you will have a new roof, you will be climbing up there at least once or twice a year for maintenance, cleaning, resealing, etc....

[Thenoob]

These are great replies and I now agree about doubling arches for vents is a waste, they are light and you guys are correct.


I don't have an Ac unit and most likely won't add one.  I need to come to that decision pretty much now as I don't want to cut into the roof later.


I was worried about 1/4" because I wasn't sure of how much the arch would be on the wood  and that it would hold its strength and not start to snap. 


Fibreglass is a good idea for covering everything, I'll look into Roxol.


Thanks so much for the Input!!!!!!

[brians1969]

You could always frame in for the a/c. Then if you ever decide for a/c, it would be a simple matter to cut it out. Or you could put a vent in to act as a "placeholder" for the a/c unit.

If you put 2 of your cut down 2x4's on the ground at whatever distance you plan on having them, throw your plywood on it and crawl or walk on it. It will give you an idea of the flexing and you won't be way up in the air. :-)

Marine plywood is very expensive isn't it?

[Thenoob]

For some reason it's very expensive here
4x8 1/4" was 70 bucks a sheet (Canadian)


If you guys are saying 1/4" will do the job I believe you guys.  Lots of guys on here who have done this job.


What's the average opening needed for an ac? Standard vent size?

[TerryH]

The actual arch gives the roof more integral strength. Consider a bridge span. If it were flat it is inherently a weak structure. Add a positive arch and you greatly increase both the strength and the resistance to load weight. Degree of arch doesn't - in this case - have to be huge. The fact of the arch is what works in your favor.

[TerryH]

Also, while framing, don't make the mistake of forgetting whatever you are using for the interior ceiling and how it will be fastened. If you are using 4' material you want to maintain 24" on centre truss spacing. If you adjust off the spacing you may have difficulty fastening the interior panel, particularly where they adjoin.

[Thenoob]

I'll be using frp
On the original design, how did the crappy
Hardboard attach?


I always thought they were just layed across and screwed on the ends?

[TerryH]

Generally also fastened to the trusses side to side as well. Helps to eliminate 'droop'. Joints covered with a tudor style finish strip.
Try Windsor Plywood, 7th & Fir? or Smith plywood in Langley for your plywood. Better prices and far better selection and quality than big box. Windsor also may carry or be able to suggest a better supplier for FRP.

[Thenoob]

Ya I went to Windsor for the marine
70 a sheet made me meeeeeehhhhh


I'll check back for normal 1/4" plywood
Any certain types you guys recommend?

[TerryH]

Another one to try is PJ White. East Kent, south of Marine, between Knight and Fraser. Marine plywood and hardwood specialists.

[brians1969]

I didn't end up going with 1/4". That's why I'm saying you should evaluate that for yourself.  You're in Canada, think snow load. You're going to have (an actual) 1 1/2 x 3/4  24" o.c. rib. Cut an actual 2 x4 up and block it up off the ground and put your weight on it. As Terry mentioned, the ply will stiffen things up, but do some "on the job evaluating".

I think marine plywood is a bit overkill. Both marine and exterior use waterproof glue. The difference is marine ply has no voids.

[Thenoob]

What did you end up going with?
I'm lucky I went out and spent the money for a nice 20ft tent that the motorhome stays under.
Rain and snow don't touch it thankfully. Best 700 I ever spent lol.


But what did you end up going with? 3/8? 1/2"?


Thanks for the info!

[Rickf1985]

Here is another option. Go with the 1/4" but on your rafters put in a cross brace front to back a third of the way in from either side. This will give you some support. As far as Marine vs. standard, go to a site called "Rot Doctor"(http://www.rotdoctor.com/) and look for their CPES epoxy. It is a epoxy resin that has the consistency of diesel fuel and you can paint/spry it on the plywood for a totally waterproof finish. Coat the edges of the wood, 2x4's included, and it seals the grain and plywood against moisture from wicking into the grain. That is where rot comes from. The resin is wood based and remain flexible enough to not crack like polyester resins. I use it in any glass work I do. They make all kinds of resins for any type of glass work you are doing. Not real cheap but you get what you pay for. And they are out in Washington State so they are close for you West coasters.

[Rickf1985]

The actual arch gives the roof more integral strength. Consider a bridge span. If it were flat it is inherently a weak structure. Add a positive arch and you greatly increase both the strength and the resistance to load weight. Degree of arch doesn't - in this case - have to be huge. The fact of the arch is what works in your favor.

Terry, I am not sure you gain any strength in this case considering the "arch" is actually a cut down 2x4. The base piece of wood is a straight piece and is still the same straight piece regardless of the arch cut into it. It will actually be weaker that the original 2x4 due to the loss of material at the ends. You might gain a very small amount in the positive arch of the plywood but that will be offset by the loss of the wood on the cut. Overall what you are looking for is a roof that sheds water, not a party platform. It will work just fine for that.

[Thenoob]

Good to know
Thanks for that link!


Question about the front metal, how should that be attached to the rubber roof once laid down? Super wide eternabond? Screwed? Both?