Roof Collapse around A/C - Now leaking

Under the rubber membrane and over the existing sheathing... good idea. That should make sealing the topside much easier.

Did you apply adhesive before setting the new plywood? I would have applied adhesive to the repair patch before sliding it in place for added support and strength.

Do you plan to screw the patch to the roof sheathing from the underside?

These pictures are much more descriptive of the problem. Had they not cut that lare aluminum brace so far back you likely would not have had this problem. Should have left it overhang the joint a couple inches.

Good luck and I hope it works well for you.

Thanks again for the help. I have decided to go with plywood above the existing wood roof but below the rubber membrane. I cut a piece of plywood 20" x 20". I cut a 14" square hole in the middle and cut a 45 degree angle on all the outside edges and sanded them off a bit. I cut it in half so I was left with 2 U-shaped pieces of plywood. I pulled up the rubber membrane (not an easy task) and slipped the wood in between the membrane and the existing wood roof. This will allow me to level off the roof, provide a solid surface to seal against and as the added bonus of raise the A/C unit 1/4" to prevent any future puddling near the seal. I must say it looks pretty darn good right now. I ran out of daylight. I still need to fasten the plywood to the roof using the advice on this thread. I have a new A/C seal in hand and will set the A/C unit back on soon.

I wish I would have taken a picture of the plywood pieces before I installed them but I will take some pictures before I re-install the A/C unit so others can learn from my (hopefully good) experience.

Here are a couple of extra pictures with the A/C off. I'll share more with the fix in a few days, maybe this weekend.

That is why I was thinking to "sleeve" the joint with channel iron that fit tightly to the plywood. The extra layer of plywood around the opening is also a good idea as well. The key is to bring the two free ends of the plywood back up together and make it all one piece.

westend has a good idea by sneaking in an additional roof rafter, but I'm not sure he'll get the $4490 check in the mail anytime soon.

Figuring the OP's camper roof is built in a similar fashion as ours, it's made up from a laminated construction, much like the walls and floor. Under the roofing material you get some luan plywood, ~ 2" of Styrofoam and then another piece of luan plywood with a finished surface for the interior. You also get some rectangular aluminum tubing that runs side to side, spaced every 16" (I think) on center for structural support. That's about it.

The tubing is surrounded by the Styrofoam, so I don't think the OP will be able to sneak in an additional roof rafter or joist. The open area you see in his pictures stops at about 10" inward (if like ours) and allows for the AC ducted air flow throughout the roof. It's only that open area on each side for air ducting that leaves the plywood joint unsupported, go inboard that 10" and then it's backed/supported by the Styrofoam insulation.

If you do as westend suggested and you use good quality adhesive, once it sets you may find you do not need fasteners along the new rafter, only on the ends where the box frames the hole to hold it in place while the adhesive sets. Modern adhesives are stronger than the material they adhere.

Any half-way decent carpenter (I count myself in this group) would tell you that sheathing is never installed without the joints supported.
It's difficult to get perspective from the close-up pictures but I will assume that the unsupported sheathing joint runs from side to side. Even if the opposite is the case, the cure is the same.

Here is what I would do: What the intention is, is to install a roof rafter underneath the length of the unsupported joint. It appears that the unsupported joint is a few inches from one existing roof rafter and a greater distance from another. I would first cut apiece of lumber that is the same dimension as the existing rafters. For this discussion lets call that 3 1/2", the dimension of a standard 2 x 4. I would estimate that the length of the unsupported joint is around 3' (8' width less 2' cutout). What ever it is, cut the new 2 x 4 rafter 1 1/2" less than that 1/2 span.
*Here comes the tricky part*--measure the offset from each existing rafter to the unsupported joint. On your new rafter piece attach filler blocks on the narrow offset side (one each end and one in the middle). On the side of the new rafter that faces the larger off set, make a triangle that will span about 2/3 of the distance of the new rafter, the height of the triangle being the same as the off set less 1/8" or so and the 3/4" to center of the new rafter and attach that so the peak of the triangle is at centerpoint of your new rafter (1 x 3 would be my material of choice for this triangle). You should now have a new rafter that has three blocks on one side and a triangle attached to the other side. Fill the triangle, the spaces around the triangle, and space between the blocks with insulation (I'll let you figure out how to do this). Put glue on the top and bottom edge of your new rafter, on the blocks, and anywhere else the rafter assembly will make contact and slide it under the unsupported joint. you should now have a rafter under the joint except for the last 1 1/2" adjacent to the hole. Cut another rafter sized piece, the length of the AC cutout and attach that in the same manner, including fasteners that attach to the new rafter. Repeat rafter installation on the other side and box in the remaining two sides of the cutout hole. You may feel it's necessary to run fasteners in from the top and bottom but I would forgo that until you estimate the strength of what results without them.

If you wish to know my mailing address to send the $4490 or wish to have a drawing, send me a PM. :B Good luck with the roof.

Edut: Forgot to mention---If the AC cut out area has a dip towards the floor, jack and brace the ceiling on both sides before installing new rafters and box. I used a "T" made of 2x4 and a bottle jack to raise my ceiling for rafter installation.

It looks like they cut the AC hole through a joint of two pieces of plywood. It seems like they would not join sheets where they intend to put an opening. Structurally, it just seems like an awful idea. I would attempt to use something lightweight to reinforce the hole such as aluminum angle iron. It won't rust, and it's light enough to not cause any added weight. You you have to remove that AC unit to really see what's up under there. You'll need some help. When I removed mine, it was pretty heavy. It took one man on each side to lift it clear without doing any damage to the rubber roofing.

I just took a look at our '08 Rockwood Roo (a hybrid model), but which I'd suspect is quite similar in construction in this area. I removed the plastic interior trim/cover and I find no area in the AC opening that contains a joint between two pieces of luan plywood, it's one piece with a hole cut in it.

On our Roo I had removed the AC unit to replace the gasket a while back. As part of the process, I decided to build up the mounting surface (I'll call it a "curb", you can see it just above the edge of the roofing material in the photo). The curb material is just some trimmed pieces of poplar trim boards. After installing the curb, I caulked and I used Eternabond tape to wrap it and seal it to the roofing.

On Edit: Hmmm... There sould be a picture in this spot. I'm Having trouble with linking photo from Flckr... I give up...
>> Try seeing it here instead... <<

I believe that if the OP could remove the AC unit and install some curbing like we did it might be a simple, but viable solution. I'd suggest the curbing be bonded and then screwed from below where ever possible to rejoin the 2 pieces of luan plywood and provide some form of structural rigidity. It might be a good idea to use some aluminum flat stock from below to help "sandwich" the two pieces of luan together. He'll also need to obtain a new AC gasket and build up (the thickness of the curbing) the few perimeter mounting pads around the steel AC pan.

I appreciate all of the ideas! This community is such a wonderful place. I so needed the help and I am feeling much more encouraged now that when I started.

I really believe the wood is dry already but I'll look more closely once the air conditioner is up. I did find a lot more information by searching for "RV roof sag leak." It is not exactly the same problem but the answer proposed in several articles would work here I think. They propose building a second layer of 1/4 plywood to raise the air conditioner to prevent puddling of water near the A/C unit. To do that, they suggest installing two U shaped pieces of plywood that together lift the entire unit 1/4" It is the same concept openspaces suggested but using 1/4 plywood instead of 2x4's and putting it on the top.

http://bryantrv.com/roofacleaks.html
http://rvtravel.com/publish/rvdoctor381.shtml
http://www.motorhome.com/rv-how-to/roof-ac-gasket-replacement/

I have been thinking about this overnight...

How about this:

Remove the A/C unit as described in previous post.

Completely dry the plywood if wet or damp.

Get a section of channel iron where the channel is the same thickness as the plywood and the sides are at least 2 inches in length.

From the A/C opening, cut the channel iron to the length of the opening at the sides where the plywood seam is located. Curve the cut ends with a saw or grinder.

Press the two ends of the plywood together so they are even with each other and slide/drive the channel iron over both sections of plywood, making them even with each other. The channel iron should be in between the rubber roof membrane and the plywood at the top side so that the rubber covers the channel iron on top. If there is a decorative payer of ceiling then the same on the underside so that the channel iron only wraps the plywood and not the coverings.

from inside the rig, drive short screws through the channel iron and in to the plywood making sure they do not go all the way through the plywood so that the channel iron does not slip.

This should gusset and strengthen the opening as well as level the section so that the A/C will seal properly in the opening.

Could even use some epoxy on the plywood to help make the repair permanent and more solid.

Then get a NEW A/C seal and put the unit back in the hole after everything (including the epoxy if used is dry.