New Roof Time! Can I just layer over the existing plywood?

[211Racing]

Got an old, unkempt 2002 Tioga 25' Class C RV recently (really cheap). Fixed the mechanical issues. Now going after the roof. Whatever they last used for a roof membrane, it is almost completely gone. Bare plywood in many places. Some dry rot. Did exploratory surgery this morning with a hole-saw. See the images. The plywood forming the exterior roof and interior ceiling is approximately 3mm thick. Between that roof and ceiling is 3" of foam (presumably injected). The adhesion between the plywood and foam is very strong. What problems do I cause myself if I leave the current plywood in place, strip, clean and seal it, patch wherever needed, than lay down (put up) a new 5mm plywood layer on the roof and ceiling? This will be a low-use vehicle, mostly for day trips to motocross/hare scramble races (need someplace to cool off). I am willing to accept the added weight. Thank you for your insights and shared experiences.

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[211Racing]

OK. Got the roof stripped. Why the heck is there a gap at the edge of the roof all the way down both sides? That's where the roofing/membrane failed and water got in. And ... why is a thin layer of (what looks like) fiberglass patch over that gap? Seems unfinished. Also seems like the source of lots of work for me.

[dougrainer]

Yes, you can overlay the existing plywood once the EPDM is removed. Just Glue and screw the new plywood onto the old plywood. YOU CANNOT USE THE OLD DECKING AT ALL. You must use new plywood. Doug

[B_O__Plenty]

Look up AZ Expert on You Tube. He has several roof videos.

B.O.

[Veebyes]

JMO but if the existing plywood is in good condition I would consider giving it a dose of preservatives & go from there with whatever you deem good for top coatings or coverings.

[211Racing]

I'm not in deep enough into the tear down to get a reading on leaks or mold. I'll remediate that as it appears.

[bukhrn]

I take it you have found no evidence of leaking, (interior or exterior), no signs of mold.

[BurbMan]

I should also that when you cover with new plywood, glue it down with a good construction adhesive like PL Max (get it one of the big box home stores). It's very strong yet flexible and will make the new plywood part of the structural panel. This way you only need a few staples to hold it while the PL dries.

The Lance that I rebuilt (link in my signature) had an aluminum roof, that's another option if you can get a roll of aluminum wide enough to cover with no seams. The aluminum would be sturdier than the rubber but much harder to work with outside of a factory setting.

[Lwiddis]

I suggest following Burb Man’s recommendations.

[RLS7201]

The adhesives don't stick well to the old surfaces. Most times new lauan is used to get a good bond for the new roof membrane.
Dicor has been punishing RVers for years. Given time it cracks and leaks. If you're going to all that work spend a little more and use Sikaflex 715 for sealing around your EPDM roof. Sikaflex doesn't harden and crack like Dicor.


Richard

[211Racing]

That's what I wanted to hear.

Thank you.

[BurbMan]

That is a structural panel where the styrofoam and plywood is all vacuum bonded together. I would clean up the roof as you describe, then go over it with 1/8" (3mm) plywood so you have a nice clean surface, then get a roll of EDPM rubber membrane and cover the roof with that. Glue it down. Seal around vents, etc. with Dicor self-leveling lap sealant. If the rig had a rubber roof on it before there is probably trim around the edges you can reuse.