replacing plywood roof

You will need glue on the luan before you put EPDM down. If you have fibreglass caps front and rear don't put your new material down any more than the existing. The new EPDM will need to go under the caps.

One consideration
Make sure you don't add so much thickness replacement AC fastening screws will still work..
When my Rubber roof was replaced very thin Luan plywood was added on the roof to provide a smooth surface for the new Rubber. Roof is much stronger now to walk on but a replacement Coleman AC required clamps to squeeze the gasket enough for the 4 fastening screws to grab. Was NOT a problem for Dometic ACs.

LocTite PL3 Construction adhesive (puts the others to shame) with proper screws for what you are screwing into.

Thank you all for your response, it all is very helpful...I was going to use a staple gun but now I think you are correct, screws and glue are probably best...again thank you all for your input...Bob

Veebyes wrote:
If you are into a restoration that deep, use marine grade plywood & give that a coating of an additional preservative so that you will never be doing the job again.

Real marine grade plywood is incredibly expensive ! (Hint: You will know it it the "real thing" if it is sold in mm thickness and NOT inches !) 1/4-3/8 ACX or BCX is more than adequate for the job.

Any additional coating should NOT be required if the roofing material is doing its job !

If you are into a restoration that deep, use marine grade plywood & give that a coating of an additional preservative so that you will never be doing the job again.

How are the beams? In excellent shape I hope. Personally I find modern torx head construction screws hard to beat. I would glue it with construction glue too. But ring shank glue coated nails (nail gun) are very good as well and much faster.

Personally I need to mark the beam locations on the plywood with chalk lines to keep the fasteners in the beam.

I'd use foam sheets as insulation maybe with reflectrix.