Here is my summer vacation project: I want to redo an old garage roof by replacing the old tongue and groove boards with sheets of regular plywood (not marine grade) but I do not want to re-shingle. Is there a modern day coating that I can just roll onto the plywood that will seal the roof and make it waterproof? Hopefully , if the answer is yes, I can buy this coating at Home Depot or Lowes :-) I don't care what the roof looks like,i.e.; the coating can be black or any other color.

  • I'm confused, do you want to place the sheathing over the existing shingles? Also, they are asphalt yes? At first read, I assumed cedar – Ack Mar 22 at 21:20
  • No, I am ripping off the old shingles and boards. – William Hird Mar 22 at 21:22
  • How long do you want this roof to last? – Harper - Reinstate Monica Mar 22 at 22:23
  • Five years tops – William Hird Mar 22 at 22:29
  • A "rubber roof" (EDPM) would be a more reliable solution. As far as I know the "paint on" solutions that might not be garbage require a fabric layer first, and do not come from big box stores, be they Orange or Blue. – Ecnerwal Mar 23 at 3:44

What you can use is roll on roofing, here's some information. The issue with a coating, like a thick paint type of thing, is that joist in the plywood sheathing, there will be differential movement, especially in the vertical direction (in and out of the sheathing face).

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  • Yes, there is always movement, but I'm looking for a coating that is "rubberized" so that it can move with the underlying structure. – William Hird Mar 22 at 22:26
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    The amount of movement will be too great. You can try it. I see in another comment that you only want 5 years out of it. You could apply and then patch as needed. Here is one option homedepot.com/p/… – Ack Mar 22 at 22:37
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    Looks good , I'll try it. – William Hird Mar 22 at 22:48
  • @William Hird I'm not sure if you want to do the work but you can block the sheathing joints between the rafters with 2x4s to all but eliminate the movement. Or even scraps of wood. Doesn't even have to be attached to the rafters, just between the sheets. If you use short screws through the sheathing face, it'll be MUCH easier to install. You could even use cheap sheet rocks screws. If you use screws with no threads and only shank for the same depth as your sheathing, it'll suck the block up tight too. – Ack Mar 22 at 23:34
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    Thank you, yes I'm familiar with truss design :-) – William Hird Mar 23 at 1:00

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