You guys might be interested to learn from my recent mistake. Well, it's a mixed outcome, not 100% mistake.
I needed to re-roof my garage. I really love standing-seam steel roofing, and I've written here before about why, so I'll skip the retelling. But last fall I didn't have the time and money to put the steel roof on the garage, and yet I needed to get it to stop leaking right then.
So I bought two used billboard vinyls from a sign company. They were 14'x48' (= 672 sq ft = 62 sq m) and cost $25 each. I've seen them for free, but I couldn't find any free ones at the time. For comparison, a 600 sq ft heavy-duty tarp is $96 at Home Depot, so this is a pretty fine price.
I did a little reading and decided to adhere the vinyl to the plywood decking with vinyl flooring glue. That stuff's formulated to glue vinyl to plywood, right?
So the first side we did didn't stick well. It blew loose in areas and flapped around all winter. Where it flapped, it developed holes.
The second side, we had gotten the hang of brushing on the right quantity of glue, stretching the vinyl smoothly into it, and making it nice, and that side has stayed flawlessly watertight for 7 months or so.
The vinyl is an appropriate underlayment for the metal roofing, too. That was the scheme- I'll put the vinyl on in the fall, it will last through the winter, and then I'll put the metal on top of it in the spring.
So. Would I do this again? Yes. With very careful glueing plus mechanical fasteners around the perimeter, yes I would. Did it go right this time? Not really.
How green is it? Mmmm, medium. A vinyl on the roof is better than a vinyl in the landfill and some ice and water shield or tarp on the roof. How frugal? Quite frugal. Cheaper than tarps, much cheaper than ice and water shield, and can be accomplished for free if you're lucky.
There ya go! One more tidbit of real-life knowledge for the community.