Propane usage

Has anyone ever documented, how much propane is used per square of roof, per ply? Thus 1 square per gallon? 2 per gallon???  

2 rolls per gallon? No

it is the opposite. 2 gallons per roll.
but it is not gallons, it is pounds.

2 pounds per square.

in other words i get 10 square out of a standard 20 pound cylinder.

now if i blast it out all at one time with no breaks than i will get less. More like only 8 square. The tank will freeze up on the bottom. That is why it is good to have multiple tanks on the roof and switch them when they are starting to freeze and go back to them later.

IU have not kept track, however would guess about 1/2 gallon or so per layer of torchdown