You can cut the felt with a utility knife, to whatever dimensions you need. The roll is 3' wide by 80' long ( I think). Easier to just staple the felt in place.
No, not that I am aware. Product does not have any adhesive and I assume joist tape has an adhesive.
30# felt paper but 15# works in most cases just as well
Ordinarily roofing felt contains some asphalt, so any adhesive that is used for tile is unlikely to adhere well at all.
I have always used a heavy duty stapler to hold it down and then shingles/ freeze edge on top with roofing nails
No,Chip. One is Not lucky enough to have a computer. One is barely lucky enough to have a phone. And when one has clicked Any number of times to find out the item is Still out of stock then one gets annoyed. And btw,One should read the question correctly before one comments.
400 sq. feet
The specs on the website say that this will cover 432 sqft . Your math ...10 x20=200 sqft. You will need just under 1/2 of a roll. In roofing and applying felt paper there is always extra left over. Good luck on your project.
The website says 432 sqft