Revisions log for Answer #1400

You won't like the answer:

After years of difficult experience with roofing felt (aka bituminous membrane), I see here the typical problems:

-flat laid membranes will eventually leak because the welding/adhesive seams will

tear. If there are puddles standing on it, water will get in at some point.

— Surfaces that can be walked on are at special risk. At some point someone will put a chair on it and make holes in it.

If it were possible, I would

— Slightly tilt the floor

— Put a hard top layer on it or at least block access.

Even with proper installation, these are typical problems with bituminous membranes.