Tip: never patch a felt roof, you will trap moisture IN and cause ROT to start -
then things get REALLY expensive.
This balcony had leaked for 20 years because the patio door detail was wrong.
Unfortunately a local roofer suggested pouring “this great stuff” onto the roof.
It never went hard and this was the mess we had to strip. Years of patching had rotted
the joists. Needless to say the customer was delighted with their Permadeck.
Many extensions were built with the original roof penetrating them.