Revisions log for Answer #1678
This is the answer to the question What should be considered when remodeling the attic of a two-family house?
Revision 1
I can recommend AlfaFlex as an adhesive tape. It sticks like a glove and is much cheaper than similar "brand name tapes". The experts at our construction site have concluded that it is good.
Do the rest as described above and work carefully.
If you still have strength and energy (and money), you can put thin OSB or GC directly on the counter battens, so that with a little carelessness will not damage the foil immediately with boxes or shelves. The GC made the room lighter, the OSB made it darker. I would paint the OSB directly white to make the room lighter.
I once did dormer windows myself about 15 years ago (> 100 year old deformed old roof). Personally, I will NEVER do it again. This is a job for professionals, even on a straight and relatively new roof. The connections to the roof and soffits are especially important (heat, rain impermeability, etc.). Also, any replacement(s) that may be required must be installed professionally.