This thread prompted me to look up the black Irish DC2 I used to own, it hasn't had a NCT in almost 5 years. To this day, I still regret selling that...
Water will just pool between the foil and the timber joists, all you would be doing is concentrating the drips to one area. As it will with anything...
That could be an option too, but still feel the roll of foil might do a better job and sealed in between the purlins with foil tape and sealant. The...