I purchased the Sunroom/Greenhouse plans to use in rebuilding a leaking 7-year-old greenhouse roof. It has two banks of four patio door replacement insulated tempered glass panels originally installed on an extruded aluminum track system ([Brother Sun]. It has leaked almost from the start. The builder is concerned about using only the butyl tape to bridge the gap between the first bank and the second bank. It seems to me that adding a metal sloped "bridge" over top of the tape (his suggestion) actually gives the water more of an obstacle to flow over, and thus to leak through. Is the butyl tape alone standing up to the test of time in this kind of application?
The tape is holding up for many decades (3 and counting) when it is covered. The foil can delaminate off the rubber when exposed for long periods to sunlight, snow and ice. Still, there are no leaks that have overcome the tape seal even then. Other things such as roof and skylight flashings can still leak, of course.
It is always best to use something like this as a flexible seal but to also do proper flashings in order to keep things moving down slope and not let them back up.
This tape is not designed for a wide unbacked bridge - over about 3/8". It isn't structural as I'm sure you already know.