In order to let as much light as possible into a glasshouse the glazing bars are by necessity very slender. Glass is a brittle material and very stiff whilst polycarbonate is more flexible. Logically, this would imply that there is more chance of the polycarbonate being displaced by strong winds. I suspect, also, that the coefficient of expansion for polycarbonate is much greater than that for glass and that this implies the need for greater tolerance in fixing.
Normally polycarbonate is fixed to very slender aluminium bars with spring clips which allow for expansion and contraction. The above information is based on logic, not experience and I would welcome comments from readers who have practical experience. Is there anybody out there that can supply more precise assistance?
A further check that should be considered is that of light transmission as polycarbonate absorbs around 5% of light per millimetre thickness, e.g. 3mm thick polycarbonate would only transmit 85% of light striking it, I cannot instantly locate information for the transmission of horticultural glass. Transmission of ultra violet light would also be of interest,
I look forward to replies from more informed readers.
Hope this helps a little.