I am hoping to construct my first ever greenhouse this winter, as a DIY
project, doing my own design & sourcing materials rather than buying a kit.
What I'm wondering is:
1. If I use polycarbonate for the roof (as I'd like to for strength and
lightness), will it let through enough of the light spectrum to be good for
the plants, or do I need to use glass?
2. Is standard annealed glass OK to use in the windows, or do I have to use
some special 'horticultural glass'? If so, how does horticultural glass
differ from normal glass?
3. Is there any regulation relating to domestic greenhouses which say I have
to use safety glass?

( almost) all comments gratefully received!