Greenhouse glazing

Why don't you try a local Glazier first, they may stock it! It may be cheaper as well

When I was researching the sort of glazing I should buy for my new greenhouse I got the impression that polycarbonate twin-wall sheets are becoming more popular. The main disadvantage seems to be its greater flexibility compared with glass which means it can pop out of its fixings more easily in high winds (but won't break if it does so.)

I opted for ordinary horticultural glass in the end, but if I start losing some to breakages I will certainly consider replacing them with polycarbonate; it appears to be very similar in price.

PS. It was all in a thread started by Celaji, which I took over somewhat ( apologies and thanks C!)
" Building a lean to greenhouse"

Hers a quote from it regarding acrylic.

Sent off my cutting list to the perspex supplier last week and collected it the other day. Quotes for the job ranged from £760:00 to  £379:00 but I settled on one at £384:00 which  with careful manipulation  included half of it in 4mm instead of 3mm and one long diagonal cut for two roof sections which I did not relish doing at home...... I opted for collection in my van rather than take the £35:00 plus vat delivery charge. If anyone wants to know anything about perspex supply I think I am moderately qualified now.
For fixing perspex is really quite fussy:  Holes drilled for screws need polishing to avoid stress cracking later, and of course there are certain limits on the size of spans related to thickness, and requiring deep rebates for all round edge support.
Initially I was to use screws and cover with glazing beads, but I have found a way round this and am fixing with no screws at all.
I looked up on what sealant to use. This is not straightforward either.....Silicone is good but must be a particular type: Low modulus and neutral cure.
Low modulus means low resistance to movement when set, so it allows for expansion and contraction movement and the cure is the means by which it sets. Most are an acetic acid cure , the smell of vinegar is a giveaway for this. However the acetic acid reacts with and degrades the acrylic and it will make a right mess before long.
Found a batch of suitable tubes of silicone on EEbyGumBay for £3:89  so promptly ordered.
Began glazing yesterday.......Tricky diagonal bits on the roof first. I had drilled holes and lightly screwed the panels with screws with rubber washers, but on final fixing after running silicone on all the faces where the perspex touched the frame, found that the screws were not needed. The silicone acts as an excellent adhesive as well as a weatherproof sealant.
I also found that the DIY adhesive backed lead look flashing sticks really well to perspex as well ! So progress is being made.
Now with the fixing described above, this means that sections of the roof are put together ( with an small expansion gap between( and so the whole effect would be of one sheet covering the whole roof, which I  think looks a bit dead and dull.........So to get a more traditional pleasing look of glazing between roof bars I am using fence panel capping, also fixed with silicone, to follow the lines of the roof timbers, with the odd nail through the capping into the gap between the panels. This should look bonny and act as an extra sealing barrier.
Pictures would be better I know, so will try for some today weather permitting.

PS the spec on perspex is really quite good, ideal for gardening purposes.


Hope it helps.