I'm sorry to say that I think it's your contractor that is the problem not your Lexan sheets. Greenhouses all over the world use Lexan and if there was a problem with warping and leaking no one would use it.

I'd get a second opinion from another contractor.

Here is a link that might be useful: G.E. Lexan Brochure

I'll offer a different situation as allegory. I recently got four small solar panels, wired them up, and mounted them to a board with epoxy. After a few weeks outside, three of the four were cracked down the middle, and thus dead.

What went wrong? I used epoxy. The board and panels expanded at different rates, and the forces cracked the panels. What I should have done (and plan to do with my new panels) is mount them either with an adhesive that can expand and contract, or mount them to an intermediary layer that can expand and contract.

Perhaps the problem you are experiencing is something like this: not necessarily the lexan, but how it's mounted. Perhaps the lexan is expanding at a different rate than the frames, or the frames are expanding at a different rate than the material that they're embedded in. Or perhaps it's not thermal expansion. It could be settling, or warping of wooden structural elements, or all sorts of things.

I wouldn't blame the panels for being warped. It seems to me like an installation problem.

I agree with karen's theory. When installing polycarbonate it is recommended to drill a large diameter hole in the panel then use a silicone-rubber gasketed screw that covers the large hole. This means drilling two different sized holes and is quite tedious. Some contractors might try to avoid this extra effort...

You can check this by carefully unscrewing one screw and seeing if the hole in the lexan is bigger than the screw diameter.

Hi Nathan, you wrote: "This means drilling two different sized holes and is quite tedious." This isn't necessary as there are special fixing screws for polycarbonate material that have a extra piece on the shank of the screw that drills a bigger hole than the starting hole. These screws also have a washer on them. They allow for the expansion that happens with these sheets. Barbara B

Interesting, I've used tin roof screws with a wider part near the head, but these are thicker all the way to the top. So these special screws have some kind of cutter flange? Do you have a brand name? Buildex don't seem to have anything like this.

(I'm interested because I'm planning to replace our house roof with polycarbonate, meaning 50m^2 of holes to drill :)

Hi Nathan,
I asked Tony and he said he thinks they're called "one Shots" and they should be available wherever you buy Laserlite or polycarbonate. Yes, they do have a flange about halfway down the shank. Have a look at http://www.taittimber.com.au/laserlite.htm Barbara B
PS My glasshouse's frame is now painted, all windows and doors are painted. Concrete slab is down. Assembly starts next week. (We have a sort of "open day" in our garden on Sunday for sheltie owners.)

I have an entire 9x22 ft. greenhouse covered in corrugated polycarbonate sheets (Lexan is G.E.'s brand name). I built it myself so I didn't have the advantage of "professional installation". I have not had one bit of problem with leakage or warping. Did you use corrugated or flat twin wall sheets? Corrugated is overlapped on the edges like a metal roof. Flat is usually joined together with a H channel joiner. The twin could leak if it isn't fitted in the H channel and if the slope of the roof is too shallow. A too flat roof can cause leakage. If you have to replace it, I suggest using corrugated polycarbonate and checking the slope.

Lexan expands and contracts a lot with temperature changes. Proper installation allows for movement and overlap. Bad installation means you will get popping and leaking as the sheets move.

Twinwall on a flat roof can cause problems because it is not stiff and will bow under load. I'm not familiar with the necessary pitch under potentially large snow loads.

Thanks so much for ideas and information......

Update on Lexan or polycarbonate uses with home construction.

So far, we have used .24 thickness polycarb panels as windows or panels to enclose our 10 x 10 porch and now have a sun porch. When we ordered the big panels, it took a special blade to saw them the proper width and length. My DH is an engineer and he did the figuring of expansion for our particular use on the porch, and then fitted the 2 x 4 framing to allow for that expansion. He tells me that as long as NO DIMENSION EXCEEDS (OR EQUALS) 24 INCHES THEN YOU DO NOT HAVE TO ALLOW FOR EXPANSION. But the sealant is special, and you must allow for the panels to have room, or else you will be faced with buckling or distortion.

Here is a picture of our new sun porch, now 2 years old and quite nice year round...in Mobile AL.
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I cannot get the smaller window pictures to load. Maybe another day.

We had a Florida room built using Lexan corrugated panels for the roof.The contractor installed the roof according to the specs. When it rained it literally rained inside,although the contractor came back 3 times to tighten screws it just kept leaking.We decided to purchase tubes of lexel sealant and went to work applying a dab around each of the 157 screws. Very time consuming but it worked!