DebbieG

Hi all!,

Im about to start building a patio for the upper part of this patio (see photo)
and want to put on some type of clear roof to keep the rain off of the patio furniture but still allow all of the light thru. Looking for a low cost solution that will not yellow.
It will also need to be able to hold up to Michigan winters unless it will be easy enough to remove that time of year??
Some options I've come across are Polycarbonate, Lexan, and FPR Panels(fiberglass reinforced panels)......Ive read that Polycarbonate gets way too hot underneath though, but would that really be an issue under an open air pergola? (I will be adding curtains to the sides for privacy.)
I'd really like to hear from anyone who is using these products.....post photos of your applications if possible.
Thanks

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Nestor_Kelebay

Lexan is a polycarbonate. Deciding whether to use Lexan or polycarbonate is like deciding whether the glass is half full or half empty.

Probably your best bet would be Plexiglas. The reason why is that Plexiglas is unaffected by UV light from the Sun. So much so, if fact, that exterior water based (latex) wood stains have to have UV blockers added to them to provide protection to the underlying wood. Without those UV blockers, then the acrylic film the exterior stain would form on the surface of the wood allows UV light from the Sun to pass easily through it, and the result is that the wood deteriorates under that acrylic film.

Since UV rays from the Sun have a lot of energy in them, they tend to deteriorate whatever they hit. In the case of clear Plexiglas, the ray goes right through the Plexiglas without harming it, and it deteriorates whatever is under that Plexiglas.

Plexiglas is the trade name for rigid plastic panels made from polymethyl methacrylate. And, in fact everything made from polymethyl methacrylate is referred to as being "acrylic". If a rigid panel of polymethyl methacrylate plastic is made by the Rohm & Haas company, it's sold under the trade name "Plexiglas". If an identical panel of the same kind of plastic is made by DuPont, it's sold as a sheet of "Lucite". If you're in Britain and you buy exactly the same thing made by ICI Ltd. (Imperial Chemical Industries), then you're buying a sheet of "Perspex". Plastics are confusing because the same plastic made by 5 different companies will be sold under 5 different trade names, and if the same plastic is made into a rod or film, it'll be sold under yet other different trade names.

What I can tell you is that polycarbonate (Lexan) is stronger than polymethyl methacrylate (Plexiglas), and that's the reason it's now used to make airplane windows, whereas they used Plexiglas for that back in WWII. Both are shatterproof so both will stand up equally well to baseball size hail stones.

I think your best bet would be to look in your yellow pages under "Greenhouse Equipment & Supplies" or "Solariums and Sunrooms" and you should find someone knowledgeable about the pros and cons of both polymethyl methacrylate and polycarbonate and whatever else they may be using nowadays. I do know that most greenhouses do use Plexiglas instead of glass because of the risk of hail, but whether there are any advantages in using polycarbonate instead is something I don't know.

DebbieG

Thanks for the info, but I'm not sure I understand...are you saying that only if I were to use plexi that I need stain with UV protection or is that for the poly too?
Does most exterior stain have that, or do I need to look for a special type?
As for calling some greenhouse /solarium suppliers in my area....I should have thought of that....I will make some calls.
Thanks

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Nestor_Kelebay

No. What I was saying is that Plexiglas is probably a good choice because it doesn't deteriorate due to exposure to UV light from the Sun.

And, to explain why I knew that, I brought up the example of exterior water based wood stains.

The difference between an interior wood stain and an exterior wood stain is small. The only difference is that the exterior wood stain will contain some "binder resin" that will form a film over the wood. That film helps protect the wood outdoors because it prevents the wood from absorbing moisture from the air on hot humid days (and causing the wood to swell) and from drying out on cold dry days (and causing the wood to shrink).

Both exterior oil based and exterior water based stains will leave such a film behind to prevent the wood from forming cracks due to it's swelling and shrinking due to seasonal changes in temperature and humidity.

Normally, the film left behind by the exterior oil based wood stain would deteriorate due to exposure to the UV light from the Sun.

However, the exterior water based wood stain would form an "acrylic" film behind over the wood. That term "acrylic" means anything made out of the plastic called "polymethyl methacrylate", which is the plastic that Plexiglas is made of. And in the case of acrylic films formed by exterior water based wood stains, that acrylic film is so transparent to UV light from the Sun that it doesn;t deteriorate due to exposure to UV light. Instead, the UV rays go right through the acrylic film and cause the underlying wood to deteriorate due to exposure to UV light just as much as it would if that acrylic film wasn't even there. As a result, UV blockers have to be added to exterior water based wood stains to protect the wood from the Sun.

So, what I was saying was that Plexiglas would be a good choice because exposure to UV light doesn't harm it. And, to illustrate that point, I brought up the example of exterior water based wood stains that form an acrylic (Plexiglas) film over the wood that behaves like it's not even there when it comes to blocking UV light.

I know that greenhouses often used Plexiglas for their windows. However I expect polycarbonate is better simply because it's stronger and can stand up to a bigger hail stone. However, you'd have to weight that advantage against any cost difference.