Best greenhouse roof (polycarbonate?)

[mmcavall]

Hi all,
I’m planning to do a more definitive greenhouse integrated to the garden. What would be the best material for the roof (the sides will remain opened because I don’t need to worry about temperatures here)?
Is polycarbonate a good material? I would like something that allows strong light to pass through. I like the reddish color displayed by some plants when they are under full sun.
Is it durable?
Are there many kinds of polycarbonate?
And, what about polypropylene?
Thanks in advance for any input.

[ElieEstephane]

I was thinking too of building polycarbonate roofing above my cacti to stop the rain and thrn add a 30% shade cloth in summer. I read that 16mm should be the best option for a greenhouse roof (but that's in a colder location than yours). Glass will reduce the the amount of ultraviolet rays so you won't have the thick spines you want.
As for durability, polycarbonate is very strong and very hard to break and will not deteriorate in the sun.
That's all i know and i'll leave it to people with greenhouses to give more in depth advice.

[greenknight]

In addition to various thicknesses of twin wall polycarbonate, there is also corrugated, It lacks the insulation value of twin wall but has higher light transmission, and can be a bit cheaper.

[DaveW]

One of the main advantages for us in colder climates with twin wall polycarbonate is it's thermal insulation is better than the usual greenhouse glass, but in an open sided greenhouse that is not important and as George says the cheaper corrugated polycarbonate sheets would do. Glass reflects more of the heat back into the greenhouse than polycarbonate, but again that does not matter with an open sided greenhouse.

I like the final quote in the link below, though I think the UK is a bit to cold for nudist gardeners!

"The final advantage for any nudist gardeners among us is that polycarbonate filters out nearly all harmful UV rays, so you need have no fear of sunburn."

https://www.telegraph.co.uk/gardening/g ... glass.html

http://www.wintergardenz.com.au/glass-v ... -film.html

[ElieEstephane]

"The final advantage for any nudist gardeners among us is that polycarbonate filters out nearly all harmful UV rays, so you need have no fear of sunburn."

I thought polycarbonate is preferable to glass for cacti because it does not filter uv light. I stand corrected.

[mmcavall]

Thank you very much, Elie, George and Dave for the replies and links. Reading it leads me to the conclusion that the best material, considering costs and benefits, is corrugated polycarbonate of a reputable brand (not sure I can afford that, but this is another question…).

My only concern is about the levels of sunlight that will reach my plants. I like strong spination and the reddish effect of strong sun. Maybe it is not a problem at all…but, if possible I would like to see pictures of plants that are grown under polycarbonate. I would appreciate if someone could post some pictures, or even just provide a link to a thread with pictures of plants under this material.

Thanks again!

[DaveW]

Depends really what you want the roof for? If it is just rain protection in winter, already being open sided, if you can make it so you can take the sheets off leaving just the frame in summer they will get full sun anyway.

[mmcavall]

Hi Dave, I see what you meant, but this would not work fine here. During summer, we have strong sun and strong rain in the course of a single day. It is better to keep a translucid roof permanently.
But I’m more convinced now that polycarbonate will work fine for me; lots of radiation will still pass through. Otherwise, you guys in more cloudy climates would’nt use it, isn’t it?
Thanks

[esp_imaging]

I guess most of us, wherever we are in the world, have a set of compromises to make.

In the UK, for most of the year, we want our plants drier, brighter and warmer than the local climate allows. And we want to do this at the least cost.
Growing most succulents without rain protection and protection from the cold isn't an option for us, polycarbonate allows us to at least make plants warmer and dryer, at an acceptable cost of money and brightness for many, even though glass cover may be better in some ways.

[mmcavall]

Yes, esp, I see. All I need is a permanent roof which allows good light to pass through. Polycarbonate may do the job. Thank you!

[greenknight]

http://www.greenhousemegastore.com/cate ... ate-sheets says their corrugated polycarbonate has up to 90% light transmission, while twin wall is up to 80%.

You guys can call me George if you want, but I'm not changing my name.

[DaveW]

Don't know where I got George from Spence, I must have been reading something else just before!

[cactushobbyman]

The only product I haven't used is glass. My pick is polycarbonate double wall 8mm in my area. I have built one greenhouse and used 8mm, bought two small ones with 3.5mm and a shade bench with greenhouse plastic 6mil and then change the plastic out for corrugated polycarbonate. Cost is more than plastic, but I found plastic a pain when it came to wind and rain. Much more under support needed with plastic. These structures are much more permanent and I do use plastic for temporary or seasonal usage.

[mmcavall]

Thanks for all the replies. I see many members here use polycarbonate, so I'll try to find it. I've found already polyetilene sheets, they are very cheap. I'll try to buy both materials and grow some plants under them for a year or so, while I'm not building the new greenhouse.

Thanks to all people here and sorry Spence for calling you George

[mmcavall]

I decided to test myself the usefulness of polyetilene covering, and did this small “place” to grow some plants.
All plants under this covering have “twins” under the plastic cover of the greenhouse, for comparison.
Until now, I’ve noticed that the covering lets lots of light to pass through (which is good). Plants are getting red or very spined. So I’m happy with the results (until now).