polycarbonate over glass?
 

I'm hoping someone has some experience to help me. We are thinking of putting polycarbonate over the existing glass on our greenhouse in order to save on heating bills in the winter. I'm worried that I won't be able to get good results on my orchids that need lots of light, although I now use shade cloth. Does any one have any suggestions on "Do's" or "Don'ts" which might help? Has anyone tried polycarbonate over existing glass?
Will love some input.
Pam :)

Seems odd, but I doubt the PC will reduce the light enough to be significant.

I haven't any experience with pc over glass, but I can tell you from my search for glazing options two years ago that the amount of light admitted by pc glazings does vary somewhat. Mine allows between 80-85% of light through, I think 90% is as high as it goes, and I've seen it as low as 67%. You will want to factor in the % shade you currently use and go with a new lower % based on the % sun admitted by the new glazing. They don't seem to have a lower grade than 20% so if you're already only using 20-30% shadecloith, you may end up having to improvise to keep the same level of light and use a shade paint (they have ones for pc that turn clear when wet for rainy days) or just screen.

I switched from 75% shadecloth the first summer to 40% last summer and now 30% this summer and am seeing better color in the bromeliads which is what I've been using as my gauge. This gave me:
Last year: shadecloth admits 60% sun to the pc: 60x.85=51% sun in GH
This year:shadecloth admits 70% sun to the pc: .70x.85=59.5%sun in GH

=Big difference in blooming and growth, especially in the higher-light plants such as cattleyas, etc.

But I'm still not getting the response from the vandas I'd hoped for and am considering trying to find something around 20% but haven't been able to locate it yet (.8x.85=68% sun in GH). Bear in mind I'm in the cloudy, frozen northern wastes of Ohio.

Tennis, have you considered no shade cloth at all for your vandas?

You and I are at similar latitudes, and I use vandas as the "shadeclorh" for the plants below.

I don't know how I'd manage that as there are so many other plants needing the shade, and the vandas can cover only a small percent. I also can't figure any way to cool the GH if I cut the shade much more. It's already running 85 degrees on hot sunny days with the cooler running on high and the current shadecloth (except for the underbench 'tunnel' in front of the cooler for the trichopilias, etc, which tops at 72-75 degrees). Due to the configuration and location of the GH the vandas are in the middle on the slope and can't realy fit anywhere else, so it's not like I can just leave off the shadecloth from one end or such. I considered hanging them outside but the GH took up all the room I would have for that and when i tried it once before I got crown rot in most of the vandas from our periods of weekslong rains and cloudy days (except for our periods of intermittent drought - love Ohio weather!).

I considered using polycarbonate externally...............until I calculated the price. Polycarb has an excellent light transmission, but the cost for doing my two 8X12 houses with 10mm dual layer could not be justified against any possible cost saving. I opted for a new type of internal plastic shading in the uk. It is UV inhibited and really like a blanket with large bubbles between two layers of polythene - not at all like bubblewrap. It is so clear that one can see through it almost clearly, much better than my previous lining which is just translucent. I wanted to let more light throughin winter so this looks like it will do the job. Only difficult task is fitting it into a house full of plants!
Richard

I would like to see the internal plastic shading from the UK. Do you have a link to the web page?

No, sorry, I only have the same info that you see in this forum. You might try sending a message to Richard. I would like to know more about the product also. This is the only place I've read or heard anything about the internal plastic shading.

Like everybody here it sounds odd to me also. Actually I have never heard about this polycarbonate for the greenhouse or something. So basically you should not think further for that. Instead of that you can use the other shadow things for your greenhouse.

There are a variety of poycarb glazing. Single or twin or triple wall (insulated). All transmit light well. Some panels or sheets can be ordered that are white (not opaque), which diffuse the light. Stuff can be expensive. Heavy 6 mil plastic film with a UV protectant can be used over the glass to keep in heat. (Or stapled inside under the glass.) There is clear and white plastic film.
I still use old fashioned white wash greenhouse paint for my glazing. In the winter, I wash some of it off. In the Spring, I apply more for shade. But Aluminet shade cloth is good. It deflects the sun, while keeping the greenhouse cooler. Black shade cloth, if it's too close to the glass, can absorb heat.