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Greenhouses & Garden Structures

Polycarbonate panel color for greenhouse roof

6 years ago

Hi all- I’m hoping to get some greenhouse insight- we’re working on converting a backyard structure into a greenhouse here in Portland, Oregon and are installing a new roof with polycarbonate panels- we’re trying to figure out what color panels will be best for our setup.

Some info on the space:

The roof will be 16’ x 24', the shed is southern facing and the pitch drops to the north. The sides of the shed are wood slats that let a bit of light in but not much (we will eventually insulate the walls with plastic panels)

We will be keeping a mix of cacti, succulents, houseplants and tropical houseplants in the greenhouse.

The two colors of polycarbonate available are :

CLEAR / 8mm / Light transmission 79% / Solar Heat Gain Coefficient .74

ICE / 8mm / Light transmission 32% / Solar Heat Gain Coefficient .49

the brand is Polygal (http://www.polygal-northamerica.com/polygal-standard/)

We worry the CLEAR will be too bright or hot, but are also concerned that ICE will be too diffused, especially since we have such overcast conditions here in the Northwest.

Any insight on this would be greatly appreciated!

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Comments (5)

oakhill (zone 9A, Calif.)
6 years ago
Considering your regular cloudy weather, the ICE polycarb will allow very limited light. The 32% light transmission factor is based on full sun. It you only have 50%, or even 30%, on cloudy days, the ICE can only transmit about 1/3 of 50% or 30%. Most plants do not do very well with only 10%- 17% of full sun. As for the inside temps. on full sun days in the summer, the CLEAR would result in high temperatures inside. Supplemental ventilation and even evaporative cooling may be necessary on full sun summer days with the CLEAR.
e l thanked oakhill (zone 9A, Calif.)
bossyvossy
6 years ago
I vote clear also. We have clear polycarbonate sections in our barn roof and light is great but it has dimished with time as debris/dust dulls the panels relatively soon. Therefore, damage from the clear brightness is very short-lived.
e l thanked bossyvossy
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North wall would be a zillion times better, as you'll get more winter sun, when you need it most. Good to hear you're going for a big greenhouse. If you can afford it you'll be thankful for going bigger. A door directly into the greenhouse is fantastic as you can go out there and read a book in the middle of winter! You will have 24m^2 space. People have lived comfortably off veggies grown in 50m^2 without any extra food in temperate climates. You might be able to do this, with the bonus of some of the more hardy sub tropical crops (perhaps grow some ginger?). domeman: analysis looks good. Depending on what your goal is, you might even use 93% transmission PC (clear) and 50% shade cloth inside. This will give the lower light, but collect more heat. In summer you would either vent, or move the shade cloth outside. PC is also half the price of colourbond (but only lasts 1/3rd as long). If you put the shade cloth on the inside, two things to note: a) it would be good to have a light clear film of something like PE (say drop sheets) directly under the PC (like double glazing) to protect the PC from hot humid conditions (apparently PC breaks down quickly in hot humid conditions, but not when just hot) b) keep the shade cloth say 20cm from the surface to allow good air movement. A large diameter fan such as a ceiling fan at the top of the greenhouse could then move heated air down when required (thermostat).
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We bought polycarbonate panels .24 inch thick, forget what dimensions but somewhat like a plywood sheet. Then we cut it to use for walls in our sun porch, and clerestory windows in our northside closet and tub bumpout. Not corrugated. No UV filtering. No coloration. We found it at a local plastics dealer. The one in Mobile is called Ala-Fla Plastics, but some similar suppliers are probably all over the country. Just run a quick search on POLYCARBONATE SHEETS or POLYCARBONATE PANELS, and choose the one in your area that you are familiar with. Pay particular attention to expansion requirements with larger sized panels. In this photo, the upper panels are about 2 x 6 feet and the lowers are about 2 x 2...
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That type of gasketed screw typically needs no additional sealant. although it won't hurt to put a little under each head. Unfortunately, replacing the screws may not solve the problem. I have some experience with skylights and overhead, pergola-like structures. Unfortunately, water is very resourceful and, in installations like this, leaks can occur in one place and appear inches or feet away from where you think the problem is. Since you don't explain or show how your structure is constructed, I can't comment more specifically. I just wanted to caution you to not be surprised if you still have leaks after replacing all the screws. It may be necessary to do more or something else to permanently fix it.
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fruitnut Z7 4500ft SW TX
6 years ago
There are better choices than either of those. There are materials in between your two choices. Something like SolarSoft 80 http://www.greenhousemegastore.com/product/solarsoft-80-polycarbonate/polycarbonate-panels which has 80% light transmission but 95% light diffusion. Then if needed put a shadecloth over that.

Of your two choices I'd also get the clear because you can lower the light and heat with shade cloth. If you get the opaque material you are stuck with a possibly inadequate light level. Shade cloth can be removed in winter and just used when light/heat becomes too much.
roseguy
6 years ago
I use Soft Lite polycarbonate panels on our greenhouse. I could not be more pleased. It diffuses the light so that the light reaches deep into the canopy of any plant. It does such a good job that you cannot make a shadow anywhere in the greenhouse. This is where I purchased it, they should be able to give you more information. http://www.imperialbuilders.com/greenhouse-materials/coverings/polycarbonate-panels/soft-lite-polycarbonate-panels/
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5 years ago
last modified: 5 years ago
A great alternative would be Polycoolite by Polygal. It only shows a 50% light transmission, but that is an overall light transmission. I have included a section of the chart for Polycoolite light transmission between 450nm and 700nm. This is where photosynthesis takes place. You can see that Polycoolite has between 60% and 70% light transmission in this range. I have used it on my personal greenhouse in Louisiana and loved it. That is my greenhouse in South Louisiana in the snow. That was quite the odd day. Polycoolite has diffused light properties as well. The ice sheets will not give you enough light. If you are choosing between ice and clear the choice should be clear.

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