Acceptable Greenhouse "skin"

[chuckhydro]

I am considering using either a thin polycarbonate sheet or a double thick sheet (6 mm) for a commercial greenhouse covering. The polycarbonate seems to withstand UV well, and the sheets appear to withstand hail and other impacts well. The visible light transmission is greater than 82% which is important.

Does anyone have any comments on this application of polycarbonate?
Can anyone recommend any other material to consider for a greenhouse covering?
Thanks.

 

[chuckhydro]

Computer problems (or software) did not recognize my title.
It should have quote marks around the word skin.

 

[patprimmer]

UV stabilised PC should be fine.

Not all PC flat sheet is UV stabilised, so take care to ensure you get UV stabilised. The UV stabiliser will filter out the UV, so yuo get little UV transmission.

Single skin will transmit most light.

Twin wall PC sheet will be lighter and stiffer, and will span further, but you will loose a little in transmission when new, and more so when the cavity between the walls gets dirty, as it is exceptional difficult to clean it.

Twin wall PC sheet sometimes has the UV stabiliser concentrated on one surface, so that surface must face out.

Twin wall has somewhat better thermal insulation properties if the cavities are blocked of at the ends.

PC is very susceptible to a large number of common chemicals, so care must be taken when spraying the plants.

Acrylic is much better to UV and transmitts UV without damage to the acrylic, and is much better to some chemicals likely to be encountered in the garden, but it has quite poor impact strength, and could easily be damaged in a sever hail storm.

Acrylic is the material traditionally used in aircraft windows, but they will be thick enough to withstand all expected impacts.

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ornerynorsk]

The "traditional" material is fiberglass sheeting. Excessive light transmission will cause more problems than you are anticipating. Lower transmission helps protect delicate seedlings from sun scald.

 

[chuckhydro]

Patprimmer, does the UV stabilized PC have a coating similar to eyeglasses 'anti glare' coating? Or is it a chemical additive to the Polycarbonate during manufacture?
Ornerynorsk, Yes, the sun is definitly a heat source to be taken into account - especially here in the Texas summer. I anticipate using some shade cloth.
Thanks for the comments.

 

[patprimmer]

It can be done by co-extruding on the surface a thin layer of PC heavily loaded with UV stabiliser, or by surface coating, although I think co_ex is the prefered method for twin wall sheet.

My info is 15 years old, so I cannot comment on current trends.

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[TheAnswerGuy]

chuckhydro,

The material that you are looking for is called "Polygal" it is a GE material which is manufactured for the greenhouse industry. The UV stabilizers that are used in the material (if I remember) are warrantied for 20 years. A single sheet of PC at the correct thickness to standup to the weather would be more expensive that the extruded sheet of Polygal. You can also get the Polygal in a pre-tinted form which is good if your growing foliage plants.

When I was in the greenhouse business (back in the Chicago area) my houses were covered with Polygal and one sheet of Poly (flexible sheet), which I then put the blower in place to inflate the poly. Heating was my highest expense and that extra layer helped a bunch. Maybe with being in Texas, heat may not be your major expense. But I know living here in Orlando, FL that in nearby Apopka (The Foliage Capital) that heating is their biggest expense.

 

[chuckhydro]

TheAnswerGuy, Thanks for the tips.
I have begun collecting product information for the various polycarbonate alternatives: corrugated, flat sheet, and extruded twin walled. The luxury of tripple walled extruded sheet is not justified for my project. The performance and life specifications for polycarbonate material is very impressive.

Did you install the poly sheet on the outside? Only for cold weather? Can you comment on the scratch resistance or the surface toughness of the Polygal? I found their website (

http://www.polygalusa.com)

and found that they can supply related installation hardware.

Can you comment on the advisability and severity of pitfals of the "do it yourself" approach vs a turnkey professional crew? (1120 sq ft roof, 7 X 40 ft walls less waterwall & fans).

 

[patprimmer]

This site also has some interesting info, but probably over the top for your application.

http://www.austpolyproducts.com.au/dansolar.htm

Polycarbonate has very poor scratch resistance unless specifically coated for protection. These coatings are typically used on automotive headlights.

I don't know if the scratch resistant finish is compatible with the UV resistant layer.

I don't know if scratch resistant PC is avaliable as twin wall sheet.

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[chuckhydro]

Patprimmer, That is a very interesting web site. It is a bit over the top of my project, but is a great cocept.

 

[TheAnswerGuy]

chuckhydro,

The Polygal material is very easy to use for the do-it-yourselfer! The material is easy to handle and you cut it to size, with a razor knife. The one mistake that most installers make is that they should only close off one end of the sheet. This allows for the air to be in a dormant state and makes it become an insulator. By closing off both ends, you will get condensation to form within the cellular wall. By leaving one end open, the moisture has a place to drip out.

If you can put up decorative wood panelling in a room then you will have no problem with the instalation of Polygal. The inflated polyethylene sheet was put on the outside. This way it kept a pretty good cusion in the case of snow. I've seen the triple wall material. In most cases, I see that as overkill.

Re: Scratch resistance
One of the things that they liked to demonstrate at Greenhouse and grower shows was that you could pound on the wall of the Polygal greenhouse (they used a 16 oz. claw hammer) and not have a noticable reduction in light transmission and you could not crack the material. I am not sure about the resistance to scratching, but I have seen greenhouses that have had Polygal installed on them. They all looked pretty good.

Re: Pitfalls
There is not enough space here for me to sum that up!
The good thing is that if you have a basic knowledge of construction and can follow the directions that they will provide to you from Polygal?
It will be an easy task!
I have seen poorly constructed greenhouses that will make money. Although these growers could probably do better (return-on-investment) if their structures were better done.

If you are looking for a crew to install?
You may want to check out either "Stuppy Greenhouses" or "Nexus Greenhouses". Those companies are the ones that I remember, built the Cadillac of greenhouses.

 

[chuckhydro]

I appreciate the insight from TheAnswerGuy. I will be actively digging for details from the possible sources next week when everyone is back from holidays.
I have enough data now to begin a data base of features to compare between various manufacturers.
Macrolux (CO-EX Corp) and SUNTUF Inc are two other suppliers of the double wall PC.