solar greenhouse materials

I am looking to build a green house, partially underground, plenty of thermal mass etc.etc I want to know the best form of glazing to put in. I recently visited the eden project in cornwall and they had domes with a double skin made of plastic. does anyone else know of small scale versions of this. I'm guessing that double glazing glass would be the best but don't want to spend that amount of money

Used windows and sliding glass doors can be had for cheap if not free.  The big box hardware stores often install these products by subbing out the job to contractors.  If you can get hold of these contractors, they usually take them to the dump.

More recent sliding glass doors have double walled safety glass, 72x34, makes a fine greenhouse cover.  If broken, they shatter into pieces about 1/8" wide.  There are some which are sealed with argon between the glass sheets, providing a better insulating value.

Regular run of the mill glass from old houses/sheds/barns can be used.  Some woodworking skills can help in building frames suitable for your use.

The plastic you speak of sounds like polycarbonate.  It will hold up for a while but tends to get brittle after a few years.  Glass is the best.

There is a great product called KalWall that I built a green house with years ago. You can get it as a flat roll 4' x 50' or buy them as panels with both the inside and outside sheet bonded to an extruded aluminum I- beam. It was great because when light hit it it was dispersed inside instead of being concetrated in one patch, much better for the plants. Plus you can't see through it, it's kind of a milky white, transculscent.

Hi jamesb,

What about cob?

It makes such a nice thermal mass and the glazing is just more cob.

jeanna

Light doesn't pass through cob very well  

(sorry, cheap shot, but I couldn't resist)

There is a sort of double walled plastic stuff that comes in big rolls.  Made for greenhouses.

Based on what little I know, I would think that single pane would work fine if you have a rocket mass heater in your greenhouse.

Oehler's greenhouse was single paned and full of holes to the outside and he had tomatoes in december in north idaho.

You might be thinking of Vivak PETG sheet.  I hear it's good stuff -- strong, durable, and inexpensive:

http://www.usplastic.com/catalog/item.aspx?itemid=23337&clickid=redirect

not UV stable? doesn't sound like it will be durable long...

Yeah, I wondered about that myself, but I think they do have a UV-stable variety:

http://www.portplastics.com/plastics/commodities/VivakUVSHE.html

Here's a link to a place that sells KalWall. I built a solar, double walled house in the early 80's with a green house that went the entire south wall. As far as i know the KalWall is still fine.

http://www.solar-components.com/panels.htm

With KalWall I'd worry about it's insulative value.  With an attached greenhouse to the south wall (northern hemisphere) of a house, you'd want the heat of the low winter sun to enter, store heat in a trombe wall/floor and release it at night to the rest of the house.  In summer, you'd screen off the high rays with a shade and ventilation.  Check the diagrams in Pc: A Designers Manual.

Yep, that's what I did. Had KalWall water tubes with black dyed water in them up against the north wall or the house wall. And shade cloth on the outside in summer w/ two high vents on either end.