insulating greenhouse floor

I'm getting ready to turn a bunch of recycled double pane windows into a greenhouse. I read that I should dig a trench around the outside perimeter and put a 1" to 2" piece of styrofoam down at least 1'. I want to do that but it got me to thinking about what else I could do to insulate.

I read that Vermiculite is used for insulation. What if I dug down 1' in my greenhouse floor, poured in 6" to 8" of Vermiculite, then poured in rock on top for thermal mass?

Or do I need to even worry about heat loss/cold gain from the floor/ground?

Awesome question. I don't know how much heat would be lost through the ground. But, I know heat is gained through the ground. I don't know how much cold is gained through the ground, either.

Off the top, I would think it's not worth going to too much trouble to prevent. I would think you would spend your time with what is exposed to the air.

Just after some quick poking...

"Information from studies cited by Cuestaroble show at most 3% of heat lost through the perimeter. This, presumably, is that the temperature differential between soil under floor and GH is far exceeded by the temp differential between outside air and GH. If you alredy have the perimeter dug up, by all means, go ahead and put in the insulation. But if not, you would be far better off to spend the time and money on the roof glazing, through which over 50% of the heat is lost.

I have come to believe that in this setting, the concrete will not have a great impact as thermal mass. The reason is that its heat will not be given up at 3am when you need it to keep the temps in the house at 58F and reduce your energy consuption. It will be given up from ~4pm to 9pm as the temps drop from the daytime high to the low of 58F. During that time there will be a temp differential favoring loss of heat from the concrete. By the time the heaters would kick on to keep the house at 58F, the concrete will have lost most of its heat already. I kept my GH at 57F last winter. This is what my water thermal mass experiments suggested last winter, anyway. This winter I'll confirm that by checking temps in the floor." -came from this thread.. http://forums2.gardenweb.com/forums/load/strucs/msg0622215017850.html (I hate referring away, but this time I believe it's necessary.)

There are more interesting reads in there, too. However, I tend to agree with the people saying it's not worth the trouble/expense to insulate the floor/slab.

If you are going to insulate the floor, do it right. The idea of digging footers below your freeze line is outstanding. That should sever to conduct a little heat up to the floor in the dead of winter. Also, the fan on the floor idea was interesting. But, above all, make sure your slab is not much bigger than your greenhouse. Too much bigger and any insulating you do will be ineffective comparitively.

We have friends up here in Alaska and they just dug down put in some hwy matting and then covered it with rock built the hot house on it and they have no trouble there things grow like crazy and they use fans to circlulat the air along with a gas heater. can get more inf if you like.

I think I'll just leave it be for now and see how it goes this winter. I agree BBG it doesn't seem worth it. I will probably just go ahead and put down some gravel for thermal mass.

BackyardBirdGardner is right on with the information about insulating greenhouse floors. You might be interested in the link below for more details.

http://www.keepandshare.com/doc/view.php?id=3174623&da=y

What a great source of info! Thanks so much.

Your welcome.... Unfortunately the link just changed addresses. Here is the current one:

http://www.keepandshare.com/doc/3179224/greenhouse-floors-insulating-355k?da=y

Check out this photo of what to do with your greenhouse floor - build worm bins. I thought this was a genius use of the space!

http://www.motherearthnews.com/multimedia/image-gallery.aspx?id=117666&seq=1

I'm actually planning on doing that. I was only planning on making mine deep enough to use 2 X 12's but I see in this picture that Havery's are much deeper. Does anyone have experience building these? The size of of the bins in the picture seem a little heavy to be putting table scraps in every day.

I've never actually done this myself and unfortunately, don't have a greenhouse. I would think, though, that you could adapt the idea in any way you wanted to suit yourself and your circumstances. You wouldn't have to do it on as grand a scale as these folks did.

I hope you'll keep us updated as to how your plans go!