Cristo Balete wrote:You might get more information looking up Ferro-Cement. There is a version of it that can be made with styrofoam popcorn stirred into the cement mixture. The ratio of styrofoam to cement matters so it will be structurally sound. Most often it's used in boat construction and floating dock construction. I don't know the engineering strength of it, if it is not floating.
Sometimes that really matters, because a floating platform can often support more weight than if it is on the ground trying to support weight. That is the case with dock floats, and we are warned not to let them be in a location where the water will not be under them for part of the year if they are supporting the weight of a dock/roof/several people/furniture, etc. because they aren't capable of supporting weight when there is only soil under them.
Because cement with foam or styrofoam in it is lighter it's not going to be as much help holding a structure in place as heavy cement.
This is just my old guy, curmugeonly opinion, since I've had 100 feet of greenhouses for 20 years. A lot of the posts about greenhouses here are so into the architecture, the amazing structures, as if these buildings were for humans, not plants.
1. First and foremost, a greenhouse is about the soil in it. Pots up above ground are just as subject to freezing as the air inside a greenhouse. When the soil in a greenhouse is improved with hugel trenches, shin-high compost layers covering the entire floorspace, and maintained at that level, active composting layers provide the heat that keeps the air inside just above freezing. It's only a matter of keeping it a few degrees above freezing, not making it 75 degrees all year 'round.
2. Hot air rises, so if the point is to keep plants from freezing, the ceiling needs to be just high enough to walk into comfortably with a hat on. We all know how difficult it is to heat a house in winter, yet some of these greenhouses have ceilings in them we wouldn't even consider for a house, even when we have some kind of fuel heating system. If all the hot air is up at the ceiling, where is the protection for the plants in the ground?
A few barrels or troughs of water aren't even going to come close to keeping the temps up. Sepp Holzer in the Alps has lakes a couple hundred feet across and deep enough to keep from freezing that provides protection for his plants.
3. Plants need serious airflow, even if it's freezing outside. Sealing up a greenhouse in order to keep heat in is a recipe for plant diseases and pests inside that will make you crazy. Which means when the air is freezing it needs to be moving, slowly, with fans, in addition to heat from compost, which probably means an electrical connection, since batteries won't last long on a fan.
4. Greenhouses need to be able to withstand very high MPH wind gusts. The foundation needs to be below ground low enough where it won't freeze or heave. It needs to be wide enough and deep enough to support the entire weight of the greenhouse. Does anyone know what their greenhouse weighs? Are there proper tie-downs built into the foundation? Any building that is tall catches the wind at the top, sends it straight down the wall and back the way it came. That kind of force, at high MPH, even a couple times a winter, is enough to move the structure if it is not tied down, and cause an inadequate wall to fail.
5. Light: Because they make most greenhouse coverings with some kind of sun protection, that lowers the amount of light inside the greenhouse. The average is 80% of the light. The best I've found is 90% of the light. In fall, winter, early spring that missing 10%-20% is a big deal to a plant. So that's why both walls and ceiling should be transparent and let in as much light as possible.
Short days in winter are going to limit plant growth, so even if the temps are above freezing inside a greenhouse plants are still getting the message there's not enough sun hours.
Ferro cement yes. But look up doing it with basalt fiber materials as your concrete will be really damp a lot of the time. Messed with the concrete canoe contest 40 years ago in college. The foam beads need to be treated with a wetting agent so the concrete adheres to them properly. Needs some sort of fiber added for strength.
As for the green house being to light what if the foundation material is just for insulation. Suggest looking up screw pile info. Has looked like a really good answer for greenhouse stuff rather than true foundation because it can be reused and reset. For high tunnel stuff 2 other answers used here in a high wind area is screw in ground anchor and burying some sort of deadman anchor deep and really packing the dirt over it.
Now for #1 yes raised beds by themselves are not the answer. But several books make a good point though. If you can keep the dirt warm either thru heating or thru insulation having some place for the cold to fall off the bed and down is advantageous.
#2 most definitely true. Most common counter answer is some sort of GAHT system. (ground air heat transfer) There are both active systems and passive system. Heat storage barrels only work if they can be thawed out each day. If they are going to steady freeze solid over days or weeks they are basically wasted once the water freezes solid.
#3 From the early Ceres' greenhouse information they said 83 feet of 4 inch drainage pipe buried at stable soil temperature depth could pull cold air all winter long and still be above freezing some spring. Why 83 feet? Guessing because it is 1/3 of a standard 250 foot roll of pipe. So proper venting and above freezing air should be compatible with very little addition.
#4 Are foundations needed? Still betting screw piles (helical piles) are a better answer. Can be reused and reset. Thinking some sort of buried insulated skirting will be needed. But can probably be reduced. Say 2 feet down and 2 feet out in a swedish skirt maybe?
screw pile
#5 One of the suggested light improvements is smaller greenhouses was mylar reflectors so the plants were getting light from both sides in winter. Now it is a bit expensive but one of the ones I read suggest getting the christmas wrap mylar when it specialed after the holiday. It was apparently a better reflector and more durable than the typical answers. Another piece of the puzzle here is some plants can be tricked into thinking they got enough day light when they didn't. Say they are getting 6 hours a day and need 8. Apparently for some running a grow light for only 30 minutes to an hour at one end or the other of the cycle will mostly make up for the missing hour or hour and half and the plants chemistry stays in grow mode in spite of being short on light hours.
