Hi Steve,

Welcome to the forum. I share many of the same goals as you and live in a similarly cold place.

I'm not too sure about south vs southeast for orientation. It seems that either could work. Are there other factors like wind or other structures to consider?

For insulating the foundation, most people go to the frost line (1-2 feet) but deeper is warmer, so I can't think of any harm in digging deeper, except for the effort of digging. You can make this insulation as thick as you want - thicker is obviously warmer. Don't insulate the floor because that will prevent the "chimney effect" that you are after with insulating the perimeter of the foundation. The idea is to allow warmth from the ground to penetrate upward into the greenhouse.

Do you plan to use the greenhouse in the summer or other warm times? If so, you may also want to plan for ways to keep it cool.

Happy planning!
Karin

I don't think it makes sense to worry about insulation if you're not going to heat it. Your heat of the day will disappear quickly after the sun sets. Trying to use mass as heat on winter nights will be frustrating to say the least.

Welcome Steve. A few thoughts (maybe answers):

Going down to the foundation bottom with the insulation is the norm. Probably because that depth is excavated already. But as you bring insulation deeper, you get diminished returns, as well as creating potential structural issues with the foundation (depending upon your soil type and degree of compacting you are willing to do). Probably better bang for the buck putting thicker insulation on the foundation walls and above rather than continuing down. If you think you need more, you might add Swedish style in ground insulation around the outside ground in addition or instead of foundation wall insulation (really depends upon size as the Swedish method increases the thermal mass of the GH, which depending upon your sun and GH size may or may not be a good thing).

Insulation at the bottom of the GH soil area (the horizontal bottom) is generally a waste of time and money.

Rather than water heat storage, you might want to investigate SHCS. It is a grid of air tubes in the ground of the GH with a small fan. Your soil becomes the heat storage media, which saves space and provide better heat for winter greens and the like. Works well in Colorado, not sure with your climate and water table

Orientation can generally be with the long side facing S +/-15 deg or so in norther climates. Variations from true S depend on the site, and if you want to maximize morning heat vs afternoon, as well as site logistics (big tree or hill in the way). Really your call.

You might want to check out Elliot Coleman's book on winter GH growing (sorry forget the title right now). He grows greens in Maine, which I guess might be similar to your climate.

Good Luck

Karin - my frost line is 3.5 feet not 2 feet - so should I go down that far in your opinion? Steve333 - what is Swedish style? Also Ihave Eliot's 4 Season Harvest, is that what you mean?

I am going totally passive so I do not want to heat it, run fans, etc. It seems to me that insulation will be even more important for passive as I must hold onto whatever I gain. I have some good ideas from "The Solar Greenhouse Book" published in 1978, many other posts here and your responses. Thanks again and if anyone has anything else to add, please do so.

Steve,

Whoops, sorry I missed that in your original post. That's an impressively deep frost line. Do you not get much snow cover? Steve from CO makes a good point about creating instability for your foundation if you dig a giant hole around it. Would you be digging by hand or by mechanical means?

When you say you don't want to run fans, does that include summer?

My garden is now sandy loam. It gets cold here... real cold. I recently dug through over two feet of snow in my garden to get some soil for seed starting. There was NO frost in the ground. Frost only develops where we walk,shovel, drive etc. We destroy the insulating value of snow by compacting the air spaces out. You can follow the posted link to read my recent blog posting on The Insulating Value of Snow.

If you grow on benches, you will lose the latent soil heat. Maybe high raised beds will be a compromise. I'm in the research mode too, prior to construction this spring. BTW, all the advice I get says SE orientation is best because it allows the heat to start building up earlier in the day and rejects a bit more of the late day heat, especially valuable in summer.

The regional climate here is zone 3b, but my microclimate is about Zn 4+. I have a Japanese Maple growing in ground for the last ten years and it only gets a wrap of burlap to keep the sun and wind off it.

Here is a link that might be useful: Lively Dirt - the Garden Blog

Good info guys, I appreciate it and I am rethinking things. My neighbor also insists that it never freezes more than a foot or two even though the official frost line is 42" especially if you do not walk or drive on it. Yes we do get a lot of snow and a snow cover 5-6 months. It sure will be easier on me to only go down 1 or 2 feet (and this way I can do it by hand if I have to).

This foundation stuff is the toughest decision area because I can add insulation to the above ground structure later but once the foundation is in and the greenhouse is on top of it I am not going to be able to work with the foundation again.

"Lively" I went to your blog. I am also using the soil blocks this year. Also, if you are known for your compost making abilities are you going to figure a way to put a compost pile in your greenhouse? I have been reading some neat things about digging out a section under your center walkway and either composting in there or vermiposting?

Guys - again I appreciate your help - I am not going to go all the way down to the frost line.

Nice going Steve, one decision done!
Next, what are you going to use for insulation? And how thick? We used styrofoam sheets which were easy to work with. We doubled them up. I think each sheet was 2 inches. Do you have something locally available?

Lively, I'm a geologist too. Playing in the dirt has always suited me. :)

I am going totally passive

Is that because you want to, or because you have to? Passive solar just doesn't work that well. The heat output of the water is the opposite of the outside temperature over the course of the night. You would need heat the most from 4-7am and it is then that you would have very little. And that's assuming you had sunshine. If the high temp for the day is below freezing and it's cloudy, then after a few consecutive days of that weather, you're going to have barrels of ice and frozen plants.

I am two zones south of you and only use my greehouse in the spring; I run an electric space heater in a germination box and also have an external forced air wood-burning furnace. And it's still a big pain to keep it heated. I have to refill the wood stove 2-3 times to get through one cold night. I can't imagine doing this all winter.

If I had it to do over, I would build or buy an insulated cover that I could place over the non-insulated part of the greenhouse at night. I have seen a Chinese design with an insulated blanket that rolls up and down, and the building has a wood or biomass stove adjacent to it. I was trying to duplicate how they placed the wood stove and that part works well, but due to the low r-value of the plastic, a blazing fire only gets me about 15 degrees of gain over the outside temperature. Nothing clear holds heat. Retractable insulation is the best solution to that problem that I have seen.

I've made a rough sketch of a method I've used to trap heat from my home basement walls and you may find it useful in your GH. A pic is easier than a thousand words - if you can see it. Hope it is legible, but you will have to lay on your desk to read it. Should have been portrait orientation. Steve, it sounds like you are planning on putting insulation below your footings since you say you can't install insulation later. I think that is over engineering. You need good drainage under your footings and the footing bed needs to be well compacted - water and a tamper work well for small projects - really soak the gravel then pound it with the asphalt tamper or something similar. I also think the question you posed is "how far down do I insulate?", which is different than how deep the footings should be. If you are on well drained glacial till (gravel) like I am, you don't have to get as deep. If you are on clay, that's a different matter. You will be compacting the soil at the entrance to your GH, unless it is attached to another building and you access it through there, and thus driving the frost down at the enrtrance. You will also have passive heat in the GH to offset some of the frost around the perimeter, but this will not help at the door. I write all this building stuff from a lifetime of building experience and many years of paid "handyman" work after I retired from my first career. Summary - if it were me, i would go deep around the entrance. Here's another thought I just had. How about a plastic "porch" to mitigate some of the temps at the entrance? It would also act as a temperature buffer when entering the GH.

Regarding heating with compost, I don't think so. Compost is only actively heating for a couple of weeks after the pile is built, then you are walking on mush that you will compact into YUK, and then it will stink because it is now gone anaerobic... and I'm too lazy to dig that big a hole in my GH and keep doing it over and over.

I think I've mentioned this before, but it bears repeating. Check out Eliot Coleman's The Winter Harvest Handbook and find him on YouTube. It is amazing how much heat is in the GH. Sure it will freeze, but ot nearly as hard as if you were dealing with raw exposed earth. He harvest year round in Zn 5 from unheated GH's 12,000 square feet of them.

Hope I haven't confused or depressed anyone. If so, just say so, and I will try to clarify.

First - "karin" - I want to use 2" extruded polystyrene. The other day it was more than twice as expensive as the 1" so I was wondering if I could double up on the 1" but today it is cheaper .... go figure.

Second "Cole robbie" - I am choosing to go totally passive - personal reason. Again I "grew" crops all winter this year in a cold frame, with agribon inside it and a low hoop house above it (rule of thumb, each layer adds one growing zone so I moved from 4 to 7). At a minimum I will do the same thing with my greenhouse to keep crops going all winter, just substitute a greenhouse for the low hoop and make my back feel a lot better, I know I can do it and it will be more convenient. Next goal is to get a earlier start in the spring, 3rd goal is to see if I can keep it warm enough to grow other crops during the winter. Sorry but I can NOT be talked out of that.

After insulating the greenhouse I do plan on using a cover of some sort at night and cloudy days, hopefully I can figure a way to do it inside the greenhouse instead of outside.

Third - "Garth" - your picture is my plan for insulation of the foundation. I am not planning on laying it flat on the ground under the greenhouse, just up and down the foundation and maybe lower using a ditch witch. I like your idea of going deeper at the entrance and I am also going to go deeper on the south side where the beds will be.

I have trouble doing compost well anyway so I doubt I would try it in a greenhouse but I know some do and "lively" said he was an expert composter so I figured if anyone could figure a way - he could.

Thanks everyone.

Steve, to answer your questions:

Yes that is the Coleman book (and I see others have suggested it as well).

The "Swedish" method (my name for it, probably not the right one but it was developed in northern Europe) is just like the almost horizontal board of foam in Garth's drawing. The system is approved now by quite a few building depts. The concept is that that almost horizontal insulation keeps the soil under it warmer. Effectively increasing the coupled thermal mass of the structure. I would not use it instead of foundation wall insulation, as it assumes a heat source in the structure. But it can mediate heat loss from a GH underground and is much easier to add than more foundation wall insulation after backfill.

My caution on using this method is that it increases the thermal mass of your GH. Depending upon the sun your getting in the winter, that may make it harder/slower to raise the internal temps of the GH during winter days. Not unlike how long it takes to warm up a log cabin when it has been unheated for a while mid-winter.

A passive solar GH is really a fine dance with the climate. If you have enough sun, and a good means to save the excess daytime heat you can do quite well. Problem is many of the conventional systems don't work well enough (that is they don't have either or both enough storage capacity and surface area) to be effective. This is aggravated if you aren't using fans or pumps to move the heat around when you can.
For many of the systems, only a small fan or pump (which can be a DC solar PV powered one) is needed. But it makes a big difference over not having it. And as someone pointed out not having powered ventilation in the summer can raise problems too.

One point which you might want to consider, that the energy gain/loss equations change quite a bit from small structures (like cold frames) to large GHs. In other words, you may not be able to duplicate your cold frame results in much larger GH, both in terms of heating and cooling.

I plan on doing an experiment the first winter. Set up a Cold frame in the greenhouse and two experiments with less protection to see what works and what does not.

I was guessing that was what you meant by Swedish but I quickly googled it and did not find a definition so I thought I would ask. I think the idea of partially insulating a foot or two away from your greenhouse is a good one.

"cole robbie" - a little more info - I happen to think the Peak Oil crowd is correct or mostly correct and that it will soon be too expensive for any of us to heat our greenhouses with anything but wood. I may be wrong but since I am building a greenhouse from scratch right now I might as well make sure it would work in that scenario in case I am right.

Have you seen the "active solar" designs? The one I saw used solar power to run fans that moved air through drainage pipe buried in the gravel floor. The fans blow hot air down during the day, then reverse at dusk and pull air out of the warm gravel. It is supposed to be much more effective than passive solar.

If I tried to build a greenhouse off-grid, I think I would build a solar collector that heated water, and then make the floor of the greenhouse basically a big slab of water. If it's all aligned correctly, you can use the thermal energy of solar-heated water to make it move uphill at a slight angle and into your water reservoir; then gravity will move water back to the collector to complete the loop.

I like Garth's sketch, too. It makes some intuitive sense, and isn't hard to pull off. Run an inch of insulation down to the footing; if you don't, it will try to settle despite your best efforts to adhere or fasten it to the foundation. Do 2 inches if you want, but the first inch will do 80 percent of the work.

As for the orientation: Pay attention to the weather in your microclimate during the underheated part of the year. Look in particular at the times of day - you should be able to get nearby NOAA data to help. The "east of south" orientation may make sense particularly if you are down wind from one of the Great Lakes. There, the sky is more likely to be clear in the (cold) morning when you really need the heat, and more likely to be cloudy in the (somewhat warmer) afternoon when you do not need the heat as much. We found that there's a surprising amount of available solar energy during light cloud cover. We also found that the "come and go" periods of strong solar gain don't justify a lot of investment in additional thermal mass. Do experiment with aquaponics once you get under cover: you can get double duty out of the fish tank water as thermal storage.

Try to find an old favorite book "Design with Climate" by Victor Olgyay. He and his brother had all of this figured out back in the days before the first great solar scare of the 1970s.

I'll bet you'll be growing some gangbuster Swiss Chard next winter!

The system CR describes in his last post sounds like a variant of the SHCS that I mentioned. Basically you use a fan to blow hot humid air during the day down thru irrigation tubes which are buried in the GH subsoil. It has several advantages:

1. You are using the subsoil which is already there as thermal mass, Doesn't take up room up top.

2. Much of the time you will get a moisture condensation cycle with the hot air on the cool tube/soil walls. This transfers more heat than a simple heat exchange and dehumidifies.

3. Warming the soil extends plant survival over just having some warm tubs of water radiating heat.

I can tell you more of how well it works next year, as I am currently building a GH that will use this system. However I have been in some local GHs which use this system and it performs well in our location (Colorado front range).

There used to be a website with a spreadsheet which would calculate suggested number of feet of pipe underground and fan CFM for these systems online. The link to the main description page is with link to the spreadsheet (Note that John the owner of the site has passed away, so some of the links and the forums may no longer be active):

http://www.sunnyjohn.com/indexpages/shcs_faq.htm

The spreadsheet includes calculations of money payback based upon conventional heat source not used.

My expectations for my system are that it will not provide all the heat I need during cloudy winter spells. But it should be enough to keep some tomatoes and peppers alive and producing through the winter, with occasional supplemental heat now and then (a dozen or so days). I know next year if it will live up to those expectations.

Hi Steve,

My husband and I are hoping to break ground on a greenhouse this summer. We have been researching greenhouses since 2007, trying to find the right strategy to use little to no energy for reasons similar to yours. -We are concerned about Peak Oil and "Peak Everything". I have read the 1978 Passive Solar Greenhouse book you mentioned and took a lot of inspiration from it but a word of caution; A lot has changed in the world of building science since the 70s when a lot of passive solar designs were developed. Insulating is really important but without proper air sealing, the insulation has limited effectiveness. Really watch your construction detailing. I highly recommend the green building blog: www.GreenBuildingAdvisor.com for more information.

A few people have mentioned Subterranean Heating and Cooling Systems which is the strategy we are using in our design. Sunny John's website has a lot of information but his website is hard to navigate and he has not updated it in awhile. However, a professor at Virginia Tech headed a SHCS greenhouse project a few years ago and has lots of helpful data on his website:

http://www.roperld.com/science/ymcasolargreenhouse.htm

In short, the reason why a SHCS works so well is because it takes advantage of a phase change to store a ton of heat. Because greenhouses are hot humid enviornments when the sun is shining but cold when it is not, the SHCS works really well. You take the hot, humid air and send it underground through tubes. Underground there is a forced dew point and the water vapor condenses, giving up its heat to the soil heat bank (because of this, the potential for heat storage is enormous). The air comes out the other side, cooler and drier. At night, when it is cool, the fan comes on again and blows air warmed by the heat bank. The beauty of this is that you can actually bank heat from the summer and use it in the winter! The amount of electricity it takes to heat a 1200 square foot greenhouse is equal to the electricity it takes to run a large refrigerator. -It is just one slow-moving fan per 1200'. Here is an example of a backyard greenhouse using this system:

http://www.roperld.com/science/SGHBackyardSHCS.htm

However, maybe this system is not for you. I tend to agree that passive solar is tricky. But then again, it depends on what you are growing. Before we decided on the design we now have, we were going to go with an attached passive solar pit greenhouse. The Passive Solar Greenhouse book talks about the wisdom of this design. By lowering the floor of your greenhouse to a few feet below the frost line, you are taking advantage of the earth's heat to ensure stable temperatures. You also get more height to grow things like fruit trees with minimal air leakage from the walls since there is less proportion of walls to the pit. We still are using a lot of that kind of thinking but we are using much of the pit for our climate battery for the SHCS.

Another option is Phase Change Materials. Water is a very cheap PCM but not that effective for greenhouses. The amount of water you would need to maintain temperatures of the greenhouse would almost entirely fill the greenhouse. Furthermore, you don't want to shade the water with plants in the remaining space you do have. (With a pit-style greenhouse, you don't need it because the earth is your thermal mass) PCMs are used all the time in data storage centers to absorb heat from the computers and then discharge it later but can also be used in greenhouses to maintain temperature extremes. This also helps keep stress of the building materials to a minimum. Rgees is a PCM company that is trying to create a new market for PCMs in greenhouses and they have a pretty helpful blog:

http://greenhousefashions.blogspot.com/

When I wrote to them with questions they were very, very helpful. I plan on incorporating them into our greenhouse to further make it resilient should any of our other strategies fail.

A final thought, have you read the Underground Solar Greenhouse book? He did some interest experiments with cold frame-like greenhouses where he trenched the aisle so that he could stand upright and be comfortable. What he stumbled upon while doing this is the added advantage of having a lower area for the cold air to sink and settle away from the plants where it could do harm. It would then get warmed by the earth, rise and other cold air would take its place, progressively making the temperatures warmer.

In any case, there are lots of options for a resilient greenhouse. I look forward to hearing about your design as it evolves. Happy greenhouse designing!

Who wrote the Underground Solar Greenhouse book?

I am reviewing the other sites - thank you very much for the info.

Solar Greenhouses: Underground by Daniel Geery, is this what you meant?

I remembered the title wrong. It's "The Earth-Sheltered Solar Greenhouse Book" by Mike Oehler.

http://www.undergroundhousing.com/greenhouse_book.html

Let me know what you think!

curlygirl, thanks for the link to the YMCA GH project, looks like some useful info there.

The reason Sunny John's site has not been updated in a while is that he has past away. It's sad, because his blogs (which are now down) were a great source of info.

One comment on the YMCA site, I would hesitate to use ICFs in a GH project. Most have insulation (usually foam) on both sides of the concrete. Not really what you want, which is to have the insulation on the outside only. When I built my first GH, I used ICF for the foundation, but ended up stripping the inside foam after the concrete cured and moved it to the outside. This kept the R value the same, but gave me a concrete wall on the inside, and extra thermal mass inside the insulation envelope.

Steve,

I had no idea about Sunny John. I am so sorry to hear that. He seemed like he was up to some big stuff that really could help us live more sustainably. What a huge loss for us.

Thanks for telling me. My husband was starting to worry that maybe SHCS was not what it was cracked up to be since there did not seem to be much other activity on it. Online, it seemed like a couple of people were getting that impression too. I hope enough of us can keep it going since it has so many possibilities.

Thanks for the tip on the ICFs. I was not planning on using them but I was planning on insulating the interior because that is what L. Roper did. It will be nice to save some money on the insulation.

Thanks again!