A Winter Greenhouse Construction Plan for Northerners

[Aquamaple]

First off, happy 2014 fellow aquapons! I am building a winter-ready greenhouse this spring, currently building a materials/cost list which led me to some questions you all may have valuable experience with. I hope this thread will be invaluable to others such as I who wish to grow year round in cold climates. It is currently January 2, 2014, and it has been below 20°F for a couple weeks now with air temperatures monday expected dropping to 5°F, possibly below 0°F for the rest of the week. I need serious thought to go into this greenhouse, and I have thus far researched much and pondered greatly on the topic. If I remember correctly, I live along the 42nd parallel, in Michigan.
Please excuse the jumbled communication, I'm using my phone and apparently it doesn't like the mobile interface because I can't scroll up to edit my text. I will add to this thread and edit at home, when possible.
I have found successful designs I plan to base my greenhouse off, and I will soon link those so you may have an idea where I am headed. Essentially, it will be tall and insulated on the North side, a steep glazed roof sloping toward the South with a shorter wall there. I will explain more of my ideas later, but that is the gist of it. I plan on using a combination of SHC and geothermal energy.
My first questions:
1. I am capable of building, but not too knowledgeable about building trades, as of yet. WHAT would be the benefit of using a concrete perimeter foundation as opposed to just planting my treated posts in the dirt? I plan on using foam board underground all the way around to assist with insulation. Im sure a concrete foundation would look prety and work well, but I currently see it as an unnecessary cost. Am I right? The inside square footage of my GH will be dirt, for many reasons I will later explain.

Thanks for all your help, this is going to be a fun project!

[Glenn]

Greetings,

It IS important to have a stable foundation. A kneewall or stem wall is recommended to reach well below frost line where you are located. In northern areas that can be several feet. The purpose even in warmer climates is to prevent the heaving of the structure as the soil freezes and thaws making components buckle etc.

I have seen simple pole foundations heave even though they were planted at least a foot below frost line. Someone told me and  haven't heard otherwise that a simple landscape cloth with a vapor  barrier plastic around the perimeter would prevent the heaving action. But just so you know the risk.

[Aquamaple]

Glenn,
Good to know! But, hokey pete, that will add some cost! We have to bury our water lines 4 feet deep to avoid freezing. Would the knee wall have to go all the way down to 4'?
I wonder if anyone else has experience with the vapor wrap method? If only insulation is required to prevent heaving, would not the foam board prevent that, perhaps if the edge of the board was up to grade or even a little above? I am planning on running flashing around the perimeter to prevent rodent damage, as well.

[Robert C. Wood]

If you do not want to put a cement wall in you can get away with putting up a wood perimeter for a base just make sure you replace the earth that the walls will sit on with grade "A" or "B" dirt because is will drain water better than the typical top soil the most yards are covered with and to help with the frost heaving you can use bails of hay to line the outside of the GH. I believe that 2 wide from the wall should be enough to reduce or stop any frost heaving.

[Aquamaple]

My greenhouse is going to be sitting on top of a couple feet of crushed asphalt. Do you have any idea what crushed asphalt would do? Currently my yard is too low for my comfort, and too low for my subterranean heating and cooling. I plan on raising the whole thing.

[Aquamaple]

I suppose I could also ask the guys who I'm going to buy it from.

[Robert C. Wood]

so long as the crushed asphalt (aka rap) does not get compressed when hot in the summer it will stay pourous. it will be the same as a driveway no insulating properties at all. the frost line in your area is most likely just 2 feet deep at the most. the reason that I say use A or B grade of gravel is because of it's high draining, you want as much water to drain away or below the frost line to negate the heaving of the ground in winter. if you are going to raise the ground level of your yard then you have to remove the rap because it will compact and hold the water in your soil which you don't want.

[Glenn]

Aquamaple,

It might help to know or understand how large of a structure you intend to build, how long would you want it to last as in a few years or several decades, and what kind of terrain will it be built upon. Assuming that commercial occupancy permits wouldn't be required, and the size is relatively small, you really might consider The Buried Post Footing on concrete alternatives. Here's a link to something I've seen in the way of pole barn construction in Colorado.

 The Buried Post Footing

  https://www.decks.com/deckbuilding/The_Buried_Post_Footing

 And here's a map showing the EXTREME case depth of frost line in the continental U.S.

  https://www.decks.com/deckbuilding/Deck_Footing_Frost_Depth_Map

Hope this helps.

 

[Aquamaple]

Robert, you have given me plenty to reconsider concerning the RAP. I was planning on putting that down mainly because it has been described to work well with SHCS, but I am sure I can find a suitable replacement aggregate.

Glenn,
I have more detailed rough sketches and measurements of my yard in my notebook, but here is my plan in basic... I want to build as wide N-S as I can afford and fit inside my sunny spot. I believe my maximum usable space including space needed for a lean-to structure off the N side, is 13yds. I think I have something like 22yds the long way, E-W. I am planning on designing and building this greenhouse sort of in phases. Phase 1 will be probably end up being 1/3 the length of the finished GH. I kind of have some ideas about how to build the E wall in a way that I can fairly easily take it off in two or three large pieces, add phase 2 length, and re-install the wall. Probably this weekend I will crunch some numbers and determine how much volume of GB I want to start with, and that will help me get a closer idea on my phase 1 GH length. Probably somewhere around 20'. My yard has a LOT of clay. And it gets very wet when I get a lot of rain or melt off. Thats why I'll be bringing in a lot of aggregate to bring it up, so all my mess drains AWAY from the GH. Too bad about the crushed asphalt, I can get it fairly cheap. I may still use it way down deep, then put something else on top. I'll have to price out a comparable aggregate that wont pack so tight.
Thanks for posting those links! I will spend some time checking out that info.

[Sonja Martin Young]

We just finished our 22x 36 greenhouse here in Homer, Alaska. Not quite as cold as you get but for longer. Probably similar frost line. We put 2 inch R tech on our cleared pad and then put Amvic blocks (that you normally fill with concrete) around the perimeter. We filled those with packed sand. We put hot water piping on the R Tech and air pipes ( for a climate battery). Then we put 18 inches of packed sand on top. We laid timbers on the Amvic and built the greenhouse on top of that. Then we put R tech 2 feet laterally around the outside to keep the frost from heaving the foundation. Oh yes it is expensive but I hope to only do it once and do it right.

[Jeremiah Robinson]

Hi Aquamaple,

I don't know much about foundations, though I did help build a pole barn here in Wisconsin a few years back and it's doing well.

The most important things to think about with designing your greenhouse is where you're going to store the sun's energy.  Black-painted barrels filled with water against the back wall are a great way.  You can also do one of those fan systems with plastic tubing buried in trenches to condense water at night and evaporate during the day for more energy storage.

It might be worth also considering how much energy, time and money you want to go into insulating your greenhouse and how much you want to spend insulating and air sealing your aquaponic system itself.

[Aquamaple]

Jeremiah, thanks for the suggestions. Man I am so far behind in my plans! I broke my ankle about 2.5 wks after I started this post and I JUST got out of my air cast four days ago! I do plan on using subterranean heating and cooling as my thermal mass, in combination with home made geothermal fishwater cooling, and supplementing the SHCS with geothermal. I hope that I will be able to out it together similar to Sonja's greenhouse, but I plan on an aggregate floor tamped down, or a drainable brick pattern. I still haven't found the perfect material to surround the SHCS tubing, but I suspect it will end up being screened stone, or crushed stone crushed big enough to drain.

Thanks!

[Aquamaple]

Sonja,
How did your greenhouse perform this winter? Was all the insulation worth it? What would you do different? Is the hot water piping on the R Tech coming from a water heater? Outdoor boiler? Solar collector?

Another project I have in the works is a stratified downdraft gasifier (FEMA Gasifier) and this process has a byproduct that is a LOT of heat. I am thinking of adding PEX tubing into the greenhouse to take advantage of this extra energy. I'm not sure if I would use it above or below ground yet.
Thanks!