Indoor raised bed design w/SHCS

Hello Permies... we are just finishing up the structural work on our solar greenhouse and will begin building our maze of raised grow beds. Each bed is about 4x18 and they sit on top of a subterranean heating and cooling system. Each grow bed has an insulated heatsink consisting of washed stone warmed by buried pipe which circulate air beneath the stone. The south side of the building is glazed with 16mm Lexan. That said my main question is how to build the grow beds, made of rough cut lumber supported by rebar. i'd like 3-3.5ft tall, two feet of washed stone, 1-1.5 feet of potting mix, separated by weed barrier. The foreman says 2.5 feet is the most economical and stable. The primary consideration is being able to keep the rootzone from freezing, the second is ergonomics... we don't want to be bending over all day long. Thanks for any suggestions or help developing the design. Ace

Ace, Iam jelous. Thats a great looking greenhouse. It might look good to have vines covering the metal too. What exactly do you mean by subterranean heating and cooling, how does that work?

For the weed blocker, upgrade to silt fabric. Erosion control and masonry suppliers carry it in 3' and 10' wide rolls around here. Its much thicker, longer lasting and effective.

For the beds, it really depends on what you can find or have sawn up for you thats the most economic. Looks like youre east coast so locust, white oak, cedar or even hemlock could be good species. If youre doing a rough cut floor too then I may specify two floor beams with short 4' lengths at 2" thickness (2x6(or random)x 4'). That could reduce bending over height too. For the walls, butted 2x material with alternating corners held with structural screws. Would need to reduce to 16' lengths max I suspect and would need some collar tie type thing. Rough sawn 2x is the thinnest material I see being cost effective but going thicker would obviously be better.

Hey Brian Thanks!!! She is ready to sail the seas any day! A subterranean heating and cooling system is a series of perforated PVC pipes that are buried under many tons of washed stone within insulated beds. Air is blow thru the piping to either warm the stone beds or to blow cool moist air into the greenhouse depending on soil temps and also ambient temp. Utube 'solar greenhouse, SHCS, Earthen Path to see the model we worked from. Now...since I have your attention... each subterranean bed will have a raised grow bed built directly above it so we can actually directly warm our soil during cold months. Being NY/PA border trash, we have more days below 45 than above so we imagine using this focused heating system alot. Here lies my current question....using rough cut 2x8 as the frame we dont' want the beds to short(burn roots, dry soil, lots of bending over) or to tall(too much heat loss, cost of building). We need about 1.5 feet of soil sitting on top of X feet of washed stone. Would like that X to be 2ft for a total of 3.5ft raised bed for ergonomics sake but 2 ft is the most logical from a materials standpoint.

Interesting! What drives the air? Passive or active fan?

42"/8" = (5) 2x8s and a 2x2. Or, 42"/12"= (3) 2x12s and a 2x6. Or, (7) 2x6s. Youll definitly need more collar ties at those heights. Probably one per 8' but 4 would be better is my wild guess. How many beds? Thats going to keep someone busy for awhile.

Active fans, solar powered and thermostat controlled. We decided to do build a few different beds for this year to run tests between different heights and washed/cobblestone. After building two beds 24 inch tall with 2x8x16's its am hesitant to use any more material. Pics attached...

Hi Ace,

Great looking building you have. What type of wood did you use for the beds? I see it looks rough cut, are you going to line the inside with plastic to help protect it? I will be doing my raised beds shortly and also plan on the SHCS design (building still under construction, way behind schedule and over budget . I was torn between wood and concrete blocks because concrete blocks take up so much space (8" wide). But then I saw someone using blocks leave the concrete block holes open on top. Each top block has two built in 4" containers. He grew one onion or other herbs in each square and herb roots would stay put and not wonder. I guess you could also grow about anything in the holes. So the width of the wall was not wasted space and the block helped keep the soil inside the block a constant temperature.

I see a lot of people using rock for the SHCS system. I read somewhere using well drained soil was ok. Seems the more surface contact with the pipe the better and they could possibly wick up moisture to the plant bed. Also the natural organic structure of the soil was better for keeping mold and mildew down verse rock which doesn't have the same organics critters in it. Some SHCS remove so much moisture they run the exit of the pipes into a sump to be pumped out. If that was captured in a soil bed it could help water the plants. Can you give me your pros and cons between rock and soil?

Best Regards and I look forward to your progress.

Jason

PS found the links:
http://infolightandliving.com/projects/care-n-share-greenhouse
http://forums2.gardenweb.com/forums/load/cornucop/msg0416480222824.html

Hey Jason.... glad to hear I'm not the only one over budget(but money is cheap and I got a sweet business loan if you need a biz plan to copy). We toyed around with various potential substrates for the SHCS as well as which style of vented plastic pipe. We decided on rigid PVC(to prevent any underground pipes from collapsing), crushed rock was used for its thermal mass and we worried about ground moisture causing a finer material to clog piping.
The raised beds are 2x8 rough cut, we chose wood over concrete for price and thermal mass(wood holds more than concrete). We will line the beds with UV stable plastic, fill half way with more stone(testing cobble vs. crushed rock), then about 16 inches of potting mix. this winter will be alot of data collection to gauge how well the SHCS works and how 2' beds compare to 3' beds, etc. If you are interested in following along on FB here is our page.... https://www.facebook.com/WellsvilleNyBiodynamicHenhouse?ref=hl

Hi Ace,

I just liked you on Facebook. I see where wood would be better at retaining the heat. The clog factor I also understand, that would keep the moisture from draining out. So many things to think about...

Hi Ace,

Have you read: http://www.sunnyjohn.com/indexpages/shcs_faq.htm

what is the size of your building? was it designed by you or was it a kit?

Jason