This Summer's Project: An earth-sheltered greenhouse

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bill@geektrap.com

(But I'm telling the neighbors it's a fallout shelter, if they ask...)
For some time now, I've wanted a permanent greenhouse that would shelter our veggies from ravenous hordes of grasshoppers, and which would stay above freezing inside through the winter, so we could grow fresh food all year-round. A few years ago, I bought a copy of "Gardener's Solar Greenhouse - How to Build and Use a Solar Greenhouse for Year-Round Gardening" and had occasionally dragged it out and flipped idly through it on cold winter nights. Finally, I decided _this_ was the year!



Going Under
The version I'm building, pictured here on the back of the book, is built underground, so only the glass and part of the back wall extend above ground level. This allows for better insulation, more thermal mass for heat storage (more on this later), and a smaller impact on the view.


First, dig a big hole...
Amazing what one determined guy can do with a shovel, isn't it? (Well, I'm sure it is, but I hired a guy with a Bobcat to dig this one... ;-) It's 4 feet "below grade", where the floor of the greenhouse will sit. There's also a trench from the corner of the house to the back of the greenhouse, into which I've placed a couple of plastic water lines, a drain pipe for "gray water" from the house, a power line (for running fans, seed bed heaters, etc.), and some "Cat5" cables for temperature sensors, controls, internet access, etc.


Concrete forms
After the hole was dug and leveled, I built forms out of 2x8 pine to produce a rectangular slab with a rectangular cutout in the center which will be filled with gravel to provide a walkway between the raised beds. Observant members of the audience may notice that the forms are not parallel with the sides of the hole. This is because some dope (me) used a compass with the magnetic deviation from true north (around 7 degrees) conveniently marked on the dial to lay out the hole, but only after it was dug realized that the compass was an antique _German_ army compass, and the magnetic deviation in Germany is 7 degrees _west_, while the deviation in eastern Nebraska is 7 degrees _east_. *DOH!* Fortunately, although being a few degrees off from true south with the face of the greenhouse wouldn't result in _much_ loss in solar gain, I was able to rotate the forms inside the hole enough to compensate for the 14 degree error in the layout of the hole. *whew!


Crushed rock, rebar, & remesh

We filled part of the form with crushed limestone to control how thick the concrete was in various areas; it has to be 8" thick around the outside, but significantly less than that elsewhere, and concrete is expensive. On top of the crushed rock, we laid out 5/8" reinforcing bar and appropriately-sized pieces of reinforcing mesh, wired all of it together, and propped it up on chunks of broken cement block to position it roughly in the middle of the poured slab.


OMG, there's a cement truck here!

Sadly, I didn't get any pictures of the concrete pouring process, because I was up to my ankles in 80 cubic feet or so of concrete most of the time, but it went great. I hired a guy (hi, Will!) from Craigslist who had some concrete-pouring experience, and he, AJ, and I shoveled, wheelbarrowed, threw, dragged, screeded, and troweled about a million pounds of concrete into the forms. The red tubes sticking up out of the concrete will lead from the bottom of the growing beds to the "French drain" (a fancy term for a hole full of gravel) under the greenhouse, to drain out excess water and allow occasional flushing of mineral-salt buildup from the soil.


Block It Out
I got about 250 8x8x16" concrete blocks from a building torn down after the Hallam tornado fairly inexpensively via Eco-Stores, but I ended up buying the 200 or so 6x8x16" blocks for the inner wall new, since Eco-Stores didn't have that size. You may notice that some of the blocks are white on the outside; apparently the wall they were in originally was partially painted, so just in case it was lead-based paint, I faced it to the outside, away from the growing beds. The blocks in the outside wall are mortared together - something I'd never done, so I had to read up on it via a lot of web sites and books, but I think I got the hang of it. My mortar joints aren't particularly pretty, because I didn't go back and clean them up the way you would if it was a visible wall, but they seem to be plenty sturdy. I could usually mix about 75 lbs of mortar with a shovel, and lay about 20 blocks before I was hot and tired and ready to go do something else for a while. I left out part of the south wall until the foundation is done, so we'd have a place to bring in material without lifting it over the wall.


Bonding
The inner wall went a lot faster, because only the bottom row is mortared in place. The rest of the courses are "dry-stacked" with nothing between them, and then you trowel a 1/4" or so layer of "surface bonding cement" over both sides. The top course is solid blocks (and boy were _those_ heavy) so you don't have holes in the top of the inner wall. The top of the outer wall is capped with concrete and has anchor bolts for framing sticking out of the top of it, so the holes there don't matter. I had to cut some blocks to fit for the inner wall, which is surprisingly simple to do. You get a big chisel and a sledge hammer and just score the blocks on three sides, then give them a good whack or two on the fourth side and they crack apart on the line (more or less... usually...). I've got a lot of ideas I want to try with the surface bonding cement now, like using it to layer over carved styrofoam and/or wooden shapes to make light-weight but sturdy statues and fountains for the yard. AJ decorated the inside of the inner walls with mosaics made of broken-up colored glass, pennies, bits of composite counter top material, and a bunch of little aluminum disks I picked up some time back with the intent of melting them in my foundry.


It's Legal!
I finally got the analysis back from the engineer that was required by the building permit office, and got a building permit yesterday. Better late than never, right? ;-) I called for an inspection this morning, and the gentleman came out this afternoon to check out the foundation. He seemed to think it was just fine. Yay!


All Blocked In!
8/13/09
Four-hundred-fifty cement blocks, twenty 80-pound bags of dry concrete mix, five 60-pound bags of surface-bonding concrete mix, 120 gallons of water, and a couple hundred gallons of sweat later, the block work is finished! I told AJ that I thought we were supposed to sacrifice a virgin to consecrate the site or something. Since neither of us knows any, we skipped that part.


Here we see the (very) local building inspector checking the setup of our sump drain and pump.

The top of the sump is covered with pressure-treated 6x6 sections and then buried under a couple inches of crushed limestone to match the rest of the walkway.

Here are the cool mosaics AJ made out of colored glass, pennies, and aluminum disks on the walls around the walkway. We're having a little trouble with the pieces falling out of the concrete, so we may have to go back and glue them in with some caulking or something...

...and the steps leading up from the walkway to ground level.


Honey, I Buried the Greenhouse...


8/31/09
I ran copper pipe through the crawlspace of our house, connected it to the black poly tubing we previously buried out to the greenhouse, and tapped it into an existing water pipe a couple of days ago. Today, I finished connecting the two freeze-proof spigots (one inside the greenhouse, and one outside, since the next nearest place to hook up a hose to water the garden is about 80 feet away.) Five soldered connections and four hose-barb connections and no leaks! Woohoo! We then rented a Caterpillar skid-steer loader and backfilled the hole around the greenhouse with dirt. Seven thousand pounds of diesel-powered destruction, and the only mishap was one steel fence post I snagged without realizing it and bent into a new and interesting shape. Win! ;-)


(The pink and white stuff around the outside is expanded foam insulation four inches thick to help keep heat stored in the greenhouse from being drawn off by the surrounding soil. It extends all the way to the bottom of the walls, with more pieces covering the slab where it's exposed underneath the walls.)


9/7/09
Spent the last couple of days mixing 3,300 lbs of concrete mix, hauling it in buckets to the greenhouse, and pouring it inside the outer concrete block wall. This will provide a considerable amount of additional thermal mass. I also installed a couple of dozen anchor bolts to which the sill plate will be attached once framing begins. We then used the "sawzall" (I think it's my favorite power tool!) to trim the top of the insulation even with the top of the block wall.

Making the Bed
9/14/09
I spent the afternoon carrying and mixing nearly 4,000 pounds of concrete mix. I'd mix up a batch in the portable cement mixer and tote it to AJ in a wheelbarrow. She would then spread it around the bottom of the growing bed area and trowel it smooth. Prior to this, we had covered the broken brick "heatsink" (also from EcoStores) with sheets of cardboard (free from Slumberland and Pioneer Overhead Door) to keep the concrete from running down amongst the bricks, and pieces of concrete reinforcing mesh. The floors of the beds are sloped towards the drainpipes at the inside corners, to drain any excess moisture into the sump. We also buried three digital temperature sensors (potted in epoxy resin) and the associated wiring under the concrete slab at strategic places, so we can track the amount of heat stored and released by the rock beds.


We also poured a collar around the freeze-proof spigot outside the greenhouse.


Sensor Readings
9/15/09
I took a computer out and checked the temperature sensors this morning to make sure they survived being buried under concrete. The three currently read 72 (bottom of heatsink), 67 (top of heatsink), and 64 (inside of cold air return vent). The ambient temperature is 61. I'm guessing that the slab and the bricks had soaked up quite a bit of heat from the sun, and are now releasing it. By George, I think it works! (The completed greenhouse will have two ducted fans up near the top that will pump warm air down through 4" plastic pipe and out through perforated pipe buried in the the heatsinks, to store the heat to be released after the sun goes down.)


We've Been Framed!
9/20/09
Look! Walls! Kind of. I spent the last two or three days framing the walls and roof (where the glass will be mounted). It's starting to look like a greenhouse, instead of just a big hole full of concrete. I'm excited.


In the Pink!
9/27/09
I spent the last few days stapling up plastic sheeting (to keep moisture out of the walls) and putting green-treated plywood sheathing on the inside of the walls (the ones that won't be glass). I installed the packing in the lower window bays to fit the operable windows I found (which will also double as vents). There's a sample in the picture. I've also cut and installed pieces of 2" thick extruded foam insulation in all the stud bays. Wiring from the various blue boxes in the picture (receptacles, lights, and switches) will run across the face of the pink insulation and will then be covered by additional 1" thick sheets of insulation and finally by siding. The two large rectangular areas visible on the back with no insulation in them will be cut out and covered with insulated doors for ventilation. Oh - and there's a door now. Which caused my cat no end of confusion; he got all excited about going through a door into a place he'd (presumably) never been before, but when he ran through it and was still "outside" I think it almost made his head explode. He had to go back and forth through it several times in a row, and still looked really confused. Poor cat...




A Glazed Look in My Eye
10/17/09

Lots of new developments. I've been so busy working on the greenhouse that I forgot to update the blog!

As you can see, there are now windows in the lower front (which can be opened to allow air circulation as needed). They're installed "backwards" because we decided that they would be hard to reach over the plants from the inside, and they might even hit the plants if they opened in. As a result, the handles are on the outside, so they can be opened outward.

All of the wiring for the receptacles, lights, fans, thermostat, etc is in place and connected to the electrical sub-panel in the potting shed. (Did I mention I framed in the potting shed since our last installment?) The electrical inspector came out and gave the rough-in his blessing, so now I just have to install the receptacles and so on (after the wall insulation and siding is in place) and get a "final" electrical inspection.

I've also installed the support rails and horizontal rafters which will hold up the sliding glass door units which form the lower part of the "roof". I discovered that some of the glass doors I had picked up had glass that was significantly larger than the others, so I ended up having to go back to EcoStores for one more set of doors. I also located a company in Omaha (Regal Plastics - some really good folks, especially Joe, the operations manager - Hi Joe!) that had several sheets of "Polygal" multi-walled plastic glazing they were willing to sell me at a good price. I made a road-trip to Omaha yesterday and picked up enough to fill in the two front openings on each side of the greenhouse, as well as make the pieces the book specifies for the upper part of the roof. I'm hoping to be able to use three of the remaining glass door units mounted horizontally across the top instead, but we'll see.

I ordered some painted steel flashing from AJ Roofing (no relation to my AJ, but also good folks to work with) to go around the outside of the foundation. It will cover and protect the vertical insulation sheets where they extend out of the ground, as well as the narrow horizontal pieces of insulation AJ cut out and put in place on top of the foundation wall today. I spent most of the day cutting and fitting the flashing pieces into place while AJ put in the second layer of wall insulation over the top of the wiring. Tomorrow, I'm hoping we can hang some of the siding and prime it for painting.

BesideingMyself
10/21/09

I spent today putting up the siding on the north side of the greenhouse. It's kind of a booger because although the plans called for siding the greenhouse and _then_ building the attached potting shed, I built the potting shed first since that's where the electrical sub-panel and a lot of the wiring is located, and I had to have it in place for the inspection. As it is now, I've had to cut the siding out around around all the electrical boxes and around all the rafters and wiring from the potting shed. It drizzled all day, and I've lost track of the number of times I smacked my thumb with the hammer. I would have used the pneumatic nailer, but I didn't want to drag the compressor out in the rain, and it seemed silly anyway, since there were only "a few" nails. A few in this case ended up being about 150. Ugh. Tired and sore, but I got the whole north side covered. Just one sheet on each side (with no cutouts!) left on the greenhouse, and then I can side and roof the potting shed. That should go fairly quickly (he said, naively) because there's only one cutout for a light fixture on one piece of siding. I'm planning on putting corrugated translucent fiberglass sheets on for a roof, so it will let natural light into the shed during the day. (It got dark before I got a picture of the new work - maybe tomorrow.)


Potting About
10/25/09

Here's the potting shed with all the siding on it. I put that on a couple of days ago. Today, I trimmed it off to match the slope of the roof, and installed brackets and purlins to support the corrugated fiberglass roof.


Put a Lid On It!
10/27/09

Today, AJ primed the siding for me. It was factory-primed, but it had been piled in a guy's barn for about 15 years, so I figured a fresh coat of primer couldn't hurt. I spent the day trimming, drilling, and screwing down the translucent fiberglass roof panels on the potting shed. I guess I didn't get a picture of it, but all the purlins (the horizontal pieces) have support strips made to match the "waves" in the panels, and all the rafters (the vertical pieces) have special half-round molding tacked to the top of them to coincide with the peak of a "wave" where the panels cross them. It was tough getting the spacing of all the support pieces right, so the "waves" in the supports lined up with the "waves" in the fiberglass, but I'm pretty pleased with the way it turned out. It took a lot of special "pole barn" screws, which come with a neoprene washer bonded to a steel washer on each one. You have to pre-drill all the holes in the fiberglass so it doesn't crack, and then when you tighten down the screws, the neoprene washer gets squashed between the steel washer and the top of the fiberglass, forming a waterproof seal around each hole. And only minor injuries were incurred, so it's a good day! ;-)


All the Trim...ings
11/04/09

After spraying expanding foam insulation in gaps around the windows, and caulking all the seams in the framing, I cut and installed the trim around the front windows today. And sealed it with more caulking. I think I'm up to something like 18 tubes of caulking and five cans of spray foam so far on this project. We started priming the whole interior today too.


AJ has been working tremendously hard, shoveling black dirt out of the trailer, mixing it with Perlite, Vermiculite, and compost, and shoveling it into the growing beds. Looks like good stuff; if I were a plant, I'd want to grow there!



We'll Leave a Light On for Ya'
11/07/09
The electricity has been on in the greenhouse for a couple of weeks, but these are the first pictures I've gotten after dark, with the lights on.


Growing Panes (Sorry. Really.)
11/08/09

Thanks to the help of Chris and AJ, the greenhouse now has glass in the lower part of the roof, courtesy of recycled patio door panels purchased from EcoStores, most for around $5 each because the wooden frames were pretty well shot. (Contrast that with the $200+ each for new ones I was quoted by several local glass companies. Yay, EcoStores!) We inserted backer rod in the gaps around the panels and I went through roughly 16 tubes of caulking sealing up the outside of all the panels. Tomorrow, I'll probably caulk the _inside_ of the panels. With a greenhouse, it's kind of a toss-up whether the inside or the outside will receive more moisture, heat, and humidity.


Are We There Yet...?
11/13/09

The weather is turning colder by the day, and every time I think I'm almost ready to install the Polygal multi-wall plastic windows in the east and west walls, and _some_ kind of glazing in the upper part of the roof, there's always some "little" detail I forgot, that takes up the whole day to finish. Like measuring, cutting, and installing the trim strips that hold the Polygal in place. And the ledges under the east and west window openings, carefully sloped to shed water. The original plan in the book called for using squares of Qualex (a material similar to the modern Polygal) to fill the openings above the patio door panels in the roof. I wasn't too excited about having that much plastic overhead in an environment where we get as much snow, hail, and wandering cats as we do. I kept sort of ignoring that part and hoping something would come along that solved the problem. Last week, EcoStores' new featured item was a bunch of odd-shaped, insulated glass windows that were bought by UNL, but were apparently ordered in the wrong sizes. Two of them were 102" x 31", which is almost exactly what I need for the overhead glass. I snapped them up the next day and brought them home, only to discover that they are "Low-E" treated glass, which means they block quite a bit of sunlight (and heat) from entering the building. Normally, this would be a good thing, but in a solar greenhouse, you want as much light and solar heat gain as you can get. After much stress and reading many web sites about Low-E glass, the consensus seems to be that if you live in a relatively warm climate, you want the Low-E coating on the inside of the outer glass pane, to reflect back a big portion of the sunlight. If, on the other hand, you're living in a colder climate (or a solar greenhouse!), where you want to capture as much solar heat as possible, you have the Low-E coating applied to the inside of the _inner_ glass pane, where it will allow solar heat in, but not let heat from the inside radiate back out. Based on some testing I did after dark, using a digital camera with an infrared filter and an IR-emitting remote control transmitter, it _does_ appear that most of the IR gets through one way, but not the other. Based on that, we're going to give it a shot and see what happens. Accordingly, I built a bunch of supports across the top of the greenhouse to hold the new glass pieces. As soon as the weather is warm enough to paint and prime the new wood, we'll install the last of the glass panes and the Polygal end windows. More to come.


Light at the End of the Tunnel!
11/21/09

AJ painted the new supports for me a couple of days ago, and by using the three of us, a couple of heavy-duty cargo straps, and some wood blocks, we were able to slide the last two (very heavy) glass panels into place on the top part of the roof. With a little tweaking and adjusting, they fit great. I also cut and installed the insulated plastic panels in the east and west ends of the greenhouse. With the addition of a couple of pieces of siding material along the ends of the new glass to fill out the opening, the greenhouse was enclosed! There's still a lot of caulking to do, both inside and out, and a bunch of trim I cut out and painted today to install on the outside to cover and protect the seals between the glass and the wood, but the end is in sight! Woo hoo! I also installed and hooked up the big ducted fans that will circulate warm air from near the peak of the roof into the heat storage areas under the growing beds. It's already been staying quite humid and very warm inside (in excess of 80 degrees on a day when it was 45 outside, using only captured solar heat!). I think it's going to work. It's starting to look a lot like the picture on the cover of the book, huh? :-)

I Feel My Temperature Rising
11/28/09

Chris built a neat little box using an Atmel microcontroller and an LCD display on a custom circuit board that reads the temperature data from four different 1-wire temperature sensors and a combination temperature/humidity sensor, displays it locally, and transmits it to this web server for logging and display. You can select graphs for the past 24 or 48 hours by clicking here.


Happy little veggies growing in Nebraska, a month before Christmas... Yay!

Shamble for Your Lives!


1/30/10

AJ found a pretty healthy crop of aphids starting on a few of the plants, so we ordered a box of ladybugs as a biological control. The smallest order was 4,500 bugs, which should be plenty.

We released about half of them (no, I didn't count! ;-) the day they got here, and the rest today.


The plants are all looking pretty happy. Growth has been slow due to low temperatures (and probably even more due to cloudy/overcast days) but they're coming along. We've had some radishes and some salads from the greenhouse and enjoyed them quite a bit.






One of the cauliflower plants that AJ transplanted has bolted, probably due to the sudden warmth. We won't get any food from it, but it's pretty, so we've left it.






Here's to the cutest, sweetest "farmer" I know. I love you, kiddo!



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