I love my veggie garden, but I've always wished the summer was just a bit longer here in Vermont. I wish I could keep some lavender and rosemary alive through the winter. Every spring our few south-facing windows are jam packed with seed starts, which we eventually have to ferry in and out on nice days to start hardening them off. So, like everyone does, I longed for a greenhouse. A couple years ago I started collecting used windows whenever I could find them. I've seen some greenhouses cobbled together from a hodge podge of old barn windows, but I was aiming a little higher than that and scored some nice finds. I ended up with a bunch of aluminum framed storm windows, six sliding patio doors, and a few panes from former casement units, all for free! Regular checking of the craigslist free section and materials section can really pay off!
I didn't want to go to the trouble of a full foundation for a small, unheated, unplumbed greenhouse, but since this is made with real windows and framing I also wanted to make it secure and long-lasting. My neighbor gave me some old heavy galvanized angle iron in 4-5' pieces. I dug 8 holes down to frost depth. Actually I dug them until I hit a rock big enough that I couldn't get around it. Most of the time, that was ledge 2-3' so hopefully that's good enough. I put a scrap of rebar through a hole in the bottom of the steel, stuck them in the holes, and poured two bags of concrete around each one. To the tops I bolted a sort of perimeter beam of 2x10 oak, milled off our land. And the framing went up from there.
Windows were on the east, south and west walls, and covered the south slope of the gable roof. Anywhere that wasn't glazed I sided with locally milled (4 miles from my house) pine tongue and groove. I debated whether or not to have glass in the upper parts of the gables. But I did a quick sketchup model, did some shadow analysis, and decided I wouldn't lose that much sunlight to make it worth the hassle of glazing those areas. I shingled the roof with white cedar, which was a bit of a splurge over something like used tin roofing. But I think it looks nice and will have ever so slightly better insulation than metal. I also used some lower grade cedar shingles around the base, to cover the gap between grade and the oak 2x10s. Then I banked up some shredded bark mulch against that ($12.50/yd from the same local sawmill). I did think about putting some insulation in the north wall and the roof. But in the end I decided not to. It's not a heated, production greenhouse and I'm not really counting on growing tomatoes in January. I'd rather keep it all glass and wood without any nasty foam or anything.
I put the patio doors on the south facing roof. I took the double panes out of the door frames and screwed them down to the rafters with strips of wood, leaving the bottom edge free which should shed the snow nicely. I put a fan in the top of each gable wall. They are directly powered by small 15 watt solar panels (won't mount those until the spring). So on a hot sunny day when it needs the most ventilation, the fans will kick on full force. I have them both oriented to exhaust hot air from the top. Not sure if this is the right way to go? Another craigslist find by the way. I'll probably cover those holes in the winter.
I wanted to brace the windowed walls, but obviously not with plywood, and even a 1x4 brace blocked too much light. So I screw some eye bolts in the corners and ran small steel cables diagonally, tensioned with turnbuckles. That's our new ADU (additional duck unit) in the background too, with our 8 Welsh Harlequins and 3 Cayugas.
I debated for a long time over what to do for beds inside. There's limited room, so anything like cinder blocks or strawbales was out. I didn't want to cough up the money for cedar but really like boards as raised bed containers. A lumber yard about 45 minutes away was closing its doors, so I got all these 2x10s for a song. I also had a couple 16" rolls of aluminum flashing (craigslist again!!) so I tacked those to the inside of the boards before filling them. It doesn't make them waterproof by any means, but I think they will last longer by being somewhat isolated from contact with the wet soil. My girlfriend was a little concerned about growing food in beds lined with aluminum. I wasn't worried. Thoughts? I also dumped some old rotten logs in the bottoms, both to reduce the amount of soil needed to fill the beds, and as a kind of impromptu hugelkultur! The floor inside ended up being the same shredded bark.
I'm looking forward to seeing how this thing works. I plan to string up a hammock or sky chair for sunny winter days. At some point I might try to stack some thermal mass along the back wall. I have a little pump in the stream (about 50 ft away) that I use to fill the duck's water tub. I'll probably use that to occasionally fill a big barrel in the greenhouse which I can use for hand watering, unless I ever get more sophisticated.