Greenhouse build

Darren Wright

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I've been thinking about building a greenhouse for a while. I've been looking at various designs and the Gothic style seems to be one that would be a good year round structure. I'm looking at one of the DIY kits that your use the 1 3/8" chain link fencing top rails for most of the structure. I've ordered a bender and several of the gothic hoop kits from the following site. The kit is per hoop and includes the top connector, connectors for the brace, and connectors for each purlin.

It's looking like for something that would endure snow load 4' OC hoops would be needed, so I'm starting with what would be a 14.5' x 24' x 10.5' greenhouse. I don't have the braces in the drawing, but they would connect across the hoop between the top purlins. The lower purlins on each side would most likely be 1x4's run the length of the structure for attaching wiggle wire tracks and to allow for roll-up-sides for the lower halves to allow a cross breeze through the greenhouse.
GothicTunnel 24ft.png

Hopefully the bender will arrive this week and can start assembling the jig table to start making hoops.
 
I would strongly suggest auto vents in the top of the end caps (looks like that's part of the stock plans maybe?)

The connectors and fencing rails seem like a nice way to put this together, should be a smidge stronger than the bent EMT based structures.
 
I would strongly suggest auto vents in the top of the end caps (looks like that's part of the stock plans maybe?)

The connectors and fencing rails seem like a nice way to put this together, should be a smidge stronger than the bent EMT based structures.
Yeah, vents are in the list of things to research/add. If I build it down at the farm a spring fed water wall for cooling will be included. High winds shouldn't be an issue down there, mostly concerned about snow loads for our area.
 
I like the looks of this style. Better snow load handling over the typical high tunnel. I have the 12' hoop bender from Johnny's and want to try a 12' x 25' in my garden but haven't figured out where I want to put it. I think you can also get polycarb panels to skin them with for more strength.
Top rails, T Posts, EMT, 6"x6" welded wire mesh (WWM), and cattle panels can be big players in the garden. EMT slipped over rebar makes great frames for WWM or cattle panel trellises. A roll of WWM makes tomato cages that will last for a long, long time. I bent cattle panels to make a walk through tunnel for growing pole beans and squash. They also make great and long lasting trellises for things like cucumbers. All my raised beds have EMT hoops, also bent with a Johnny's jig, to support various covers like Agribon, insect netting, shade cloth or green house plastic. The chain link fence top rails and posts are great for creating garden structures where you want more strength than 1" EMT. I used them to build the frame for bird netting over my blackberries. Lots and lots of uses.

A couple of places that sell fittings for the top rail: here, and here. Have not used them, but they look interesting.
 
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A couple other notes from my greenhouse design books. You might already have most of these on the docket but figured it was cheap to throw them out there :)

I would highly suggest designing in a cold sink. This is a 2-3' wide trench dug at least one preferably two feet below the frost line alongside the southern edge of the greenhouse. At the ends of the sink you want cold drains, if you're on a slope and can run a pipe downhill from them that's an option but easier is to use 3" black standpipe and just run that up the outside of the corner of the greenhouse from the bottom of the trench (an L at the bottom of the pipe is fine). The black pipe will act as a thermal flue and pump the cold air out of the bottom of the trench. Because cold air sinks this pulls a lot of the colder air out of the greenhouse and adds about a climate zone. I think this makes sense to design in and build up front for two reasons, first its part of the location choice, and second it probably won't get done otherwise (at least at my house haha). You can cover the trench with boards as long as they have some spaces between them so air can flow through. A raised bed on legs above it works quite well.

A portable water wall along the north side will also add about a climate zone maybe more. This may well be overkill, I'm not sure on your actual temperature ranges at the property. This mostly makes sense imho if you're planning on making this a true 4 season greenhouse (and if not you can save the snow load problems by just pulling the plastic off over winter..). This would probably be be something you'd want to put in in the fall and then remove in the spring for more space. If you can find some 55g plastic drums and paint them black a double stack of those on the north side would simultaneously give you a LOT of thermal mass and could also potentially act as part of the snow load support system (might require a bit of thought on tying it together.. but a 55g drum full of water isn't moving very easily). Those are pretty light (empty) and easy to get. If you ran even a trickle of the spring water through it it would never freeze and you'd have a lot of thermal mass (in that case think of each row of drums connected at the bottoms and one inlet and outlet near the tops of the end drums. The black wall also gives you a warm place along which to plant some stuff that likes a little extra heat over the winter. Water when it freezes is tremendously exothermic so even milk jugs full of water as a wall on the north side make it pretty unlikely for the rest of the greenhouse to freeze except in extreme weather. In really cold areas you'd want to build a solid structure and sink the north side into a dirt hill then face that with a water wall but where you are I think just a water wall would buy you a ton of temperature regulation. If this proves inadequate or marginal a stack of straw bales as an insulation layer behind the water wall would give you a few more degrees of temperature pretty cheaply (and recycles into mulch and compost in the summer nicely, you'd probably get 4 or 5 years out of the bales for this use though). In either case a a plastic curtain behind the bales or drums to create a dead space and stop airflow from the cold side would also help a lot). I'm bringing this up now because it might change your bed layouts somewhat.. I could see maybe three rows of beds and the south two are four season with the north row being abandoned over winter behind the thermal wall.

For a four season greenhouse I think it might also make sense to plan on some way to hang a second layer of plastic on the inside if your overlay is a single layer sheet. I don't think it would be super hard to add some hangers and use the snap clamps around some EMT every 2'-4' or so. I'd probably only do this on the south side and across the top and just curtain off the north side as above. This doesn't need to be perfect but a bit of dead air space can go a long ways towards keeping freezing temperatures out. There's some trade off here between letting enough sun through and the extra layer of plastic, it also doesn't have to be structural so 2 or 3 mill is generally more than sufficient for this layer.
 
Thanks guys, lots of great info. Yeah the plan is to eventually do four season with it.

I plan to do two layers on the top and blow air in, supposed to give about an R5 value. The end walls may be solid at least on the lower half, but insulated.

This one will be setup here at the house with natural gas ran to it for heating. Eventually I'll do one at the farm, we have a wood burning boiler to heat the house using baseboards there, with a heat pump and propane backups. I believe we can add additional pumps/lines to the boiler, which I'm hoping to add some blowers in the greenhouse for to warm it over the cold months, with propane as a backup.
 
This gets into experimental design a bit, but I've thought a rocket mass stove would be a pretty sweet way to heat a greenhouse. I've been trying to convince my one friend to let me build one in his greenhouse :D

I suspect for a lot of the winter with some tweaks though you could be 90% passive. I like passive systems both because they're cheaper but also there's just less to break.
 
This gets into experimental design a bit, but I've thought a rocket mass stove would be a pretty sweet way to heat a greenhouse. I've been trying to convince my one friend to let me build one in his greenhouse :D

I suspect for a lot of the winter with some tweaks though you could be 90% passive. I like passive systems both because they're cheaper but also there's just less to break.

I've been considering ways to store the warm water and take direct load away from the boiler. One idea is to use a large water tank and basically bury it in a couple of layers of straw bales. if memory serves me correct, they are about and R75 value when tightly stacked.
 
Yeah straw is pretty awesome insulation and in an ideal world reasonably cheap (I say ideal world because the cost here has gone way up the last few years).

I'd be careful about putting something that has significant temperature differential directly in contact with them though due to condensation concerns which could rot them out pretty quickly. I think a bale wall behind the warm wall would be safer and about as effective. The other challenge is to avoid airflow through the bales. In straw bale houses this is accomplished with plaster which breathes nicely as well. For the greenhouse use case I think sheeting the cold side with a bit of an air gap between the sheeting and the bales (so condensation doesn't roll onto the bales themselves) would be pretty effective.

I've also seen various more complex designs around the cold sink with putting coarse rocks into it as a thermal mass and pumping in hot air in the winter (in mostly passive systems this can be air captured near the top of the greenhouse by turning on a "vent fan into a tube" if the peak temperature rises above a set point) and using it as a source of cool air in the summer (reverse the fan's flow...)
 
Discovery Channel has a series called "homestead Rescue" and they seem to do a lot of green houses and some in some pretty severe temperature area and one of the things they often due us create a heat storage bank by burying rock and circulating the air onto the rocks during the day an d letting the rocks heat the green house at nigh. Seems like a great idea for a passive heating system.
 
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