Glenn's passive solar greenhouse build

After much research and observation, I have started my dream of building a passive solar greenhouse. I’ve decided to use Permies as the medium to share my project. I love this site.
I drew inspiration from many sources but the core design came from uMinn’s Deep Winter Greenhouse project. The exact plans are self-designed and so far construction has been just me, but definitely influenced by what I’ve learned from other threads on Permies. I welcome questions and comments.

Some quick points:
• I’m in New Brunswick, Canada. Zone 4.
• Growing goal is to extend my season from March and to November (outdoors the growing season is only June to September)
• Dimensions: 32’W x 16’Dx  14.5’H (I tried to hit 2-1-1 ratios). Oriented so the long side faces South.
• 2x6 wood construction, steel roof/siding, insulation TBD (narrowed down to mineral wool or fiberglass)
• It will have a Climate Battery/GAHT (Ground to Air Heat Transfer).
• Glazed with SolaWrap

Climate Battery:
The GAHT was a huge factor in the overall design and cost, but I felt it very much inline with my goals. I could have built several hoophouses for the cost of just this system but I want to grow in March, not 4x the size in May when I’m already busy outside. I also don’t want to rely on supplemental heating. I’m going with the full rock bed style like uMinn instead of layers of drainage pipe surrounded by native soil. I live very close to a quarry that has suitable rock and eliminating hundreds of feet of pipe seems very appealing from a construction standpoint.

Foundation:
The foundation is on concrete piers, as inspired by some of the Ceres Greenhouse photos I saw online. I did not want any wood touching soil, but also didn’t want a full concrete “basement”. This option seemed the perfect hybrid. The pit was excavated down 4’, I went with 6ft tall 8” piers on 19” footings. I’ll be landscaping the perimeter so the new grade is a foot higher the originally, sloping away. Doing the math that leaves a foot of clearance above the ground before any wood construction. The entire perimeter of the foundation is going to be wrapped in R10 styrofoam insulation. The foot that is above ground will be covered with flashing.

Glazing:
For the glazing wall, originally I was going to go with a straight wall at 60 degrees, glazed with inflated poly. Much like the Bradford Research Center greenhouse. I ultimately opted for a gambrel style roof instead. Partly because a straight wall calculated to 13’ and I figured if I’m going to splice, why not use as much of both 8’ pieces as I can and can some head space by putting them at an angle. Partly because I feared the plastic would “bounce” a lot on a flat surface whereas having a change in angle would keep things tighter. Partly because I really like the look of Penn and Cord’s greenhouses (though structurally very different). Although I haven’t purchased the glazing yet, my current plan is go with with SolaWrap. My quotes have it at double the price of poly over a 12 year timeframe, but that doesn’t account for the labour savings of replacing poly every 4 years or the blower to inflate it. Polycarbonate is a dream; it’s way outside my initial budget. R-values seem comparable on all 3.

This build greenhouse is more of a starting point for personal growth than just a one time project to grow more food. I have many future projects in mind for the interior, often things that I can’t do in the house because it would void my home insurance. For starters, a rocket mass heater. Secondly, interior rolldown bubblewrap as an insulated curtain. Even with an insulated glazing surface, that wall is a relative gaping hole when compared to the rest of the structure.
I’m late in getting this thread started, as the build has already begun! So here are a couple pictures to get things going. One of the profile of the greenhouse (not to perfectly to scale), and another showing the inaugural ground breaking.

Plenty more to come of course. Since it’s not entirely built yet, still chances to change as opportunities are discovered.

Here is a picture of where things currently stand.

The concrete work is done. I have 6x6 cedar beams forming a perimeter frame, except for the north side where I made a 3 ply laminated 6x8 to handle the roof weight).

The greenhouse is going to have a 4.5x11.5 ridge beam (3 ply 2x12, already built just waiting to go up), supported on the end walls and by 2 piers to in the middle of the greenhouse. Originally I was going to do 2 ply 2x12 with the center piers on 8' spacings (as per the uMinn DWG design), but I had a beautiful Spruce tree topple over in a windstorm this past winter and want to use that on the piers instead of cut lumber. They are much larger than the 4x6 called for in the plans and I felt it would make the greenhouse seem too cramped so I changed things to have just 2 supports and spread them out. I welded custom concrete holds for the logs as per a design I saw on log cabin construction.

I've started adding in the rock for the climate battery. Plans for call for "1.5 inch+, no fines", and most of the DWG prototypes having using river rock. I'm using 3"-5" limestone sourced locally. So far I have about a foot of rock dumped in. I'm using my tractor to dump it in, one bucket at a time.  I had originally naively thought the dumptruck could just dump a whole load in, but no can do for a few reasons:
- I need the perimeter posts in place to support the concrete until the rockbed is full, this gets in the way
- Most obviously from the picture, the North wall is already in place (construction done out of order to do availability of some help)
- I have to build the rock level up slowly, balancing it with dirt on the exterior of the styrofoam so that it doesn't break.
It's actually going well it just slower.

For ducting, I'm using 12" forestry grade culverts for both below grade and above grade inside the greenhouse. The plans called for 10" diameter, but 12" forestry grade is cheaper than smaller diameters (for which only heavier DOT grade was available) so a nice bonus. Most surprisingly, it's cheaper than regular HVAC ducting so I'll be using it above grade inside the greenhouse too.  For the below grade ducting, I drilled 1/2" holes through the pipe. I wasn't sure how many I'd need, so I decided to drill enough so that the cross sectional area of the all holes equaled the cross section of the duct itself (12"), and then added a buffer. So I drilled 4 holes in every rib to hit at least 576 holes over the course of 30' (times 2, one for the inlet and one for the outlet). It ended being very quick and easy to do.

Keen eyes may notice an extra concrete pillar in the front left of the photo, only spaced 4' instead of the usual 8'. This is where the door will go. I added a second version of the photo with mockups for clarity.  I felt like I was breaking with convention with this part. Typically with concrete pier construction, the floor is above the top of the piers. But in my case they are 1.5' below! That meant cutting right through perimeter beams, but then what braces the door and takes vertical load? So I added another pier, the door will be sandwiched right between them. I plan to use concrete screws to anchor the jack studs to the concrete piers.

Hi Glenn, welcome to Permies!  Awesome build you have going on there!  I did a bunch of research as I built my own passive solar greenhouse so if you have any questions, I might have been through it already.  Here's My Thread.

A couple things spring to mind:

1.  How much ventilation do you have built into the design?  I see the 1' vent at the bottom of the south wall, do you have an upper vent(s) as well?
2.  Do you think the snow will shed off the north roof well enough?  Maybe it's fine if it stays on there as added insulation.  
3.  Have you figured out the summer and winter sun angles and how much of the interior will be illuminated?  I'm guessing the summer sun will not hit the 5' closest to the north wall.  Don't forget the ridge beam when figuring the sun.  It's not too late to make it a bit taller
4.  With a high roof and low plants, it could be fun to add an attic or loft to just hang around on in the winter.
5.  How cloudy is your area in December?  What are the minimum temps in late Dec and in the depth of winter?

With R20 insulation and a climate battery, I wouldn't be surprised if it would stay near or above freezing all winter.  You may be able to grow some interesting trees like figs or avocados.

Mike, thanks for your insightful comments!

Ventilation. I've gone through numerous iterations and am still not fully settled. The base design I’m following has 2 awning windows up high on each side wall; 2’x4’ each. I’m cutting costs and not using windows. Instead I plan to build removable insulated plugs. I’ll monitor temps next summer and might upgrade one of them to louvered fan. Combined with the venting on the front, this puts total ventilation space at 10% of glazing which I know is on the low side but it also doesn’t account the climate battery.

I don’t think the snow will shed off the roof but I have accounted for snow load in the design. I’m actually going with a steeper roof pitch than the original design. I’m not sure if it’ll offer any insulation value though, because there will be a 1” air gap under the steel for ventilation to ensure no moisture ever rusts the steel roofing. I still find this crazy, but the insulation in the roofing is actually going to be sealed in from both sides; plastic vapor barrier on the interior and synthetic roof underlayment on the exterior  (there will be small vents along the ridge to permit venting of any moisture that does find a way in).

Great question about sun angles, I had not calculated that yet! I looked into this last night and based on my latitude, the sun will stop 2.4ft shy of the north wall. So you weren’t far off I’m quite comfortable with this number, as the long term plan is to have a rocket mass heater with the mass bench running along the north wall. I would not want to have that soaking up sunlight in the summer; so this number works quite perfectly for passive solar design.

I am quite interested in adding a row of 55gal barrels along the back for thermal mass in the winter. My worry is the weight, technically they’ll be directly above the underground 12” climate battery. I’m not sure how much 3’ of rock and soil depth helps to disperse the weight.

December is a cloudier than January and February but generally is reasonably clear. It’s much warmer than the depth of winter; December lows are 25F with an average of 34F, January lows are 20F and average of 29F. There isn’t much reprieve from the cold, without heating it just permeates everything. Long term I do hope to keep temps above freezing year-round, but initially I plan on leaving the greenhouse dormant for those months and will be satisfied simply with the ability to overwinter some warmer climate perennials such as a tea plant as well as perennials seedlings started the spring prior.

Funny you mention a loft to hang around; while I haven’t thought of that do I am planning to have a 10’x10’ space designed as a multi-purpose area. While the greenhouse will otherwise have a dirt floor, this space will have patio stones. The wall will have a fold down table for coffee/tea or small meals. A hammock can be strung between one of the center log posts and the wall.  The ceiling above it will have a set of tracks from which greens will grow in gutters; they can be simply be pushed out of the way to clear the space for other temporary uses like pressing apple cider.

I've attached current draft of the interior layout. I'm planning on growing in raised beds on the ground.  It's pretty earlier in the build so I expect to be adapting this part as a I go.

Good point on ventilation with the climate battery.  That could ease your needs significantly.  My greenhouse doesn't have a battery and it keeps ventilated on hot 90 degree days with about 46 square feet of low intake and 26 square feet of upper exhaust (passive) for a 40' long greenhouse.  But I have 17' of chimney effect to help the air move.

I bet the snow will still help even with the air gap.  The air gap just adds to the R value.  Better to have 45 degree snow sitting on the metal than 25 degree air.

I find that enclosed insulation idea a bit worrisome too.  I'm assuming that comes from the DWG plans?  I'd build in a drain at the bottom to let collected moisture out as well.

Wow, your winter temps are balmy!  With my greenhouse, without a climate battery and without heat, on a -29F morning, the inside temp dropped to +20F.  So if my greenhouse could passively keep a 49 degree delta T on the coldest night, I'm guessing yours can easily stay above freezing.  You may be able to keep it closer to 40F all winter.  This should be interesting...

Hopefully you get it built in time to see how it works this winter.  Then your plans can evolve for what you grow.  Who knows, you may have avocados in there a year from now

I converted the winter temps incorrectly from Celcius. Winter temps will definitely hit lows of -25C (-13F), possibly -30C (-22F). Very different from the +20F I accidentally stated.

With regards to combating those temps, the second phase of the build (which is likely to happen around 2021) will include 2 key things:
1. A rocket mass heater
2. Water thermal storage system. One part mimicking that of another Permie's greenhouse, David Maxwell. It will consist of an automotive radiator at the peak to capture heat, and water lines running through the grow beds to heat the soil (with the soil then acting as additional mass as well). The second part is to run pex lines through the Cob mass of the rocket mass heater to siphon away wood heat. At this point I have no interest in trying to capture heat from the RMH barrel itself and prefer to stick with sub-boiling temps.

Ahh, that makes more sense.  

Regarding the RMH, there is an alternate design for greenhouses.  It's often so damp in them that cob melts away.  I think it uses gravel and rocks as the mass.  Just something to think about.

I'm planning out my own heat storage system using barrels of water and a radiator.  I'll duct hot air off the ceiling down to the radiator.  Then store the heat in a series of drums.  Then when the system is in "heat" mode, that warm air will be down low by the plants.  Maybe more of an issue for my tall greenhouse?  I'm also thinking of incorporating phase change material in with the barrels as a second round of experiments.

I'm long due for an update. After I went back to work last fall, construction went on hold. I restarted again last week. I had to shovel out a fair bit of dirt that had collapsed in over the winter. Then I cut the Tee's into the culverts and joined them. I used spray foam to seal the joint. Then I slowly added in 4.5 more dump truck loads of rock, one tractor bucket at a time. As the level of the rock went up, I added more dirt on the outside to balance the pressure.  Tomorrow I hope to have the rock done, it will be 4' deep.

Next up I plan to add a layer of geotextile fabric over the rock and then a foot of dirt, which will become the greenhouse floor.

I've been busy! I made alot of progress on the greenhouse in the past week and capped it off today with finally getting the ridge beam in place.

First I filled in the climate battery and got 4' of rock in place.
Then I added a layer of geotextile fabric, and was finally able to start adding the dirt cap/floor. (one foot thick).
I also painted and installed 24" flashing around the perimeter styrofoam. Based on final grade, about 8" of the flashing will be underground.

The perimeter of the greenhouse ix 6x6 cedar beams, which I had not yet fastened to the concrete piers, so I removed two of them in the front and was then able to simply drive my tractor right into the greenhouse to load dirt.

After I had sufficient dirt in, I couldn't wait to start working on the framing. I built the sidewalls first, the East wall has a 2x4 cutout for a ventilation plug (perhaps someday a window but staying cheap for now).

I've been saving two windfall spruce since last year year, to use as supports for the ridge beam. I used a chainsaw to cut a slot in the bottom of each, so I could lower them down onto a steel plate that was set in the concrete when I poured the piers. The posts set very nicely on the piers. I decided not to try cutting them to length before installing them, opting to do that after using a plumb line. Still to do is to drill through the log to install a bolt through the log and plate.

Today was ridge beam day. I cut the two logs to the correct height and installed strongties. The beam itself is 3 layers of 2x12, and 32 feet long, so about 400 pounds heavy. For the tractor the weight was no problem, the challenge was height, the top of the greenhouse is 13.5 feet above the ground. Using a pole on my front end loader I had a friend help me and we got it in place. It all fit, very pleased since this is the first framing job I've ever done, and I'm following my own calculations for dimensions.

Enjoy the pics!

I made some progress on the roof, getting regular rafters installed on the north side. The glazed South side is going to have a gambrel roof with rafters every 48". I built the bottom half first and then put in place with some temporary bracing. For the upper half I painted the boards first and then started to install them; I'm halfway now.  

Once the rafters are all in place, I plan to work on the roofing/siding. I've decided to go with steel for both. My plan is to put down synthetic underlayment right over the roof rafters, then nail purlins over that, which the steel will be screwed to. Most roofs seem to go with a full layer of OSB sheathing, but I want to give the steel an air gap to allow any moisture that finds it's way in, a way out. If I use purlins for the airgap, the OSB then seems to be pointless aside from being a nice deck for working on and put the underlayment on; so I'm skipping it.

This also means getting the door frame figured out and installed. Without a full concrete foundation or slab, I don't have a sill for the door to sit on. But unlike a polebarn, I still need a tight seal so I can't have a floating door either.  During the concrete pour, I added an extra pier so I would have one on each side of the future door. My plan is to run a steel plate between the two columns and bolt it to the concrete. The door jamb and threshold will sit on this.

Amazing work,  beautiful design!
I'm curious, what are you using for insulation?
I'm guessing rock wool for the moisture resistance,plus it can be wedged in place easier than fiberglass, without loosing it's insulative properties.
A layer of foil faced foam board insulation,  taped at the seams might also be a good choice.

I was very surprised at the 10"(12") pipe size, and I'm wondering what fan specs the design calls for?

Since Air to Earth  geothermal is powered by the process of condensation,  I have  thought the way to add rocket stoves into the mix could be via steam production.
Boiling water and directing the steam into the air  intake  might be an effective way to move heat into the system.
With your earth capped stone storage battery, saturation/ drainage shouldn't be an issue.

Thanks for sharing your build,  it's very inspiring!

Thanks for the interest William!

I've not made any final decisions regarding insulation yet, but in all likelihood I'll be going with fiberglass. The price difference is just too large, rock wool would exceed my budget. I'm planning on being extremely meticulous with sealing the inside with a combination of sprayfoam, caulk, and lots of paint. Current thought is for the ceiling to be painted half inch XPS styrofoam. It'll add R2.5, and it's half the price of plywood.  No wiring or lighting will run through walls or ceiling so I won't have to deal with sealing those.

The earth battery ducting is actually 12" inner diameter, 14" outer diameter. I based my designs off the University of Minnesota Deep Winter Greenhouse 2.2 plans, which is a 24" wide greenhouse that calls for 8" ducting. Since mine is 32, for simplicity I went with 50% greater size. That actually would have been 10", but the 12" duct was actually the same price since it is more common.

The uMinn plans call for a 400cfm fan; another earth battery design calls for 2-5 changes per hour. I'm planning for around a 1000CFM fan.  My greenhouse will be approximately 4,000 cubic feet inside which puts that at 1 change every 4 minutes. What research I've done says that 1,000 CFM in a 12" duct should be ok.

I have to say, the design requirements for dealing with moisture have been very annoying so far, in how far it has forces me to stray from my desired outcome. It seems the moment that insulation is added; all kinds of additional requirements come into play. Vapour barrier on the inside, I can understand. But the design of the roof is basically the same as a cathedral ceiling in a house. The insulation in the rafter cavities has to be vented on the top (so it can "breath" and shed moisture), and the steel has to be vented from the bottom (so it too can "breath"); but everything I've read says they still have to be separated from eachother. If they share a cavity then the moisture leaving the insulation will rust the steel. So I have to separate them with underlayment. And then I need soffit at the end of the roof to promote airflow. So much increased complexity compared to a poly tunnel or even a barn; just because of the addition of insulation.

Update on progress; I got all the roof rafters are installed yesterday and pop riveted the flashing together. It's been decades since I've used pop rivets;  I couldn't use any normal fastener because there is nothing behind the flashing to anchor too, below the 6x6 beams the "wall" is just styrofoam and flashing.

Today I brought in a 275gal IBC which I'll be using for more thermal mass, then I finished framing in the East wall. I plan on adding a second IBC for potable water but with the pandemic the local supply has dried up. These IBC's won't fit through the door; I'll have to remove the glazing if I ever want to take add or remove one. I plan on adding some black steel barrels too; this IBC is more of a central storage tank, which in the future will connect to pex lines that run through the grow beds to heat the roots, I'd also like to add in circuits for heat capture, either pex lines running through the cob of a rocket mass heater, or a radiator up near the peak. I'll see how well the climate battery works first before adding further complexity.

I also installed one of two ridge beam braces that the design calls for. I'm using a 5ft long 6x6 and used my chainsaw to cut a seat into the log to support and a wratchet strap to haul it up and hold it in place while I secured it (lag bolts into the log and a Simpson bracket at the top).

I noticed I'm in one of the pictures, I'm 6 feet tall if it helps for scale. September first and I'm wore my winter coat this morning for a bit; I can't get this greenhouse finished soon enough!

Yesterday I ordered steel for the roof and walls, hopefully this weekend I can start installing the underlayment and 1x3 purlins; though first I have to finish the West wall framing and cut the rafter tails and trim the climate battery intake down to below the rafters.

Further updates.  I Finished the second ridge beam brace on the other log. Then I started working on the opening for the door. The door will be 6” above the final ground level. Since there is no conventional foundation at ground level, only styroforma, I bolted a 5” wide steel u-channel to concrete piers. I had to add a shim, as I original poured the concrete expecting to get a 36” door, but then ended up getting a 34” one. I then cut out an opening in the Styrofoam that goes around the outside perimeter. Since I couldn’t leave that exposed, I covered it with a pressure treated 2x8. This covers both the doorway (2x6) and then juts out enough to cover the foam. I bolted it down to the steel so it would be secure. Then I folded the flashing over top for water sealing and aesthetic. This is just the rough opening, a 34” framed door will sit inside this with it’s own trim and a proper door threshold, so everything I did today will be covered up.
With that done I started working on the eave. I got the rafter tails cut, the hurricane ties nailed in, and started to apply the fascia board. I ended up going with just ½” plywood for the fascia, instead of a more typical 1.5” board because I forgot to account for the fascia board when I ordered the steel roofing, so I just don’t have the length to spare.
Next steps are to finish putting on the fascia, then cut the circulation duct (culvert) down to the proper height and angle so it doesn’t stick out above the roof. Then I can start on the roof. Progress will be slower this fall as I go back to work, but I’m committed to getting it closed up before winter.

I finished the steel roofing this weekend. It was my first time working with steel roofing but with a bit of guidance from Youtube it went well! It's going to finally start looking like a building.

I had a dozer come yesterday and finally got the exterior landscaping finished. Since my foundation walls are just styrofoam, this step had to be done after the interior soil was filled back in. It's very late (probably too late) in the season here to get grass seed established. I'm going to put some on anyway and then add oats as well. The oats will winter kill but hopefully build enough roots first to hold the soil in place.

Looking good Genn.

I'm getting the hang of putting the steel on, East and North walls just about done. Trim will come later.

We had heavier frost this morning (-2C, 28F), and I noticed that the climate batter is already working, passively without a fan. While the entire roof was covered in frost, there was a frost free path directly above the what will be the intake vent (which is taller than the exhaust vent). It's a natural thermosiphon since the natural ground temp is still warmer than the air. This is not visible in the picture, that was taken the prior evening.

That last picture makes it look a very sealed structure, I do have ventilation planned!
The sidewalls are going to have hinged plugs (maybe someday windows) but for simplicity and speed I just covered everything for now. In the spring I'll cut out the openings install the plugs.

The greenhouse isn't finished yet but I figured I should post an update. I hit a milestone last weekend, the Solawrap glazing has been installed. Each section is held in place by sliding through a plastic channel at the edges. The installation guide says to put the channel pieces at 48" intervals. I found 48.25" gave a better fit. Lubricating the channels when installing made a big difference, as did using a utility knife to bevel the edge where the track first slides in.

It's very strong material, I'm sure it would easily hold my weight if I stood on it and it bounces right back when pushed on (elastic enough to not permanently stretch). It's not much tougher than regular greenhouse poly though. It cuts like butter with a utility knife and I had a screw slip away once and it instantly popped a bubble. I suspect that it will have no trouble withstanding any natural forces, the biggest danger will be my kids.

Next up is to get seal the tops and bottoms of each section and then get the steel ridge cap on. After that all I need is a door and I'll finally have a watertight building.

Looks awesome Glenn!
The solawrap seems like a good way to go. I've been researching for building my own Passive solar greenhouse here in the Okanagan, and between Solawrap, Polycarbonate and Solexx, the solawrap is coming out the winner.

Cheers
Rick

This is greenhouse goals in my opinion. I'm coming up on 1 year since I built my first one, and so far its proven to be a great lesson on what NOT to do. Oh well, its the kind of lesson only lots of hours of work, satisfaction, and disappointment can teach. Looking forward to following this build, seems well thought out. Great work so far!

I finally got the door installed over the holiday break. I keep forgetting to go out and take a picture on a sunny day, here is a one on a cloudy day.
It's water tight now but not airtight so I won't be growing in as early this year as other future years.

Inside, I setup some arduino based sensor nodes, so I'm now collecting data on indoor temperature, humidity, air pressure, and brightness (lux).  I also started building the raised beds. I'm planning to have 4 foot wide beds, 16" high, with 2 foot walkways between them. I built the first bed out of rough cut hemlock lumber sourced locally.

My goal for 2021 is to get the climate battery running (I still need to buy a rather expensive 1000CFM fan), and get growing!

Hello Glenn,

I live in New Brunswick as well. I love your greenhouse project. I would like to construct a similar structure some time. I will keep reading your posts so I can see how things are going.
I am in Shediac Cape, are you anywhere close to there? I am part of a project at the Greater Shediac Community Garden where we have built a kind of hybrid greenhouse (it's a greenhouse but will have other uses as well) and hopefully we will be able to start growing something in there soon.  I am really curious how your climate battery will work out. I like to learn from others experiences and then hopefully apply them to my own design when I finally build my own four season greenhouse.

Carla

Thanks for you interest Carla!
I'm located outside Petitcodiac, about an hour west of Shediac.
I'm very excited to get the climate battery going. The benefits of heat storage, day/night temperature regulation/reduced fluctuation, and humidity regulation seem perfect. It wasn't cheap, but it will benefit the greenhouse for decades.

Hi Glenn, Location: Magazine AR, zone 7. Thank you for sharing your greenhouse build with us. I have been doing lots of research for a greenhouse that will work in my area as we get a very strong wind and also to withstand a heavy snow storm which we just got couple of days ago. So would you say the structure of your greenhouse will withstand strong wind such as 50 to 70 MPH? Thanks again.

Hi Mandie. The final state of my greenhouse should be able to handle those winds. I am at the tail-end of hurricane alley so I had to anticipate that.

My greenhouse it a bit "two-face" in terms of strength.  
The North side with it's 2x10 rafters every 24" is probably overbuilt. Just useful for squeezing in R28 insulation.
Compare that to the South side which is 2x6 rafters every 48".

I made design choices for my South side that reduced overall strength, which you wouldn't have to depending on priorities.
1. Go with a simple flat pitch (60 degrees or the angle most suitable for your location), instead of the "gambrel" roof that I went with. I just find having another "joint" introduces more chance of movement.
2. Decrease the rafter spacing, go with 36" or 24". My Solawrap required having something every 48" and I opted to "skip" having an extra stud in the center of each sheet.

So far I have no regrets. Snowload has not been an issue, the steep pitches have caused everything to slide off before it gets too heavy.

Based on my last post I figured some further pictures may be helpful.

The snow has accumulated about 3 feet high on the glazing side. For reference, that stack of pallets outside is 4 pallets high. Inside you can see the snow gently resting on the glazing.

Inside I've also added some cross braces. These were not in the plans, something I added. My thinking is that triangles are strong. Plus now I have something to hang twine from for tomatoes, pepper, cucumbers, etc.

For the ones that are going to study the rest of picture too and are curious:
- 300gal IBC is for future thermal storage. I will be running poly lines through the soil in the grow beds to circulate the water. Heat sources TBD (rocket mass heater, radiator at the peak, external solar thermal panels, etc)
- One and a half raised beds built. The beds are 4x10 and 16" high (2x8" boards). I just have it sitting 3 sections high to save space for now
- Lumber stacked in front is for the remaining beds. 2" rough cut hemlock. I'm consigned to simply replacing it sooner than if it was cedar.
- The sides of a new Salatin-style chicken tractor are leaning against the back wall. Will assemble in the spring.
- A hammock is setup for my family to enjoy the mid-day sun. It will remain a semi-permanent feature but move to beside the door which will be a multi-purpose area without raised beds.
- Climate battery intake (12" culvert) is capped off with plastic until I am ready to move to the next phase of that project


So, now a question to all of you reading this! The two log posts, which are the centerpieces of my greenhouse (pun intended) - how should I finish them?

- Paint them white as every other interior surface will be?
- Seal them with a clearcoat to keep the wood colour (I just can't bring myself to say "color,")
- leave them untreated and enjoy entirely nature beauty for as long as they can last.

Great posts. Thank you for sharing your build. It looks fabulous. I am also from NB, Fredericton area, and am reading your posts with much interest as I am in the research stages of building a greenhouse. I have a shipping container house and plan on a lean-to style on the south side on the container. Your culvert pipe was a great tip. Keep up the good work, and l am looking forward to hear what your temperatures are inside your greenhouse on these cold nights in February. Cheers

I've been keeping track of temps since the holidays but the current data is rather useless at the moment because it's not airtight yet. In fact I have a huge draft. The soffits on the North wall are wide open and there is also a 2" opening all along the peak - so any heat gain in the day disappears immediately once the sun sets. The ceiling needs to be sealed with insulation and vapour barrier before I'll be able to retain anything.

Right now night time temps match outdoor temps within about 2-3 hours of sunset. Daytime temps are fun to watch - cloudy days don't  change much but on a sunny day I can hit a 20 degree Celsius difference. I can tell that next year with things sealed and insulated there will be a HUGE improvement. My goal was start growing in March indoors without any supplemental heat (whereas outdoors my last frost date is almost the start of June) and I have confidence that I'll hit that next year.

Thanks Glen. WOW...looks really nice. Not exactly sure the measurement of your greenhouse, maybe you did mentioned it somewhere in the post. I will have to go back and reread it. I am planning to build a 20' X 40' with about 13 to 16' tall and maybe more since I want to grow some tropical fruit trees like papaya, coconut trees (may have to get a dwarf kind as they grow pretty tall).  Do you think a greenhouse with that measurement will be ok with the heavy wind and snow if I use similar plan structure like yours?...OR I may have to change some things due to the size?

As far as the color of those 2 posts, for me, I would paint them white if I were to have everything inside white.

Thank you so much for your time and kindness for sharing your talents with us:)

Hi Mandie, I think that this style greenhouse (passive solar greenhouse, uMinn Deep Winter Greenhouse, Penn and Cord greenhouses, Ceres greenhouse, etc), are probably the strongest greenhouse of all. Only a geodesic dome might be superior if dealing with extreme wind.  The final shape will just come down to your personal goals. I don't think that absolute size makes any structure less able to deal with wind, it just comes down to how it's engineered. 20x40 is a very common size. From a construction standpoint, I compare my greenhouse more to detached garages than greenhouses,  it helps with making comparisons and assessing resistence to the elements.

Awesome Glen. Thank you.

With outdoor growing in full-swing most further work on the greenhouse is on hold until the fall, but I thought I should post an update as to the current state. Since last time I have now:

-  Built and planted3 out of the 4 raised grow beds. I ran a loop of poly hose along the bottom of each bed before filling with topsoil, so that someday I can run heated water through the beds. I'm going into my first growing season mainly as an experiment to understand how things will be behave with no particular goals for production. I have tomatoes, bell peppers, stevia, basil, rosemary, melons, and cucumber. I also kept a number of newly potted tree/shrub seedlings in among the peppers for convenience until the Peppers start to crowd them.

- Cut out my ventilation window on the East wall. With the door open on the West end I get a good natural airflow through, though I do need to rely on a box fan in the vent to keep temps reasonable on days that are full sun but windless.

-Purchased the fan that will run my climate battery, a 12" duct fan rated for 1000cfm, I'll be installing early in the fall.

- Finished plumbing running water so I can irrigate.

I'm really looking forward to insulating/finishing the walls and ceiling this fall so it will finally be complete.

I didn't realize how long it's been since I posted an update, there are a few updates to share.

Based on how thing were warming up this spring, I decided to starting growing on March 15th this year. That's 10 weeks earlier than my last frost date outside. The week before that I ran the climate battery fan only on warm days to bank some heat. After March 15, I set it up to run at night to keep things from freezing. Here's what I have growing at the moment:

- overwintered seedlings that will go outside later (kept inside to ensure no winterkill):
     - sedum
     - thyme
     -gayfeather
     -caragana
     -chives
     -6 black locust (an experiment, I have another 20 that I moved outside, so I'll see this fall what kind of advantage this 6 gained)
- new seedlings:
      -2 50 cell trays of coneflower
     - 1 50 cell tray of hyssop
     - half a tray of gayfeather
     - brussel sprouts and kale for outdoor planting
-vegetables in raised beds:
     -broccoli
     -tomatoes
     -bell peppers
     -melons

In terms of building/construction, it's done yet but as my hobby continues, progress has been made.

The ceiling, north wall, and half the side walls are now insulated, sealed, and covered.
I have ready many tips saying NOT to use OSB inside a greenhouse (due to the humidity). I'm going to try it anyway; I could not find any other material that seemed as cost effective. All edges will be sealed with caulking and the surfaces sealed with white latex paint.
While the walls needed a durable cover, the ceiling does not. So I capped the fiberglass insulation with 1" XPS styrofoam insulation. It was cheaper than wood AND adds another R5 to the insulation value (for a total of R32 in the ceiling). So far just one coat of paint, I'll add more after everything is taped and sealed.

I setup an automated misting system for humidity/cooling. I used an patio misting system + a solenoid valve. It's activated by a relay controlled by a "mini computer" (ESP8266). I had some creative fun coming up with a good misting cycle. Intuitively I knew that I wanted to mist more often when it was hot or dry (low relative humidity) or both. That's when I learned about "Vapour Pressure Deficit", basically a calculated number that determines exactly how comfortable any RH/Temp combo is for plants.  The misting system and the climate battery fan controller both communicate wireless with temperature sensors I added, and report there statuses to an online dashboard. I could post a whole separate thread about this system so won't get into it further here other than share a screenshot.  I don't aspire to have "tech" in my greenhouse, but at least this is setup is all open source and self-maintainable. To date, I have discovered that generally my greenhouse is too dry instead of too humid.

I built another raised bed and filled with a soil mix.  Mainly two year old compost from our horse manure pile + lime + clay top soil + peat moss. I also added 8 gallons of biochar that I made.

Oh, and I started the task of covering the floor with woodchips. This winter showed me that a bare dirt floor is NOT going to work. I would walk accross the clean snow to the greenhouse, and once I stepped inside the greenhouse the snow would melt, with the floor and turn into mud, then I had to deal with mud everytime I came back into the house. I chose to go with woodchips because it drains well, it's free, and I don't have to worry about trying to keep it tidy. If I put in gravel, how do I clean up a spill of soil? Either soils ends staying in the gravel or gravel ends up getting added to the beds. Woodchips seemed more compatible. It's pleasure to walk on. On hot days I intentionally spray water on the chips to give a little boost to the humidity and cooling.

Glen Van Agten wrote:

Oh, and I started the task of covering the floor with woodchips. This winter showed me that a bare dirt floor is NOT going to work. I would walk accross the clean snow to the greenhouse, and once I stepped inside the greenhouse the snow would melt, with the floor and turn into mud, then I had to deal with mud everytime I came back into the house. I chose to go with woodchips because it drains well, it's free, and I don't have to worry about trying to keep it tidy. If I put in gravel, how do I clean up a spill of soil? Either soils ends staying in the gravel or gravel ends up getting added to the beds. Woodchips seemed more compatible. It's pleasure to walk on.

I totally agree. There was a lot of gravel in places when we bought the property we're on. I gave up years ago trying to keep it as gravel, and much of it is mowable weeds now. Wood chips eventually turn into soil. Faster if you actually plant things that will take some foot traffic and you don't care about.

Hi Glenn,
I just wondered how the winter went. We are contemplating a climate battery under a new greenhouse build this summer, but we are in zone 3a. I really wonder how it is going to perform in -40 with short, short days. Only about 5 hours of daylight in winter here. TIA.

This past winter went very well!

I started some cold hardy crops in late October (spinach, broccoli, swiss chard), and they survived the winter and started regrowing again late January. No supplemental heat, just the climate battery fan. I had a fair bit of mizuna lettuce in my "mixed salad greens" bed that were not killed off by frost either. I did a fall crop of carrots and just picked them whenever we wanted to eat them (finally eating the last ones in March), they all stayed alive and perfectly fresh.

The temperature of my rockbed never went below 4 degrees C, so even on the coldest nights I had "warm" air to heat with.

I have some potted strawberries inside that started flowering about 2-3 weeks ago. I currently also raising some silkie hens in there.

The biggest factor I've seen over winter is cloudy days vs sunny days. Sunny days have incredible heating ability, cloudy days are almost like nighttime.  I live on the East Coast which doesn't get quite as extreme cold, but it's cloudy alot more often too. The prairies get colder but that is offset by having more sunshine.
I am observing that sunny days yield an excess of heat, and that with enough thermal mass it can make a real difference on subsequent cold nights. For the climate battery - having enough airflow/heat transfer area is key. The more you have the faster you can capture the heat in the daytime and release it at night.

My 32x16 greenhouse has a single 12" duct fan rated at 1000cfm (actual will always be less), and I'm finding I should have doubled up. Even in March I have days where it can be freezing outside but I have to open a window vent to keep from overheating inside. 8 hours later the fan is running again to keep the temp above freezing. On a sunny morning, sometimes the fan is only off for less than 2 hours (running to heat till 8am, then kicking in at 10am again to cool).

All in all a climate battery with an temperature controlled fan is an amazing solution. So much temperature regulation for 0 effort and almost no running cost (my fan uses 200w), and no long term maintenance. If you plan on keeping a greenhouse for a decade or more it's worth the investment.

It all comes down to your goals; what you want to grow will determine how what temperature you will have to plan for.

Thanks, that is a huge help. I actually want to just increase my spring growing season, not necessarily grow year around. While there are many fruiting trees and bushes that can withstand our winter temps, our summer season is less than 90 days frost free and our nights are almost always lower than 50 F, so very few things have time to fruit. The greenhouse is to house in-ground fruit trees and berries that will withstand zone 3/4 winter without input, but will give them an early spring so they have time to fruit. We have incredible winds here, so venting in the spring has been a big concern for me, I'm worried they will immediately break. It sounds like I can use the battery for cooling if I have additional fans, so I won't have to open vents perhaps. Maybe I'll post to see if any one has had success with fruiting trees in doing something like this. Thanks again for your help, I had almost decided not to do the climate battery, but I think it may be the way to go!