Straw Bale Passive Solar Greenhouse

This thread will document and describe the building of a passive solar greenhouse. We are located in West Bench, just outside of Penticton BC in the Okanagan Valley. Zone 6b/7a, 12" of annual precipitation.
The greenhouse is 20' x 43' outside dimensions. I decided to build using straw bales on the north half of the building, after seeing a video on a straw bale greenhouse built in Canmore Alberta. I was interested in gaining experience working with straw and this seems like a good opportunity to gain that experience.

I spent a bunch of time over the winter using Sketchup to make the design:

Around the end of January I began the project. I planned a climate battery, using barrels as manifolds. I would have used large diameter plastic culverts, but the cost was extremely high for those pieces and I had several barrels around that could be used for the battery. I decided to split the climate battery into two separate systems, so that there would be enough space in each barrel to run the 4" perforated pipe. So there will be 2 fans, linked to thermostats that will control them both at once.

All that planned, I ordered rental on a Bobcat skidsteer and excavator to level the site and dig the foundation. I had no prior experience with either machine.  The first task was to scrape off the topsoil and set it aside to replace afterward. I quickly realized that staging materials was going to be a challenge, with very little open space available on my site. I'm working around a hoophouse, a duck shed, and many mature fruit trees. As a result, soil had to be moved into fairly inconvenient areas, which I am still dealing with at the moment.

I decided to dig the pit for the climate batteries first, then backfill and go back and dig a trench for the rubble trench foundation. Also it seemed that the only way to make the excavation work was to do the climate batteries one at a time, back fill the first one and then use that space to operate the excavator for the second one.

We have about 18" of fairly nice silt soil, below which the subsoil is sand and rocks. Rocks of all sizes ranging from fist sizes, to boulders that easily weigh 500 lbs. This made digging challenging, if you hit a big rock the only choice is to get it out and leave a bit of a mess around it.

Long story short, I used the machines for long days while I had them, making the most of the week of rental time. We got the climate battery piping installed (2 levels at approximately 3' and 18" depth.) We screwed each pipe into the barrel to hold it in place while we backfilled and tamped around the pipes.

Next post will discuss the rubble trench foundation.

Really looking forward to seeing the next phase and operations! We are just north up the valley from you in Vernon. Awesome to see so many projects on the go in the Okanagan!

Wow, it's been a while since I've posted here. I meant to keep up with this build log but I got pretty busy.

I'll just do a photo dump and try to add some interpretive language when I can!

OK...so in the previous post we made quite a bit of progress! It looks so easy, looking back at the photos from my comfortable chair.

Having backfilled the climate battery, I marked and excavated the rubble trench foundation. Having no experience with the excavator, I made a bit of a mess of it. Nothing fatal, but I definitely dug the trench too wide in some areas which resulted in having to fill afterwards using more gravel than necessary. The outer perimeter of the trench was insulated to R-20 using the GPS graphite-enhanced expanded polystyrene. Then I installed perforated pipe in the trench and filled it with gravel.

Next step was to build the gravel-filled earthbag stem wall. I can't overstate the labour intensiveness of this process. I have true respect for anyone who builds their whole house with earthbags. We filled, wheelbarrowed, set in place and tamped the earthbags, using approximately 20,000 kg of crushed rock. Since the earthbags are inside the insulated envelope, this is additional thermal mass. Using gravel ensures good drainage as opposed to soil filled bags.

We poured 3 concrete footings for the main support posts and installed the posts with bracing. By this time, my friend Angus was back to work full time at our regular place of employment so I had his help only on occasion for the heavier tasks. I began framing the south window wall, and the two side walls. With help, we got the main support beams up in, one piece at a time, and secured them in place.

The straw bales arrived in a shipping container, which was extremely handy to be able to work out of the dry container while building the walls. We did have an exceptionally dry spring.

After a layer of poly as a damp barrier over the earthbags, I began stacking the bales. This process went fairly quickly and was immensely satisfying. I have good memories of listening to the audiobook of "The Idiot" by Dostoyevsky during this time. Admittedly my inexperience in this field showed itself later, as some of the bale courses weren't perfectly aligned which resulted in some wavyness in the wall. Nothing too major however.  I was concerned at first with how much the wall would sway and give, but I had read that the walls would stiffen up considerably once strapped down with the box beam (straps were installed under the first row of earthbags every 2')

In the last photo you can see the box beam installed and strapped down tight. I used a pallet strap type tightening tool, which ratchets the straps nice and tight. After this step the walls felt much more solid.

Ok, time for another photo dump!

Here's the next photo barrage!