Monday, March 1, 2010

Building a Straw Bale Greenhouse: Phase 3 by Gardener Cumax

Editor’s Note: In September, 2009, Peter Bockenthien (aka Gardener Cumax) began construction of a straw bale greenhouse and shared his initial work on this blog. The next three blog postings will chronicle his successes and challenges in completing the project.

I'm happy to report that my greenhouse is 97% complete. I would be happier if we had some actual sun to warm it up but I don't control the weather. Let me explain what has transpired since November 2009.

In November I didn't get the stucco done because it was turning too cold. As a result the stucco I did complete cracked here and there. But that's normal for stucco that is drying in a freezing climate. I covered the entire greenhouse's lower straw bale walls in a large tarp I found on craigslist. Heavier snow dumped into the greenhouse interior onto the dirt. Not wanting the exposed strawbales to attract any moisture, I covered the entire wall system with black plastic. That's where I left off.

Late December into January saw serious R&R: researching and reconfiguring. My original roof was to be polycarbonate. Drawback: expensive and doesn't diffuse light the way thermal film does. Also, it would require more labor to install. I went with AC Thermal Film from in Wisconsin. Pros: it costs 1/20th of polycarbonate. it would be easier to install. It diffuses light very well. Cons: I'm going to have to watch out for hail storms. I have an extra section that can replace the roof. Another factor to consider: I don't need the roof during hail season.

So that was my roof choice. Now what would I do for roof support? How was this all going to come together? By mid-January I was freaking out how I was going to build the short roof walls just so, and how many rafters I should have spanning the 18 foot length.

Conventional construction would have it at every 2 feet. The problem with that is that would block more sun that I want. Plants are sensitive, so I don't want to make this more complicated than it has to be. I settled on 4' widths. You can buy a nice cold-frame greenhouse with 4' to 6' purlin widths. I've seen them up in Boulder County totally exposed to the elements, so 4' seems reasonable to me.

Still, I was freaking out: how would I even attach the greenhouse film to the roof and walls? My mind was stuck on how it would be done via polycarbonate systems.

While in this freak out mode, I visited a constructional professional friend of mine who was busier than busy. On my way over I passed Timberline Gardens and noticed Kelly's greenhouse out front, the one that is parallel to 58th. I did a U-turn back into Timberline and checked out house that film was attached at the bottom of the support.

Fortunately for me, Kelly was there and told me where I could get the same locally: American Clay Works. Those of you who attended or volunteered at the ProGreen Expo might have run into their booth. I had two options: Nexlok or Wiggle Wire. And both were in stock and local (from American Clay Works). I went with Wiggle Wire. The wire is far stouter than its name implies.

From Timberline Gardens I drove a short distance to my builder friend's residence. Glenn Griscom gave me a step-by-step approach on how to level the sill plates, build the walls and cut the wood according to the pitch I wanted. Excitement and relief replaced freak-out.

Here are links to Phase 1 and Phase 2.