permaculture

[Toby Hemenway <toby@patternliteracy.com>]

Stephen,

You may want to contact Jerome Osentowski through his website, 
http://crmpi.org

He's been building and living with innovative solar greenhouses, heated by 
his brilliant "thermal battery" for a couple of decades. He knows a lot about 
what structures work. And a browse around his site will give you some idea of 
how the thermal battery can reduce daytime high temps and use that heat to 
raise nighttime lows, if you aren't already familiar with them. If you 
contact him, I'm sure he'll be happy to help. He's writing a book about these 
greenhouses, too.

Toby
http://patternliteracy.com


On Jan 29, 2012, at 10:07 AM, Stephen Sherman wrote:

> I am in the design phase for a solar heated greenhouse. Dimensions 
> roughly 20' x 40' lean-to format on the south side of a barn. The 
> location has high wind and snow loads, which need to be handled in the 
> structure. Several options for the roof trusses/joists come to mind, but 
> none seem like an obvious choice:
> 
> Simple bent steel tube rafters (commercial GH and high tunnel types) . 
> Relatively inexpensive, long-lived, but structurally not sufficient for 
> the loads I need, without several mid-span support beams. (may still be 
> the most cost effective and minimal shading choice)
> 
> Custom steel trusses. Long-lived, quite strong but fairly expensive.
> 
> Steel channel trusses. Moderately expensive, quite strong, but seem like 
> they may pose problems with cleaning and longevity (basically galvanized 
> sheet metal, rolled into various U or hat shapes. Should be rust 
> resistant, but the various faces may tend to collect dust/dirt and be 
> hard to clean).
> 
> Wood 2x or truss.  Moderately expensive, (getting hard to find good 
> lumber), not as long lived, although easy to work with. Trusses have 
> cleaning and painting issues, will case a bigger shadow than the metal 
> alternatives, and may require mid-span support.
> 
> There may be other choices as well, but these seem the be the most 
> common ones, at least that I could find. I was planning on having some 
> animals in the barn which attaches to the GH, and so corrosion and rot 
> resistance are important factors, I believe. [As a side topic, does 
> anyone know the current "wisdom" of having enclosed animal quarters in 
> air circulation with a GH? I have heard/read conflicting reports on this.]
> 
> Thoughts/ideas on the truss/joint design and material? Any experience 
> with good or bad choices here?
> 
> TIA
> 
> 
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