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  • From: Stephen Sherman <spsherm@msn.com>
  • To: permaculture <permaculture@lists.ibiblio.org>
  • Subject: [permaculture] GH truss design
  • Date: Sun, 29 Jan 2012 11:07:59 -0700

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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