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Copyright © 2002-2007
Glenn Caffery

The Greenhouse Frame

Design Goals: The greenhouse frame had to be strong, withstand high winds, and shed snow well. It also should be optimized to capture the low winter light. We sought a design that was affordable and durable, and one that would require minimal maintenance. The frame should permit flexible use of the greenhouse space underneath. Finally, the frame should be compatible with the the glazing system (i.e., it must have a flat outer surface at least 2 inches in width).

Design Loads:

Snow Load (north roof)
40.0 psf
 
Snow Load (south roof)
15.0 psf
based on 12/12 roof pitch, the reduced friction of the polycarbonate glazing, the heat loss through the glazing, and data from the Standards for Design Loads in Greenhouse Structures published by the National Greenhouse Manufacturers Association.
Wind Load (windward)
6.6 psf
Load on 12/12 pitch roof. Assumed 80 mph. Exposure B. Reference Wind Pressure at 20' = 16.4 psf (0.4) = 6.6 psf
Wind Load (leeward)
8.2 psf
Load on 12/12 pitch roof. Assumed 80 mph. Exposure B. Reference Wind Pressure at 20' = 16.4 psf (0.5) = 8.2 psf
Dead Load (north roof)
12.0 psf
 
Dead Load (south roof)
2.0 psf
 


Structure: Our frame sections were welded locally from 2x3 inch tubular steel and 2 inch angle steel. The frame was then sent off to be galvanized in the Boston area. The frame sections are bolted together 6 feet on center with 2 inch angle purlins spaced 43 inches on center.

Plans: The plans (3 pages) that were used by the fabricators are available in PDF format. The frame drawings might make more sense if you looked first at a drawing of the whole greehouse cross section, viewed from the east. The frame assembly is highlighted in red. (Both files require that you have the Adobe pdf reader installed. Click here to download the free Adobe pdf reader if you don't have it.)

Costs:
Our frame consisted of 8 frame sections and 63 purlins, all predrilled, mounted with connector tabs, and galvanized. Total frame costs including materials, welding, shipping, and galvanization was $3,557. A large part of the cost was shipping the welded frame members to Boston (2.5 hours away) and back for galvanizing.

Pictures:
Inside view of erected frame
Outside view of erected frame
Closeup view of frame with EPDM gaskets