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10 Snow-Related Causes Of Greenhouse Failure

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10 Snow-Related Causes Of Greenhouse Failure

 

By: David Kuack

June 4, 2013

 

John Bartok Jr., an agricultural engineer and University of Connecticut Professor Emeritus, says snow varies considerably in consistency and weight. It can be light and fluffy with a water equivalent of 12 inches equal to 1 inch of rain. Snow can also be wet and heavy with 3 to 4 inches equal to 1 inch of rain.

 

Snow having a 1-inch rainwater equivalent loads a structure with 5.2 pounds per square foot. This amounts to about 6.5 tons on a 25- by 96-foot greenhouse.

 

Bartok says there are several reasons for structure failures during snow storms.

 

1. Drifting Snow: In nor’easter storms, adjacent greenhouses or bays of gutter-connected houses that have a north-south ridge orientation tend to collect more snow on the leeward side. Snow that is lifted over the ridge of the first house can be dumped on the windward side of the second house. This creates an off-center load on the roof.

 

2. Proximity Of Adjacent Greenhouses: Building greenhouses too close together is a common cause of failure. This is especially the case with overwintering structures that are only 4 to 6 feet apart. When snow slides off the greenhouse roof, it fills the space and crushes the house’s sidewall frame. Usually there is inadequate space to get in with a bucket loader to remove it. To save the structure, some growers cut the plastic covering to allow the snow to flow into the greenhouse and relieve the pressure. Other growers install two-by-fours to brace the side frame.

 

3. Greenhouse Frame Shape: The gothic-shaped greenhouse was developed to eliminate the flat spots that can collect snow on the top of hoop-shaped structures. Since 1994, when the nursery industry changed from the hoop design to a gothic design for overwintering structures, there have been fewer structure failures.

 

4. Poor Frame Connectors: Check and tighten all bolts and tek screws before the winter season. These fasteners tend to loosen over time. Brace bands and u-clamps can slip if they are not held in place with tek screws. The screws should be at the side of frame members, not at the bottom. Several greenhouses have failed at the point where tek screws were placed at the bottom of hoop tubing. This created weak spots.

 

5. Greenhouse Frame Racking: Many manufacturers do not include bracing with their greenhouse kits. All greenhouses should have diagonal braces from near the peak at the endwall to the baseboard about 16 to 20 feet from the endwall on all four corners. This provides stability and keeps the frames vertical. Frames lose considerable strength when they are not vertical. Install tubing or a 1- by 4-inch board and secure with a U-bolt at each hoop.

 

6. Poor Welds: Welds that are not continuous or that have burned through the metal are weak spots. Areas that should be checked include truss braces,.........

 

 

http://www.greenhousegrower.com/technology/10-causes-of-greenhouse-failure/


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