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1/2" vs 3/4" EMT for Greenhouse

 
Posts: 2
Location: Rochester, NY
forest garden books homestead
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Hello!

I have, what may seem like a very trivial question; can anyone speak to the difference, if any between a 1/2" and 3/4" EMT conduit used for greenhouse ribs? Our structure is very small, about 19'x8'.

Our main question is if one is more reliable/stronger for winters in a 6a/b zone (cold, windy, lots of heavy snow).

thanks,
JM
 
pollinator
Posts: 335
Location: Boston, Massachusetts
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Both of those seem totally inadequate.

I'd take a look at some commercially available structures to educate yourself.
Rimol, FarmTek, Griffin, and dozens more...

Also check out Johnny's Seeds for their DIY "Quick Hoops" benders for four different styles of houses.
None of these are using less than 1-3/8" chainlink fence top rail for bows or purlins, only bracing might be 3/4" but more likely 1" EMT conduit.
The top rail tubes come in different thicknesses (gauges - 17 is thin, 16 is a bit thicker, 14 is a bigger step thicker/the commercial stuff) so be sure to compare $$ for equal gauge materials.

Our small house is 17' x 34', gothic, made of 1-3/8" tubes, and I'd say barely adequate for Boston.
It is heated, with 2 layers of inflated poly, and a single ridge pole. I've added some braces (collar ties) made of 1" EMT.
The snow tends to slide off this one, though not always, and of course depends on having a clear place to slide to. Before it was heated/inflated, it tended to collect on top.

Our large house is unheated, single poly, 21' x 48', gothic, made of 1-5/8" tubes, ridge and two purlins. It is stronger, but with the added width...not by much.
This one, the snow collects on top more, being a bit flatter slope, and the purlins allow a pocket to form (I may try pulling the plastic a bit tighter while it is still warm out), and so needs more manual clearing.

Whenever we are expecting a heavy snowstorm, I put 2x4 props under every other rib ($40 in lumber is cheap insurance).
I clear both houses of snow during heavy storms, sometimes multiple times if it is a Nor'Easter.

I've seen photos of some epic failures of houses that failed by having wind strip snow from one side and drift it onto the opposite side. Acting a bit like a snow fence...
So, I always clear my snow from both sides evenly, rather than going all the way down one side, then the other.
I use one of those foam snow "brushes" (Sno-Brum) on long broom handle, and work from inside, pushing up on the plastic between the ribs just enough to get the snow to slide, alternating Left-side, Right-side, down the length of the house.
 
Jm Scipione
Posts: 2
Location: Rochester, NY
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thanks Kenneth, you're probably horrified because I listed the wrong measurements...my mistake!!

your feedback was helpful thanks again
 
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Jm Scipione wrote:Hello!

I have, what may seem like a very trivial question; can anyone speak to the difference, if any between a 1/2" and 3/4" EMT conduit used for greenhouse ribs? Our structure is very small, about 19'x8'.

Our main question is if one is more reliable/stronger for winters in a 6a/b zone (cold, windy, lots of heavy snow).

thanks,
JM



If you don't plan on growing when it snows or plan to have a greenhouse in the spring then by all means go ahead with either 1/2" or 3/4" emt.
 
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