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

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

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.

thanks Kenneth, you're probably horrified because I listed the wrong measurements...my mistake!!

your feedback was helpful thanks again

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.

A line of 98 pound weaklings can hold up the same ampunt of weight as one strongman or woman.  I would say the emt is totally adequate IF you plan to use it calculating a lot of overbuilding and tons of extra emt and bracing.  I build a hoophouse out of 1 3/8 top rail dog chainlink fence and it was strong but i could have used a dozen emt to do the same trick and this was in zone 4a with heavy snow hurricanes etc.

Its all in the engineering.

Hi Jm,
I built a greenhouse out of 3/4" plastic conduit. **Full disclosure, my greenhouse is currently sitting in a broken heap under a pile of snow... but it was not caused by the snow** The plastic has a little more forgiveness than the metal kind I think. I made a gothic style based on a video from Eliot Coleman. a couple 4x4 posts with 2x4's on top to hold up the middle. I believe there were two primary reasons for failure, and neither of them had to do with snow loads.

Problem #1 (which I believe led to problem two)
I pounded 3" PVC into the ground about a foot and then put the conduit inside that pipe, bent it over, to connect to a 45 elbow at the peak, and did the same thing on the other side. What I did not do was make sure all the PVC pipes were an even depth and did not make sure the inside was filled to the same level. When I was constructing things, I adjust the pipes up and down to make the peak more level... this resulted in some of the conduit pieces not being on the ground and were just "floating" inside the PVC container from the friction of being bent over.

Problem #2
I dry fitted the conduit pieces to save time and to be able to take it apart more easily later. This combined with problem one meant that the pieces kept coming apart at the peak which reduced the strength of the overall design. I did not do a good job at putting them back in immediately, (though I did use some electrical tape to keep them together).

My greenhouse survived the first winter, though I had to go shovel snow away from the base to remove pressure after storms. Unfortunately there was a big wind/rain storm the following fall that took it down. It wasn't perfect, but it let me put my chickens in, during the winter, and let me grow some tomatoes during the summer. All total I probably spent $300 for a 12x30 greenhouse. And while the plastic is ruined, I should be able to reuse all the other material and rebuild it fairly easily. I'm going to try rebuild in the spring, and correct those two issues.

Can you build a greenhouse that survives Maine winters with 3/4 metal conduit? I have no idea
Can you build a greenhouse that survives Maine winters with 3/4 plastic conduit? yes.
Is it simple to build and forget? No, I had to do all kinds of maintenance... but the bigger commercially made greenhouses were not in my budget and this worked ok enough.

Link to the Maket Pipe company's crushing strength of 1/2, 3/4, and 1 inch emt to give a very rough idea of material strength.  I would sacrifice test a specific piece before planning and building a structure.

https://youtu.be/1oCEMd4v9B4

I am from central Maine originally and my gothic arch hoop was 1" emt on 4 inch centers for a 20 foot long 14 wide hoop structure.  Held up to neglect for 3 years and not brushing snow off.  I sold everything and moved south because 20+ winters is more than enough for me.