Snow will crush a top rail structure, too, although not as quickly as pvc, The wider your greenhouse, the faster it will collapse. Center support posts help a lot to hold snow.

Unless you have a northern-style greenhouse with a pitched roof for the snow to slide off, greenhouses just aren't meant to hold snow. You're supposed to get out in the blizzard and sweep off heavy snow as it falls if you have plastic on it. That's all part of the fun.

This post was edited by Cole_Robbie on Mon, Mar 11, 13 at 12:48

I live in Northern MI and we get snow and winds for 5-6 months. There are hoop houses all over the place and they do not get crushed. I NEVER see snow on them so they must brush them off, and I have talked to a couple who say they put 2 x 4's under the hoops at the tallest points for support during the winter.

I used low hoop houses this winter with electrical conduit to support the plastic and they held up fine.

I live in East PA. And have been covering my koi pond with a hoop house for the past 3 years without Any issues. My hoops are made from 1-1/2" gray PVC with no center supports.