ive used a number of differant types over a number of differant years with a lot of differant crops. i like them so much i plan on graduating to a 30x96 "store bought" type soon. ive always used 3/4 to 1" pipe. ive also had wind damage. the pamphlet green winters has a good plan also many sights on the web. stay away from suggestions to use fittings on the pvc-tape and deck screws etc are much cheaper. ive got a differant climate and have always used 6 mil plastic in winter and shade cloth in summer. if you use plastic in warm weather (any season really) plan on ventilatig- open ends, roll up sides, rips and tears-they can really cook on a sunny day.

I have 2 small hoop houses. They are made with irrigation pipe bended and sections welded on the ends and set down over rebar. They are covered with greenhouse plastic which lasts about 6 years. They don't come down as it is a lot of work to put them up. The ends have channels with wiggle wire wire that locks the plastic tight. The sides roll up at 3 feet for ventilation and we also put vents on both ends and ended up putting a door on one end to make entry easier. They are framed in wood. They are 24 ft wide and 1 is 24 foot long and the other 35 to fit the space we had. I have seen them 50 feet long. I grow tomatoes, peppers and cukes for market in them. I have a friend that grows tomatoes, melons, hanging baskets and strawberries in theirs and they have a number of them and long ones. Theirs don't have doors and end vents. We have never had a problem with snow as it slides off. We have had hail damage. Google hoop houses and you will find a lot of information.

I've used small tunnels without a great deal of success - crops were a little earlier but frost damage occurred through the 4 foot wide, plastic covered structures. However, a larger size works much better.

A couple of years ago, I decided that our greenhouse wasn't adequate to handle the number of flats weÂd generate just before outdoors planting (along in April). So I built an 8 by 20 foot tunnel. I used 3/4 inch PVC pipe - 15 foot, placed over 1/2 rebar driven in the ground - ran a length of twine down the peak to hold the pipe straight. I dug out a path 2 feet wide and 18 inches deep from just outside the door, right thru the structure. Outside the door, I built a little "foyer" with bricks (concrete block would have worked better), framed in a door in my foyer and a ventilation window at the other end of the tunnel with 2 by 4's. I use lathe to secure the plastic to the frames and stretch a couple lenghts of twine over the top of the plastic to keep the wind from lifting it.

Years ago, I was in a range of glass greenhouses that had been built probably in the 1920's. They were essentially just roofs sitting on the ground - probably not over 6 feet above grade at the peak. Down the center of each of these narrow greenhouses was an excavated walkway. The soil level was about waist height, covered with gravel, and served as a bench for potted plants and flats. Worked darn well. Those old greenhouses were pulled down probably about 1985.

Anyway, my effort utilized the same idea of a structure that wouldn't be tall enough for me to stand upright in but because the center path is excavated, movement is easy. Further, the warmth of the ground helps keep the frost at bay.

The tunnel works well. I think that digging down more than 18 inches would be better for moderating the temperature (there's no heater). I didn't put gravel down and instead plant cold weather greens in February for our own consumption. As the greens are pulled, we gain room for the extra flats from our overflowing greenhouse. It gives us a few extra square feet for the couple of weeks before the plants can go in the outdoor gardens. Oh, I've got to put down slug bait.

After the tunnel is emptied of flats, I leave the door and window open and plant the ground to basil to sell during the farmers' market season. We have basil earlier than anyone. A few tomato plants and some edible gourds have also done well in there. The plastic is removed along in late July when the weather is really heating up. The gourd vines like to climb up the PVC pipe.

Stan suggested that you look at "Green Winters." I see that is available thru Peaceful Valley Farm Supply, the author is Jack Frazier. You can google that if you don't get their catalog.

All in all, our tunnel cost very little, was fairly easy to build, works fine and is very useful. Good Luck with yours.

Steve

Everytime I think about PVC plastic arches There are the questions of strength,connecting and incompatability with plastic films. I do bow a few plastic pieses over rebar and cover with double Remay layers to help some herbs overwinter. They are always flattened during the winter but I feel they do some good. Even without the snow you will have wind gusts that will destroy the flimsy structures. I did some testing on PVC a few years ago before I attempted to build a tunnel and I had a pile of broken and kinked plastic pipe to dispose of. There are a few better grade plastics available but they are more costly than galvanized pipe and you will need to paint the plastic where it contacts the film or it will degrade the film. And the third problem of connecting... metal crossconnecters will work but why use a steel beam to build a straw house? And for the duct tape and bale twine users... you'll be constantly taping and twining when you should be harvesting.

If you want a simple portable structure buy a few canopy connectors and pipe sections to make a canopy frame. The galvanized connectors,usually for either 3/4" or 1" pipes, are sold at most larger flea markets for $5-$6 each. You can usually work a better deal if you buy a hundred. Then you can build your structure as long as you want(width is best left to 11'-14'[6'-8' pipes]).Ventilation is still a problem but you might as well use a Remay breathable fabric for your purpose. I'll admit that winds will still rip the fabric but I've never had frame problems after many years of temporary "Season extension" use. This is a temporary "fix" but it goes up in an hour like constructing tinker toys.

For a better solution spend a little more and buy a greenhouse frame. I would suggest looking around for a used one to save money if you are not in a hurry. I think you can pay off the frame and film in the first year if your bedding plant sales are good. I've concentrated on tomatoes and cucumbers for produce sales in two permanent structures and my goal of season extension is the same as everyone else's. If you build a secure structure it won't take much longer to construct than a plastic one and you'll enjoy it for years. Plus it can have dual purpose use.. I just pulled 2 large tractors,2 gravely garden tractors, an SUV and truck into my 30x96' GH last night to shelter them from tonights anticipated big snowfall. If my GHs were made with plastic arches I believe I would be moving everything out.

last spring i put up a tunnel made of 20 ft.half inch rebar for hoops every 3 feet then instead of a purlin put 6"x6"remesh over the hoops. platic over that and frame the endwalls and i has a 11 ft by 30 ft g.h. for $450. see northerngreenhouse.com for similar ideas.

i use 3/4 electric conduit for the ribs 4 foot on center uv protected overwinter film . iuse this to give my potted hosta a month jump solid wood ends made from scrap lumber lay weed cloth inside add drip irragation and your growing