Just a note on the heat requirement. Using your figures of 25 ft X 40 ft, 12 ft high, 40 ft bows, double poly, -30 f outside, 60 f inside, I came up with 138,600 btu/hr. It can be done, but at quite an expense.

Have you got Eliot Coleman's books? Are you planning to market tomatoes? I have a less ambitious single layer plastic hoop house but it was cheaper to build a wooden frame with peak because of snow loads here in NH. It usually slides off. Spinach is very durable other things are not. I found I could get tomato plants to last a little longer but the flavor was poor. Advice was it was better to use hoop house to get them in the ground sooner in spring instead of keeping them going longer in fall.

Other vegetables such as chard are must hardier plus they sweeten up with the cold. Love the flavor. So my question is why focus on tomatoes?

As a builder/farmer with 6 high tunnels. Building a 25 by 50 tunnel with 3/4 inch conduit would be an epic failure. 3/4 inch conduit is a reasonable material to build a low tunnel out of. A spacing of 5 foot would also be a complete failure. I have a tunnel with 6 foot spacing and the pipe is 2.5 inch galvanized steel.

You need to build it out of chainlink fencing toprail, bare minimum. A spacing of 3 ft, maybe 4 ft, but in your location, 3 feet would be better.

Sorry to be so negative, but I just would prefer you to be successful and not have an epic fail.

Jay

Agree on the current plan being way under built especially for all winter gardening and a big heater. The snow will crush it if the wind doesn't blow it away first.

Also you can't get quality poly covering for that price. That's almost as big as mine and my coverings have run ~$600 for cheapest 4yr 6mil poly to $1200 for double layer woven.

Double poly is only an advantage in high winds and for a heated structure. For season extension single layer is about as good.

I'd estimate the cost to heat that structure to 60F in a WI winter at several thousand dollars maybe 5-8 thousand.

Without heat you aren't going to gain enough to make it worthwhile IMO. You'll gain some on cool season crops but those melons are too late with or without unheated high tunnel.

I'd scale way back to gain experience.

This post was edited by fruitnut on Fri, Jul 4, 14 at 23:39

Sorry I haven't replied in the past few days. I have been busy.

Anyways regarding the 3/4'' conduit I did not mention I would also be running either 3/4'' conduit or maybe even 1' conduit straight across each hoop every few feet high (haven't worked out an exact spacing yet) and there will be some kind of support going all the way down the center of the green house that will be anchored at least a couple feet into the ground. As far as hoop spacing goes my original plan might be pushing it so I will probably go half of that (2.5') just to be safe.

As far as the plastic goes I looked on a few websites for 25' x 50' 4yr 6 mil poly greenhouse plastic and came up with some estimates of prices. First of all for a single layer the price runs around $160-$200 or so. For a double layer tube I am looking at $400-$500. Am I missing something here? Am I not looking at the right kind of plastic? Also what are the advantages/disadvantages to using a tube versus 2 single layers?

As far as heat goes I have a few options for that that I will get into at a later time but that is not as immediate of a concern. As far as scaling back goes I am scaled back compared to what we have planned here. We want to eventually have 3 greenhouses this size up and a lean to greenhouse going most of the way around the house. Not to mention a bunch or raised beds. But all of that is going to take time and I have to start somewhere.