Advice sought on large hoophouse

[simy1]

The neighbor has two 40X40 (all units in feet here and after) sheets of clear poly that he will give me, since he sees that I have tunnels for my winter vegetables (this year I will get to harvest until end of january at least, he actually told me as I was getting back into the house with a paint bucket full of just picked radicchio). I just love these hot stove projects, but before I embark in it, a question or two for those who have built hoophouses.

1) those sheets are clearly very large. If used without cutting, they will cover a 24X38 area, with a maximum height of 12. That is an unusually wide hoophouse.

2) I think I want to use PVC pipes, glued with plumbing solvent. The question is, can I make them withstand a windstorm or snowstorm. I have seen lots of pages on the web, so I have seen what can be done. Amongst other solutions, I noticed that there were hoophouses with poles supporting the central beam, and of course one can always anchor the hoops to the ground. I guess I am more concerned about the snow than the wind.

3) I am thinking about getting a double layer of poly for extra insulation. Any experience with that? I would need a double hoophouse.

4) I plan to make two trap doors at opposite ends, and have one set of doors with poly and another with chicken wire. Will there be enough ventilation with the chicken wire doors in place?

[Frank Miles]

That is HUGE!

PVC works well for smaller units, but I think (guess) that this is too big for snow. Even wind can be tough, though IMHE putting guy lines between the hoops can make a world of difference -- there's just too much tension in the plastic to depend on attaching to the perimeter of the material, even if the tension is distributed by tape over a relatively broad periferal area.

You didn't say anything about where you live (e.g. frequency/magnitude of snowfalls) nor how much spacing you might have between hoops. My guess is -- if there's a chance of having 6" or more of wet snow, it will probably be more stress than any reasonable PVC system could withstand.

Might you get a warm sunny day? It's incredible how much heat you can build up in one of these. Doors might be enough if you could supplement with a fan. How big might these trap doors be?

[Rick]

That would be quite large. Try this link for a 12x14 foot green house. I built one of these and have been happy with it. The width is pretty much set by what one can do with PVC pipe, but the length is arbitrary. One could easily make it 28 foot or longer if you have the room. I'm planning to set up a second one. I did not do anything to heat the house, and was picking vine ripe tomatoes on December 7th in zone 6.

I modified the design a bit. Also, double check the amount of wood on the check list for the ends of the hoop house. IIRC there was only enough listed for One end!

[Bill Bolle]

Before you start building with PVC take a look at this hoophouse:

[simy1]

nice site, thank you. Indeed cattle panels could be a better choice.

[simy1]

In my present tunnels (each over a 4 ft bed) I have hoops, and I have a central beam.

I live in Michigan. My experience is that snow will happily slide down a hoophouse unless there is a sag. But I concur, it is probably too much. I know that the poly, properly clamped, will not get loose no matter the wind (poly clamps bought at Territorial Seeds).

Maybe 4.5 ft by 7 ft, if I have to go in with the cart full of manure. I have already calculated that there is not enough heat storage in a wall of water drums. The heat input is probably 50-100 W/m2 in the winter, and the heat sink is the soil. Not clear how fast it can absorb heat and probably depends on it being moist.I know from experience that mulch and hoophouse is a deadly combo (plants fry, or freeze, or both), which is a problem because all mulch must completely decompose within the growing season (that means only leaves or cardboard).

That is probably what I will do. The hoophouses will still be 6ft high. By placing them side-to-side I can take care of half the watering, since the water will pool in the middle, evaporate, condense on the poly, and drip all over. It certainly works for my current tunnels. One can even consider a sunken hoophouse (I have sandy soil, and sunken will help with the wind), with a sloping floor so as to redistribute the water.

[simy1]

some more considerations that will probably interest only backyard hobbyists:

1) the link above uses cattle panels (basically very strong rebar), and (this is important) they bend them quite a bit, so the hoophouse is taller than a semicylinder. The rebar then provides some tension to push up against the snow, in fact they easily hang pots onto the rebar without having the house sag. But, if you want to use the soil, you have less area underneath. I suppose the tradeoff between tension and surface is inevitable. Incidentally, my 11 feet PVC hoops don't do that. After two years at most the take a permanent hoop shape. They are still strong enough to shed snow without collapse. Rebar also provides excellent support to the poly, effectively preventing pooling of water or accumulation of snow. 2) when using the rebar, they have two problems. The first is that all sorts of of rough spots will scratch and break the plastic. IMHO, this is the perfect place where to use that old hose you have in your garage. Slit it lengthwise and fit it over the ends. The second is that they have trouble clamping onto the rebar. the PVC clamps are great (amongst other things, they are capable of holding the plastic even when the wind is blowing from the inside, such as may happen when one leaves an opening after harvest) but alas, only come in PVC sizes (3/4 and 1). Probably just a matter of clamping a PVC pipe to the rebar on the inside, then clamp the poly on the pipe (that will be a pain when one removes the poly for the summer, but safe until then.

Various other issues include anchoring the whole thing (probably enough to bury a few cinder blocks around the perimeter, with hooks at the surface for strapping), double layering (do the second layer inside, it will sag, do it outside, it will sag and touch the first), chicken wiring (when I take off the poly, I still want the rabbits out of my garden), and how to do the ends. Nice clean design overall.

[simy1]

I am settled on the cattle panel hoophouse (a PVC one has too many techincal problems which I won't mention here, though I will use PVC pipes at the edges for the clamping of poly). One last question: the hoophouses( two of them, each

38X12, side by side), should be oriented N-S or E-W? Light hitting the poly at an angle below 40 degrees is totally reflected.

[Bill Bolle]

I really don't know which way would be the best-----I've seen greenhouses around here pointing in all sorts of directions, based mostly, I guess, on the topography of their land. Logically I would assume that the benefits of a hoophouse would be in its use during the winter and I think that with low sun angles that you would get the best perpendicular angle of the suns rays with a East/West orientation. One problem with E/W would be that the hoophouses would have to be end to end and not side by side. For what it's worth-------Bill

[simy1]

Yes and no. In Zone 6, one would use a greenhouse for, say, tomatoes, until June 1. At that point in Ann Arbor the sun is 71 degrees over the horizon at noon. Also in the winter one has plants that grow during the growing season (mostly), and are kept alive for consumption through the winter. In winter, a N-S house will have shade near the edges on the N side. In May, it will have shade along most of the edges. Then again this is the kind of midday shade many plants actually want. A E-W house will have little shade in winter but all edges will be shaded in May. not much difference. It seems like one is better off orienting the house so as to have the broad side against the prevailing winds. So I will orient it NE-SW...

[jfrost]

below is the connectors to build a shed out of 2x4's maybe it could be used as a greenhouse?

or harborfreight.com and search 33707 its around $50 and is 7x8

hope it helps