Greenhouse Collapse

Hey folks! Well darn it.

I've been trying to become a "organic gardener/farmer" for a few years now, in between jobs.
Last fall I installed my first tunnel. 100 feet by 16ft. I was very happy. Didn't get to use it even once.
It got destroyed by the snow. Every single pole, bent and crushed.

Does anyone have experience with rebuilding standard steel poles?

Thanks
Charles

First of all, I am sorry for your loss. I know the heartache of putting a lot into a venture and then suffering a devastating loss. To that end I am not just sympathetic but empathetic.

If it was me, I would not go with steel hoops, but wooden ones. Around here wooden boat builders use this technique to great success. It takes very little wood, has the benefit of a double arch span and is rugged. They put wooden hoops 4 feet on center made out of strapping and envelope some pretty big yachts. They throw a space heater in there and have a cheap, big, heated working shop all winter, which of course is the same principals of greenhouses. I tried to find a picture, but I couldn't. I know there is a company that sells the frames locally.  saw them at an organic fair touting up the construction virtues.

I have never done one myself, only because I am a sheep farmer and the dynamics of building what would be a barn for me, are different. But I have considered it when I was running out of barn space before.

Another alternative you might consider is the frames I build in my barns. Mine are posted 4 feet on center, but you could easily go 8 feet on center. That would drastically reduce the number required and would not collapse. You can read more about it on this thread. Permies Thread

I built a hoop house, and on the money I saved on the labor, I splurged on the materials.  I put a bent steel conduit rib every two feet.  We get very heavy snow loads and zero problems.  This is my 3rd winter.  I have seen many of the inexpensive kit greenhouses and quickie garage substitutes squashed in the snow, or damaged by the wind.  They use the 4' spacing, but evidently, not heavy enough.

Your damaged steel tubes/ribs can most likely not be repaired.  Once that tubing has a kink or a crush, it loses 3/4 of it's strength.

What size and kind of tubes did you use??


Sorry for your loss my friend.

Troy Rhodes wrote:I built a hoop house, and on the money I saved on the labor, I splurged on the materials.  I put a bent steel conduit rib every two feet.  We get very heavy snow loads and zero problems.  This is my 3rd winter.  I have seen many of the inexpensive kit greenhouses and quickie garage substitutes squashed in the snow, or damaged by the wind.  They use the 4' spacing, but evidently, not heavy enough.

Where do you recommend ordering from? I'm looking for a small but very sturdy hoop house to put up myself this year.

Brian McCune wrote:

Troy Rhodes wrote:I built a hoop house, and on the money I saved on the labor, I splurged on the materials.  I put a bent steel conduit rib every two feet.  We get very heavy snow loads and zero problems.  This is my 3rd winter.  I have seen many of the inexpensive kit greenhouses and quickie garage substitutes squashed in the snow, or damaged by the wind.  They use the 4' spacing, but evidently, not heavy enough.

Where do you recommend ordering from? I'm looking for a small but very sturdy hoop house to put up myself this year.

The nearest big-box lumberyard.  

I built a simple plywood bending jig and made it out of EMT (electrical conduit).  Two 10' 1" emt conduits make a perfect 12 1/2' hoop.  There's a ton of youtube videos on how to.

For big ones, people use the top rail of chain link fence.

The kits were almost double the money to get the same size, but half the ribs.

I put up some pictures and description over on hearthdotcom, because that's how I store and dry my firewood:

http://www.hearth.com/talk/threads/i-built-a-12-5-x-28-greenhouse-to-store-and-dry-wood-working-awesome.129149/page-2

I can't edit the title/first post, where I mistakenly describe the emt as 3/4".  It's 1" for the ribs and 3/4" for the purlins that run the length of the greenhouse.

It's also worth considering what shape you use.  Semicircular, Quonsett hut designs don't shed snow well, but a gothic arch will.  It offers a somewhat higher profile to the wind, and a little bit less square footage for the materials used, so there is a tradeoff, but it's less likely to be crushed by snow.

I agree with Peter. Gothic or other steep slope roof.  Also, there's a few other tricks to keeping roofs from collapsing. 1: tight plastic, no sag. 2: whipe off snow load.

I'm sure that's horribly frustrating to have that collapse. Good luck on the rebuild. Mines a dinky little wooden one made of scraps.

For very heavy snow loads, you  can also put some vertical posts in every so often, tied into the ribs and/or purlins.

This does put some constraints on your interior space.

I purchased this one in 2009 and it's still standing with the original film. I bought new film to replace the old because it's torn in a few spots but wound up being too late to set it up this year. This is the first year I didn't get much of a season extension due to the tears in the film.

I've got 7 ducks and a chicken overwintering in there and they seem to be doing fine despite getting down into the single digits.

The quicky  garages that are gothic style got squished. One of them was fixable and the other not.

I'm thinking about building this one

hello Charles,

Yes i have experience REBUILDING a Crushed by snow hoop-house!
just don't give up...
 
because it happened to me and my 16 x 100 foot hoop-house on a freaky
 Halloween snow storm  and i only had shade cloth on it.

 Here is what i did...  I took every single arch that had a usable HALF
and i  sawed them in Half  so i could rebuild a "smaller" hoop house.

    the home depot sells sleeves  that you can join your salvaged Halves
 back together again . I built a ridge pole supported by posts and screwed
the sleeves to it so  it became more solid and supported the other end
on top of a "pony wall "  short enough you can swing a leg over it.

 on the top of this pony wall i drilled holes in the 2 x 4  every 22" inches
to shove the bottom ends in .Actually i drilled the holes in the pony wall to receive
the sleeves THEN i shoved the arches into them.

here's a photo showing the construction of it , it supported 2 feet of snow.
i use 3 inch deck screws on EVERYTHING !!!  make it super strong!

http://i25.photobucket.com/albums/c66/ravenob1/greenhouse1.jpg

Brian McCune wrote:

Troy Rhodes wrote:I built a hoop house, and on the money I saved on the labor, I splurged on the materials.  I put a bent steel conduit rib every two feet.  We get very heavy snow loads and zero problems.  This is my 3rd winter.  I have seen many of the inexpensive kit greenhouses and quickie garage substitutes squashed in the snow, or damaged by the wind.  They use the 4' spacing, but evidently, not heavy enough.

Where do you recommend ordering from? I'm looking for a small but very sturdy hoop house to put up myself this year.

Small ones are very easily built by using cattle panels bent into the hoop shape.  I have two and mine have never had a problem holding up, even with large and very wet/heavy snowfalls.  I made mine by following this guy's plan:  Hoop house

He sells the plans complete with all measurements.  I built mine just from watching the youtube video, but I appreciated the work he put into it, so I bought the plans as a "thank you".

I built mine from a collection of parts from portable garages that had collapsed from snow or torn apart by wind..  The connectors held up fine but the tubes ben and broke where thy were out of alignment.  The secret is to have all verticals plumb and locked tight at the bottom. The rest has to be braced with cables, turn buckle tight length wise and cross wise. You might consider wood purlins on the sides that the wiggle wire fasteners can be attached too to hold the fabric tight.

What usually dooms the hoophouses and row covers I've seen is that the hoops are parallel, and go straight across the bed like a covered wagon. That means that each section of plastic is rectangular, and starts to bag, hold water or snow, and fail.  The hoophouses, tunnels, and grow-domes that I've had success with in Alaska and here in Northern CA are built with supports that cross, looking like a series of XXX's from above. That means two things:

One is that you have made a groin vault, just like a Gothic cathedral. It is an extremely strong structure, with the stresses well-distributed and conducted to the ground.

Two is that each section of plastic is now a triangle. It has a smaller surface area, and the inevitable stretch and sag forms a trough leading to the ground rather than a bag up in the air with no exit for water or snow.  It sheds rain or snow very efficiently. Moreover, the triangles are stronger than squares, and the hoops support one another. The longer diagonal run means that the poles are not bent so abruptly and are under less stress.

To do it this way, the poles need to be longer than if you are just going straight across the bed (or area to be covered by the greenhouse). You place your poles so that they cross diagonally instead. Each pair of poles then makes an X as seen from above. The next set is placed right next to the first, so that they make V's when seen from the side. When all are placed, you can hitch each crossing-point together with a rope that is staked at each end of the the tunnel, for more wind-resistance and strength, or you can lash a pole up there as a ridgepole. If you don't want to do the ridgepole or rope to stabilize, then just tie the places where the poles cross with strong cord or black electricians tape so they don't shift. You'll want to make sure they are crossing at the center of the space, so it's worth marking the centerline and using a plumb bob to find the proper place to cross, to distribute the stresses evenly.

I have had this style of greenhouse survive winds in excess of 60 knots, when my neighbor's with parallel hoops was torn to bits. His was reinforced with lumber purlins. Mine was not--didn't need it.  And they are beautiful structures.

In summer, you can take the cover off to save it from UV damage and use the supports to grow pole beans, with lettuce underneath.

Built my greenhouse out of 2x4s on 24" centers. Had very heavy snow loads on it and tons of wind with no issues even when I just used 6 mil construction plastic. Got tired of recovering it every year so now I use greenhouse plastic on the roof.

Yes, rigidity is key.  Successful structures have some mechanism to 1)distribute the stresses, and 2) lock the structure together.  That's why the single hoops so often fail--they wiggle around, allowing the structure to distort and sag to accumulate. And they expose each individual member to the full amount of stress, rather than reinforcing one another and distributing--dissipating--the stress. (Also, the shorter, more acute curve is in itself an unevenly distributed stress.)

Any rectangle can shift, but a triangle can't. The beauty of groin-vault structures is that the main members form triangles right from the start, so no extra bracing is needed. Even without a ridgepole, if the poles are merely taped where they cross, they still cannot shift the way stand-alone hoops do. It is a single, rigid structure rather than a collection of single poles. Ever try to break a bundle of little twigs? Same thing: United they stand. Divided, they crimp and crush and fail. For a cheap, fast, short-term solution, and you are going to use pvc pipe anyway, the diagonal design wins hands down. I've built small ones in a a few minutes with willow branches that lasted for years.

For the long term, and with money or time to spend, a gable or shed roof, wood-frame structure seems like the best choice to me. I've always wanted a wood-frame greenhouse with a rigid-panel roof because bit by bit you can shift over to glass as you are able. And you can collect rainwater from the roof.

If economics is an issue starting out you can always use the greenhouse plastic. It's not expensive and is suppose to last 4+ years.

I went with some construction plastic at home depot for $6 to cover a 12x5' structure, 8' tall at the peak. I want glass or something not plastic, but it will get me going while I figure out and gather old windows and glass panes. I also made the sides so they can roll up. That means more air circulation in general, but the plastic on the sides will last longer. I'm going to try growing deciduous stuff over the rest too so that part doesn't get blasted with Summer sun.

Here in southeast Michigan I uncover the sides of my greenhouse and have a fan blowing the hot air in the ceiling out at the peak and don't have an overheating problem. The sides are screened and there is a little shade in the afternoon from a large tree nearby. Don't let that plastic fool you. It will look fine come fall but in reality the roof plastic will be brittle and start to disintegrate in the winter months. Be sure to change it.