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The bigger polytunnel/hoophouse project, post #2

October 31, 2011

A few days ago I posted about the more ambitious hoop house plans I have for this winter.

I’ve made a little progress since then.  I decided to make it a little longer so that I would have more space on the ends; the effort to engineer a 22′ structure with 6 ribs vs a 20′ one with 5 ribs seemed negligible.  Over the course of the week I  added the additional “ribs” then  worked on the laterals; for these I used 1/2″ schedule 40 pvc.  It is fairly flexible but seemed to provide sufficient stability once all three were installed.  I pre-drilled all of them at the same spacing based on the ribs at the bottom (fence) side then installed the lower one at a height I picked “by eyeballing” it.

From there I adjusted the spacing of the ribs on the top side to line up with the holes on the second lateral.  This took a minute – all but the two end ribs had to be moved at least an inch or two.    I drove in rebar at the correct spacing then moved the base of the rib to it.  The pvc is flexible enough to do this without much trouble; once completed I pulled the old rebar out and then adjusted the next one.

Once spacing was complete I eyeballed the upper lateral for both height and level then attached it.  The 3rd center lateral was easy- the spacing was already worked out and it was up in no time.

The joints were “connected” using a 1 1/4″ screw then topped with a zip-tie.   The screw was long enough to go through the 1/2″ lateral completely (duh) and just one side of the 1″ rib.  IF I do this again next year (and take the fame down for the summer) I’ll drill the joints completely and use bolts to secure them.  I wouldn’t have a lot of confidence in the current scheme for more than a season (hopefully it is sufficient to make it through the winter. 😉 )

The next 3 pictures show the finished frame from 3 angles; note that the lower bed has last year’s hoops installed and was covered at night  to protect the bed from the light freeze we had over the weekend.

The next step was to measure and cut the skin; I ordered clear 3mm “overwintering” plastic from Greenhousemagatore.com . 

I went with the lighter film for economics and flexibility. The roll has enough for 3, maybe 4 structures of this size. If this configuration works I get 3 or 4 years of coverage; if it doesn’t work I can reconfigure in a different shape or size next year.
I was happy to find that the roll was marked by the foot and folded/rolled a lot better than the contractor plastic I used last year.

Once cut, I spread the piece out in the yard and attached paracord on the corners and in the middle. To do this I taped a 6″ piece of duct tape to the edge then bunched the plastic up where the tape was and tied the cord to the bunch. The tape gave the plastic a little more “body” that I thought would keep the rope from sliding off- I didn’t want to over tighten the knots and damage the plastic.

Next I bunched up the whole covering and lightly secured it with the ropes like a mainsail. This allowed me to carry it to the lower side of the frame and lay it at the base to prepare for pulling over.

Once there, I unbound the paracord and tossed it over the middle lateral and then secured the lower side of the tarp (the side opposite of the side with the paracord attached) to the outside two ribs at their base.

Now I was ready to start slowly pulling the cover up and over the structure a little at a time using the paracord.

It didn’t take long to have it pulled up and over:

When I ordered the covering I also picked up some “snap clamps” that secure the covering to the pipe- good stuff. I ordered the 4′ ones and cut them into 6″ sections (because I am cheap).

Using these, it was relatively easy to adjust the tarp and get the tension right across the whole surface.

I was really surprised at how clear this plastic is; I guess I was still expecting something closer to last year’s whiteout contractors plastic. At dusk, I took one last shot with a 60 watt light on inside:

NEXT STEP:
The wooden base or “foundation” and the frame for the two ends.

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6 Comments leave one →
  1. November 1, 2011 5:24 am

    That looks awesome. I think I’m going to have to follow suit next year and do one of these myself.

    • November 1, 2011 6:11 am

      Thanks – I still have some work to do before this would pass a freeze test though….

  2. November 2, 2011 5:11 pm

    Great project. I’m moving in a fortnight to a bigger garden. I might just follow you once we’ve settled in. Growing more food is my aim, too! Do you have any plans to extend the seasons even more with solar heat in the tunnel? I wonderd how I might heat a greenhouse without fossil fuels.

    • November 2, 2011 8:58 pm

      Thanks.

      My assumption is that it will always be 10-20 degrees warmer inside vs outside. For the fairly hardy stuff I’m going to keep going over the course of the winter I don’t think I’ll need much in the way of supplemental heat, if any. I’ll move stuff in to act as heat sinks (rocks, water drums) that should **hopefully** carry everything through the colder nights.

      For harsher winters, you’ll find some ideas here: http://www.builditsolar.com/Projects/Sunspace/sunspaces.htm

      Also, an example of successful high tunnel winter gardening in Michigan (US) without any supplemental heat: http://fastgrowtheweeds.com/greenhouses/

  3. November 15, 2011 9:08 pm

    Awesome posts. I have been considering a greenhouse of my own for next spring. I have been wondering how to tension the poly and keep it taught from rib to rib and teh snap clamps seem like a great find. How many of the 6″ long clamps did you use per rib? How big of a deal was it to remove them after you installed them if you need to make an adjustment in the tension of the film?

    • November 15, 2011 10:16 pm

      Thanks. I’m pretty stoked about how much this will allow me to produce and enjoy over the winter.
      I used about 6 of the snap clamps on each end rib. None in between. (maybe 8? I’ll have to check again)
      You can pop them off pretty easily once you’ve busted a fingernail or two doing it the wrong way…..
      They are so tight they stretch the plastic a bit after they are removed so you want to try and get it right fairly early, ie keep the amount of snapping on/off to a minimum.

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