The Greenhouse - Construction

Building an Economical Greenhouse.

March 01 2012

 

     First, I think it would be valuable to have a little background on just how it is that I became interested in greenhouse gardening.  Going way back to the beginning briefly may provide some interesting perspective.  So, childhood; I grew up in a large, thrifty family and gardening was a large part of my childhood.  All of my siblings helped out in the garden which was roughly one-half of an acre in size, but somewhere along the line I took a special shine to it.  During high school I even did a little truck crop gardening.  I grew roughly one acre of crops, mostly your average Midwestern garden fare, which I sold at a weekly farmers market in town.  In hindsight my methods were pretty crude, and the amount of work I put in was pretty huge for the amount of rewards I reaped.  After college I moved here to Rock Island, Illinois, and bought a small house on a small lot, and along with my wife we quickly began a small(er) family.

      Now for a little greenhouse history.  I first planted some garden here in late spring 2008, which is late for me but I had been busy remodeling the house in time to move in at the end of my apartment lease at the end of May 2008.  This was enough to hold me for a year or two while I was busy with the house, but I soon began to tinker more with some solar projects.  In 2010 I built a lean-to greenhouse on the south face of the detached garage which I planned to use to start a few garden plants, and grow some greens throughout the winter.This greenhouse consisted of a 4' x 20' planter bed about 2' high, with an inner walkway about 12' long and 18" wide accessed off of the garage.  The main glazing for this was double pane glass salvaged out of three patio doors.

The First Greenhouse

      Being a tinkerer, and realizing I was probably onto something I quickly realized that the space provided was not nearly enough.  I next began with a hoophouse / high tunnel construction, which was a rather rude structure built in a quonset hut style.  It was simply 3/4" grey PVC electrical conduit bent in an arch, and anchored with 1/2" steel rebar driven into the ground.  The endwalls were of plywood, and the structure was covered with 6 mil contractor grade plastic.  The results however were excellent, and allowed me to plant about 1- 1 1/2 months ahead of normal planting time.  Like any good guy I decided to go bigger.....and so we begin.

Installed frost wall

    First I determined that integrating a frost wall into the design would allow a further early start to the growing season.  A frost wall is simply an insulated foundation which separates the exterior soil from the interior soil which allows the soil at the edges to warm faster than the exterior soil.  This was built using 2" insulation board laminated with plywood, and painted for weather resistance.  I used "seconds" paint from Menards since the color was not really an issue.




The second improvement was a sidewall, which allows working close to the edge of the greenhouse much more comfortable.  This was constructed using 1 1/2" steel pipe fence posts driven vertically through the frost wall and about 2' deep below the wall.  The post also was left about 2' above the frost wall, and trimmed to level.  The posts were capped with treated 2" thick lumber.  In order to match the height of the existing greenhouse wall I cut a piece of 4" x 4" post to notch over the top of the sidewall.  The top of this piece was cut at an angle which I pre-calculated, and drilled for the 1" PVC hoops.  where the hoop met

the existing greenhose a shim was cut, and a 1" PVC anchor fitting attached as shown.  The plastic sheeting was attached to a horizontal steel pipe attached to the original greenhouse with single end conduit clips, and PVC snap clamps.  This was how the main plastic sheeting is attached in general.




Next the hoops were erected using the PVC fittings shown below.  These are available from several greenhouse suppliers.  The hoops are of standard 1" PVC electricsal conduit.  It is important to use electrical conduit as it is UV stabilized (non UV stabile plastic will become brittle after about a year) for this.  I also used a 5 way fitting every other hoop which will allow a vertical support pipe in case of a heavy wet snow.  This was done as I was using a lower (flatter) hoop than a true arch in order to minimize the profile of the hoophouse.  Doing this made the hoophouse about 3' shorter (it is till 8 1/2' high) than it would have been with a true arch, but makes the span less strong.

West End

 Next the end walls were framed up.

East End with access door

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And painted.  Luckily for me a warm late January allowed me to paint.   Normally this would not be possible on the frozen tundra in January, and February.

An inside view, note the "compost pile" at the bottom center.  I am preparing to affix a 1" steel pipe to reinforce the ridgeline, and carry the stress if a heavy snow load were to be on the structure.  Also note the yard bags of leaves in the rear right which will be added to the compost pile.  I am planning a compost pile which should add some marginal heat to the hoophouse in late winter, and also contribute extra carbon Dioxide to encourage plant growth.

A view from the Southeast.

The same view after the plastic sheeting has been affixed.

The East end with Plastic.

The West end with plastic

     Some final photos below are of the finished hoophouse.  In the center is the compost pile.  This was taken on a sunny Sunday February 12th at about 10 A.M.  The overnight low the previous night was 8 degrees F, and the current exterior temperature is about 20 degrees F.  The interior looks dark due to the frost on the interior of the greenhouse which has not melted yet as the sun is only hitting the south face glancingly.  The south face also is shaded by a large tree until about noon which provides about a 30-40% shading. Even with these conditions the house is 40 F, and later in the day reached 72 F with an exterior temperature of 28 F.

A nice close-up of the compost pile