How to Build an Inexpensive Greenhouse

Do you like the idea of being able to extend your growing season?

What about having a great space to start seeds a little earlier?

Then you need a greenhouse.

They are a great addition to any homestead. Any expense you accrue in building one can quickly be made back with the extra product they help produce.

Material List for 28 foot by 15-foot greenhouse with PVC

  1. 5 20 foot pieces of 5/8 inch rebar (cut into 1/3’s to about 6-foot lengths)
  2. 7 20 foot lengths of 1-inch schedule 40 PVC with a small (3/16-¼ inch) hole drilled dead center, at 10 feet
  3. 2 20 foot lengths of 1-inch schedule 40 PVC (cut into 20-inch pieces)
  4. 84 feet of ½ schedule 40 PVC cut into 4-foot lengths.
  5. About 80 feet of 2X4 treated wood
  6. 4 treated 8-foot fence posts
  7. 40X24 feet of UV stabilized polyethylene
  8. 60 2 ½ inch fence staples

Steps 1 & 3a

Start by stretching a string along where you want the two long sides of the greenhouse to be. Then pound in your 6 foot long pieces of rebar every 4 feet in a straight line leaving 48 inches protruding from the ground. It is important that they be vertical and within ½ inch of the 48-inch target. 

If you plan on graveling the floor, put it down as soon you have figured out where the greenhouse goes.

Step 2

Nail on 2X6 runner to the rebar stakes. This will give you something to nail the polyethylene onto later. You can use 60 2 ½ inch fence staples. (In the picture left we put the PVC on before attaching the 2X6. This was a pain as you had to hold up the PVC while you nailed the rebar.) 

Step 3b

Slide the 20-inch pieces of PVC over the rebar stakes.

* make sure no sharps are exposed: wire ends, rebar, rough pipe, etc. It will later tear the plastic.

Step 4

Place the 20-foot pieces of PVC on the rebar stakes. (Don’t put it all the way down on one side and then do the other. Have friends do one side while you do the other, both a little at a time.

*When you first slide the pipes on, the holes you drilled MUST be horizontal (parallel to the ground). Wait about an hour and you will not be about to twist the pipe to correct the problem. The vertical rebar will bend inward as the PVC flexes. This grabs the rebar and locks up the PVC.

Step 5

Now you can slide the wire through the holes in the PVC and then through the eight four foot pieces of PVC along the roof.

Step 6

To keep the ribs of this greenhouse from shifting horizontally wire the four-foot lengths of PVC pipe with copper or baling wire. Make sure you wrap the wire so the PVC is forced inward not outward.

* This sidewall and top tie is VERY, VERY important. If the walls can separate snow or even hail will collapse the structure. The greenhouse will stand up to about a foot (2 foot?) of snow with the ties, two inches without them. If the frame stays together the snow will slide off, if the structure pulls apart the snow can build up to a weight of a 1956 Buick. This greenhouse will not support a Buick on it.

Step 7

Finally, you need to build the two end walls with doors. You should put a door on both sides as it will vent better. Either use 10-foot vertical posts (4X4) buried 3-4 feet for doorway frame or 8-foot posts with bracing back to runners(as shown). The two end walls have to be well built and cannot be floppy. They have to stay vertical so the PVC cannot separate. The door needs to be tight enough so that gusts of wind cannot inflate your greenhouse. 

Drive a few nails horizontally into the base of the posts and bury them. This will help give your posts some grip on the ground. Little mini-twisters love to hit our greenhouses and blow them up. 40 MPH winds coming in from both sides test your construction. (Our fiberglass greenhouses are cleated with lath because of this problem. Our mini-twisters have blown up some barns in the area.)

Step 8

Last, of all have someone help you, one person on each side, slide the plastic over your rib cage. Attach each end by rapping the end of your plastic around pieces of lath and then nail the lath to the triangular end walls and to that long 2X6 along the bottom. Ta-Da! A greenhouse! You can make it look a lot classier. Ours is just functional.

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