Friday, August 3, 2012

How to Build a Greenhouse

Or woodshed, or pole barn, or turkey shack... Or whatever you think this structure would be good for. This post is for jambaloney, who asked for pics to copy the construction. The design is my dad's. He's awesome. #2 has taken it to new levels, and can whip up a new shack in just a couple of days. He's awesome too. The pics are from a variety of projects, so I hope they make sense, even though they won't match up exactly.

To start, go out in your woods and cut down some tall, straight trees, with about an 8" diameter.  Trim them all up, and then...

You will need:
12' posts X2
12' poles X3
8' posts X4
and a bunch of smaller stuff I'll send you back in the woods for later, lol. Give yourself an extra foot or so to level them off later as well.
Dig your first corner post hole 4' deep (or until you hit a really big rock and figure that's good enough).  Drop an 8' post into it.  Mark a board, (a 12' 1X3 works great) or something straight at 4', 6', 8', and 12' to use as a measuring stick.  Lay it out on the ground from your first post in whatever direction you wish to put the back side of the structure.  Dig your center post hole at 6', and your second corner at 12'.  Drop an 8' post in the corner.

Measure 12' forward from each corner and mark the front corner post spots.  Then measure 12' between them.  You'll need to adjust to square it all up.  Once you have it all square, start digging.  Drop an 8' post in each corner.

Cut your first corner post off flat at 4' above ground.  Cut the matching front post off flat at a level height.  Then do the same from the original corner post to the opposite back corner.  Then that corner to the opposite front corner.  Check the level with the first front corner before cutting.

Drop your 12' center posts into their holes.  Measure one at 8' above ground, cut off flat.  level the other, and cut off flat.
Cut a notch in each end of your 12' poles, half the diameter of the pole, and long enough to cover the top of the posts.  Set them on top of your posts and nail in place.
Back in the woods, cut a bunch of poles for the roof.  These only need to be 3 or 4" diameter.  Cut the top ends on an angle so they sit flat on the top pole, and nail in place.  We only used four on each side for the greenhouses, more for the lean-tos, or anything you plan to put a solid roof on later.  Cut the bottom end of the poles on an angle after the tops are nailed in.  Nail in place.
This one ended up with two center posts because no one noticed how crooked that tree was until it was time to frame the door.  Back in the woods, cut logs to go from corner to corner, corner to center, on the ground.  Actually, if you plan to lift the sides of your greenhouse, skip the corner to corner logs.  1X3s work better there.  Nail those into place.  Build the door frame.
Cut and nail in additional logs, about two feet apart, on the back and front sides.  This helps keep the wind from slapping the plastic against your plants.
Cover with plastic from the bottom of one side, over the top, to the bottom of the other side.  We just stapled ours on, but you may want to use some strapping to help keep the wind from ripping it out.  We use 1X3s on the bottom of the sides. 

Pop the 1x3 off with a crow bar, and roll the plastic up on it, and nail to the roof to raise the sides.
Add plastic to the front and back. 

You can build a solid door if you want.  We did, to keep critters out.  The door plastic is just a strip nailed above the door frame, with a pole stapled on the bottom.  I put in a couple of spikes at the top of the door frame to rest the pole on when rolled up.
We also added a couple of one by threes on top where the seam of the plastic over lapped.  A pole would be fine as well, just something to staple the loose edge of the plastic to.

Just a side note- if you're planning a wood shed- poles from the top of the sides to the bottom are all you need to keep your rows from toppling over.

Clear as mud?  Good luck to you.  I hope this helps!


  1. It was all working out in my mind until you CUT OFF your corner poles! Why did you do that? My mind went to mush after that!

    1. lol. Well, you want your roof to be level. Even if you made sure that all of your post holes were exactly 4' deep, unless you level the ground before you start, the posts are not going to hold the side poles level. We measure by paces in the woods, so our logs are never the same length, and we're digging through lots of rock, so our holes are never quite the same. So we cut the first post at 4' above ground, and match the rest up.

    2. Oh, that cut looked like it was almost even from the ground!I have gotten it

    3. The second pic is a notch, and it was on the ground. Everything before that was related to the first pic. I never planned to do a tutorial on building a greenhouse, so the pics are kind of sporadic, from different projects.

  2. Wendy - excellent instructions. we are going to be building our greenhouse using windows - but this kind of structure is exactly what we need for sheds, carport, etc. i'll show jambaloney this when he gets in - he'll love it!

    your friend,

    1. Thanks, kymber. Yes, it is a handy little structure for all sorts of stuff, and cheap to build! We're working on a triple for a hay shed/goat house right now.

  3. Wendy:

    thank you a million times for this - my creative juices are flowing big-time, can't wait to get to building!!!

    one question - what size nails and how many to you uses to fasten the poles together?

    great tutorial!!!

    1. Thanks, jam!

      My theory is, always use the smallest nail that will do the job. I buy an assortment of nails and spikes from 2" to 12". I figure to hold anything together long term, your nail needs to be twice as long as the thickness of the piece you're nailing through. So if you're nailing an 8" diameter log, with the notch cut out halfway, you need an 8" spike. We usually only use one spike per pole, unless it bends/goes off centre/or breaks the end of the wood.

    2. Hey wendy!

      your canning progress is looking great!! tell your boys congrats on their PALs and hunter's licenses too!!

      i am getting ready to do a green/hoop house and have a few more question, if that's okay:

      is that 10 mil plastic, how long does it last?

      do you strip the bark off the logs or seal the part that goes in the ground?

      do you use cement in the post holes for the or just fill them in with dirt?

      thanks a bunch!!

    3. Thanks, Jam!

      We use vapour barrier plastic, which I think is 16 mil, but can't swear to it. It has a bit of writing here and there, but it works pretty well. Our greenhouses have been up just one winter, so I can't really say how long it will last for. The plastic isn't deteriorating, but there are quite a few rips from the wind ripping the staples out.

      We don't strip the bark off, but it supposedly will make the logs rot faster. We have fence posts that we put in, with the bark on, 4 years ago, and they're still solid. I can't say what's happening underground, but the weather strips the bark off the top through the winter.

      No, we haven't needed to cement any holes, and I would imagine you won't either. We're building on rocky/sandy soil, sometimes heavy clay. If you're building on something soft you might need to, but judging from your trench pics, you've got the same type of underground landscape as us.

      Happy to help!