This plan is for a greenhouse that is 4'x5' and is 18" tall at the base of the roof and ??? tall at the tip of the roof.
- Mitre saw
- Drill
- A way to make cuts at a specific depth. This could be with your mitre saw, a skill saw, a table, saw, or whatever works for you.
- Staple gun
- Wood Glue
- 2"x2"x8'
- 1"x2"x8'
- 3 1/2" wood screws
- 1 1/2" wood screws
- 2 long wood screws with bolt ends
- Vapour barrier (6mil plastic film)
- 4 hinges
- Staples for staple gun (preferably stainless steel)
At the end of this step, we'll have a rectangular frame that will act as the base of the greenhouse.
- Cut two pieces of 2x2 each 5' long
- Cut two pieces of 2x2 each 18" long
We will be using lap joints to join the lengths of wood together which will result in a more torsionally rigid structure. Lap joints are the secret to being able to use 2x2s to build this structure and still have it be very sturdy. You could use butt joints but the structure wouldn't be nearly as strong.
To make your lap joints, at the end of each of the four lengths that have just been cut, make a cut that is 1/2 way through the wood, and the same width as your lumber. If it's a 2x2, this is normally around 1 3/4". If you have a table saw with a dido blade, this will be a very simple exercise but if you don't, that's okay too, it will just be a bit more manual. Once you have one cut that matches up with the width, create many more until you reach the end of the length. Then, use a chisel to remove the slivers of wood that are remaining. You will be doing this procedure a total of eight times, once for each end of wood.
Once you have completed the cuts, dry assemble your pieces and make sure all the joints line up properly. Make any adjustments necessary. Drill pilot holes through each joint, this will be used to screw the joints together for even more strength. Once everything is driled, spread some glue on each surface of the joints. Make sure everything is aligned, and use a 1.5" screw to join them together.
Once all of this is done, you will have completed one side of the greenhouse. Repeat this procedure and you will have completed two sides of the greenhouse!
You are now half done the rectangular frame of the greenhouse. Repeat all of the above procedures except cut lengths that are 4' and 18". These will be the ends of the greenhouse.
The roof is built at 45 degrees so that it sheds snow well. This is especially important if you will be using this structure as a cold frame. The roof is very simple, it consists of two lengths of 2x2 cut at 45 degree angles on each end.
Cut four lengths of 2x2 each ???? long. Use your mitre saw to cut each end at a 45 degree angle such that when the two pieces are assembled, they butt up together making a 90 degree angle and each end lays flat and true against the frame.
For the main roof truss, you will use another 2x2 and cut it of the length of 5' minus 2 * the actual width of your lumber. For example, truss length = (5' * 12"/ft) - 2*1.75" = 56.5".
Drill pilot holes offset slightly so that you can screw each end of the roof at the apex together. Also drill two pilot holes on each end that will attach to the frame. Glue everything up and screw them together! No fancy joints in this part of the structure.
For the main roof truss, drill through the apex of the two roof beams into the end of the main truss. This should be a deep hole and larger because you will be using a very large bolt to secure it.
You will be creating two roof flaps, so that you can access the greenhosue from both sides. If you only want one flap, only make one! I recommend two though as this greenhouse is 4' wide and that's a long way to reach with only one flap.
For each flap, cut two pieces of 2x2 5' long and two pieces of 2x2 ??? long. Use your newly learned lap joint skills to join the top two joints of each flap, and for the bottom one, we will do something special. If you do not have a table saw that can cut at 45 degree angles, go to "I don't have a table saw". Cut one of the 5' lenghts at a 45 degree angle all the way across. This is a scary cut so if you have someone to help you it is much safer. Once this is done, you should be able to just drill a pilot hole through the ends of the roof flap and butt joint it together.
If you don't have a table saw, that's okay, you can just join the flaps like you did the other four sides of the greenhouse. The flap just won't sit perfectly flat at the interface between the rectangular sturcture and the flap.
You now have two long rectangles, and two short rectangles with triangles on top. If you don't want to be able to disassemble the greenhouse, just screw it all together! If you do, drill large holes and bolt it together. Once you have your rectangular base assembled, bolt in the main roof truss using the two large pilot holes made earlier.
Almost there, now attach the flaps using the hinges.
You've got a structure, but it's not a greenhouse yet. Using 6mil vapour barrier, cut pieces larger than each of the main areas of the frame. Staple them on and cut off any excess. Please do use stainless steel staples if you can find them. It keeps your greenhouse looking pristine.
If you don't want to have to worry about cooking your precious plants, you can install a Lee Valley automatic opener. Cut two pieces of wood like this picture needed and screw them into the frame. You now have an automatic opener!
If you used untreated wood, make sure you paint it.