Our family designed and then built this greenhouse from the ground up. Besides this awesome Instructables project, we also made a really informative YouTube video. Please be sure to watch our Greenhouse Build video as well.
What you will need depends on your specific design. If you use Google Sketchup, like we did, then you will be able to add dimensions and get a specific and precise list for exactly how much lumber you will need. We recently published an hour long video tutorial on YouTube showing how to use Google Sketchup to design our greenhouse. Be sure to check that out if you want to learn how to custom design a greenhouse in Google Sketchup. Otherwise you can use our design. The items below are what you will need for our design which is 10 feet wide by 12 feet long with a gambrel style roof:
- Safety goggles, gloves.
- Tape Measure
- Drill and 5/16 drill bit (to predrill holes in the polycarbonate). And 1/4 driver to screw in hex head neoprene washer/screws to attach panels
- Circular saw, miter saw
- Hammer or Nail Gun
- Tin Snips
- Paint Brush
- TUFTEX polycarbonate panels. These are sold at Lowes. For this build you need 22 panels. Some home centers sell cheap vinyl panels and these can warp and fail over time. These TUFTEX panels are solid and a high quality product. You will also need to pick up foam closure strips (80) and screws with neoprene washers (typically used for metal roofing). We purchased 2 huge boxes of the screws.
- Aluminum corrugated siding. Our home center sells this in 3 foot high sections. 20 pieces.
- 2x4 x8 feet boards. 60 pieces (this includes some extra, as we added some additional to the front and back and it’s always nice to have extra
- 2x4 x10 feet boards. 3 pieces. This is for the 3 foot high wall, for the bottom of the front and back the top of the back section.
- 2x4 x12 feet boards. 5 pieces. This is for the 3 foot high wall top and bottom on both sides AND it is for the ridge of the roof.
- 2x4 x12 feet boards, Pressure treated. 2 pieces (for the bottom of the side walls where it will touch the ground)
- 2x4 x10 feet boards, Pressure treated. 2 pieces (for the bottom of the front and back walls where it will touch the ground)
- 12 foot aluminum ridge cap
- 25 feet of rolled aluminum flashing (used to flash the gambrel transition in the roof.
- 8 bags of cement and some threaded rod. We dug several holes, poured cement and placed threaded rod through the bottom of each wall to secure to the ground and keep level.
- 30" Door. We purchased a basic screen door and attached plastic to it. We will remove the plastic in summer for ventilation. We also purchased a 32x18 vinyl window for ventilation off the back wall.
- Framing Nails for your nail gun or 2 1/2 sinker nails for framing
- A piece of particleboard for the gussets. A 2ft x 4ft piece is more than enough.
- White Exterior Paint
Let's Get Started!
Step 1: Build the 3 Foot High Side Walls
The first step is to build the side walls. The side walls are 36" high and 12 feet long.
With the top and bottom boards at 3 inches high, you will want to cut the studs at 33" high (33"+3"=36"). Looking at our Sketchup design we have 26 studs at 33" each.
To speed up this process I created stop with some scraps of wood next to my miter saw that allows precisely 33" to be cut. Then I just place each board up against the stop and cut, cut cut! To speed things up I cut 2 at a time for a total of 13 cuts.
The side walls are 12 feet long, so use 2 of the 12 foot 2x4s for the top and bottom of each wall. We want the 2x4's to be 24 inches on center to have a proper location to screw the walls into. This 24 inch on center will carry up to the rafters which will have the TUFTEX panels attached at each rafter, 24 inches on center.
Instead of measuring and marking the 12 foot board at 24 inches on center, I create a spacer board at 22.5". Then I just attach a stud, use the spacer board and place the stud up against the spacer and repeat. This spacer really speeds up the process and we can re-use this space later in the project. The nail gun makes fast work of things OR you can build some muscle (I already have enough thank you) by using a hammer and nails.
Step 2: Build the Front and Back Walls
Using my Google Sketchup design I print out the dimensions to get a cut list for the front and back wall.
The back wall is simple it has a 10 foot long bottom and top board and then 33" high boards at 24 inches on center (using the spacer board from the prior step).
The front wall is similar to the back wall at 10 feet wide, however we have a door in the middle. We leave the 10 foot wide board on the bottom (don't cut it out for the door, it will keep things stable). You want to allow for a 30" wide by 80" high door in the center of the wall. And then add additional 33" boards at 24" on center to the left and right of the door.
For the top of the door i sandwiched some particleboard scraps between two 30" wide 2x4s.
We will be adding on additional framing to the front and back top sections to attache the TUFTEX panels to in one of the next steps...
Step 3: Cut the Rafters
So we have 14 top rafters and 14 bottom rafters. Since it is difficult to convey the various angles and lengths and this part is critical I suggest that you use my Google Sketchup design to get the lengths and angles. OTHERWISE see the image attached for measurements. Another option is to purchase pre-made rafters from your local homecenter. I can provide the actual Google Sketchup files as well. AND then you should test fit things before you cut all 28.
So I used my Sketchup design to get my lengths and angles and I setup the angle on my miter saw and setup another stop and I cut all 14 bottom rafters. I then repeated for the top rafters. I designed the greenhouse so that the top and bottom rafter lengths would be less than 8 feet so that you can get both top and bottom parts with one 2x4x8.
Step 4: Build the 24 Gussets for the Gambrel Roof
Since we have a gambrel roof we need a sturdy connection from the top rafter to the bottom rafter. For this we will built 24 gussets. That is two gussets for each gambrel transition and one gusset on the inside of the first rafter and one gusset on the inside of the last rafter. The first and last rafters wont have a gusset on the outside because the TUFTEX panel will be attached to the outside. (In the video I say 28 gussets, but it should be 24).
To build this, take the top and bottom rafter from the previous step and mock it up flat on the ground. So it is positioned EXACTLY as it will be once assembled. OR if you have space you could mockup the 4 walls and use a board to position the ridge board and mockup the rafter by screwing it together. You want to make sure you have the precise angle when mocked up prior to cutting gussets and assembling. Then you can use some paper or cardboard to mockup a gusset. You want the gusset to look like the image above, so that it spans both rafter with plenty of space to firmly attach it.
Once you have the design cut out on paper or cardboard, mark it on a piece of particle board and cut it out. Test fit it. If it fits cut out all 24 like we did.
Step 5: Assemble the Rafters, Attach the Gussets
Using some leftover scraps from cutting out the gussets, I created a jig. With this jig I perfectly aligned each rafter and the jig holds things in place so that I can attach the gussets. Using the nail gun I attached 4 nails to each side of the gusset (4 for the top rafter and 4 for the bottom) this may be a bit overkill but that is what I did. Then I removed the rafter from the jig, lay it flat on the ground and connect a gusset to the other side.
Do this for all rafters except the first rafter should only have gussets on one side (the inside) and the last rafters should only have one gusset on the inside as well since the TUFTEX panels will be on the outside.
Step 6: Assembly and Foundation
We built all the sections inside (because it was snowing outside!) Then we took it all outside to assemble it.
At this point (it could have been done earlier) we attached the pressure treated boards to the bottom of each wall.
Next, we mocked things up and found the perfect location and screwed the side walls together after making sure everything was nice a square.. Then we painted/marked on the grass in each of the corners and in the mid section of each wall. We then moved the greenhouse and dug several holes and filled them with cement. Depending on your soil/location you should consider an ideal foundation for your situation. We used cement footers every few feet.
We then repositioned the greenhouse above the cement, drilled some holes in the bottom of each wall, over the cement and dropped some threaded rod through the floor board/pressure treated board and into the cement. Then we leveled everything and secured the threaded rod with some nuts. We left the cement to cure, making sure once more that everything was level.
Step 7: Rafters, Purllns and Paint
It's all coming together now! We temporarily affix the 12 foot ridge board above the door and precisely center it on the back wall. And then we start attaching the rafters. We attached through the ridge board with 2 long screws from the opposite side. We use our 22.5" spacer board when attaching each rafter.
After all the rafters are up we cut purlins to go between each rafter. These purlins are cut using a stop on our miter saw and each one is 22.5 inches (the same as the spacer board) EXCEPT for the purlins between the gussets.. these are 22.5" minus the width of the plywood used for the gussets. For the top and bottom purlin (see Sketchup drawing with red board) we cut the purlin on an angle to match the angle of the rafter. This is to affix the TUFTEX panel to.
Using a stop on the miter saw really speeds up this process.
After all the purlins are attached we paint everything white. The company that makes the TUFTEX panels recommends white paint to keep the heat down and we also think it looks nice.
Step 8: Front Wall and Back Wall
While the painting is in process. I build a bit of a grid on the front and back wall. The goal is to have 24" center squares to attach the TUFTEX to.
Some of these cuts can be tricky, one thing that helps when trying to frame into an angled section is to align the board in front of the angle and use the angle board as a guide, draw a line and cut it. This is what we did to make the cut pictured above fit perfectly.
We also add a window on the back. And we added a basic 30" screen door which we picked up for $25 at our home center. We plan to use this for ventilation in the summer time and cover it with plastic in the cold months. We plan to add more ventilation in a future project as well.
Step 9: Side Walls and Flashing
The final step before adding the TUFTEX panels is to add the side walls. We bought these 36" high corrugated aluminum sheets at Lowes (same place the TUFTEX is sold). We attached these with metal roofing screws with neoprene washers. These go up quick.
Then we roll out the aluminum flashing and cut in 12 foot sections. We attach the flashing to the bottom part of the top section of rafter (top gambrel) and we DON'T attach it to the bottom section of roofing. The TUFTEX panels on the top roof section will attach over the flashing, the TUFTEX panels on the bottom roof section will go UNDER the flashing. This way, any wind driven rain will not seep through the gambrel section.
We attached the aluminum flashing the the framing with some staples (just to hold it in place) later we will screw through it when we attached the TUFTEX.
Step 10: Attach the TUFTEX Polycarbonate Panels
We can finally attached the panels! These TUFTEX Polycarbonate Panels can be cut with a circular saw with the blade in backwards. We cut a few panels at a time- just don't do too many or they may stick together a bit at the cut.
We also cut some of the panels for the front and back with a tin snips which worked well.
A few notes on installation of these panels:
- Pre Drill all holes- or you can end up with small cracks in the panel. We predrilled with a 5/16 bit. It helps two have two people. One person to pre-drill and the other to drive the screws into place.
- DON'T over tighten. The panel should not deform from the pressure of the screw.
- Use foam filler strips under each point that you attached the panels. This makes for a nice tight fit and seal. For hard to reach places (like under the flashing) we used some spray adhesive to stick the foam filler in place. This helped to ensure the foam was nice and straight.
- Since you can see the foam filler through the panel- keep them nice and straight. We found that after predrilling you can stick the screw through the drill hole and adjust the foam filler strips position to ensure it's nice and straight
- We attached a screw on every 3rd ridge for the roof and every 3rd valley for the greenhouse walls. See the image above. In the roof you should install the screws in the ridge of the panel. If you were to install the screws in the valley on the roof, it would be more likely (over time) that rain water or snow may seep under the screw. So screw into the ridges on the roof. On the vertical walls of the greenhouse you can install the screws in the valleys.
- TIP- like anything, practice makes perfect. By the last few panels we were much better at installing them and getting the foam filler's nice and straight and our screw positions in line... so consider starting the TUFTEX installation on the part of the greenhouse least viewed (the back of the greenhouse) and install the final panels on the front side (most viewed) because by the time you get to the front you will likely be doing your best work!
Step 11: Flashing and Finale
With all the panels installed we are almost done! We used some aluminum edge flashing on each outside corner. We used a white ridge cap on the top of the greenhouse. This part can be tricky (as obviously you cannot stand on the polycarbonate panels. We used our tractor to reach and attach the ridge cap. If we didn't have a tractor- we would have installed it as we installed the top TUFTEX panels... attached a panel, screw down the ridge metal, move over to the next section and repeat.
For some additional "icing" on the cake we made a custom Greenhouse sign on our Cricut machine. We cut it out on vinyl and attached to a piece of wood we painted white first. Then we painted over the vinyl in red and peeled the vinyl off. Emma was the big helper so we named it after her!
Please be sure to watch the video of this project- it is a great video and will help better explain some of the steps of this project.