Our family designed and built a gambrel-roofed greenhouse from the ground up. In this article, I provide step-by-step details on how to build this greenhouse with a 2-by-4 structure. We also created a detailed YouTube video.
The items below are what you will need for our design (10 feet wide by 12 feet).
• Safety goggles
• Tape measure
• Drill and 5/16 drill bit
• 1/4 hex driver
• Circular saw
• Miter saw
• Hammer or nail gun
• Tin snips
• Paint brush
• TUFTEX polycarbonate panels
• Foam enclosure strips (80) and screws
• Aluminum corrugated siding - 20 pieces
• 2x4 x8 feet boards. 60 pieces
• 2x4 x12 feet boards. 5 pieces
• 2x4 x12 feet boards, Pressure treated. 2 pieces
• 2x4 x10 feet boards, Pressure treated. 2 pieces
• 12 feet aluminum ridge cap
• 25 feet of rolled aluminum
• 30-inch door
• Framing nails
• White Exterior Paint
Step 1: Build the 3-Foot-High Side Walls
The first step is to build the side walls. The side walls are 36 inches 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. Looking at our Sketchup design we have 26 studs at 33 inches each.
To speed up this process I created a stop with some scraps of wood next to my miter saw that allows cuts of precisely 33 inches.
The side walls are 12 feet long, so you will want to use 2 of the 12 foot 2-by-4s for the top and bottom of each wall.
We want the 2-by-4s to be 24 inches on center to have a proper location to screw the walls into. 24 inch on center will carry up to the rafters which will have the TUFTEX panels attached to.
Instead of measuring and marking the 12 foot board at 24 inches on center, I created a spacer board at 22.5". This spacer really sped up the process and we re-use this spacer later in the project. The nail gun makes fast work of things.
Step 2: Build the Front and Back Walls
Using my 3D Sketchup design, I print out the dimensions to get a cut list for the front and back walls.
The front wall is like 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/header I sandwiched some particleboard scraps between two 30" wide 2-by-4s.
We will be adding additional framing to these sections in a later step.
Step 3: Cut the Rafters
For this design, we have 14 top rafters and 14 bottom rafters. Since it is difficult to convey the various angles I suggest that you use my Google Sketchup design to get the lengths and angles. Another option is to purchase pre- made rafters from your local home center. I can provide the actual Google Sketchup files for free on request. Be sure to dry fit/test the rafters before you cut them all.
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 then cut all 14 bottom and then top rafters.
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 built 24 gussets. Two gussets for each gambrel transition and one gusset on the inside of the first and last rafter.
To build the gussets, first mockup one with cardboard and dry fit it. Then cut them all out on particle board.
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 could attach the gussets.
Step 6: Assembly and Foundation
Time for assembly. At this point we attached the pressure treated boards to the bottom of each wall. We then moved the greenhouse and dug several holes and filled them with cement.
Dpending on your soil/location you should consider an ideal foundation.
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. 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-inch spacer board when attaching each rafter.
After all the rafters are up we cut purlins to go between each rafter. After all the purlins are attached we paint everything white.
Step 8: Front Wall and Back Wall
While the painting is in process. I build 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.
Step 9: Side Walls and Flashing
The final step before adding the TUFTEX panels is to add the side walls. We bought 36" high corrugated aluminum for this. We attached these with metal roofing screws.
Then we rolled 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 make it through the gambrel section.
Step 10: Attach the TUFTEX Polycarbonate Panels
We can finally attach the panels! These TUFTEX Polycarbonate Panels can be cut with a circular saw with the blade in backwards.
We also cut some of the panels for the front and back with a tin snips.
A few notes on installation of these panels: Pre-drill all holes or you can end up with small cracks. Since you can see the foam filler through the panel- keep them nice and straight. Like anything, practice makes perfect. Consider starting the TUFTEX installation on the part of the greenhouse least viewed (the back-side) 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
We used some aluminum edge flashing on each outside corner. We used a white ridge cap on the top of the greenhouse. 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.
Photos by Kerry Mann and Jen Mann
Kerry W. Mann, Jr. moved to a 20-acre homestead in 2015, where he and his family use modern technology, including YouTube and Instructables.com, to learn new skills and teach homestead projects. Connect with Kerry on his Homestead How YouTube page, Instructables, Pinterest, Facebook, and at My Evergreen Homestead.