How to Build a Small Greenhouse
Greenhouses ensure you can grow healthy plants year-round.
Give your backyard a facelift with the addition of a gorgeous greenhouse. Why do we love greenhouses? Let us count the ways. They ensure that you can grow healthy plants year-round. You can start seeds earlier and control their temperature, which makes it possible to grow thriving plants that don’t usually flourish in the South, like citrus and orchids. They are available to buy and build in all difference price points, styles, shapes, and sizes. Follow along with these steps to learn how to build a greenhouse made of vintage windows and small in size (10’x12’x8), and we guarantee the outcome is worth the effort.
Here’s what you’ll need:
24 (32”x36”) windows
2 (36”x72”) doors, one with door casing and one without
14 (8’) polycarbonate corrugated roofing sheets
8-foot long (2x4) pieces of treated lumber
14-foot long (2x6) pieces of treated lumber
12-foot long (2x6) pieces of treated lumber
10-foot long (2x6) pieces of treated lumber
1 box roofing screws
1 (5-lb) box (3-inch) wood screws for treated wood
2 sheets (1/4”) plexiglass, cut to fit roof eave
8 window hinges
4 window hook-and-eye latches
4 window handles
4 roof ridge caps
18 metal tie down angle brackets for roof
8 metal tie down (hurricane) brackets
1 gallon outdoor paint
4 tubes caulking
How to build a greenhouse:
- Pick a spot in your yard with ample sunlight. Usually the south or southeast side of the yard will get the most sun.
- Level the ground where the greenhouse will be placed; fill in with dirt as needed to create a level foundation. If desired, spread ground with gravel for greenhouse floor.
- Measure and mark where your greenhouse will go. Dig holes in each corner and place 1 (4-inch) cap block in each hole. Along each of the long sides, dig one hole in the middle and place another (4-inch) cap block in each hole. Lay 2 (12-foot long 2x6) treated pieces of lumber on each long side, then lay 2 (10-foot long 2x6) treated pieces of lumber on the shorter opposite sides to create a rectangle. This will create a solid base for the greenhouse walls.
- Using a 5/8-inch wood bit fitted to a power drill, drill 3 holes in each of the 12-foot pieces of lumber, spacing the holes about 3 feet apart so they are even. Then drill 2 holes on each of the 10-foot pieces of lumber, about 3 feet from each end.
- Screw 1 nut and 1 washer on the end of 10 (3-foot (1/2 inch) all-thread bars. Using a sledgehammer or mallet, drive 1 all-thread bar into each drilled hole until washer is flush with board.
- Start constructing walls by cutting 16 (8-foot-long 2x4) pieces of treated lumber to 72-inches long. Place one 72-inch wall stud at one corner of the greenhouse base. Screw the wall stud into the base using the toenail drilling technique and a 3-inch long wood screw for treated lumber. Place one window on the long side of the greenhouse base and screw to wall stud and base board to secure. Place another 72-inch long wall stud beside secured window and screw into place. Add another window and secure into wall stud and base board. Continue along the long side of the greenhouse with wall studs and windows until you reach the second corner, being sure to toenail the corner wall stud into place once finished.
- Continue around the corner to the back side of the greenhouse by toenailing a window into your second corner stud. Add another wall stud to the opposite side of the window, as you did along the first long side. Screw another wall stud to this wall stud, being sure to toenail the stud into the base board. This second stud will act as a placeholder for the door casing. For the back (non-functional) door, secure a 36x72-inch tall door into the wall stud and base board with screws, be sure to toenail the door at the bottom. Add 2 more wall studs to the other side of the door, then secure another window to those 2 wall studs. Add one more wall stud to the opposite side of the window at the second back corner of the greenhouse. You should now have 2 greenhouse walls completed with 1 row of base windows.
- Continue along the third and final sides of the greenhouse as before, securing windows and wall studs into place with 3-inch wood screws, toenailing in as needed. Once you get to the front side of the greenhouse, install functional (36x72-inch) door with casing into wall studs as directed by door manufacturer’s instructions. The front functional door of the greenhouse has casing and will not need 2 wall studs on each side of the door similar the back side (the casing will take up the space used by the double wall studs on the back side).
- Begin securing second row of windows to wall studs and bottom row of windows, toenailing as necessary. Choose one side of the greenhouse to be used for ventilation and save that side for the end - do not screw top windows into this side. Before adding second row of windows to final ventilation side, you will need to affix header boards on top of each greenhouse wall. To assemble header boards, screw together 2 (14-foot 2x6) pieces of treated lumber side by side to create 1 (14-foot 4x6) piece of lumber. Affix two more 14-foot 2x6 boards the same way to create 2 (14-foot long) header boards. Carefully lift header boards and place along long sides of greenhouse, so that the 6-inch side is vertical and parallel with the greenhouse walls. The header boards are longer than the 12-foot sides of the greenhouse to allow for roof overhang. For our greenhouse, we chose to have 6 inches of overhang on the back side of the greenhouse and 11/2 feet of overhang on the front side, but you can make it even on both sides if you prefer. Secure header boards to wall studs and top row of windows on non-ventilation side, toenailing screws in when necessary. Secure header board to wall studs on ventilation side, toenailing when necessary. Once header is installed on ventilation side, you can install the final four windows on the second row of the ventilation side. To install ventilating windows, attach windows to the header board using window hinges. Hinges should be installed on the outside of the greenhouse so that windows swing open to allow for ventilation. Install hooks and eyes on the interior side of windows to latch windows shut when needed and install handles on windows if desired.
- Install 2 more header boards on shorter sides of greenhouse. To install these, measure the space inside the long side headers and cut 4 (10-foot long 2x6) pieces of treated lumber to that measurement.
- To cut roof rafters, cut 18 (8-foot long 2x4) pieces of treated lumber to 84 inches. Using an adjustable square, cut one end of each 84-inch long board at an approximate 30-35° angle to create a proper roof pitch. You can adjust angle and pitch as desired but be sure to cut each 84-inch long board at the same angle. Next you will need to assemble a top roof header where you will attach your rafters. Screw together 2 (14-foot 2x6) pieces of treated lumber the same way you did the side headers. Cut 1 (8-foot 2x6) piece of treated lumber into 4 (2-foot) sections. Screw 2 of the 2-foot long sections together to create 1 (2-foot long 4x6) piece of lumber; repeat with remaining 2 (2-foot) sections. You should now have 1 (14-foot) header and 2 (2-foot) header braces. Attach header braces to greenhouse by toenailing them vertically into the center of each short side (the center of each door). These braces will hold up the long top roof header to create a pitched roof. Carefully lift roof header and attach to the top of each 2-foot brace with wood screws. Once the top header is up, install roof rafters by toenailing the angled side to the top header and the flat side to the bottom header. You should have overhang on each side of the greenhouse. Evenly space rafters so that you have 9 per side, being sure to install the first and last rafter against the front and back headers. Once all rafters are secured, you will need to screw 8 (14-foot 2x4) pieces of treated lumber crosswise across the rafters, spacing them evenly so you have 4 on each side.
- For extra security, install metal tie down brackets on each rafter by screwing one into each rafter and top header. You can also install more tie down brackets at the bottom of rafters to attach to bottom headers if desired.
- Before installing roofing material, caulk gaps, and paint greenhouse if desired. A 10x12 greenhouse will take 4 tubes of caulking and 1 gallon of outdoor paint.
- Install roofing materials. Cut 14 (8-foot) clear polycarbonate corrugated roofing sheets the same length as roof rafters. Screw roofing material to crosswise roof boards using roofing screws. Install 4 clear polycarbonate corrugated roof ridge caps along roof ridge and secure with roofing screws.
- Use an adjustable square to measure angles and lengths for eave of roof. Have plexiglass cut to these measurements and secure to front and back roof rafters with screws. If desired, trim windowpanes to fit plexiglass and glue to create a window-like appearance.
- Enjoy your hard work!