How to Make a Simple Greenhouse

Home gardeners start searching seed catalogs in the dead of winter---it's a primeval urge to get spring going. The first greenhouses were built to house tropical plants brought back from the tropics by seafaring explorers. Today, greenhouses come in all shapes and varieties from the "crystal palaces" of the Victorian conservatory to the humble cold frame used to start salad crops in city rooftop gardens. Of all greenhouse forms, the "hoop house" is one of the simplest and, with the help of modern plastics, easiest to build.

Cypress, redwood or preserved lumber:
4 4-by-4-inch-by-2-foot pieces
4 2-by-6-inch-by-12-foot pieces
4 2-by-4-inch-by-7-foot pieces
4 2-inch-by-4-inch-by-6-foot
2 2-by-4-inch-by-3-foot pieces
2 1-by-4-inch-by-12-foot pieces (for each door)
Polyvinyl chloride (PVC) "schedule 80" or stronger:
14 ¾-inch-by-10-foot PVC pipe
Six ¾-inch-by-2-foot PVC pipe
Five matching PVC cross-joints
Two matching PVC T joints
PVC cleaner and cement
Carpenter's square and level
Hammer and screwdriver
Drill
Miter or back saw
34 ¾-inch galvanized electrical metal tubing (EMT) straps
14 to 20 galvanized strap brackets
Two galvanized door hinges (four if building two doors)
Non-corrosive screws and nails
Staple gun and heavy-duty staples
At least one tall helper
Optional:
Substitute for wood foundation: 14 ½-inch PVC tubing stakes
Substitute for ridge poles: 1 ¾-inch-by-10-foot section EMT roof ridge for electrical wiring
Door handle and latch
Shade tarp

Instructions

- 1
  
  Locate a site for your greenhouse; a sunny, well-drained location is just right for spring, but a summer greenhouse needs afternoon shade, such as from overhanging trees, to avoid overheating. Its foundation should never sit on boggy ground.
- 2
  Set wooden corner posts in concrete piles. Dig below the frost line (you can find out how deep this is when you get your building permit), line with gravel, fill it with concrete, and insert a 4-by-4 corner post in each. There should be 11 feet 8 inches between the front and the back post edges and 12 feet on the sides. Make sure at least 4 inches of post remains above the pile. Set the tops of the posts elevations for a level foundation. Set a floor of pea gravel or mulch for your greenhouse, and lay out two 2-by-6-inch-by-12-foot pieces for the ends of the hoop house.
- 3
  Make a support frame with 2-by-4-inch-by-6-foot "stiles" (sides) and a 2-by-4-inch-by-3-foot "header" (top) between them in the center of one end, attaching them to the base and each other with metal or wooden brackets screwed on the inside. Mark angles for 2-by-4-inch-by-7-foot braces by laying them under the end framing from the corner of the base to the top of the door frame, marking the resulting angles, then cutting with a miter or back saw and attaching with inside-mounted brackets.
- 4
  Make a door with two 1-by-4-by-68-inch stiles, two 1-by-4-by-30-inch rails and one cross-brace to steady it (again joining boards with brackets). Hang this door on the center support frame with two strap hinges.
- 5
  
  Attach one side base to two corner posts with non-corrosive 3-inch wood screws or nails, checking with a carpenter's level before finishing and countersinking screws or nails. Nail or screw the front base to the corner posts, bracing it with some temporary supports; the front base should cover the ends of the side bases. Repeat around the frame, checking for level as you attach each board.
- 6
  
  Fit 2-foot sections of PVC between the 10-foot "ribs" of the house, ending with T-joints at each end. Trim the end sections if the total ridge length exceeds 12 feet, 4 inches, then glue all but the end ("T"-joint) ridge sections and ribs with using PVC cleaner and cement and lay flat to dry. Fit the ends again to make sure the ridge measures 12 feet, 4 inches, then glue the end T-joint sections.
- 7
  
  With a helper, attach one side of the hoops, starting in the center of one side. Space double EMT straps 2 feet apart, starting in the center (the end straps should be mounted at the corners on the front and back of the foundation) of each side, then slide the PVC rib ends into the straps, bending the other side the ribs down after finishing the first side. Staple plastic covering to the end frames, then staple the top sheet to the sides, fold the corners over and staple to the support frames on each end.

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