How to Build Your Own Greenhouse Cheap From Used Parts

Old salvage windows can make a very nice greenhouse.
Old salvage windows can make a very nice greenhouse. (Image: Jupiterimages/Polka Dot/Getty Images)

One way to build your own greenhouse from used parts is to use salvaged doors and windows and framing materials from a house or commercial building that's being torn down. If you remove the windows frame and all, you simply have to build a set of framed openings in the roof and sides to fit the doors and windows you have. The greenhouse doesn't have to be very large. A small 8-by-10-foot lean-to greenhouse will hold hundreds of plants.

Things You'll Need

  • Salvage windows and frames
  • Salvage glass doors
  • Salvage two-by-four studs
  • Framing nails
  • Joist hangers
  • Pea gravel
  • Marker pen
  • Speed Square
  • Circular saw
  • Shovel
  • Drill and driver bits
  • Wood screws, three inches long
  • Siding
  • Plywood sheets, ½-inch thick and as many as you need to cover the roof.
  • Eye protection

Mark out an 8-foot-by-10 foot rectangle next to the wall of the building against which you are building the lean-to structure where the base of your greenhouse will be. Remove the grass, and fill the hole with 3 to 6 inches of pea gravel to provide drainage and good footing inside the greenhouse.

Lay two-by-fours on the ground to outline the base – two 8-foot boards on the sides and a 10-foot board along the front edge. Toenail the ends together.

Nail a vertical two-by-four stud against the building on top of the side base plates. Nail two boards at 90 degrees to each other standing vertically at the corners. Test place the windows around the sides, and mark the base where you will need to place vertical studs. Standard studs are 92 5/8 inches long. You can cut the studs for the front wall shorter to match the windows or to provide a slanted roof off the building to which you are attaching the greenhouse structure.

Nail two-by-four studs upright on the base plates where you've marked for the sides of the window frames. Toenail the studs to the base, and nail a two-by-four cap plate on top of the stud wall. Measure the width between the studs at the windows, and cut two boards to fit horizontally between the studs above and below. Nail them in place to form a square between the studs into which the window frame will fit. Cut a small board to fit vertically between the base board and the bottom of the window opening at the center. Cut another board to fit vertically between the top window frame board and the cap plate at the center of the top window frame board.

Frame for all the windows and doors, then place the windows and frames into the openings, and screw them into place. Cut pieces of siding to enclose the side walls around the windows and doors, and screw them to the side walls until the wall is fully sheathed.

Nail joist hangers 2 feet apart under the eaves of the building to which you are attaching the lean-to greenhouse. Place two end hangers, one directly above each of the end wall studs. Test fit a two-by-four between the joist hanger and the front wall. Measure the angle at which the rafter board hits the wall, and mark the end of the rafter with the speed square. Angle cut the board ends, and fit one end into the joist hanger. Nail it to the joist hanger and the other end to the top of the cap plate on the front wall. You can make the rafter more secure by cutting a notch in the bottom of the rafter to fit over the front edge of the front wall cap plate.

Measure and make a series of horizontal marks with the speed square between the end joist hangers on the wall and along the front wall cap plate to mark where the rafters go. Now go back and adjust the spacing between the rafters to fit the window frames you are placing on the roof. Frame the openings for the windows the same way you did for the windows on the side walls. Place the windows frames in the openings, and screw them in place.

Measure and cut plywood sheets to fit in the spaces on the roof not covered by windows. Caulk around all the window frames to keep water from leaking in when it rains. Once the siding, window frames, doors and roof sheathing are in place, you can set up shelves for pots and deeper soil trays for planting full-sized vegetable plants.

Tips & Warnings

  • The nice thing about building a greenhouse using salvaged windows is that you can always open the windows to ventilate when it gets too hot inside the greenhouse.
  • Choose a south facing wall to attach your greenhouse to. That way, you'll get full sun during the day. You can reduce the amount of sun you get by hanging screens or partially covering the roof with a tarp.
  • Wear eye protection when using power tools.

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