How to Build a Hothouse Out of Old Doors & Windows

Lay windows and doors out to form one side of the hothouse, keeping the size smaller than 10 feet per side. Lay 2-inch metal brackets across the doors and window frames. Drill holes through the bracket holes and into the frames. Attach the brackets with 1-inch galvanized wood screws. Repeat this process to create two equally sized walls.

Build a smaller wall in the same manner, less than 6 feet wide with the same height. Repeat to build another small wall of the same width but 2 feet taller, fitting a frame within the wall built of 2-by-4 boards. Measure the frame to fit around a useable door, and screw the frame to the doors that surround it. Attach the operational door to the frame by drilling 1-inch galvanized screws through its hinges.

Stand the four walls up and attach them together using 1-inch metal L-brackets positioned every 12 inches along the corners on the inside. Attach 3-inch metal L-brackets around the bottom of the walls and stake them to the ground using 12-inch metal stakes.

Build a roof on top of the walls by running 2-by-4 boards from the tall wall down to the wall opposite it, screwing the 2-by-4s to the top of both walls. Span the 2-by-4s with doors, connected in the same method as the walls. Measure the triangular area between the roof and the walls. Cut out plywood sections to fit in the spaces. Connect them to the walls with straight 3-inch straight metal brackets.

Fill in the gaps between every door and window using waterproof clear caulking. Put the caulking along the corners and edges of the walls and ceiling. Allow the caulking to dry overnight and then apply another layer of caulking, filling in all possible gaps including those around the brackets. Let the caulking dry overnight.

Check the interior of the hothouse for drafts from the walls and windows, and fill all draft spots with caulking.