Planning and Preparation

• 1). Read all the instructions before you start this project.
  
  
• 2). Choose a greenhouse location that gets plenty of sunlight.
  
  
• 3). Decide on greenhouse size and dimensions, taking into consideration space available, the sizes and shapes of your old windows and your budget and the style of door you want to use.
  
   
  
  
• 4). Decide if you wanted a heated or unheated greenhouse. Consult WVU Extension's article on "Planning and Building a Greenhouse" for a detailed description of heating and cooling options.
  
  
• 5). Choose natural or mechanical ventilation. The Institute of Food and Agricultural Sciences' (IFAS) article on "Greenhouse Ventilation" describes your options.
  
  
• 6). Decide whether to build a flat or slanted roof.
  
  
• 7). Select a lightweight greenhouse covering. "The Greenhouse Catalog" provides a handy comparison to help determine which product will work best for the sunlight and climate conditions, as well as discussing appearance, durability and cost considerations. Decide whether to cover the entire greenhouse or just the roof.
  
  

Construction

• 1). Dig two drainage trenches in the floor 8 feet long and lay perforated pipe (available at local hardware and building supply stores). The pipe should extend beyond the wall area so excess water flows out of your greenhouse instead of collecting inside and causing mold. Cover the trenches and floor with several inches of gravel to ensure adequate drainage and prevent flooding.
  
  
• 2). Dig holes 3.5 feet deep at each corner to allow the posts to support the weight of the structure. One rule of thumb is to dig 1 foot down for every 2 feet the piece of lumber will be extending above the ground. Insert the 4-by-8 posts and fill the holes with gravel and dirt to secure stability.
  
  
• 3). Lay the windows out flat and experiment with placement for walls of equal height if you are working with windows of differing sizes and shapes. Remember to design a door in one end. The simplest door is to leave one end open and cover it with a simple plastic sheet stapled to the wooden frame on two sides. Another option is building a 37-by-88-inch door frame and 33-by-84-inch door covered with plastic sheets or panels or using an old glass, wooden or screen door, or bolting a couple of 29-by-40-inch old windows together and enclosing them in a simple wooden frame. Incorporate the door and/or door frame into the wall design and bolt the surrounding windows to the frame. Use hinges to attach the door to the frame. Alternatively, you can frame an old sliding glass door in the wall design.
  
  
• 4). Secure the windows of the remaining sections together with wood or sheet-metal screws to make individual walls. Build a simple 2-by-4 frame around each wall, securing each corner joint and attaching it to the window frame with bolts, nuts and washers, two for every 4 inches. Let the vertical ends extend 5.5 inches longer than the window height, top and bottom. Connect the bottom corners with another 2-by-4 piece of lumber and fasten each wall to the adjoining wall at the corners, using bolts or screws to form the lower frame. Cover the base ventilation openings with 5.5-by-64-inch screen, plastic sheeting or panels.
  
  
• 5). Build two equilateral triangles with 75-inch-long pieces 2-by-4-inch lumber and use 3 2-by-4 pieces of lumber, 76 inch long, to connect corners and form a simple roof frame. For a flat roof, build a rectangular frame. Connect the corner posts by attaching them to the roof frame with screws leaving natural ventilation space between the roof and the lower frame.
  
  
• 6). Cover the roof, and the walls if you choose, with a lightweight material that diffuses the sunlight to protect your plants. Secure the covering to the structure using a staple gun or screws.
  
  
• 7). Cut space in both ends to install the exhaust fan and inlet louvers if using mechanical ventilation. If opting for natural ventilation, note that IFAS advises, "To be ventilated satisfactorily, the house must have both sidewall and ridge vents" to allow warm air to escape and cool air to enter. Cut the vents along the base. You created natural vents by leaving space between the upper edge of the wall and the roof, and along the base of each wall. Install an electric, gas, or propane heater if you choose to heat your greenhouse. Check with your local garden supply store or "The Greenhouse Catalog" for heating materials.