Build a Greenhouse with Upcycled Windows

Repurpose old windows to create a beautiful greenhouse and save money while going green.

article image
by William D. Adams
Brian Koehl crafted this greenhouse out of salvaged windows, opening up the opportunity to create a beautiful and useful space while giving building materials a second life.

You can spend $50,000 for an upscale curved-glass greenhouse, or $50 for a down-home one made of PVC pipe and plastic sheeting. But there’s a lot of ground in between. Here, we’re going to explore the option of using upcycled windows, doors, and other materials set in a wood framework to create a functional, sturdy greenhouse.

We won’t provide exact plans for this greenhouse; each will be different depending on the size and type of windows and doors you track down. But we will provide general plans for building an all-in-one rafter and wall system that will provide a basic greenhouse structure for you to “fill in the blanks” with windows, doors, and treated plywood.

We all know the equations for using building materials: Recycled stuff equals lower cost and more labor, while store-bought stuff equals higher cost and less labor. But there are other factors we should add to the recycled-stuff side of the equation: It’s better for the environment, it’s more fun, your project will be uniquely yours, and you’ll wind up with more bragging rights.

With most projects, you start with a firm plan, and then obtain the needed materials. In this case, you’ll start by obtaining the materials, and then create a plan based around your newly found treasures.

The Great Materials Hunt

Because the doors and windows you find will determine the spacing and height of your wall-rafter assemblies, gather your materials first. Look for windows and doors that are 32 inches or less in width to keep from spacing the wall-rafter assemblies too far apart. Locating and using groups of windows and doors of uniform size and shape will make construction easier.

See “Free and Cheap Building Materials” below for ideas on where to source materials. You’ll find windows and doors of three general types:

  1. Complete, operable windows and doors still in the jamb;
  2. Window sashes or door “slabs” removed from the jamb (just the glass and glass framework);
  3. Bare glass.

Using the approach shown here, you’ll find it easiest to use the second option. Double-paned windows will hold the heat better and will allow you to extend your growing season, but anything is fair game: storm windows and storm doors; glass patio and French doors; and double-hung, slide-by, casement, awning, and jalousie windows. To provide ventilation for your greenhouse, try to install some operable windows that you can open and close.

Free and Cheap Materials

You shouldn’t have to look far to locate windows and doors. Below are a few resources that could come in handy for finding building materials.

Craigslist. This is a useful website composed of online classifieds where you’ll find cheap windows and other materials offered by DIYers and contractors.

Habitat for Humanity ReStore. There are over 900 ReStore outlets worldwide.

Architectural antique stores and salvage yards. Often upscale in style and price, these businesses may carry that “centerpiece” stained- or leaded-glass window that makes your greenhouse a true standout. Find a comprehensive index of stores at Old House Journal website.

Building materials outlets. This is where slightly damaged, overstocked, and mismade windows, doors, cabinets, and other materials can be found at low prices.

Window and replacement-window contractors. Often contracted to do whole-house window replacements, they can be a good source for obtaining a lot of windows that are all the same size, style, and color.

Dumpster diving. Keep an eye out for remodeling projects in your area — and the accompanying dumpsters. Proper dumpster-diving etiquette mandates asking permission prior to diving in.

Window Positions and Foundation Size

Once you’ve stockpiled your windows, plan their positions in the greenhouse walls. Lay out the two side walls first. Position your windows on a flat surface, allowing 2 inches of space between each column of windows. This space will accommodate the width of the 2-by-4 wall-rafter assemblies along with an extra ½ inch of space to ensure your windows will have plenty of room to fit. Leave space for two extra 2-by-4s on the two wall-rafters at each end of your greenhouse so the front and back walls have a solid corner to butt into. For this rafter system to work, the widths of the windows directly across from one another must be nearly the same. This is where having multiple windows of a uniform size will simplify matters. Allow space at the bottom for treated plywood knee wall panels that are at least 1 foot wide. You’ll fit them between the wall-rafters to provide stability to the structure and prevent it from racking.

Click here to see the Wall Assembly Detail and End View.

After you have the windows for the sides of your greenhouse laid out, figure out your foundation size. Your greenhouse foundation will help anchor the structure and provide a flat, solid surface for building upward. If you go with our rafter plan, the width will be 8 feet, and the length will be whatever dimension you determined while laying out your windows and truss spacing.

You can pour a cement slab or build a wood platform for your greenhouse. Or you can use treated landscape timbers to create a perimeter foundation, and then use dirt or gravel for the floor. Level in at least two rows of timbers, overlapping the corners of alternating rows for strength. You may need to create a cut-out area in one of the end walls to accommodate your chosen door.

Build and Stand the Wall-Rafter Assemblies

Determine how many wall-rafter assemblies you need, and cut the wall studs and rafters as shown in the “Exploded View of Greenhouse Framing” illustration. You can cut the wall studs longer or shorter, depending on your window heights and configurations. Find a flat surface and assemble the wall-rafters as shown in the illustration. Use construction adhesive and 1½-inch shingle nails to secure the plywood rafter gussets at the peak and the wall gussets where the roof rafters rest on the wall studs. Install the gussets on both sides for strength, except on the outside faces of the two end walls.

Click here to see an Exploded View of Greenhouse Framing.

Secure treated 2-by-4s to the perimeter of your floor or timber foundation, and mark out the location of your wall-rafter assemblies. Check and double-check to make sure your window units will fit between the trusses. Stand both end wall-rafter assemblies, and then plumb and brace them using scrap lumber. Install the eave boards, and then stand the intermediate wall-rafter assemblies, making sure they’re spaced correctly. Then, secure the ends of the rafters to the eave boards. If you want a roof overhang on the end walls, cut and install the eave boards long enough to create that overhang. Install the purlins, spacing them no more than 2 feet apart, and then add the roof panels and ridge cap.

Install the Windows, Doors, and Roof Panels

Nail the wall battens to the outside of each wall stud; they’ll overhang each side of the truss by 1 inch. Also, secure the corner battens. Install the plywood knee wall panels, using caulk and screws to secure them to the inside face of the wall battens. Add flashing to the tops of the knee wall panels. Apply caulk to the backsides of the wall battens, and then install your window units. Add flashing between units when you stack windows atop one another.

Add flashing to the tops of your highest row of windows, and then install the plywood top panels. Cut and install these top panels so they cover the gaps between the roof rafters. Add the interior stops to permanently hold the windows in place, and then seal any gaps.

Use 2-by-4s to frame in the end walls based on the sizes of your windows and doors. Install them using the same method used for the side walls. Provide at least one operable window near the peak for ventilation. Use plywood to fill in any spaces not occupied by glass, windows, or doors. Use caulk, trim, and closure strips to seal any remaining gaps. Glue panels of rigid foam insulation to the backside of the plywood panels for added insulation value if you wish.

Then, paint and plant!

Spike Carlsen has written about and worked in the world of woodworking for over 40 years. His latest book, Building Unique and Useful Kids’ Furniture (Linden Publishing), is available online at the MOTHER EARTH NEWS store.

Need Help? Call 1-800-234-3368