How to Build a Greenhouse from Reclaimed Doors and Windows

It all started with a desire to build something and garden year-round in Ontario, Canada. I had just spent the summer gardening after building an elaborate arrangement of potted plants and vegetables on my back porch in downtown Toronto. The cold was on its way and the inevitable end of the planting season.

After a week away at a cottage up north, my mother-in-law Christine and I decided we would build a greenhouse and make it winterized! We would search out old doors and windows as the walls. I must admit, Pinterest may have helped nudge us along. Having worked in the window and door trade for most of my life, I had a feeling I could obtain a fair amount of the materials through contacts and searching the city.

Search for used doors and windows

I enjoy using old materials to give them a second life! Likewise, they have a history. For example, We located several doors through Facebook Marketplace, a tool I have found useful for my upcycling needs. 

For the last 100 plus years, two of these doors were dividing doors between the living room of a home in East York Toronto. They now have a second life as the feature doors at the front of the greenhouse. Similarly, the second pair of doors (I also purchased off of Facebook Marketplace) was also separating the living and dining rooms in a home in Mississauga for over 30 years.

Although they had reached the end of their purpose within each home, we were (and still are) able to see the beauty in these doors. They have so much character! The only negative aspect, they were all interior doors with single pane glass. Thus the R-value was next to zero. They also required exterior paint to withstand the Canadian weather. 

The R–value is the building industry term for thermal resistance “per unit area.”

Wikipedia

The other doors and windows were obtained from a friend who installs for Ridley Windows and Doors. Dave Darvince was kind enough to drop the doors off to my home as it would have taken me at least four trips to get them all. The doors came from an install in downtown Toronto. All of these were exterior doors with double glazed glass, thus much more appropriate for the structure we were building.

The build up

We now had all the windows and doors required to get us started. My father-in-law and I loaded up the doors and windows and transported them to his place in Whitby, Ontario, where we would construct the greenhouse.

The structure itself went up fairly fast, but first, I had to prepare the area. Two large planters had to be moved, no easy task. Now in hindsight, even though we checked with the neighbours before building, I will never again build as close to a fence, hedge, or any other impeding object. It made working on the back and right side very difficult. 

After moving any impeding objects and marking the general work area, it was time to dig four holes to set the foundation blocks. I then filled the holes with gravel and leveled them to the same height.

Next: 

• we installed the main 4×4 posts with the bottom plate, followed by attaching the top plate; 
• we installed the floor joist and added blocking underneath; 
• we bolted all the corners at the top and bottom, adjusting to ensure plum and square along the way; 
• and then we installed a ¾ inch plywood as the subfloor.

When we designed the greenhouse, we decided to build it to 10 feet by 8 feet to stay within measurements required to avoid building code requirements. We then installed the doors in order of which ones Christine (my mother-in-law) liked the most.

We placed the doors on top of the subfloor and screwed them into the top plate, directly through the doors. On the inside, I cut 2×2 wood pieces (attached to the subfloor) to screw the bottoms of the doors into. I used the same 2×2 wood pieces along the perimeter of each window location (one on each side, and one at the middle back).

The windows are lovely, but they are also single pane. The hardware was in bad shape. I took it all off and re-hinged each of them using hinges from another set we had gathered. Below, you can see how I marked out each new one, chiseled them out, and attached the new ones for installation. Then, I installed the windows.

However, later after installing the rafter joists, it became apparent I had to lower each window a couple inches to allow them to move freely. Once the rafters were up and reinforced, I was able to install ¾ inch plywood.

For the front doorway, I had installed several 2x4s to get the desired width for the door we had selected. Regardless, when framing a door, you always want at least two 2x4s on the hinged side for proper operation and security. 

Adding a Skylight

It was at this point in the build we discussed adding a skylight to allow more light into the greenhouse. At first, we tried PVC plastic for the skylight. I then shingled the roof with brown shingles, Dave and I had purchased. However, it became apparent quickly that it was too weak and would crack once the climate became cold. In the pictures below, you can see more than a few imperfections. More importantly, it was not what the client wanted.

Thus, I searched out local window and door companies, close by. I found Canada Windows and Doors. There I met with their owner Andy Van Hoof and was able to assist me in obtaining a few sliding doors. I took the door apart and installed it on the roof with some expanding foam strips on the bottom to allow for movement during weather fluctuations. In hindsight, I should have waited to get my hands on the double-glazed glass, as this sliding door glass was a single pane.

Next, I covered the plywood roof with a protective roofing material in the preparation of installing the shingles. I primed all the wood around the skylight. Later after installing the glass, I sealed it with caulking and blue skin primer with blue skin over top, followed by flashing. 

I remember thinking Christine had said she wanted black, but I said nothing. That cost me twenty hours of work and a bunch of wasted shingles, that upset me more than the waste of time. 

However, I had only shingled once in my lifetime. I was happy to have a chance to do it over as I was not 100% satisfied with how it looked finished. When I took off the brown shingles, I also decided to raise the skylight to ensure it was waterproof. During this, I managed to break the glass. Luckily, I had a spare one.

Likewise, there was good chance water would infiltrate the skylight. At that point, I decided to build a ladder truss for the front of the greenhouse to both enhance its appearance and provide room for a solar panel Christine bought.

Christine had also purchased two old stained glass windows from a market. Both are over a hundred years old from a church in England. I attempted to find the location but was not able to find the information for this story sadly.

Both needed a fresh coat of paint to freshen them up! I installed each of these in the middle of the greenhouse above the doorway. I was quite pleased how all the lines match up with the old leaded glass windows we obtained.

Floor Insulation, Flooring and Trimming

After the roof was complete, it was time to add insulation to the floor. I used 2-inch thick rigid insulation with a high R-value. Followed by ¾ inch plywood. Next, it was time to tile. Christine and I thought it would be best to use a dark colour to help absorb the warmth from the sunlight. Once the tiles were done, I was able to determine the door height. I cut the door to the required height and began to frame out the doorway. This was complex, but I managed well.

After, it was time for trim, trim, and more trim. This part took much longer than I expected. For many of the doors were different widths, thickness, and height. Thus, to hide all the imperfections and beautify the greenhouse, I added a substantial about of trim. We bought trim boards that were approximately 10 inches wide by 8 feet long. Before cutting to size, I painted the majority of it and even managed to get my eldest daughter Josephine to help out.

After installing the old stained glass, we were left with four triangles. We could have simply covered up with wood, but we wanted to maximize the sunlight coming in, and we liked how it looked. So I built some framing around each window sash and then used cheap thin styrofoam from the dollar store as templates. This way, I could cut them to the exact size for the opening. Always leave 1/8 spacing around the perimeter of the glass to allow for the wood expansion and compaction during weather changes.

Solar Energy and Heating

Next, it was time to add insulation and vapour barrier to the roof. I had to frame out around various parts of the rafters and blocking so that I could properly attach the plywood later. Before I could complete the insulation, I had to install the solar panel and run the wiring through the roof. It took a while to find what we needed and where to buy the mounting kit.

Sentinel Solar in Vaughan had just what we needed. Four mounting plates had to be installed. I drilled a hole near the middle towards the end where the wires come out of the panel. We decided a shelf for the battery would be handy.

Next was the stage of setting up a heating system with the solar panel providing the energy to a battery for storage. Either a heating mat or a small power heater may be used. We researched using large barrels, painted black, and filled with water (making sure to have the ratio of water match the exposed glass surface). Likewise, during summer, we may have to use some type of shading system, possibly with a fan, to keep airflow moving and prevent the plants from overheating. In the end, the power from the single solar panel was not enough to power a heater in the greenhouse. We used it to power a fan.

With the help of a friend (Trever Penford) who saw my Facebook post about requiring just a few batts of insulation, I was able to finish off insulating the ceiling. Then came the complicated part of covering the ceiling with plywood while working around the joists to keep them exposed. Likewise, trimming around the window was not easy. I framed out around the skylight, installed the trim on all sides, and place insulation within open spaces to avoid cold spots. Also, I tried to use leftover cutoffs to cut down on waste. It was challenging to install large pieces of plywood or trim as the ceiling joists got in the way. Finally, it was time to caulk and paint.

Takeaway

Upon completion and monitoring, there are at least 4 changes I would make to the greenhouse to make it more efficient: 

1. I would only use double glazed glass, no single pane; 
2. I would reduce the overall glass coverage to help control the temperature; 
3. I would make the North wall a solid structure with thermal mass materials that help regulate the temperature but capturing the heat in the day and releasing it at night; 
4. I would build the foundation differently, and use the earth to help regulate the temperatures as well. 

By employing these four techniques the temperatures inside the greenhouse would be much easier to control, thus leading to better success of growing plants year round.

The best resource I found after building the greenhouse was a book called The Year-Round Solar Greenhouse, How to Design and Build a Net Zero Energy Greenhouse. Wish I had read it before we started the build! 

This project emphasizes how “trash” can have both a useful and attractive use after its first life span has come to an end.

With some creativity, hard work and investment the possibilities are endless. In the future I plan to build fences, enclosed porches, furniture, and various options of small structures like this greenhouse.

If you’re interested in any of these projects and enjoy helping the environment, please feel free to contact me or follow me on Facebook to keep up with our upcoming projects.

If upcycling is your thing, you can also read How to Upcycle Furniture: A Guide for Beginner wrote by Evan from Porch.

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