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Upcycle Old Windows Into a New Greenhouse

Bobbi PetersonThere are many advantages to owning your own greenhouse, such as expanding your growing season and isolating your plants from damage caused by insects, rodents, and other pests, but building a greenhouse can be quite expensive.

The average cost to build a greenhouse in the United States is 13,893 dollars, but the amount can vary widely, from 5,000 all the way up to 25,300 dollars. One way you can keep costs down and make your greenhouse truly green is by upcycling old windows for at least part of your project.

How Much Room Do You Really Need?

If you want to build a greenhouse completely out of old windows, imagine how much space you need. Do you simply want somewhere to grow seedlings until the weather is warm enough to plant them in the ground? Do you want to grow specific foods for your family?

Unless you’re selling produce or plants, you likely don’t need the largest greenhouse and can get by with a smaller setup. For example, you can build a playhouse-sized structure out of differing window frame sizes. Even if the glass is broken out of some of them, you can replace and caulk around the edges to create a cozy, warm spot for your plants.

To build a simple structure, fit the windows together almost like a puzzle and add a simple metal roof to keep the rain out.

Steps to Take

Once you’ve decided on the size, there are some specific steps you’ll take to create your upcycled greenhouse. Check your local area about building permits before starting.

1. Gather equal sized windows for all sides of your greenhouse. If you want a greenhouse that is nine feet tall, you’ll need enough windows to equal that height. The windows can have different looks to them, but the sizing should be similar for parallel sides.

2. Create a squared frame out of 2x4s. These will hold the windows, so you want to make sure your frame is as sturdy as possible. Start by placing 4x4s in each of the four corners. To make the greenhouse even sturdier, place the corner posts in concrete and at least a foot down into the ground. Then add the 2x4s.

3. Brace the walls while you stabilize the foundation. This might include pouring concrete or adding cinder blocks.

4. Use heavy duty screws to secure the windows to the frame. Remember to use similar sized windows on opposite sides. You are essentially putting a puzzle together, so each project will vary widely. As the old saying goes, "measure twice and cut once," or in this case, measure twice and screw in place once.

5. Add flooring. Rocks work well, as they drain when you water your plants. They will help store additional heat, keeping your greenhouse at the perfect temperature.

6. Add a roof out of lightweight material or additional windows. You’ll need to build a frame to do this, and be very careful as you don’t want windows falling down on you. Make sure the roof is at a pitch so rain will run off the sides.

7. Caulk any cracks so the greenhouse is airtight.

Get Creative

Building a greenhouse out of old materials requires a lot of creativity. You may need to adjust the size and shape of your greenhouse to match the materials you can get cheaply or for free. With a little planning, you can build your own greenhouse for a fraction of the cost of buying a commercial one.

Greenhouse with open windows
Photo by Adobe Stock/biker3