How To Build a Mini Greenhouse From Old Windows

With some recycled house windows you can make your own mini greenhouse for the garden. These step by step instructions show a smart way to make a sturdy structure that will last for years.

I also have a proper greenhouse for year-round growing: see How to Build a Lean-to Greenhouse.

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Make a Greenhouse from Old Windows

This small greenhouse project started when I found a pile of old house windows marked FREE at the side of the road. It was a lucky find, indeed.

While I hauled 16 windows home, I just needed 6 for this project. You could get by with 4 if you decide to make the roof out of other materials.

The Problem With Old Windows

While we love old, handmade house windows for their charm, the problem is no two are exactly the same.

The windows here are all approximately 35 x 42-inches, but each measurement varies anywhere from .25 to 1.5-inches. And no two have the same thickness.

Clearly they were each built to fit the quirks of an old house that was neither square nor level, but this makes it challenging to frame them up for a greenhouse.

After sketching out several different plans, and worrying that I was not thinking it through properly, I decided to build a very sturdy inner frame that I could attach the windows to.

You see a lot of projects like this where the windows are simply joined to each other, but I wasn’t confident the wood was strong enough (could have some rot inside) plus, there was the problem of varying sizes. I might be able to join them together but they would be so far from square that it would look somewhat ridiculous.

The idea of setting everything on a strong, square frame solved all of these issues.

I also wanted to create the roof with windows and these suckers are very heavy. By creating a support frame, I could be confident that there would be no tricky joins or mishaps later.

Related: Decorate a Fence with Faux Windows and Doors.

Planning a Window Greenhouse

1Build a table base to hold the window greenhouse

The height was determined by how much snow we get. I didn’t want the greenhouse to sit in wet snow for 6 months of the year so this way it’s 36″ off the ground. If it snows more than that, we’re all doomed anyways.

The added bonus is that this height makes the entire structure visible from the patio, as it sits higher than most of the garden plants in front of it.

2Build a frame to mount the windows (sides and roof) on

Truthfully, my main goal was to build something really cute and quirky. The fact that it has a door that opens and closes and can house delicate plants is a bonus.

3Paint and decorate windows

First, of course, I had to sand, repair, prime, and paint the windows. Then came the fun stuff—decorating the windows with glass paints.

There was one unfortunate event which you’ll hear about….

4Assemble structure and admire

Forget measure twice, cut one. I must have measured a dozen times! I wanted to be able to build and paint the structure on the covered patio (to avoid hot sun and rain) so I had to be sure that everything could fit through the doorway to get it out to the garden when it was done. You’ll see what happened…

Tools & Materials

• 6 old wood-framed windows (4 for sides of greenhouse, 2 for roof)
• 2×4 lumber for frame and table base
• 4×4 lumber for table legs
• 1×6 lumber for table top
• Self-tapping screws
• L brackets (to attach greenhouse frame to table)
• Kreg Jig K4 Pocket Hole System
• Electric drill (used as a screwdriver)
• Compound Miter Saw (you could also use a circular saw or a hand saw)
• Palm sander and sandpaper
• Carpenter’s wood glue
• Primer, paint, and wood stain, paint rollers and brushes
• Glass craft paints, artist paint brushes
• Decorative picket fence panels
• Door hinges and handle
• Safety gloves, protective glasses, ear protectors
• Carpenter square (for marking cutting lines on wood)
• Pencil

Steps

1Build Table Base

As you can see with the completed table base shown here, it’s a simple structure designed to be very strong and sturdy. Since the windows were already a mishmash of sizes, I opted to buy wood from the seconds pile at the lumber store to keep costs down.

 Table Parts

• (4) 4×4 legs
• (4) 2×4 side panels
• (4)  2×4 for support – cut at 45°
• (6) 1×6 pieces to form table top

Table Assembly

• As you can see in the photos, I formed a square frame with the outer 2×4 pieces and attached the legs to the inner corners.
• Extra 2×4 pieces with 45° miter cuts were attached to make it really secure.
• The 1×6 table top boards (not shown) were cut to fit on top of the frame.

Once the table top was added, it became very sturdy with no wiggle room. Again, I knew the greenhouse would be very heavy so this baby had to be strong.

Next it was time to make the greenhouse frame which was my introduction to this wonderful tool:

You’ll see why it is so handy (below).

Related: How I Use My Unheated Greenhouse Year-round

2Build The Structural Frame

Now that the table base for the window greenhouse was built, it was time to create a structural frame to hold the windows in place.

I’m obviously not a carpenter (nor do I play one on TV) so it took a lot of thought (my poor brain!) to come up with (what I think is) the best way to build this.

My main concern was sturdiness. If it could be good-looking and very solidly built, I’d be a happy camper. And yes, as it turned out, I’m a happy camper.

If you’re just joining in the story, I’m making this mini greenhouse from old, wooden windows found on the curb. No two windows are the same dimensions and neither are any of them actually square, so it’s a building challenge to say the least.

This is what I built:

The frame is made entirely from 2×4 lumber:

• I made the sides to match the average width and height of windows (which are odd sizes and not square).
• Notice the height: I cut the vertical pieces extra long to allow room for the roof windows to hang down without blocking the sides of the greenhouse.
• The tops of the vertical 2x4s are cut at 45° angles. This allowed me to join the roof windows at a 90° angle (= 2 x 45).

I got this dual bevel sliding compound miter saw (with laser) at an excellent sale (see one here) and what a great tool it is. Mine has a 10″ blade. If you have a choice, I’d go for a 12″ blade so you have just a few more options for the size of wood you can cut. It truly just takes seconds to set up the miter cuts and the laser guide makes it so easy to get right every time.

Related: Decorate a Fence with Faux Windows and Doors.

Tool Recommendation

This is where the project got really fun. I finally used my Kreg Jig K4 Pocket Hole System. It’s a drill guide that lets you create perfect pocket holes in wood.

It’s simple to use. You just need to know which size wood you are using (I used 2x4s) and the Kreg system tells you which size screws to buy and where to drill the pocket holes. It takes under a minute to create the holes and you’re ready to join your pieces.

Using self-tapping screws (and some wood glue), you can join wood pieces together very snugly and securely. Once you use one of these jigs, you’ll want to make all sorts of things! It’s quite fabulous.

In the photo (above) you can see the self-tapping screws have been placed in the pocket holes, ready to be drilled into the adjoining piece of wood. No pilot holes required.

If you’re a geek like me, there’s a mini thrill to be had when you hear this little squealing sound the screws make when they’re placed just perfectly. Love that!

Assembly

As I was assembling the frame, I also sanded all the edges with the palm sander so it was smooth and ready for priming and painting.

Between coats of paint, I got to work on the windows.

3Paint and Decorate

With the base table and greenhouse frame built, it was time to get the windows ready. This is where we had a wee mishap.

Prepping The Windows

The old windows had many coats of paint and lots of layers of caulking holding them together. I removed what I could, sanded, primed, painted and sealed everything to make them strong enough to hold up in our weather lows and highs (-20°C to +40°C).

Decorations

Funny how the mind works…. I saw these little, decorative fence panels in a shop and thought they’d look sweet on the windows. This was what actually spurred me on to get this project built! Once you have a vision of what you want to make, it’s so much easier.

I painted the fence panels blue to match the shed door, hoping it would unify the look of the garden (I think it does).

Decorate The Windows

We* used an assortment of craft paints suitable for painting glass including these Crafts Satin Paints.

I had not used these paints before and they go on really nicely. But they are expensive (thankfully, we used a 50% off coupon at Michaels) and the ones in the smaller containers don’t provide a lot of paint.

I soon realized I should not be cleaning my brush so much between colors because I was wasting precious paint (instead I tried to use up what was on my brush first).

*I started out painting the windows but my daughter soon took over. I love it when that happens.

Related: Decorate a Fence with Faux Windows and Doors.

The Mishap

When all the windows were painted and I was getting ready to take them outside, Bobo (we were cat-sitting) jumped onto one window, knocked it over, and the glass shattered. She was fine—no worries there. We actually had a laugh because the window she broke was the only one I had painted! Everyone’s a critic. And it was such a Bobo thing to do.

I didn’t want to pay for a new piece of glass but I had to use this particular window because I built the wood frame to match it (and none of the other windows are the same size). So, I opted to use chicken wire instead. It’s the window that is placed at the back of the greenhouse so it works just fine.

One minor disappointment was, we had painted a series of clouds that continued from one panel to the next, and this broke my main clouds. Boo-hoo, I know! Seriously, it was just a mishap and I do not blame Bobo. She was just being her Bobo-ish self (which I adore).

This next photo shows the chicken wire:

I like how it looks.

4Assembly

Here’s a quick review before we put this all together.

Table Base

I built this table base to be super strong and withstand our crazy weather through many seasons. The 4×4 legs are pressure-treated, the rest of the wood is not. I sanded, primed, painted, and stained to match our garden shed.

Greenhouse Frame

I could not find any examples online to follow so I made up my own plan for this frame. I needed something really strong (stronger than the windows) that would hold up to wind and weather.

I attached the 2x4s together using pocket hole screws (and my Kreg K4 pocket hole jig, that I adore), sanded, primed, and painted. It’s very sturdy!

Windows Painted and Decorated

The old windows needed some TLC including removing old caulk, sanding, priming, and painting.

We used acrylic craft paints suitable for glass to decorate the windows. I came up with the design I wanted, painted one window (which was accidentally broken by the cat), and my daughter did the rest. The broken window was brought back to life with chicken wire in place of the glass.

I added some decorative picket pence panels as well.

I attached them to the windows using Goop. Any strong, all-purpose adhesive will do.

Related: Decorate a Fence with Faux Windows and Doors.

Assembly

If you’ve been following this story from the beginning you’ll know that I mentioned I did all of the building in our covered patio (so I wouldn’t be at the mercy of the weather) but this also meant I had to make sure everything I assembled could still fit through the door.

Well…. as I was working, I began to see how the fact that windows were not square was starting to throw my measurements off. It was one thing to accommodate the various lengths and widths, but this did not compensate for the odd shapes of the actual window frames.

Long story short, the greenhouse frame got through the doorway with about an eighth of an inch to spare! Worst case scenario, I would have had to take it apart and re-assemble it outside, which is not a huge deal, but it was a lesson to think about with future projects from repurposed items.

a) Set Up Table Base

I actually buried a few inches of the table legs in the ground for extra support.

b) Set Up Greenhouse Frame

The greenhouse frame was secured to the table using L brackets.

c) Attaching The Windows

I made pilot holes through the window frames and attached them with self-tapping screws.

d) Attaching The Door Window

The front window was made into a door by attaching it with two metal hinges.

e) Up Goes The Roof

I pre-assembled the roof using a 2×4 on the interior join and a 2×2 on the exterior join. It was definitely a 2-person job to lift it up on onto the support frame.

Update: A few years later I converted the roof to wood and made it into a flower garden.

f) Decorating

I like to take my time and find just the right accouterments (at the right price) at thrift shops so it may be a while before I find the touches I want.

For now I stuck a metal basket at the front peak while I think it over. The metal bird came from a thrifted pigeon racing trophy (!), reminding me of a very sweet bird that adopted us for a while (you can see the story here).

Little Window Greenhouse

Now that the project is basically completed (except for more, fun cosmetic stuff), I’m very pleased with it. There were plenty of learning curves including learning use a new saw, the jig, and figuring out a good design, but I did it, and I love how it looks in the garden.

~Melissa the Empress of Dirt ♛