Living in New York City with a cat usually means limited or non-existent outdoor opportunities for the cat. We decided it was time to give them a bit of outdoor space of their own, but we had no access to a deck, patio, or roof. So we decided to build them a little cat patio ("catio") that could be installed in a double-hung window much like a window A/C unit. Our cats (we have 3) loved it! In good weather the catio was enclosed only by "bars" made of wooden dowels. There was a plexiglass "skylight" so our cats could sunbathe. And in cold or bad weather, a plexiglass screen could be fitted against the bars so the cats would be protected from the wind, rain, and snow. Cats entered and exited by a magnetic cat door. We chose to make the flat wall of the catio out of plexiglass as well, so we could watch our cats enjoying themselves and people-watching.

Supplies

Tools:

Handsaw - we love this Japanese handsaw that has great flexibility

Drill with 1/4" drill bit and screwdriver bits suitable for your screws (I like to use hex-head screws as they tend to not strip)

Dremel with woodcutting tip, plastic-cutting tip, and small routing tip (3/32") and routing cup attachment

Materials:

3/4" plywood

2 pieces that are each 24" x 24"

1 piece that is 10" x 16"

2 pieces that are 12" x 16"

1 piece to fit the opening not covered by the catio once it is installed (to prevent drafts)

1/4" wooden dowels - enough to make 24 pieces that are each 18" long

0.093" (3/32") plexiglass or acrylic - it should be thin and flexible (we got ours from Home Depot)

1 piece that is 24" x 18"

1 piece that is 16" x 36"

1 piece that is 14" x 16"

1x3 wood (pine is fine)

1 piece that is longer than the interior horizontal opening of your window

2 pieces that are 20" to 24" long

Cat door - make sure it's 2-way so your cat doesn't get locked out

Wood glue

1 1/4" wood screws

3/4" sheet metal screws

Silicone sealant/caulking

Exterior grade paint

Paintbrush

A/C foam weather stripping

(Duct tape - optional)

Step 1: Design

The catio is designed to be 24" across the front, 24" deep at the deepest protruding point, and 16" tall (interior dimensions). The supporting bar that holds the catio to the window extends about 2 inches beyond the metal edge of the window opening.

Step 2: Cutting the Plywood Pieces

Bottom piece:

Mark the center point of one of the 24" x 24" plywood pieces. Draw a 12" diameter semi-circle along one half. Using the handsaw, cut out the shape, which should look like the shape outlined in orange in the drawing. To cut the rounded curve, use the Dremel rather than a saw.

Top piece:

Same as the bottom piece, except once the outside shape is cut out, draw a 10" diameter semi-circle centered at same center point as the 12" semi-circle. Then extend the edges of the 10" semi-circle straight down for 4" more. Draw a 20" horizontal line across to connect the ends of the semi-circle. This is the magenta outlined shape in the drawing. Cut out the hole by first drilling a starting hole in the corner, then using the Dremel (or a router) and wood-cutting bit to cut along the outline. This is the "skylight" opening. If you are careful, you can save the cutout piece and use it for the cat door piece later, as we did.

Side pieces:

Cut out 2 pieces plywood that are 12" x 16".

Door piece:

Cut out 1 piece of plywood that is 10" x 16".

Step 3: Drilling the Holes for the Dowels

Clamp the top and bottom pieces together. Draw a line about 3/4" in from the edge all around the semicircle. Make a mark every 1". Drill a 1/4" hole through the top plywood piece into, but not all the way through, the bottom plywood piece at each of the marks. This will ensure that your dowel holes line up.

Step 4: Putting the Pieces Together

Insert the dowels through both top and bottom pieces. Put a little glue on the bottoms and tops of the dowels to help them stay there. Lift the top piece up until it is 16" from the bottom piece.

Insert the 2 side pieces that are 12" x 16" so the short sides are touching the top and bottom pieces, and the are aligned against the straight (not curved) edges of the top and bottom pieces. Place screws through the top and bottom pieces to secure them to the side pieces (we placed 3 screws per side per piece - 12 screws total). Once the pieces are all secure, use the handsaw to trim off the ends of any dowels that are sticking up past the top piece.

You can see our cats performing quality control checks :)

Step 5: Adding the Wood Support Bar and Bottom Support Rails

Screw the top 1x3 wooden support bar along the straight edge of the catio. This is your longest 1x3 bar and will prevent your catio from falling out the window. We decided to do ours asymmetrically so the catio is positioned along one side of the window opening. That way, we don't have to make 2 separate pieces to close up the resultant opening in the window and can get away with just 1. You can position yours however you like.

On the bottom, attach a 1x3 piece along the bottom straight edge using screws. This should be about 20 to 24 inches long. Leaving a gap of about 1/2", attach another 1x3 piece parallel to the first edge piece. This should probably be about 10" long or longer. When the catio sits on the window frame, the bottom edge of the metal frame will rest inside the groove created by the gap, stabilizing the catio.

Step 6: Cut Out the Door

Cut out a 10" x 16" plywood. You can see we salvaged the skylight cutout for this. Following the instructions in the purchased cat door, draw the shape for the opening of the cat door and cut out using a Dremel. The cat door came with a drawing that we could trace onto the wood.

Step 7: Paint! (and Install the Purchased Cat Door)

Paint 3 layers of exterior grade paint to cover all wood surfaces of the catio. We used a semi-gloss paint so it would be easy to wipe off and clean if necessary. We used white so it would blend in more with the A/C units and not attract attention from our landlord!

After the paint has dried, install the purchased cat door according to instructions.

Step 8: Cutting and Fitting the Plexiglass Skylight

Cut out a piece of plexiglass that will fit over the skylight opening. Ours is 16" at its deepest point and overhangs the edge of top plywood piece by about 1/4". This would prevent water damage from seepage. We used a plastic cutting attachment for the Dremel to cut the plexiglass. Do it on a slow speed so it cuts the plexiglass. If you use high speed, then the friction from the Dremel generates so much heat it causes the plexiglass to melt instead.

Attach it to the plywood using sheet metal screws. Then caulk the straight edge with silicone caulking for extra water-proofing.

Step 9: Install Your Catio!

Place the catio in the window, with the bottom sill resting in the groove between the two parallel bottom 1x3s. Make sure the top supporting bar is long enough to stick out past both sides of the window frame. You can see from the pictures that the catio remains in the window even with it open (unlike A/C units, which fall out if you open the window without holding it in). This is both secure and convenient.

Place the plywood piece with the cat door where you want it. We put ours on the right side. You could screw it in or use glue if you want something permanent. We used duct tape to attach ours in place because it would allow for removing and repositioning as needed. The duct tape held up just fine.

We routed a 0.093" (3/32") grove along the bottom and top inner edges to fit a 14" wide x 16" tall piece of plexiglass that allows us to see into the catio (and the cats to see into the house). The groove allows us to slide the plexiglass window in and out, so that we can access the inside of the catio easily if needed. This comes in handy when we want to add the plexiglass weather guard (next step).

Step 10: Weather Guard

Cut a 36" x 15" plexiglass piece. This can be 0.093" or thinner - it just needs to be flexible and does not need to be particularly thick. This will be your weather guard in inclement or cold weather. Insert it through the front opening, bend it against the bars, and rest the edges of the plexiglass against the edges of the side plywood pieces. Tension will hold it in place. Ours kept out wind, rain, and snow very effectively and our cats used the catio in all weathers and seasons.

Step 11: Safety Concerns

The catio is perfectly safe, lighter than a similar sized A/C unit, much more sturdily constructed, and cannot fall out of the window. We added an A/C bracket that we bought at our local hardware store but it was probably more for show than anything else. The main wooden bar support works so well that the bracket did nothing.

However, it IS an unfamiliar item and as such, can cause concerns for safety. Our landlord was okay with us having it there, but asked us to put it away for the week when they were conducting city safety inspections.

Step 12: Finished Product

Our cats enjoyed the catio very much. They sunbathed, napped, and people watched from their catio often. It could fit 2 cats reasonably well and 2 of our cats (Russets and Mittens) would hang out together frequently (you can see them together in the catio in the 3rd picture, while Naledi, watches from the inside).

We have since moved out of NYC to rural California, so the cats no longer need the catio and instead enjoy the great outdoors. We definitely enjoyed building it, though, and gave it to a friend when we moved away so that her cat could also have a bit of sunshine and fresh air in the city. :)