How to Build a Catio

Like all pets, cats benefit from a little exercise. Don’t worry, we’re not suggesting you take yours for a walk on a leash. Instead, build your feline friend a screened-in structure that hangs from a window.

A catio, accessed through the open window, lets cats enjoy fresh air, sunshine, and bird-watching without the chance of getting into trouble. Senior technical editor Mark Powers built this two-story version, complete with a shelf for perching, over two days using rot-resistant cedar, in a look and color that match the home’s architecture.

Follow along to learn how to create a window catio that’s sure to get your cat to come out from behind the couch. The free catio plans are available for download below.

Tools Needed:

Step 1 – Overview: How to Build a Catio

Day-to-day timeline

• SATURDAY Build the frames (Steps 2-12).
• SUNDAY Attach the catio to the window (Steps 13-19).

Download and print a cut list for this project.

Step 2 – Make a Story Stick

To determine the height of the catio, mark the location of the windowsill and the head casing on a long board. Then measure the width from the outside edges of the side casings. Each of the two catio frames is about as tall as the window’s sashes and wide enough to rest on the side casings.

Step 3 – Prime and Cut the Parts

Coat all the cedar 2×2 balusters and 1×4 boards for the project with a tannin-blocking exterior primer. Once dry, cut the parts for the catio frames and window screens with a miter saw according to the cut list.

Step 4 – Build Frames for the Sides

Using 2x2s, butt joints, and 2¼ -inch stainless-steel screws, attach a frame crosspiece between two verticals, making a U shape, as shown. At the open end of the U, attach a 2×2 plywood support on top of the verticals. Repeat this step to make the three remaining sides, and coat any newly exposed ends with primer.

Step 5 – Add the Trim Boards

Using 1 5⁄8-inch stainless-steel screws, attach 1×4 trim boards to the 2×2 sides, opposite the plywood supports. Stand the side frames up on edge and join them with front and back 1×4 trim boards. Drive screws through the trim boards and into the 2×2 verticals, as shown. Center an additional plywood support between the front and back trim boards. Repeat the process on the other frame.

Step 6 – Fasten Upper Crosspieces

To complete the frame, join the sides together at the top by screwing on 2x2s.

Drive 1 5⁄8-inch fasteners through the top of the verticals and into the ends of the 2×2 crosspieces. Repeat the process on the other frame.

Step 7 – Make the Floor

Measure the interior dimensions of a frame and cut a sheet of plywood to fit. Trace a 2×2 onto each corner of the plywood and cut notches with a jigsaw. Test the fit, as shown, then remove the plywood, stain the bottom side, and set aside to install once the catio frames are mounted on the brackets.

Step 8 – Build the Screen Frames

For each screen frame, place 1×4 boards with the rails between the stiles. Glue joints together. Drill a pilot hole at an angle through the outside edge of a rail and into the adjoining stile, then drive a 2¼ -inch trim screw. Repeat at the remaining outside corners. Stand the frame up, drill an angled pilot hole through the rail and into the stile, as shown, at each inside corner, and follow with a screw.

Step 9 – Stretch the Screens

Cut an oversize piece of screening. Staple the screening to each of the six frames in this order, smoothing out any ripples before attaching: 12 to 6 o’clock, 3 to 9, 1 to 7, and so on, working around the frame. Cut any material that overhangs with a utility knife.

Step 10 – Assemble the Roof

Use 1 5⁄8-inch screws to join three lengths of fascia together with butt joints, creating a U shape. Then add glue to the top of the fascia boards, place the plywood roof, as shown, and attach it with more screws. Cut three lengths of aluminum drip edge to size with tin snips, then run a bead of roofing cement around the edge of the plywood, embed the front drip edge, and attach it with 1 5⁄8-inch screws. Next, add the side drip edge the same way, overlapping the front.

Step 11 – Attach the Roof

Position the upper frame with the trim boards facing up. To shed water, pitch the roof forward by screwing a scrap length of 1×4 on top of the frame’s upper plywood supports flush with the rear trim board. Center the roof on the frame, flush with the back. Drive screws through the roof and into the upper plywood supports, as shown.

Step 12 – Unroll the Roofing

Spread roofing cement on the plywood, then unfurl the roll roofing onto the wet adhesive, pressing it in place. Take your time unrolling the roofing into the wet adhesive to avoid readjusting. Trim the asphalt to width so it just covers the aluminum drip caps.

Step 13 – Cut Half-lap Joints for the Brackets

We set our circular saw to a 40° angle and trimmed 1½ inches off each face to form decorative pyramids on the ends of the brackets. At the square ends, use a circular saw to make a series of passes 3½ inches wide and 1¾ inches deep. Knock the slivers free with a hammer and chisel, as shown. Repeat for the second bracket.

Step 14 – Build the Brackets

Add construction adhesive to each side of the half-lap joint and fasten it together with a pair of 3-inch deck screws. Position the diagonal brace in place and drive 3-inch deck screws through the mitered ends and into the bracket. Repeat on the second bracket. Coat the exposed ends with primer.

Step 15 – Attach the Brackets

Position a bracket underneath the windowsill. Drill a shallow 3⁄8-inch pilot hole through the lower leg for the buttons that hide the screwheads. Then attach the bracket to the house with a 9-inch structural screw, as shown. Check for plumb with a level, then toe-screw through both sides of the bracket’s half-lap joint and into the house with two more structural screws. Repeat to attach the second bracket.

Step 16 – Join the Frames

With a helper, stack and center the catio frames on the brackets. Clamp the frames together, then fasten through the crosspieces of the upper frame into the lower one with 2¼-inch screws every 10 inches, but don’t seat them fully just yet. Use 1 5⁄8-inch screws to attach 1x4s to the back edges of the joined frame, between the trim boards, to pad out the window casing. Drive 3-inch deck screws through the lower frame’s plywood supports and into the brackets. Add the floor and screw it to the supports.

Step 17 – Connect the Frame to the House

Using a level, check that the catio frame is plumb and level. Measure for a consistent space between the upper and lower trim boards, where the screen frames will fit. Adjust for racking by adding shims between the catio frames before tightening the screws holding them together. Attach the cat shelf to the lower crosspieces of the upper frame with 1 5⁄8-inch screws. Then attach the frame to the house by driving 3-inch deck screws through the 2x2s and into the window trim every 10 inches.

Step 18 – Tip in the Screened Side Panels

Using a 3⁄8-inch paddle bit, drill shallow pilot holes for button plugs in each corner of a screen panel. Put the screen in place, mesh facing inside, with the front edge flush to the outside corner of the catio frame.

Step 19 – Screw Screens in Place

Drive the four screws holding each panel in place. Press in the button plugs. Repeat the installation process for the screens on the other side of the catio and then the front. Now coat everything with stain.