A catio is a fixed outdoor enclosure with a roof, and the cat never leaves it. Four numbers decide whether the build works: 3.7 m² of floor per cat, 2.4 m of internal height, 2.5 × 5 cm mesh at 13 gauge, and anchors 60 cm into the ground. Get any one of them wrong and the structure either fails inspection or the cat escapes in the first week.
Permits come before lumber. Setback, size exemption, HOA approval and, for renters, written landlord permission are 4 separate checks, and skipping the HOA step is the most common reason a finished catio gets torn down.
Parameter 1: 3.7 m² of floor per cat
A 2.4 × 1.5 m footprint gives 3.6–3.7 m², which is the minimum for 1 adult cat to walk, turn and lie in sun and shade at the same time. Add 1.8 m² for each additional cat. Floor area below 2 m² produces pacing along the mesh within 2 weeks, and pacing is the behaviour that makes owners abandon the enclosure.
Vertical space buys usable area cheaply: 2 shelves at 60 cm and 120 cm add roughly 40% to the usable surface without adding footprint. Shelves need to be 30 cm deep and 25 cm wide, because a cat will not settle on a 10 cm ledge, and each shelf needs 1 anchor into a stud, not into the mesh.
Parameter 2: 2.4 m height and a full roof
Height of 2.1–2.4 m lets a 4.5 kg cat reach a 1.2 m shelf in 1 jump and a 1.8 m shelf in 2. Below 1.8 m, a determined cat can clear the top from a 90 cm shelf, which is why every catio needs a roof rather than an open top. The roof mesh should be the same gauge as the walls and overhang 30 cm on the weather side.
Wind is the load case that matters, not the cat. Design for 100 km/h gusts: 4 posts of 9 × 9 cm, a top rail on all 4 sides, and diagonal bracing on at least 2 walls. A frame built from 4 × 4 cm lumber with no bracing racks out of square at about 60 km/h wind and the mesh then sags open at the corners.
Parameter 3: 2.5 × 5 cm mesh, 13 gauge
The mesh does 2 jobs: keep the cat in and keep raccoons, foxes and stray cats out. A 2.5 × 5 cm opening at 13 gauge (about 2.3 mm wire) stops a paw from reaching through and resists a 5 kg animal pulling at it. Chicken wire at 2.5 cm hex is the wrong choice: it deforms under a 3 kg load and rusts through in 2 seasons outdoors.
Fastening matters as much as the wire. Staples every 15 cm with 20 mm washers, plus a tension wire every 90 cm along each panel, is what keeps the mesh from being peeled back at a corner. The bottom 30 cm should be a solid panel or buried mesh apron, because a cat will dig at the base within the first 3 days.
Parameter 4: 60 cm anchors and 1 per 1.2 m
Posts go 60 cm into the ground with 10 cm of gravel at the base for drainage, or bolt to concrete footings of 30 × 30 cm if the catio sits on a patio. Anchor spacing is 1 per 1.2 m of perimeter, so a 7.8 m perimeter takes 7 anchors. Use 8 cm structural screws, not deck screws, at every post-to-rail joint.
| Parameter | Target | Fail threshold | Check when |
|---|---|---|---|
| Floor area | 3.7 m² per cat | under 2 m² | before framing |
| Height | 2.4 m | under 1.8 m | before roof |
| Mesh | 2.5 × 5 cm, 13 gauge | hex poultry net | at delivery |
| Anchor depth | 60 cm | under 40 cm | at 1st post |
| Anchor spacing | 1 per 1.2 m | 1 per 2 m | before decking |
| Door width | 15 × 20 cm cat door | under 12 cm | before mesh |
Permits: 4 checks before you buy lumber
First, setback. Most residential codes require 1–1.5 m from the property line and 3 m from a neighbour's window, and a 2.4 m structure on a 1 m setback is a complaint waiting to happen. Second, size exemption: many jurisdictions exempt detached structures under 10 m² and under 2.4 m from a building permit, but the exemption usually still requires the setback.
Third, HOA or strata approval, which takes 2–6 weeks and often caps enclosure height at 1.8 m or requires a neutral colour. Fourth, for renters, written permission from the landlord, because a catio is a permanent fixture and is treated as an alteration to the property. Budget 1 inspection visit and keep the drawing at 1:50 scale on site.
Access: door, tunnel and airlock
The cat door should be 15 × 20 cm, cut through a wall or a window panel, with a 30 cm tunnel so the flap cannot be pushed open from outside. Add a second door inside the catio to create a 1 m airlock: 2 doors that are never open at the same time remove the escape window that a single door leaves during cleaning and feeding.
A 10 cm threshold stops bedding and litter being dragged out, and a simple barrel bolt at adult height keeps children and dogs out. If the catio connects to the house through a window, fit the panel with 2 turnbuckles rather than screws so it can be removed when you move.
Why this replaces free roaming, not enables it
The catio is the alternative to unsupervised outdoor access, not a base for it. The cat stays inside the mesh 100% of the time; there is no free-roaming schedule, no evening let-out, and no tie-out line, because a tethered cat cannot escape a dog and hangs itself on fences. Traffic and coyotes take cats at night, and a cat that has never been loose outdoors tends to freeze within 20 m of the door rather than find its way home.
Introduce the space in 10–15 minute sessions, 3 times a day for the first 7 days, with the house door open so the cat can retreat. Supervise directly for the first 14 days and check the mesh at the base and corners every 7 days for the first month, then monthly.
Build order over 4 weekends
- Weekend 1: mark the footprint, call for utility locates, dig 7 post holes to 60 cm.
- Weekend 2: set posts, level the top rail, brace 2 diagonals.
- Weekend 3: frame the roof, fix mesh with washers every 15 cm.
- Weekend 4: cut the cat door, fit the airlock, add 2 shelves and a 40 cm litter corner.
Post-operative cats and cats on cage rest need the catio locked for the full restriction period; a 6-week recovery plan is the reference point for when outdoor access resumes. A 2-cat build costs more in mesh than in lumber, so price the mesh roll first and size the frame to it, and put the whole build in the one-off side of the cat budget instead of the monthly column.
Terms mentioned in this article
Frequently asked
Do I need a permit for a small catio?
Often not for a detached structure under 10 m² and 2.4 m tall, but the exemption varies by jurisdiction and almost always keeps the setback rule of 1–1.5 m from the property line. Call the local building office with the footprint and height before buying anything.
Can a catio replace daily walks or outdoor time?
It replaces unsupervised outdoor access entirely, which is the point: the cat gets sun, air and vertical space without traffic or coyote risk. It does not replace indoor play, so keep 2 sessions of 10 minutes with a wand toy, or the cat will pace the mesh instead.
How do I stop the cat escaping through the door?
Build a 1 m airlock: 2 doors that are never open at the same time, with a 15 × 20 cm cat door and a 30 cm tunnel so the flap cannot be pushed from outside. Check the base and corners every 7 days for the first month.