Catio designer

How the designer works

The rules it checks

Welfare rules come from humane societies, shelter veterinarians and feline guidelines, cited with their year; we give no veterinary advice. Building rules come from the model code (IRC 2021) and describe it: your town decides.

• ED-01 Our default: every wall is a 2x4 frame (bottom plate, top plate, studs at most 48 in apart, 24 in on a window box) with the mesh screwed to its outside face. Only the bottom plates that sit on a patio, a deck or the ground are pressure-treated.
• ED-02 Our default: the mesh laps every stud, plate and rail it crosses, fixed with a #10 x 1 in stainless pan head screw through a 1/4 x 1-1/4 in stainless fender washer every 6 in and at each end of every run, on treated and untreated wood alike (treated wood needs stainless or hot-dip galvanized, IRC R317.3.1; zinc-plated roofing screws are made for metal roofing and rust outdoors), and the cut ends are covered by the next frame member or a 1x2 strip, so no wire end is left for a paw or a nose.
• ED-04 Our default: every roof falls 1-1/2 in per foot away from the house (or from the back wall), the least the panel maker recommends (PANEL-01), so you can swap mesh for panels later without rebuilding.
• ED-05 Our default: roof purlins run across the catio on top of the side walls, with a side-wall stud under each purlin. Under mesh they sit at every band joint (at most 48 in apart), with more in between when the snow load you pick needs them; under panels at the spacing the panel maker's snow table asks, closer when the span math needs it, never closer than 11-1/2 in. The half roof puts panels over the half next to the house or the back wall (at least 24 in) and mesh over the rest, so the cats choose sun or shade.
• ED-14 Our margin, not a code number: a roof purlin may use at most 95% of the span its size allows at the snow load you pick, whichever of sag or strength governs. Above that the designer adds a purlin, closing the spacing, until it is back at 95% or less, so a board at the low end of its grade or a little more snow than you entered does not take it past its limit. It applies under the panels and under the mesh.
• ED-06 Our default: a 30 in walk-in door in the front wall when the front is tall enough for a 72 in door, else a 24 x 30 in hatch at the floor (a window box gets a hatch in its front for cleaning); a 2x4 frame with a diagonal brace in the same mesh, two hinges and two latches (one high, one low), opening out, with the bottom plate left across the doorway as a sill. The leaf is 1/2 in smaller than the opening all round so it swings free, and 1x2 stop strips on all four sides of the opening (top, bottom, hinge and latch) stand 1 in into it, so the closed leaf laps them 1/2 in and no gap is left open: the same on both airlock doors.
• ED-15 The Association of Shelter Veterinarians (2022) recommends double-door entry points on every enclosed outdoor space, to reduce the risk of escape. Our default: a mesh vestibule 36 in deep and 42 in wide inside the walk-in door, framed in 2x4 like the walls, mesh from the floor to the roof cover, and an inner door built the same as the outer one, opening into the catio. It needs the catio at least 6 ft wide and 24 in of catio behind it, and its floor comes off the space per cat.
• ED-07 Our default: shelves are two 1x6 cedar boards (11 in deep) on Simpson SBV galvanized shelf brackets, one on every stud under the shelf (two at the least, never more than 48 in apart), each with 4 Simpson SDS screws into the stud and two short stainless screws up into every board; the lowest 18 in up and each next one 16 in higher (under the 18 in step we allow), stepping around the walls, with at least 14 in clear under the roof framing. Perches are a single 1x6 cedar board. A ramp is a 1x6 cedar board with 1x2 cleats every 4 in, at most 45 degrees. Simpson publishes no load rating for the SBV on its product page, so we give none.
• ED-11 Our default for a window box: the floor sits 2 in below the window sill, on 2x4 joists that bear on a pressure-treated 2x8 ledger bolted into the house framing every 16 in (WIN-06), held up by 2x4 knee braces at 45 degrees or 4x4 legs to the ground. We size it for 20 lb per cat plus 6 psf of frame and floor plus the snow on a solid roof, and draw it only at ground-floor windows (sill up to 8 ft).
• EDIT-09 Our default: a tunnel 18 in wide and 18 in tall outside (about 15 x 14 in clear, above the 12 x 12 in we allow), a 1/2 in plywood floor on two pressure-treated 2x4 runners, 2x4 frames at most 48 in apart and mesh on both sides and over the top. PAWS: tunnels give cats a safe way between the house and the catio.