The complete, versioned list the planner checks designs against — what each rule looks for, how serious it is, what to do about it and where it comes from.
CAT-ACC-001 v1Wind, a curious cat or a predator can open an unlatched door.
Fix: Choose a latch: a hasp or keyed latch for human doors, a slide bolt for hatches.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-ACC-002 v1A door left ajar for a moment is the most common way cats escape from catios.
Fix: Use self-closing spring hinges on human doors.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-ACC-003 v1A gravity latch on a door cats can push from inside may be nudged open.
Fix: Use a hasp, slide bolt or keyed latch, or a second latch at cat height.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-ACC-004 v1Walk-in catios need a door you can pass through with a bucket and tools (about 24″ × 60″ or larger).
Fix: Widen or heighten the door.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-ACC-005 v1Litter, water, plants and shelves all need regular cleaning; without a door or hatch you cannot reach them.
Fix: Add a human door or a cleaning hatch.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-ACC-006 v1An attached catio is most used when cats can come and go from the house.
Fix: Add a window-access insert or a cat door through the wall, or connect a tunnel.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-BLD-001 v1Wide bays or tall 2×2 walls flex, letting mesh sag and fasteners pull out.
Fix: Keep posts within 1.2 m (4 ft) and use 2×3 or 2×4 for walls over 1.5 m.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-BLD-002 v1Corrugated panels need slope to shed water; a flat solid roof ponds and leaks.
Fix: Give the roof at least 1:12 slope (1″ fall per foot) by lowering the front.
Manufacturer constraint· reviewed 2026-10-12 · OpenCatio3D
CAT-BLD-003 v1A frame member is longer than the longest lumber in the stock lengths, so it would need a splice.
Fix: Shorten the structure, add a post to split the span, or allow longer stock lengths.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-BLD-004 v1This structure type is shown for planning only; its attachment and framing need a site visit.
Fix: Use it to explore ideas and share them; ask a builder for a site-specific plan.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-BLD-005 v1One or more dimensions are outside the range this template is designed for.
Fix: Bring the dimension back within the shown limits, or split the design into two structures.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-BLD-006 v1A door, hatch or cat opening runs past the end of its wall, above the wall height, or into another opening.
Fix: Move or resize the opening.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-BLD-007 v1A shelf, ramp or other item extends past its wall or above the structure.
Fix: Move it, shorten it or lower it.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-DIM-001 v1Build outputs need measured, confirmed dimensions; typed guesses make wrong cut lists.
Fix: Measure the site, then confirm each key dimension in the Site workspace.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-DIM-002 v1The footprint overlaps something marked on the site (a tree, AC unit, hose bib or no-build zone).
Fix: Move or resize the structure, or remove the obstacle from the site if it is gone.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-ELEV-001 v1A box mounted off the ground puts its whole weight on brackets and wall fasteners.
Fix: Fasten the ledger into studs or masonry (not siding only) and check the brackets’ rated load.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-ELEV-002 v1Elevated installations involve fall hazards and structural attachment beyond these checks.
Fix: Have the attachment and supports reviewed by a qualified professional, then record the review.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-ELEV-003 v1Structures over 20 m² or taller than 2.7 m may need a permit and engineered framing.
Fix: Check with your building department and have the framing reviewed, then record the review.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-ENC-001 v1Cats can squeeze through surprisingly small gaps; openings 2″ (50 mm) or wider on the short side let many cats out.
Fix: Choose a mesh with openings of 1″ × 2″ or smaller (1″ × 1″ is the common catio choice).
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-ENC-002 v1Young kittens can squeeze through openings wider than about ¾″ on the short side.
Fix: Use ½″ × 1″ mesh, or add a band of smaller mesh along the lower walls.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-ENC-003 v119-gauge and lighter wire holds cats in but is easier for raccoons and dogs to tear from outside.
Fix: Use 16-gauge or heavier welded wire where predators visit.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-ENC-004 v1A window or door that is only partly inside the catio opens a gap straight to the outside.
Fix: Move or resize the catio so the opening is fully inside or fully outside it.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-ENC-005 v1Neither end of the tunnel reaches a house opening or another structure, so cats cannot get in.
Fix: Extend the tunnel to a window, cat door or catio, or add a cat door at one end.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-ENC-006 v1A cat that rushes doors can slip past you while you step in to clean.
Fix: Add a vestibule (a small airlock with a second door) in front of the human door.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-GND-001 v1Cats and predators can dig under a frame that sits on grass or soil.
Fix: Add a mesh ground skirt (an apron laid flat outward and pinned) or set the frame on pavers.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-GND-002 v1Pavers alone may not hold a light frame in wind, and gaps open as it shifts.
Fix: Add ground anchors at each corner post.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-HOME-001 v1Dryer exhaust is hot, full of lint and (for gas dryers) combustion gases; it must vent freely outdoors.
Fix: Move the catio or reroute the dryer vent outside the enclosure (have a professional do any vent work).
Authoritative requirement· reviewed 2026-10-12 · U.S. Fire Administration (FEMA)
CAT-HOME-002 v1Utility workers need unobstructed access to gas and electric meters.
Fix: Keep meters outside the enclosure.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-HOME-003 v1A bedroom egress window must stay usable for escape and rescue; enclosing it can block that route.
Fix: Keep egress windows outside the catio, or have the design reviewed by your building department or a fire-safety professional.
Authoritative requirement· reviewed 2026-10-12 · International Code Council
CAT-HOME-004 v1Bathroom, kitchen or appliance vents blow moist or fouled air into the enclosure.
Fix: Check what the vent serves; keep exhaust vents outside the catio.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-HOME-005 v1Roof runoff will soak the catio floor.
Fix: Redirect the downspout outside the enclosure.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-HOME-006 v1The catio rises above the wall it attaches to, so the top ledger has nothing to fasten to.
Fix: Lower the catio or attach it to a taller part of the house.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-MAT-001 v1Galvanizing before welding leaves bare weld points that rust sooner.
Fix: Prefer galvanized-after-welding, PVC-coated or stainless mesh for long life.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-MAT-002 v1Untreated wood in ground contact decays quickly, loosening the bottom plate and opening gaps.
Fix: Set the frame on pavers, or use lumber rated for ground contact (AWPA UC4A) for the bottom plates.
Authoritative requirement· reviewed 2026-10-12 · American Wood Protection Association · USDA Forest Service, Forest Products Laboratory
CAT-MAT-003 v1Modern pressure-treated lumber (ACQ / copper azole) is widely used outdoors, but cats should not chew it.
Fix: Seal treated members inside the catio, or use cedar for parts cats can reach.
Professional guidance· reviewed 2026-10-12 · U.S. Environmental Protection Agency
CAT-MAT-004 v1Every cut edge of welded wire leaves sharp wire ends.
Fix: File cut ends, fold them over or cover them with trim; wear gloves.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-MOB-001 v1Jumps of more than about 30 cm between levels are hard on stiff joints.
Fix: Add a ramp or intermediate shelves so each step is 30 cm or less.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-PLT-001 v1This plant is listed as toxic to cats, with organ damage or death reported (true lilies, sago palm, cardiac-glycoside plants…).
Fix: Remove it from the catio and the home. If a cat may have eaten any part, call your veterinarian or ASPCA Animal Poison Control.
Professional guidance· reviewed 2026-10-12 · ASPCA Animal Poison Control Center · ASPCA Animal Poison Control Center
CAT-PLT-002 v1This plant is listed as toxic to cats, usually causing stomach upset or mouth irritation.
Fix: Swap it for a plant with no known issue, or keep it out of the catio.
Professional guidance· reviewed 2026-10-12 · ASPCA Animal Poison Control Center · ASPCA Animal Poison Control Center
CAT-PLT-003 v1This plant was not found in the reviewed toxicity source, or sources disagree. Missing from a list is not proof of safety.
Fix: Keep it out of chewing reach, or ask your veterinarian before planting it in the catio.
Professional guidance· reviewed 2026-10-12 · ASPCA Animal Poison Control Center
CAT-PLT-004 v1Toxicity lists cover common plants only, and individual cats can react to plants listed as non-toxic.
Fix: Watch for chewing and call your veterinarian about any symptoms.
Professional guidance· reviewed 2026-10-12 · ASPCA Animal Poison Control Center · ASPCA Animal Poison Control Center
CAT-WEL-001 v1Cats need a secure place to retreat and rest (AAFP/ISFM pillar 1).
Fix: Add a bed, hammock or hideaway cube.
Professional guidance· reviewed 2026-10-12 · American Association of Feline Practitioners / International Society of Feline Medicine · American Association of Feline Practitioners (catvets.com)
CAT-WEL-002 v1Vertical space lets cats survey their territory and avoid each other.
Fix: Add shelves or a bridge at a second height.
Professional guidance· reviewed 2026-10-12 · American Association of Feline Practitioners / International Society of Feline Medicine · American Association of Feline Practitioners (catvets.com) · The Ohio State University College of Veterinary Medicine, Indoor Pet Initiative
CAT-WEL-003 v1With several cats, a single high spot becomes contested; a dead-end perch can trap a cat.
Fix: Add a second perch and a second route (a bridge or ramp) so cats can pass each other.
Professional guidance· reviewed 2026-10-12 · American Association of Feline Practitioners / International Society of Feline Medicine · American Association of Feline Practitioners (catvets.com) · The Ohio State University College of Veterinary Medicine, Indoor Pet Initiative
CAT-WEL-004 v1Scratching is a normal behaviour that marks territory and keeps claws healthy.
Fix: Add a sisal scratching post.
Professional guidance· reviewed 2026-10-12 · American Association of Feline Practitioners / International Society of Feline Medicine · American Association of Feline Practitioners (catvets.com) · The Ohio State University College of Veterinary Medicine, Indoor Pet Initiative
CAT-WEL-005 v1Cats in a catio for more than a short visit need water, especially in warm weather.
Fix: Add a shaded water bowl.
Professional guidance· reviewed 2026-10-12 · American Association of Feline Practitioners / International Society of Feline Medicine · American Association of Feline Practitioners (catvets.com)
CAT-WEL-006 v1Cats prefer food and water away from their toilet area (AAFP/ISFM pillar 2).
Fix: Keep at least 1 m between the litter enclosure and the water bowl.
Professional guidance· reviewed 2026-10-12 · American Association of Feline Practitioners / International Society of Feline Medicine · American Association of Feline Practitioners (catvets.com)
CAT-WX-001 v1An all-mesh roof gives no shade; cats can overheat in summer sun.
Fix: Add a partial or full solid cover, shade cloth, or place the catio in afternoon shade. Keep water available.
Professional guidance· reviewed 2026-10-12 · National Weather Service
CAT-WX-002 v1Cats use a catio more when part of it stays dry and shaded.
Fix: Cover part of the roof (a partial polycarbonate cover is cheap and bright).
Professional guidance· reviewed 2026-10-12 · American Association of Feline Practitioners / International Society of Feline Medicine · American Association of Feline Practitioners (catvets.com)
CAT-WX-003 v1Snow collects on mesh and solid roofs alike; heavy snow can sag or break light framing.
Fix: Plan to clear snow, add rafters, or have the roof framing reviewed for your snow load.
Product best practice· reviewed 2026-10-12 · OpenCatio3D
CAT-WX-004 v1Light enclosures and solid roof panels catch wind.
Fix: Anchor the frame to the ground or deck at every corner and fasten roof panels at every purlin; consider professional review.
Professional guidance· reviewed 2026-10-12 · National Weather Service
A finding means a rule matched; no finding means “no issue detected by the current rules” — not a guarantee. See limitations.
Free to design and check. Fit a catio to your wall, window and yard, run the safety checks, and see the materials list before you buy a single board.