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Free starting design · Window box catio

Window box catio

A 42" x 18" box for a 30 x 36 in window, 5.3 sq ft at the sill

Kept in, kept out: 1 x 2 in welded wire screwed every 6 in, no gap over 1 in, the hatch on two latches. Roof under snow: solid panel roof and purlins checked at 30 psf. Not verified by the planner: wind uplift and anchorage.

8 of 8 planner checks green
The window box catio, drawn by the catio designerThe window box catio with its footprint and heightsThe 2x4 frame of the window box catio, without mesh or roof panelsInside the window box catio: shelves, ramps and litter nook, the roof and the near walls cut away
Drawn by the designer from this plan
Customize this design, free

As drawn, at 30 psf of snow

Window
30 x 36 in, sill 36" up
Box
42" x 18", floor 2 in below the sill
Support
2 knee braces at 45 degrees
Fastening
2x8 ledger, 4 lags per row into the framing, never veneer
Gaps
none over 1 in; the window stays open behind
Access
24" x 25-1/2" hatch, two latches

About $433 in materials, before sales tax, delivery and tools.

Building it? The $29 builder's plan dimensions every stud, every cut and every roll of mesh. See sample sheets

Planner checks

8 planner checks passed at 30 psf of snow.

The bar is the roof purlin span against the longest the planner allows at 30 psf of snow. The open part is allowance this design does not use.

  • Roof purlins under panels3' 6" of 8' 1-5/8" allowed57% of the allowed span unused; deflection governs

what this design asks room to spare

Green meets the source or the default we checked against, amber asks you to confirm something on your wall, your site or the product before you buy, red is outside what a source accepts or what we draw. Planner checks don't replace your local building department or a look at your own wall.

Specification

The window box catio, part by part.

The catio

Footprint
42" x 18"
Floor
5.3 sq ft
Height
39" to 41-1/4"
Door
24" hatch

The frame and mesh

Studs
2x4
Purlins
2x4, 1
Mesh
1 x 2 in welded wire
Ties
2 H2.5A

Cost and time

What it takes to build.

Catio materials, before tax and delivery$433.05

  • Hardware and fasteners$182.62
  • Lumber and plywood$94.99
  • Roofing$92.45
  • Mesh$62.99

Shelf prices read at Home Depot, Hamilton Mill store, Oct 8, 2026; Home Depot, Hamilton Mill store, Oct 13, 2026; Lowe's, Atlanta-Edgewood store, Oct 8, 2026; Tractor Supply, Augusta, Kansas store, Oct 8, 2026; Home Depot, Bronx Terminal store, Sep 30, 2026; Amazon.com, shipped, Oct 13, 2026. Before sales tax, delivery and tools.

Per sq ft at the sill
$82.49
Mesh
1 x 2 in welded wire
Build time
8 to 13 h
two people with basic power tools, by our estimate (shopping, ground prep and painting not included)
Labor if you hire it out
$800 to $2,600
Separate from the materials.

Prices differ by store and by week: type yours into the catio cost calculator to get your own total.

Free and paid, side by side

Design it free. Build it from the $29 plan.

Free

On this page and in the designer, no account

  • This design in 3D, and every change you make to it
  • Every planner check, with its rule and source
Cost estimate
About $433 in materials, line by line, on this page. See the estimate
Summary PDF
The design, its checks and its materials list on a few pages. A summary, not the build drawings.
Customize this design, free

$29 once

The drawings you build from, for the design you finish. About 24 to 30 Letter sheets, 27 for the 8x6 freestanding catio.

  • Every wall framed, each stud dimensioned from the end of the plate
  • The cut list, every cut assigned to a store board
  • The mesh cutting plan, every panel placed on a roll
  • The roof, the door, the shelves and the details, drawn to scale
  • The shopping list with store prices and the build, step by step
Get the $29 plan for this design

You check out in the designer, with this design loaded. If the plan has an error, we fix it or refund you within 30 days. Guarantee terms.

Real sheets from the 27-sheet sample plan for the 8x6 freestanding catio

The sample was printed on an earlier date, so its prices can differ from the estimate above. Your plan prints the same prices as the estimate.

  • Sample sheet 14 of 27: wall framing

    Wall framing

  • Sample sheet 11 of 27: cutting plan

    Cutting plan

  • Sample sheet 20 of 27: mesh plan

    Mesh plan

  • Sample sheet 24 of 27: build steps

    Build steps

Build phases

From the first wall to the last shelf in 6 stages.

About 8 to 13 hours for two people with basic power tools, by our estimate (shopping, ground prep and painting not included). Each picture is this design at the end of its phase, drawn by the designer, with that phase's parts in full color.

  1. The window box catio after phase 1: ledger, braces and floor

    01

    Ledger, braces and floor

    Lag-screw the 2x8 ledger into the wall framing under the window, fix the knee braces under the side joists, then square the joists and screw down the plywood floor.

  2. The window box catio after phase 2: box frame

    02

    Box frame

    Frame the box walls on the floor, plumb them and screw them to the floor and to the ledger at the wall.

  3. The window box catio after phase 3: roof framing

    03

    Roof framing

    Lag the roof ledger to the house and set the purlins on it and the side walls, a tie at both ends of every purlin; the roof falls to the front.

  4. The window box catio after phase 4: mesh on the walls

    04

    Mesh on the walls

    Screw the mesh to every stud, plate and rail with stainless washers every 6 in, lapped onto the frame.

  5. The window box catio after phase 5: roof

    05

    Roof

    Lay the polycarbonate panels, pre-drill and screw on the ribs at every purlin.

  6. The window box catio after phase 6: hatch

    06

    Hatch

    Build the hatch square with its brace to the hinge side, hang it on two hinges, fit two latches and the stops, then push-test it.

This is the summary. The $29 builder's plan breaks these phases into a build order with the new parts highlighted, a how-to detail and a check at each step.

The guide to building a catio walks through each stage in general terms.

Questions

Anything else? Write to us or read how the planner checks a design.

Questions about the window box plan

A window box is safe when it is fastened to the house framing, not the siding, closed in welded wire or hardware cloth with no gap over 1 in, and used with the window open behind it so the cat can always go back in. It must never cover a bedroom's emergency escape window.

Lag-screw a pressure-treated 2x8 ledger into the wall framing under the sill, never into siding or veneer alone, flash over it, and carry the front of the box on knee braces. This design puts 4 lag screws in each row of the ledger; the box floor sits 2 in below the sill so the cats step straight out.

1 x 2 in welded wire, 16 gauge, galvanized, screwed to the frame with washers every 6 in. Hardware cloth (1/2 in) is the stronger choice with kittens or where small predators roam. Chicken wire is red in our checks: it can hold a cat in but does not keep predators out.

This design's materials list comes to about $433, shelf prices read at Home Depot, Hamilton Mill store, Oct 8, 2026; Home Depot, Hamilton Mill store, Oct 13, 2026; Lowe's, Atlanta-Edgewood store, Oct 8, 2026; Tractor Supply, Augusta, Kansas store, Oct 8, 2026; Home Depot, Bronx Terminal store, Sep 30, 2026; Amazon.com, shipped, Oct 13, 2026, before tax and delivery. Hiring the build out adds $800 to $2,600 in labor by our estimate of 8 to 13 hours for two people. Every line and its price is in the materials list on this page.

Kits we found listed on Google Shopping on Oct 14, 2026 ran from $124.99 to $1,699.00 before tax and shipping, and most of the cheap ones are steel or fabric on a smaller footprint. Building this design costs about $433 in materials, in 2x4 framing and welded wire you can resize to your wall and your cats.

Ask your building department first. The model code's exemption for small structures covers detached buildings only, so a catio fastened to the house is their call; HOA rules and setbacks can apply too, and it must never cover a bedroom's emergency escape window.

Sizes to compare

All 9 free catio plans

Your catio, your cats

Make the window box yours.

Change the size, the roof, the door, the shelves and the number of cats. The space check, the mesh, the snow check and the materials list follow every change. Free, no account.

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Builder's plan
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A pine window box catio on knee braces under an open window, two cats inside: a catio like this oneIllustration