Quick answer: For a multi-cat cardboard castle, use three to five medium moving boxes, give every room at least two exits, cut doorways about 7 inches wide and put a separate lookout on each tower. Glue boxes with PVA or flour paste, not tape, and set it in an open area so no cat can be cornered.
A cardboard castle is one of the best one-hour projects for indoor cats: boxes are free after a move, cats love hiding and climbing, and nothing is permanent. With two or more cats, though, the design has to change. A single doorway becomes a guard post, and a lone top perch becomes something to fight over.
This version is built for shared use. It follows the basic one-hour moving-box castle steps but changes the layout so every cat has an escape route and a place of its own. For multi-cat behaviour in general, International Cat Care's guide to multi-cat households is worth reading first.
What changes with more than one cat
Cats in the same home often get along best when they can avoid each other. Rooms with one way in and one way out let one cat block another. Tunnels that are too narrow force cats to pass nose to nose. A single high perch lets one cat control the whole structure. The design below fixes all three.
- Two exits for every enclosed space.
- Doorways wide enough for two cats to pass, around 7 inches.
- At least as many perches as cats, at similar heights.
- An open ground floor with no dead ends.
Materials and time
| Item | Qty | Note |
|---|---|---|
| Medium moving boxes (about 18 x 18 x 16 in) | 3–5 | Clean, dry, no strong smells |
| Box cutter + spare blades | 1 | Fresh blades cut cleaner edges |
| PVA glue or flour-and-water paste | 1 bottle / 1 bowl | Safer than tape for chewers |
| Wooden skewers or dowels | 6–8 | Pin boxes together |
| Pencil and a plate (7 in) | 1 | Trace round doors |
Allow 15 minutes to plan, 30 to cut and assemble, and 15 to tidy edges. Glue needs a few hours to dry before the cats move in, so build in the morning and open the castle in the evening.
Lay out the floor plan
Place two boxes side by side as the ground floor, with their open tops facing down. This gives a long base about 36 inches wide that is hard to tip. Cut a door at each end and one in the middle wall between them, so cats can run straight through.
Stack one box on each base box, offset by a few inches so each tower has a ledge. The ledges become separate lookouts. If you have three cats, add a third tower on a box set slightly away from the main castle, linked by a short ramp of flattened cardboard. Spread-out lookouts reduce competition.
Cut doors and windows the right size
Trace a 7 inch plate for main doors and cut them with the box cutter, keeping the bottom of each door at least 2 inches above the floor so the box keeps its strength. Windows can be smaller, about 4 inches, and are great for paw play between cats.
Every upper room needs two openings: one door into the tower below and one window or door out to a ledge. Trim any frayed edges and fold back flaps so there are no sharp corners at eye level.
Join boxes without tape
Packing tape is tempting but cats chew it and the adhesive can stick to fur. Instead, run a line of PVA glue or flour paste where boxes touch, press them together, and push a few wooden skewers through both walls to hold them while the glue dries. Snip the skewer ends flush. Our safety guide to tape, ink and staples explains which materials to strip off moving boxes before you start.
Remove all staples, plastic labels and heavily printed panels. Plain brown cardboard is the safest surface.
Introduce the castle to the group
Set the castle in the middle of a room, not against walls in a corner, so cats can approach from several sides. Toss a few treats in different rooms and on different ledges at the same time so no cat has to compete. Let each cat explore on its own terms.
Watch for one cat sitting in a doorway and staring at another. If that happens, add another exit or move a perch further away. Some groups enjoy chasing through the castle together; others prefer to take turns. Both are fine as long as nobody is trapped.
Keep it fresh and safe
Cardboard castles last a few weeks to a few months. Check daily for crushed corners and loose skewers, and replace damaged boxes. When it gets dirty or a cat sprays it, recycle it and build a new one. Rearranging rooms every week keeps it interesting.
Looking for more ideas? The cardboard castle hub has variations, building one with kids works well as a family weekend project, and the multi-cat litter layout covers another place where cats need two ways in and out. For compact homes, try the apartment castle version.
Adapting the castle to different cats
Not every cat in a group uses space the same way. Bold cats like high lookouts; shy cats prefer low, enclosed rooms with a view out. Build at least one ground-floor room with a window but no upper access, so a quieter cat has a private den. Older cats appreciate low steps, so add a flattened box as a ramp or step at the base of each tower.
If you have a kitten and an adult, give the kitten small entry holes it can use but the adult cannot. This gives the adult cat a break from constant play.
Common multi-cat mistakes
- Building against a wall, so the back room is a dead end.
- Putting food or litter inside the castle, which creates conflict and mess.
- Using one large box as a single room that only one cat can hold.
- Leaving the castle in a busy hallway where cats have to pass each other closely.
- Adding catnip to only one room, which starts competition over that room.
Most of these come down to giving cats choices. When in doubt, add another opening or spread perches further apart.
Share scent before sharing space
Cats rely on scent to decide whether a new object is safe and who it belongs to. Before the castle opens, rub a soft cloth on each cat's cheeks and wipe it across a few doorways and ledges, mixing the scents. A castle that already smells of the whole group feels like shared territory rather than one cat's prize. Put a familiar blanket from each cat's favourite resting spot in a different room of the castle.
For the first few days, keep play sessions near the castle short and positive. Drag a wand toy past several doorways so cats chase through different routes rather than meeting in one tunnel. If a cat hisses or swats at a doorway, end the session calmly and try again later. Most groups settle within a week once they learn there is always another way out.
What the castle teaches you about your cats
A cardboard castle is a cheap way to learn where each cat likes to rest and play before you invest in permanent furniture. Notice which heights each cat prefers and how they move around each other. If one cat always claims the top, plan for two equal high spots when you buy a cat tree. The DIY cat tree hub and cat-friendly home design ideas can then build on what you have seen.
Watch the castle at different times of day as well. Many groups share space happily in the evening play hour but want separate spots in the morning. Noticing these patterns helps you place permanent perches, beds and scratchers where they reduce friction. International Cat Care's play guidance also suggests short individual play sessions for each cat, which can take pressure off shared spaces like the castle.
Cardboard castles for multi-cat homes: FAQ
How many boxes do I need for two cats?
For two cats, three medium moving boxes of about 18 by 18 by 16 inches are enough: two side by side on the ground floor and one stacked as a tower. Add one more box and one lookout ledge for each extra cat, so nobody has to share the only high spot. Use clean, dry boxes with no strong smells.
How big should doorways be?
Trace a 7-inch plate for main doors, which suits most adult cats, and cut larger openings for big breeds such as Maine Coons. Keep the bottom of each door at least 2 inches above the floor so the box keeps its strength. Smaller 4-inch windows are fine for paw play, and every upper room needs two openings so nobody gets trapped.
Is packing tape safe for cardboard cat houses?
It is best avoided in a castle that several cats will chew and scratch. Cats can peel off strips and swallow them, and the adhesive clings to fur. Pin the boxes together with wooden skewers or dowels and glue the joins with PVA or flour-and-water paste, then leave it a few hours to dry before the cats move in.
My cats fight over the top. What do I do?
Add a second high perch at the same height, ideally on a separate tower or a sturdy shelf nearby, so the top spot stops being a single prize. Give each upper room two exits so the cat below can never be cornered. If one cat keeps blocking the others, spread food, water and litter across different rooms too.
How long does a cardboard castle last?
Usually a few weeks to a few months, depending on how hard your cats play and scratch. Check it weekly and replace any box that is crushed, damp, soiled or shedding loose flaps. Because the castle takes under an hour to build, many multi-cat homes simply rebuild it from the next delivery boxes and change the layout each time.
