How to build a fun cardboard fort

Photo of my son crawling through a cardboard tunnel with a red balloon under his chin. His sister is visible in the background sitting in a cardboard chamber.

My son crawling in a tunnel between two watermelon bin chambers. A glow-stick is taped above each tunnel entrance.

In this installment we discuss spending 8 to 24 hours converting a room in your home to an awesome cardboard fort. I’ve done it three times, for my daughter’s 3rd, 5th and 6th birthdays.

Here we go.

Step 1. Thank your fort sponsors

Thank you Ray’s Food Place, the gracious grocery store chain in California and Oregon, that made our fort’s awesomeness possible. (More about that below.) You don’t need a blog, but you do need to be visibly appreciative because most stores won’t help parents acquire boxes.

Step 2: Obtain gobs and gobs of boxes

Fridge boxes — These are the holy grail in fort building. If you can score one, you have a room ready to go. If you score several boxes, you have an over-sized tunnel super fun land.

Most stores won’t save them for you, and most fridges aren’t shipped in boxes anymore (just foam and plastic wrap). Try calling a company that is contracted by a large impersonal retail store to do home installations. Unless you have a huge truck bed, you will need to cut the box on its long edge and fold it into the bed, then tie it down. There are no fridge boxes in today’s fort.

Wardrobe moving boxes — These make great tunnels. They are roughly 24″ square by 48″ long, big enough for even an adult to crawl through. The box has one open side you tape into place to complete the tunnel. If you open the flaps and tape them together, you can add up to an extra 24″ to the tunnel length.

Watch Craigslist and Freecycle for offers of moving boxes. Or, buy from a local moving truck rental company, or its corporate website.

Photo of my daughter peeking out a doorway cut into the bottom of two watermelon bins stacked on top of each other. A cardboard tunnel attaches to the bins and other cardboard structures are visible.

Photo of my daughter peeking out a doorway cut into the bottom of two watermelon bins. During the party, one of the kids found a jump rope and used it to make a drawbridge, looping the rope under the door and around hand-holes on both sides of the door -- making it possible to slam the door shut whenever I banged on the wall and yelled that I was coming in. Yes, I digitally added the Ray's Food Place logo on photos featuring their wonderful watermelon boxes.

Watermelon and pumpkin boxes – Stand one on top of the other and you have a really cool octagonal room. Cut a couple of doors in the bottom box and it can become a great secret room hidden in the middle of a tunnel. Cut peep holes higher in the box for looking out.

These boxes are fantastic. They’re just so unusual that they become a focal point for the kids to crawl into, stand up in, and look out the peep holes.

Be careful prepping the boxes. You want two identical boxes (from the same produce company) so they connect well for taping. Secure them with a massive amount of duct tape inside and out. If the top box should ever get pushed askew from the lower box by rambunctious kids, you want enough tape to hold that sucker on there and keep your kids safe.

Photo of three kids looking up laughing as a photograph is taken of them during my daughter's party. They are inside a watermelon box chamber.

Looking down the skylight of a watermelon bin chamber. The room's capacity is eight 5-year-olds and one 2-year-old, but it's a cramped sardine-tin mess. It's a good thing the fire marshal didn't show up.

The bottom of a watermelon box has four protruding folded edges and a big rectangular hole in the middle. When stacked together as a room, you have skylights on both ends. I covered the bottom skylight with a thick sheet of taped-down cardboard. I left the roof skylight alone.

Obtain the boxes from a local grocery store. If you need many boxes that the store will need to set aside for you, speak to the store manager. If you need just 1 or 2 boxes, try an employee working in the produce section.

So, this is a big shout out to Ray’s Food Place which set me up with five watermelon boxes. The store went above and beyond the call, storing these boxes aside in a loft (accessed by a ladder no less) until I could pick them up. Someone at Ray’s has burly muscles, no doubt. The boxes barely fit in my station wagon one box at a time after we’d carried them to the loading dock at the back of the building.

Going local totally beat my experience two years ago when a watermelon box from a far away store went flying out of the back of a borrowed truck on the highway.

You’ll have better luck getting boxes from a store like Ray’s, one that still has a measure of small town feel to it, where the employees actually give a damn about the customers instead of viewing them as a necessary nuisance. Yeah, Safeway, this is me sending bad vibes your way.

Roof and pillar boxes – Futons and bedroom set boxes seem useless because they very long, but very shallow, often no deeper than 12 inches. Think of them as roofs.

Find a bunch of small, identical boxes to tape together as pillars, then attach them to a roof to create a small room. Selectively wall in the room using more of the smaller boxes, or staple scrap fabric to the roof and drape it to the floor to make curtains.

Only make curtains where it’s impossible for kids to exit, such as when the room butts up against other parts of the fort. Because kids run through the fort, it’s critical that nothing obscures the view of an exit; otherwise kids will run into each other going in and out.

Find futon and bedroom set boxes at a furniture store, ideally an independently owned store that is capable of being sympathetic to a parent in need. Boxes are normally cut up and tossed in a recycling bin at the moment they are unpacked by the store. Ask when they receive shipments and whether you can be there to grab some boxes.

Find pillar boxes on Craigslist and Freecycle, seeking 12″ x 12″ moving boxes. If you’re lucky, find a retiring eBay seller who has a cache of postal service boxes that were ordered for free via the USPS website that the seller no longer needs.

Photo of my daughter sitting inside a room, looking out through a doorway.

Two different halves of Weber BBQ grill boxes obtained from a local hardware store, topped with a half box from our new bedroom set.

Other huge, but weak boxes – Dishwasher, oven and barbecue boxes are big, but often made from flimsy material… too short for a tunnel and too small for a room. Experiment with them. We converted two halves of two thicker BBQ boxes into side walls and tossed a half of a futon box on top as a roof. It was a super-fast room to build, connected with box rivets (see below).

Step 2: Equip yourself

Box cutter – Needed to create doors and windows and sometimes to make two boxes fit together better. Be sure your razor blade is new.

Packing tape – You’ll need a lot of it for connecting boxes and taping edges.

I go overboard taping every exposed edge of a box when it’s going to come in contact with a hand, knee or foot to avoid paper cut-like accidents.  In the pandemonium of a party, I fear someone getting their hand caught and crunched under a box flap or something. Taping adds hours and hours to your build time.

Duct tape – It’s needed for serious safety issues, such as connecting watermelon boxes. A hardware store sells duct tape in several levels of strength. I suggest using stronger-than-usual tape for the watermelon boxes.

Mr. McGroovy’s Box Rivets – These rivets are specifically made for cardboard forts. Pop a pilot hole with a screwdriver or power drill, and then insert a rivet to connect two boxes. They’re most easily installed with a helper. Often, I’m lying inside a box pushing a rivet and my wife is on the outside connecting the other half.

Due to my desire to have every loose edge of a box taped down for safety, I have limited applications for box rivets. When appropriate, rivets are a huge time saver. They come in two sizes (labeled for fridge boxes and moving boxes). Buy some of each type because you’ll find your needs change based on what you’re trying to do, not necessarily the box type in front of you.

Overview photo of the cardboard fort with many structures visible.

The whole fort crammed into our front room. The angled box at right was a leftover extra propped up for show. The green strands over fort doors are dollar store hula skirts I unfurled.

Another viewpoint angle of the cardboard fort.

Another viewing angle showing the other side of the fort.

View of the back end of the fort near the drapes revealing an otherwise obscured tunnel leading to a watermelon box chamber.

This is the backside facing our front window, obscured in most photos by the big cardboard roof/room at left.

Step 3: Clear the room

Move all furniture possible out of the room. Consider whether you spend most of your time in your living room or your family room. Build the fort in the lesser-used room.

After the party, the more the fort impacts your daily routine, the faster you’ll want to demolish it. Conversely, the more time you spent building the damn thing, the less you’ll want to tear it down quickly.

Step 4: Design the fort

When the kids are in bed, start moving boxes around and brainstorming with your spouse or other construction partner regarding fort configuration. Plan on this taking several hours because you’re lifting boxes around and testing out different ideas. You’re not working tomorrow, right?

Give yourself two nights to build the fort if you do lots of taping instead of box rivets.

Build two or three entrances to the fort. Kids running out, around and back inside again becomes part of the design.

Plan for the kids to beat the hell out of the fort, another reason I tape every part of the fort together.

I favor O-shaped forts that have a large pillared-room in the center and an exposed area so adults can see into the fort and know what’s happening.

For 2-to-4-year-olds, consider how you will access the fort if a child begins crying inside. It helps to have a heavy freestanding room (that the kids can’t move during play) that you can pull out to access most of the fort fast in case a child has a problem.

Carpets vs. hard floors

If you have a choice, build the fort over carpet. Crawl-running through forts takes its toll on knees, especially adult knees, when pounding away on a hard floor.


At age 4, balloons were a big hit. After the initial 30 minutes of excitement died down, I began tossing balloons into the fort to liven the scene. For the most fun, introduce balloons secretly by tossing them into the watermelon room’s skylight.

At age 5, balloons backfired. Kids used the balloons to hit each other in the face.

Glow sticks

I taped glow sticks above the doorways of each room and tunnel exit to make the environment less imposing to potentially scared kids. Use the thicker glow sticks sold in single units. The super thin glow sticks sold in packs of five at dollar stores have a tendency to break and leak.

Alternately, give each child a glow stick to hold.


Don’t bother painting the fort to look like a castle or other structure. That’s totally your thing. The kids don’t care. The fort can be the ugliest thing in the world and they’ll still have a wild time.

Mom vs. Dad soliciting for boxes

Consider whether you or your spouse is more persuasive, then have that person do the asking for boxes at a store. Experiment with whether you get better results by bringing your kid with you when you ask.

For Craigslist and Freecycle, Mom should respond to ads. My experience is that if the person giving away an item is female, she is more likely to give that item to another woman. I see it as a safety issue… if you’re home alone during the day, you’re less threatened by a strange woman visiting your home than a strange man. Also, in your e-mail indicate when you can pick up the boxes, and be prepared to do it the same day because Freecyclers want their giveaway items gone as quickly as possible.

Photo of my son walking through a cardboard tunnel with his back hunched as he clutches a red balloon. He is visible through a doorway cut into the middle of the tunnel.

A close-up view of the torn bottom lip on a mid-tunnel entrance. It was blown within the first 10 minutes of the party. Next time, I'll cut the door to the bottom edge of the box.

Photo of my daughter crawling through a cardboard tunnel as seen through a door cut into the tunnel.

With 18 kids at the party, I made extra exits such as this one in the middle of a tunnel. In the foreground, you see a room made from pillar boxes. This sort of wide open area was important with so many kids. I lobbied my wife to hold two parties on successive days, dividing kids by demeanor (quiet vs. rambunctious) but she always nixes the idea. The size of the party this year was due to my daughter entering kindergarten -- suddenly so many important friends to invite. Sigh.

Photo of a red balloon in the air obscuring my son's face as he crawls through a tunnel, as seen through a doorway in an adjoining cardboard chamber.

My son crawling out a tunnel into a watermelon bin chamber, pushing a balloon ahead of him.

The fort dominated our front room for more than six weeks, but never achieved the same level as fun as during the party. Forts need a sizable number of kids to build excitement.


9 Responses to “How to build a fun cardboard fort”

  1. observer says:

    that’s sooo cool. another box to use are those your kitchen cabinets come in. as a kid we had a bunch of new cupbords put in, and the boxes were fantastic. the long ones made great rocket ships. i have an affinity to cardboard forts. i always loved them as a child.

    July 28th, 2010 at 4:07 pm

  2. Nadia says:

    It might be easier to just dumpster dive at the loading dock of a big hardware store. They have dumpsters that are full of only boxes, so no worries about hygiene, and to be honest I’ve never been worried enough about stealing someone’s rubbish to ask them first.

    July 28th, 2010 at 10:04 pm

  3. Shannon says:

    Awesome kids party idea. How far in advance did you begin trolling for boxes?

    July 29th, 2010 at 8:44 am

  4. AJ says:

    Nadia, my concern with dumpsters is that boxes are usually carved up before they’re placed inside. Bigger stores lock their dumpsters or place boxes in a compactor right away. Some stores have offered to let me dive in, but I’ve never been present when good boxes are there.

    Shannon, I’ve had the wardrobe boxes for 3+ years, stored away after each party. Assuming you have space to store boxes (another huge issue), on your first time, I suggest beginning to look at least 6 weeks in advance. Your party invitations might go out as early as two weeks before the birthday. You need to be certain you can pull off the fort before you send the invitations.

    Fridge and futon boxes may not be immediately available if a store doesn’t receive regularly weekly shipments.

    July 29th, 2010 at 10:12 am

  5. Mocha Dad says:

    This fort looks like it would provide the kids with hours of fun. I’d love to build one myself, but my wife would kill me for taking up so much real estate in the house.

    August 3rd, 2010 at 12:03 pm

  6. MIdge says:

    This is so awesome! Now that I have a start with some of your boxes, I’m definitely getting more to build a fort once the rains come.

    Thanks for all the tips/ideas!

    August 3rd, 2010 at 8:46 pm

  7. Jed G says:

    I discovered that WalMart would give me boxes, but they compact them twice a day here (at something like 8am and 8pm) so you have to hit them at the right time.

    August 5th, 2010 at 8:20 am

  8. AutumH says:

    Awesome!! I just might have to do this for my next son’s b-day! Or even just for us to play around with on a rainy day.

    August 20th, 2010 at 7:45 pm

  9. Emily says:

    really cool forts im going to try making a fort with ceral boxes and such i wonder if that will work

    February 20th, 2012 at 8:11 am

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