How to Build an Indoor/Outdoor Kids’ Fort With Tent Poles

Determine Pole and Tarp Size

The size of your tarp and poles determine the size of your final structure. Consider the smallest room in which you plan to set up the fort when selecting your materials.

Floor Tarp

• Set your desired width and depth, and find a ground tarp or other flooring that hits your dimensions.
  • I used this 35-in. x 83-in. ultralight tent ground tarp to create a narrow structure that will fit on the floor between beds. It also matches the shape of a yoga mat, which makes a handy padding option on wood floors.
  • DIY Option: Sew loops or press grommets onto the corners of a robust picnic blanket.

Cover Tarp

• Covering material depends on what you have on hand and want you want to achieve. Try a simple rain-resistant tarp or a light UV-resistant sheet. Or go natural from here and use some scavenged sticks and branches to make a wind-breaking lean-to.
  • We used an old Boy Scout tarp (10 ft. x 10 ft.), but any large tarp or cloth will do.
  • Bonus if your tarp has eye holes. You can hook those over the tent pole ends, for extra sturdiness.
• Sizing your cover tarp will depend on how long your poles are. If you get a tarp that’s at least as wide as your poles are long, you should be able to cover any configuration.
  • With my design, a 10-ft. tarp was just barely wide enough to cover the arc created by my 11-ft. poles.

Poles

• Lay out a long, bendable object or string on your floor to eyeball an approximate pole length. You could also use free modeling software like SketchUp to get the measurements.
  • I used these 11-ft.-long aluminum rod tent poles.
• Prefer math? Read on for a couple of additional, more exacting methods. If not, skip to Step 2.

Method 1: Circumference Calculation

If you’re going for an approximately constant-radius arc — picture a perfect circle, halved — calculate the circumference of a circle, to represent the circle passing through the corners of your ground tarp. Then divide it by two to get desired pole length.

To calculate, you’ll need to find the diameter of the circle, which is equal to the corner-to-corner distance of the ground tarp you chose. If you’re ordering one and unable to measure it in person, use the Pythagorean theorem to calculate the diameter: Tarp length squared + tarp width squared, then take the square root of the result. Example using a 35-in. x 83-in. ground tarp:

35 squared (1,225) + 83 squared (6,889) = 8,114

Square root (√) of 8,114 = 90 (your diameter)

Desired pole length is then found by multiplying pi (π) x diameter to get circumference, and then dividing it by two. In this case, that’s: pi (π) x 90 / 2 = 141.37 inches, or about 11.75 feet

Going slightly shorter and using a standard 11-ft. pole would result in a structure shape with a slightly lower peak than a perfect half-circle.

Method 2: Arc Calculator

To achieve flatter or taller arc shapes — picture an oval halved — you can use an arc calculator to calculate arc length, a.k.a. your desired pole length. You’ll need to set two inputs to enter into the calculator:

• Arc Width in this case is the distance, corner-to-corner, of the floor tarp size you chose. Follow directions in Method 1 to calculate.
• Arc Height is the height you want the center peak of your structure to be.
  • Tent poles don’t necessarily arc in a perfectly uniform way, but this will give you a decent approximation to work with.

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Establish the Base

• Scout a sufficiently flat and preferably soft surface, free of bumps, sticks or rocks, which could be uncomfortable or cut your flooring material.
• Lay out your ground cloth or tarp.

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Connect Poles

• Assemble your tent poles to make them straight.
  
• Insert one end of each pole into neighboring corner eye holes on one side of the ground tarp.
• Lay the poles down on the ground cloth, crossed over each other.

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Set Up Poles

• Put your electrical tape or twist-tie in your pocket so you’re ready for the next step.
• Bend the poles upward into an upside-down U shape, and insert into the eye holes on the opposite corners of the ground cloth.
  • This step can be tricky! You can do it in one movement by stepping your foot on the ground cloth to hold it tightly in place, grabbing both tent poles near the ends and pushing them up, with tips pointed straight down on each side of you, before sliding them straight into the eye holes on your left and right.
  • For interior use, if you have scratch-sensitive floors, lay down an area rug or invest in some right-sized rubber feet for the tent pole tips.

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Secure Pole Crossover Point

• Center the top crossover point over the middle of the ground cloth.
• Affix the tent poles together at this point with electrical tape or a grippy rubber twist tie.
  • This point is key to structural stability, so whatever you use just make sure the poles can’t slide!

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Add Cover Material

• Drape your covering material over the top of the tent pole structure and move it around until you’re satisfied.
• Focus on getting two neighboring corners of your covering aligned with the bottom of the tent poles that you want to be the open entrance of your kids’ fort.
• If your cover material has eye holes, loop these onto the pole ends.

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Secure Cover

Here are some ideas for clips to secure your cover to the tent poles:

• Clothespins: For a light covering or light-duty/short-term use.
• Tent Pole C-Clips: It may take some searching to find a size that matches your chosen tent pole diameter.
• DIY C-Clips: Something with slotted plastic pipe, similar to what we did with our indoor fort project, or perhaps on old pen or marker barrel would do the trick.

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Stake It Down (Optional)

• Use ground stakes outside for stability against nature and whirlwind kiddos.
  • Stakes can also help extend your fort, as pictured above, if you have the tarp material to do so.

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Customize

• Encourage kids to add the finishing touches, such as a pillow nest, homemade pennant banner or a hanging lantern affixed to the poles overhead. Or talk through what you’d bring on a camping trip, for a practice version of the real thing! You can even practice playing family camping games together.

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