Architect Ben Pell remembers precisely when his two kids started building pillow forts, and it began with their Lego obsession: “There’s a moment when they go from seeing objects as solid to seeing things with an interior. First, they built towers by stacking, but then they start thinking about how the men can go inside. It’s a simple function of play, but it’s a mental switch. They weren’t interested in making things they could inhabit until their Lego men could inhabit things.”

Of course, it helps when your dad designs stuff like this for a living. Here are tips on pillow fort building that Pell has learned the hard way: By giving his kids free reign over the living room.

Think Like An Architect

• Sort your available pillows based on which ones are best for walls and which ones are a good for laying on inside the fort.
• Identify which pieces of furniture you’re going to work with.
• Figure out where the opening will go.

“Kids, left to their own devices, pile up pillows and then figure out how to get inside. Or, they’ll build it around themselves and then they can’t leave without destroying it.”

He’s a lazy old lab, so sometimes we just tuck the sheets under him while he’s sleeping. They make good weights.

Choose From The 3 Basic Fort Types

• Buttress Fort: Furniture is used like a primary retaining wall and the fort is built off of that.
• Tunnel Fort: Furniture – usually the couch – is built into the fort itself, which runs the length of the furniture.
• Compound Fort: Multiple pieces of furniture are connected with a series of “rooms.”

“Tunnel forts are usually too small to get into, so that’s what my kids build if they want their own little fort. With a buttress or compound fort, you’re not limited by the furniture, but you might have to move things around a little bit to create space.

Become A Roofer

• Use sheets instead of blankets, which are heavy and more likely to collapse.
• Identify what you’re going to use as ballast weights (shoes, stacks of books and coffee table legs all work well); then wrap the sheets over the top of the pillows and pin them to the floor using the ballast.
• If the sheets are lightweight, use layering to make the roof more substantial.

“We try to make sure the dog isn’t in the room, because if he gets interested he knocks things over. But he’s a lazy old lab, so sometimes we just tuck the sheets under him while he’s sleeping. They make good weights.”

Hang The Door And Say Goodbye

• Small sheets can be used like tent flaps.
• Properly sized pillows can be used like boulders

“Once they’re inside the fort, they don’t want to be seen – it’s a world in and of themselves. It does take over the living room and it’s often unclear where the fort begins and ends. I wind up dealing with a tension between wanting to keep the house clean (the OCD Modernist in me) and making things that last (as all good architects should do).”

This article was originally published on Sep. 9, 2015