Introduction: Kids Indoor Fort/Treehouse

Hello fellow woodworking enthusiast,

I found inspiration for my latest creation on Pinterest for an indoor treehouse. I wanted to repurpose cedar wood from my old fence. My kids have been asking me to build them a treehouse, so I thought this might be the best way to utilize this old material and be a fun place for the kids inside during this COVID-19 stay-at-home order.

You can make this as fancy or as rustic as you want. If you feel like you may not have enough skills to do this, you are wrong. Your kids will love it no matter what it looks like. Even if its not square or level, your kids will appreciate what you make them. It's a lot of fun to let your imagination run wild like a kid! Try to think like your 4' tall again. Follow me along as I walk you through the steps.


Power tools:
- Miter saw
- Circular saw
- Drill
- Impact driver
- Jig saw

- 18 ga brad nailer
- Air compressor
- Kreg drill bit set
- Clamp for Kreg bit set (I used a 4" C clamp)
- Countersink drill bit
- Wood clamps
- Sliding T Bevel
- 2' level
- 1' level
- Hammer
- 6" speed square
- 2' framing square
- Long straight edge
- Tape measure
- 2" Kreg screws
- 1 5/8" hex head wood screws
- 2 1/2" hex head wood screws
- 1 1/4" 18ga brad nails
- 1 1/4" wood screws
- 1 1/2" 18ga brad nails
- 2" 18ga brad nails

- Safety glasses/googles
- mask/respirator
- hearing protection

- Table saw
- Carving tools (draw knife, wood chisel)
- Router
- 4' level
- 1' framing square

Step 1: Sketch/Material List

I start all of my projects with a sketch drawing. I use this to show my wife and kids what it might look like, and a tool for a material list. I may redraw my ideas several times until I get the look that I want. Luckily, there was an indoor treehouse that I found on Pinterest that I used as a rough idea of what I wanted, with a big cost of $9,249! I knew I could build this for around $200 using the old wood that I already had laying around the garage. After my initial sketch, I started to get measurements for my material list. I had an old twin mattress from my sons room that I wanted to use in the upper portion of the treehouse, so I used it to decide how big the inside dimension (ID) of the fort needed to be, as well as the outside dimension (OD).

Lower level material:
- Corner post: 4"x4"
- Horizontal supports: 1"x3"
- Bed frame support: 1"x4" and 3/4" melamine board
- 3/4" cedar pickets. (I'm not going to put lengths because I had to build my treehouse very specifically to the height in our basement. I measured my daughters head height while she was sitting on the mattress and added a couple inches. I then added the mattress thickness in order to get the upper level height dimension to the bottom of my floor joist. To calculate the length and width of the treehouse, I added roughly 12" outside the mattress for ease of making the bed and extra room for my kids' feet as they sit on the edge of the mattress. I added dimensions to the sketches so you have approximate dimensions for all the materials.

Upper level material:
- 1"x3"(used to build a mini stud wall)
- 3/4" cedar pickets
- 3/4" plywood for roof
- cedar shake shingles

- 4"x4" vertical frame
- 1"x4" horizontal rungs (I fastened them with 2" Kreg screws from the bottom)

- 3/4" cedar pickets
- 1"x4" for horizontal supports
- 1"x3" for Z pattern
- 1 1/4" wood screws
- 4ea. 3" door hinges
- door latch

Step 2: Build Bottom Base

I had some old rough cut pecan wood laying around that I used to build the base. Additionally, I had been saving an old cedar tree that I wanted to use as the main corner post. Luckily it was the right length to screw to my floor joist to strengthen the base and stabilize the structure. If I wouldn't have been using this old rough cut pecan and cedar post, I would have used four post that would have went from floor to ceiling. It would have been easier to build, but I really wanted to use this material because it added to the look I was going for.

To start, I cut the three corner post to the length I needed. I wanted to distress them so I used a draw knife and chisel to "rough up" the wood and distress it. Then I very lightly stained it to give it a little different color and make it look older. I knew my basement floor wasn't level, so I took the corner post to the basement where I was going to build the treehouse. Then I used my straightedge and level across the top to decide which one was too high. If you hold your level and have a gap on the left side, this means you need to cut the right leg. Then I labeled all my legs on the bottom using cardinal directions (NW, NE, and SW). The SE post was my cedar post. Once my legs were cut and level, I cut the horizontal supports to length. I then labeled the ends that attach to the post (ex: N top, N bottom). After I labeled them, I used my Kreg drill bit set to pre-drill the screw pockets. I didn't like how close my Kreg jig put the holes on the 1"x3" horizontal supports. My jig has 3/4" spacing between the screw holes. So I drilled one hole 3/4" from one edge, then slid the jig over and drilled the other hole 3/4" from the other edge of the board. If I just centered the board with my jig, then my holes would have been 1 1/8" from the edge's. This took more time because each board required 4 holes and me handling the jig 4 different times.

After I predrilled the horizontal supports, I took them down to my basement and installed them. One of my corner post was bowed pretty bad and had a large piece of the corner missing, so I had to use a scrap piece of wood in the corner to fasten the horizontal board to the top.

I knew I wanted a 1/2" reveal of the corner post, so I fastened the horizontal supports 1 1/4" from the outside edge. This is 1/2" reveal and 3/4" thick siding. For the horizontal supports that touched the concrete wall, I was going to put an X brace behind the horizontal boards, but after I screwed the horizontal boards to the corner post, it was really sturdy and I didn't think I needed them. That is why you see a gap on the back of the supports that are against the concrete wall. For this treehouse, I knew I wanted to install a door on the bottom. This is why I don't have a complete horizontal support on the bottom where the door is. I used the Kreg jig to fasten the vertical boards for the lower door.

After the base frame is built, I attached the 3/4" cedar pickets with an 18 ga brad nail gun and 1 1/4" brad nails. I used this length because the pickets are 3/4" and the horizontal support are 3/4" which adds up to 1 1/2", so I used 1 1/4" brads so they wouldn't poke through the back side. I used three on top and three on bottom for each picket and sometimes more if they were split or bowed. To cut the cedar picket around the cedar tree post, I took measurements every one inch to get as accurate of a fit as possible.

I then, cut 1"x4" pine boards to bridge across the top of the base frame. The length I cut them to was from the concrete wall to the ID of the lower cedar pickets, this way my top layer cedar pickets would be flush with my lower layer. I spaced the 1"x4" boards with a gap width of 3 1/2". I fastened these into place with 2ea 1 5/8" screws on each end. Be sure to pre-drill the pine boards because they like to split on the end. Next, I installed the 3/4" melamine decking that the mattress will sit on. I started off by putting a 1 5/8" screw on the outside edge on every other board and one screw in the middle, in line with the outside edge screws. I noticed the 1"x4" boards that didn't have a screw were not touching the melamine board when I looked underneath. So I ended up putting a screw in every board down the middle. You have to use the countersink bit to pre-drill the melamine before you screw into this material, because it is so dense. After the decking was all screwed on, I had my wife and kids get on top and move around while I checked underneath on how stable the base was. With all the cedar pickets, 1"x4" pine boards, and melamine fastened together, it was extremely stable and didn't move around at all. I was really surprised.

Step 3: Build Top Portion

Next I built the upper framing directly on top of the melamine board. I used 1"x3" pine boards as studs for the upper portion. I didn't worry about the spacing of the studs being on 16" centers since the wall is so short. I was only going to attach the cedar pickets on top and bottom anyways, so the stud centerline doesn't matter as long as you have enough to give the wall some strength. IMPORTANT NOTE: Ensure you measure the mattress cross measurement of the width to make sure you can put it through the door opening. (bottom left to top right while looking at the end of the mattress) Then make your door just a couple inches wider to make sure you can get the mattress in and out. I roughly measured my mattress and thought a 21" door opening would work based on that width and the height I had predetermined. So I made the opening 24" wide just as extra precaution. When I later installed the mattress, the opening was't large enough. I had to grab the edges of the mattress and squeezed them together to shove it through the hole. It was really hard, but I got the job done. Once it was in, I wasn't going to remove it unless I absolutely had to. So I covered it with an old sheet to protect it while I finished the project. I kept the height of the stud wall 2" from the floor joist. This allowed me to screw the "stud wall" together on the ground, then stand them up and attach the stud wall to the melamine board. You have to use the countersink with these screws as well since they are going into the melamine board. Ensure the wall is plumb (level) with a level. I attached the stud wall that was floating to our house with small pieces of wood to the sill plate. Next attach the cedar pickets to the stud wall.

Step 4: Build Ladder

After the top was complete, I built the ladder. This could be accomplished either now, or after the roof is complete. I made the OD of the ladder the width of the opening, but you can make the ID of the ladder to the opening of the door. Just don't make it too wide or it will be flimsy when you walk up and down the rungs. I wanted it sturdy enough to hold an adult.

To get the angles right, I have attached a drawing of how I did this. I forgot to take a picture while I was building this. I used a 1"x4" board for my vertical straight edge and my metal straight edge on the bottom. I then used my framing square to square them up and make marks on the concrete once you get them square. I knew the height of the ladder and how far away from the wall I wanted it to land. I marked those on the 1"x4" and the straight edge. Then lay the 4"x4" directly and carefully across the top landing on your marks. Look directly over the top to make your marks. Use the bottom angel as the angle for your rungs. On a kid ladder, spacing is around 10". Make a duplicate for the other side.

I routed a pocket for my rungs to set in, but they can be cut to the ID and use just screws to hold them in place. The pocket just gives additional strength.

Step 5: Build Roof

As you can guess, the next step was to install 3/4" plywood for the roof. I made a drawing of the floor joist edges so that I could make it fit as precisely as possible, but not make a bunch of trips up and down the stairs. Use a 2' framing square and tape measure to get these measurements accurately. The square was used to see if the floor joist were square. One of my joist was really twisted and I had to cut the plywood at an angle. Be careful not to make it so tight that it doesn't fit. I measured tight and drew them that way and when I cut the plywood, I put my saw blade on the outside of the line. This worked perfect and it only required a few minor trims to fit into place. I used 2" 18ga brad nails to attach it to the top of the stud wall. I cut 1"x1" blocks and 1 1/2" brad nails to attach the block to the floor joist, then came around to the outside of the treehouse and nailed the roof to the block. I had to have help from my wife to hold the plywood while I nailed the blocks in place.

The other hard part was cutting the tiny fill-in piece around my cedar post for the roof. I really wanted shake shingles for the roof because I love the look, but they are really expensive. I found that they were cheaper at my local lumber yard verses the big box stores. I ended up negotiating the price because they had some old and unpackaged pieces laying around in the back of their building. I calculated how many I needed based on the total square foot of the roof. I needed roughly 20 square feet of shingles. I figured this without removing the area of each floor joist. I used this as my "extra buffer". I was able to get this for $50 instead of $84. I just had to rinse them off and set them out in the sun to dry before installing them. I nailed these into place with 1 1/4" 18ga brad nails and was careful not to let them go through the plywood on the back. Otherwise the kids might hurt themselves on the brads that stick through.

Step 6: Build Doors

The only thing I had left to build were the doors for the top and bottom. This is optional, but the kids really wanted doors. For the top, I built a half door with a latch to add additional safety for smaller children. For the bottom, the kids wanted a full door so they could be completely enclosed on the bottom and play with their legos.

To build the doors I had to find a couple good pieces of wood without large cracks in the grain of the wood. I wanted to leave the natural old edges for the top to give it some character. Then I had to rip the outsides board to the proper width. Next I measured and cut 1"x4" pine boards to put on top and bottom. I used 1 1/4" wood screws so they wouldn't penetrate through. Next I laid a 1"x3" board across the top of the 1"x4" boards. This is captured in the pictures above. Next I look directly over the horizontal boards to make my marks. When you are making a Z pattern, there is a proper way to fabricate this. You want to attach the lower outside portion of the door to the hinge. This gives support to the door and keeps it from sagging. When I went to attach the door, I used some old scrap wood and one lego piece to level my door and screw it to the frame. Ensure you pre-drill the holes for your hinges. Otherwise it may split and you will lose strength in those screws.

I added a latch so the kids could keep the door shut from the inside and lock their furry and nosey pets out. A different kind of latch could be built with a dowel rod that goes through the door and parallel arms that would drop down over the door frame. This would be like a chain link fence gate, and could be opened from the outside if your kids are younger and you worry about them locking themselves in. I added a drawing of what this kind of latch would look like. Additionally, you would have to add a small block of wood on the inside or outside that the latch would rest on. Without this, the door latch would fall down and wouldn't latch the door.

Step 7: Finish Work!

Now all you have to do is decorate. You can be as fancy or minimalist as you want. The kids wanted to string Christmas lights in the top. I bought some LED tape lights from WalMart for the bottom. These were inexpensive, easy to install, and had a remote to change colors. Our kids really liked it.

If you have smaller kids, you may want to add a vertical and horizontal thin board to the windows (in the shape of a plus sign), to keep them safe.

I decided to seal the wood with a water based polyurethane to protect the wood and keep the kids from getting splinters. I chose a satin so it wasn't too shiny. I also chose the water based polyurethane in order to reduce the fumes indoors.

I had some old scraps from cutting out signs on a plasma cutter that I used to screw to the fort for decoration.

Now your kids can enjoy themselves inside during the winter, rainy days or during these quarantine times. They love watching movies and doing their homework up on the top level. Down below, they have stocked a mini fridge with their favorite drinks and put some snacks down there as well.

Good luck and happy building! I had a blast building this for my kids.

Woodworking Contest

Participated in the
Woodworking Contest