Tree Fort Platform

The ‘foundation’ is complete…

This is likely the most important part of the tree fort build. If you don’t start with a good and level platform, it will create issues later.

Tree selection…

At this point, I have already picked the tree. I decided on the red oak that has a 5′ to 6′ trunk circumference, and there are also no branches on the tree for at least 20′. In addition and coincidentally, the tree is at the perfect location in the yard…not directly in view of the neighbors or from inside our house.

Upper and lower beams…

Having selected my ‘rock’ so to speak, the first task is to attach the two lower beams to the tree. The two lower beams run parallel to each other in one direction, then the second set of beams, the upper beams, will run in the opposite direction on top of the lower beams. All (4) of these beams I attached with 1/2″ x 9″ galvanized lag screws. To provide space between the beams and the tree (allowing for growth) I used two 1/2″ galvanized washers on the tree side at each of the lag screws.

My lower beams are 8′ in length, which was a little difficult to handle at times, as I was mounting them by myself. Fortunately, I was able to rest the lower beams on my step-ladder while I figured the exact location for the lag screw. I used a 16d common nail inserted into the tree just to help support the beam while I marked out the location for the lag screw.

Note that the lag screws are purposely offset of the center of the beams width. This was a detail pointed out as high importance in the Black & Decker book. There is a lot to think about when attaching the lag screw, and it depends upon what type of tree you have and what type of tree fort you will build. This is one of the points I was not comfortable deviating from…so I went by the book.

Once the location was marked, I pre-drilled for the lag screw, and used a socket wrench to tighten the lag screw. However, once the lag screw made it’s way into the old growth of the tree, I could not get enough force behind the wrench. A few sore muscles later, and a smack to the forehead…followed by “duh”,  I realized I needed some more leverage. Therefore, I slipped a pipe clamp onto the end of the socket wrench, and was then able to tighten up all lag screws with ease.

I repeated the process attaching the upper beams to the tree. This time I was able to use the lower beams as support while marking out for the lag screw on the upper beams. The most difficult thing to do during this task was keeping everything level. With just one lag screw in each beam, the beams are still able to move around quite a bit. Things didn’t really stop moving until the rim joists and knee braces were attached. This was something of a surprise to me…I thought I had done something wrong when I attached the lag screws. Now I know, this movement is fine.

It might be a good idea to insert some shims during the beam attachment step…this might prevent some movement while the frame is being built. However, I can tell you from experience, it can be done without.

Rim joists & floor frame…

I cut my rim joists to size and then came up with a plan to attach them to the upper beams. I am building by myself, so I had no one to hold the rim joist in place while I nail. I found a scrap of red oak I had lying around in the shop and clamped it to the bottom of the upper beams so as to basically create a shelf to rest a board on. I set one of the rim joists on this board, and nailed it in place using 16d galvanized common nails. I repeated for the opposite side.

The end rim joists were a little easier…I just had to set them on top of the lower beams while I nailed them into the side rim joists. The only difficultly was that I had to counterweight the joists with the joist on the other side as the whole platform would tip in my direction. I filled in the rest of the joists at 12″ on center.

Knee braces…

After completing all the joists, the platform still had some movement. This was a big concern of mine, as I stated earlier in this post, until I attached the knee braces…they really solidify the foundation. To build the knee braces, I cut a 45 degree angle on one end. I set the board on the corner of the platform, and then I measured from the corner of the platform to the tree trying to keep the board at 45 degrees. I used a bevel gauge at the tree side of the board to get the correct angle to use when cutting the board to length. In case you are wondering, none of the boards hit the tree at 45 degrees…too much irregularity in the trunk.

I used adjustable joist hangers to attach each knee brace to the platform. They help to make up for any irregularities, and they help to make great contact of the knee brace to the platform. On the tree side of the board, I used simple joist hangers. Due to the shape of the tree and the slight lean that the tree has, some of the knee braces are longer than the others. There are most likely no two the same length…so don’t cut them ahead of time…each one needs to be custom fit (see photo below).

To finish up the knee braces, I flush cut the top of the knee brace with the top of the platform. I started the decking as you can see in some of the photos, but I’ll leave that for another post…this one is growing far to long.


Tree Fort Kick-off

I would like to introduce the best hideout in the neighborhood…

Yikes! I hope it, and I, can live up to that statement.

I had been wanting to build a playset for my two sons since we moved into our new house. We had looked at those commercially available ‘playsets’ from all the name brand stores. The sticker shock soon turned me away. During the process, the idea came about to construct a tree fort. I’m not sure how we came to that conclusion, but I am glad we did.


Disclaimer – I have no idea how to build one of these…that’s for you Asa Christiana . When there is something that’s new to me, I conduct a plethora of research on the subject. The last thing I want to do is create something I don’t like, won’t be used, or won’t be safe.

The first place I always turn (recently anyways) is my local library. I ordered a small collection of books on the subject of tree forts/houses, and some on the subject of deck building as well. Let me tell you…there are some insane tree houses out there! Well beyond what you will see documented here. I thought my design was a little over the top…now I know it is modest.

The best book that I found was ‘Build Your Kids a Treehouse’ by Black & Decker. I really suggest getting this book if you are going to tackle a treehouse. The book details how to select the correct tree for what type of house/fort you are building, as well as the correct way to attach it to the tree. You don’t want to kill the tree, and you don’t want to have someone getting hurt…which includes your ego if the thing starts to fall down. The book demonstrates the entire building process step by step.

The Design

The design I finally settled on is a combination of a few influences. The structural framing and decking is totally the design of the Black & Decker book. I didn’t feel comfortable deviating from their advise. The railing design was adopted from one of those commercial playsets available at the big name stores…I changed things up a little to suit my taste. The roof structure was adapted from another design I found online.

Download it – You can click on the picture at the beginning of the post to take you to the Sketchup page of my blog. From there if you select the tree fort, it will take you to the 3D Warehouse download page. I tend to deviate from the design/model during builds…mostly in terms of measurements…I don’t use a tape measure that often…just in the beginning. The rest is all relative dimension. This is especially true when you attach the knee braces to the tree. They can vary greatly in length depending upon the irregularities of the tree trunk. If you print cut lists from this model you would fail…you have to adjust as you build.

I just want to add that when I create a Sketchup model for use in a build, the final project may not match exactly. There are times when I change my mind during the course of the build…actually it happens quite a bit. So don’t be surprised if a few posts from now things look a little different.

I do also plan on permanently attaching a ladder to the rim joist of the platform..Then above the ladder, I am thinking about building a temporary gate to prevent the kiddies from accidentally falling out the opening. Both of these additions are not in the Sketchup file, as I have yet to decide how they will be constructed.


I have had requests from the clients (my two sons) for things like trap doors, ropes, poles, etc. The great thing about the design is that to make additional changes in the future won’t be too cumbersome. The funniest request I got was for a telescope…really?…not kidding. The thing I really want for myself is a zip line. How awesome would that be?

The Process

The process for this build will be interesting. Not only have I never built something in a tree or off the ground, but I have never attempted a deck either. In addition, I don’t have the tools available that I had planned on using. Whilst I am building this tree fort, my father-in-law is rebuilding his deck. He asked to borrow my sliding compound miter saw and I had said yes without thinking about the tree fort. I am a hand tool only guy now…but that was intended to be just for building furniture in my workshop. I do have enough sanity to keep some power tools around to work on things for the house. We could work it out sharing the saw, but that would require multiple trips back and forth…so, I will attempt to build this mammoth will hand tools only.

Let the adventure begin

Wish me luck…and send some Tylenol,