When spring decides to show its warm unsnowy head I am planning on building a tree house as a small hobby workshop/ personal storage area. Yes I know I'm an adult wanting to build a treehouse. I've always wanted one and It will not only be useful but also tap into that child in me.

What I would like some help on is; what kind of lumber I should use. The tree is cottonwood and seems to not want to go anywhere so I'm assuming its strong. My goal is to make it like a very small apartment that can support 3 people and maybe 200lbs of tools or other things. The tree is 11 feet around so if i did it right the diameter is 3.5 feet. I plan on making it wrap around the tree ~9 feet around
Planned dimensions:
Height:~7feet Also 7 feet from the ground
~6 feet from the tree side of the inside to the outside of the inside

I cant think about how to explain it any better so questions on specifics could help. Thanks everyone.

I would use pressure treated deck wood for the floor and frame.

Ok, sounds good. what about for the walls? I already know I'm going to use 6' 4x4'* as the floor support beams that keep it up on the tree.

4x4 beams are plenty. You can put them in a bit. Use 4. If you use 2"x6"'* for the floor joist'* you can allow a 2' overhang from the point the 4x4 attaches to the floor joist'*. You say 3,.... but my experience in building things for people tells me that means 4 on occasion, 5-6 for a look see. hehehe. Don't go under 2x6. The use of lag bolts one on each side (4) will help keep it stable side to side and not hurt a cottonwood much. The 4x4 needs to be put 3 feet into the ground to ensure they have enough support under the frost line and dont sink as well. I usually start with a post hole digger and then use a trenching shovel to widen the holes to 8" minumum. It is best to fill each hole with about 4" of concrete and let that harden before setting the 4x4'* down in the hole and then filling each to ground level. It is better to let the concrete go just above the grass line, that way you minimize water contact to the wood. I'll make you a little diagram you can follow and post it here.

Edit: Walls made of 2"x4"'* are plenty strong enough for one level, even two. No more. I wouldn't go with 2"x 6"' walls. The extra weight isn't a good trade off for the extra support not needed. Space them 16" apart on center. If you aren't planing a second level or a large roof you could even go with 2 foot spacing.

John...you talking tree fort or the workshop..lol

Oh Tom...where are you ?

I linked Tom to the thread...Here'* one he did.

DSC_0026.jpg

He said he wanted an apartment style treehouse and the size lumber and the way of putting the 4x4'* in are minimum for the weights of floor, walls, and roof Bill. Go back to the garage.

I used mostly leftover 2X6 redwood from an old deck. Unless there is a code issue you are trying to avoid I would just build a really nice shed.

BTW my son likes the treehouse and is in it all the time.

I plan on adding on to my 8X8 shed this spring and making it 20X8.

Whateva old man. .. Whateva...I got Tom involved!

And both of you ignore what the OP wants." very small apartment that can support 3 people and maybe 200lbs of tools or other things."

I did spend a life building apartments and houses. Since you like pics. Here'* the last thing I build, by hand, 2 months. 7 years old, solid, and in a flood plain. Just took it. It'* my guest house.