Subject: Beam Spam for One-Tree Treehouse, No Knees

I'm building a one-tree treehouse next month in a very large Silver Maple in my backyard in Illinois. This will be my second treehouse of this sort. My first treehouse is at my mother-in-law's in Pennsylvania, an open deck structure built on the main trunk with 8' long 2x8 beams supported with 2x6 knees.

This time I'd like to avoid knees, because I want the treehouse to be as close to the ground as possible, accessible by 3-4 steps so that my 2-year-old can play in it safely.

The diameter of the tree is 3'. So I'd like to use the longest beams possible (I'm thinking 12') in order to have a decent area on the deck. I should add that I've also built a large deck, and a substantial 2-deck play area (my previous house did not have a treehouse tree), so I've got some experience.

My first thought was to use 2x12's, or perhaps even doubled 2x12s. Bolted in the middle, they would stick out 5.5' (assuming one foot in the middle where the lag bolts are) in either direction.

If it's not possible to avoid knees, I'll raise the treehouse somewhat to accommodate them. But I won't be able to go much more than about 4 feet from the ground; so even if I use knee braces, there will be some cantilever.

I'd be grateful for any practical advice on this, as I haven't been able to find out anything much about cantilever loads for treated pine beams.

This time I'd like to avoid knees, because I want the treehouse to be as close to the ground as possible, accessible by 3-4 steps so that my 2-year-old can play in it safely.

The diameter of the tree is 3'. So I'd like to use the longest beams possible (I'm thinking 12') in order to have a decent area on the deck. I should add that I've also built a large deck, and a substantial 2-deck play area (my previous house did not have a treehouse tree), so I've got some experience.

My first thought was to use 2x12's, or perhaps even doubled 2x12s. Bolted in the middle, they would stick out 5.5' (assuming one foot in the middle where the lag bolts are) in either direction.

If it's not possible to avoid knees, I'll raise the treehouse somewhat to accommodate them. But I won't be able to go much more than about 4 feet from the ground; so even if I use knee braces, there will be some cantilever.

I'd be grateful for any practical advice on this, as I haven't been able to find out anything much about cantilever loads for treated pine beams.