Will two 2x10 beams carry a a 2500lb floor for a tree house?

Question

I am wanting to span between 2 trees with 12 to 15 foot beams. I will have one beam on one side of the trees and another beam on the other side. The beams will be supported 1/3 in from one end and 1/3 in from the other. They will rest on metal plates on that will be about 4" long screwed into their undersides. The plates are mounted on tree bolts. So those will be the support points. I believe I have found that this wood will support 1200lbs each, but that is one long span. This is more like 3 spans. The beams will be about 20" apart (the width of each tree). I want to then build an 8x10 or 10x10 standard floor joist system and build a treehouse on top of that.

Including people, snow load, and the weight of all the wood and materials, it will be under 2500lbs. Will my 2 beams be enough? Could I use 2x8s? Do I need to double them up?

The drawing below is close to what I am wanting to do. My trees are straight and the overhang on the left and right is more. There will be around 1/3 of the beam extending beyond each mounting point and the floor will extend out there too.

Lee Sam · Answer

There’s several issues with your plan: 1) support 2500#, 2) connect platform to beams, 3) differential loading on cantilever beams.

1) Yes, 2 - 2x8’s spanning 4’ or 5’ can easily support 2500# depending on the species and grade of lumber. However, a 4’ or 5’ cantilever is excessive for either a 2x8 or 2x10 and will eventually fail depending on how much of the 2500# load is on the cantilever beams.

2) The platform could exert a force of over 600 lbs. due to rotation on each H-1 connector by having the live load and dead load on the cantilever. The Simpson H-1 clip is only rated for a resistance of 400# to 500#, depending on the species and grade of the joists and beams. H-1 clips are not suitable for this installation.

See: https://www.strongtie.com/resources/product-installers-guide/h1-installation

3) Structures like this will not have uniform loads distributed throughout the structure evenly. A more detailed design and structural analysis should be done by a structural engineer (not civil engineer) or architect if you decide to stay with the extremely large cantilever design.

Btw, there are many videos about how to connect beams to a growing tree for a tree fort.

Will two 2x10 beams carry a a 2500lb floor for a tree house?

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