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I am building a tree house. The platform will be 16 x16.

Customer Question

I am building a tree house. The platform will be 16' x16'. There will be two 16' foot beams spanning the distance between two different sets of trees located in a square. Upon those two beams floor joists will rest and will be 16' long. The tree house will be 12' x 12' and sit in the middle of the platform. Two questions: 1) what must the dimensions for the two beams be; and 2) what must the dimensions of the floor joists be?

Already Tried:
Nothing. I'm waiting for an expert opinion.

Submitted: 290 days and 11 hours ago.

Category: Structural Engineering

Value: $30

Status: CLOSED

Accepted Answer

Expert: StructuralEng replied 290 days and 11 hours ago.

StructuralEng : Hi

StructuralEng : I can help

StructuralEng : Let me read closer.

StructuralEng : Can you tell me your city and state?

StructuralEng : I can size this for gravity loading, but you'll need to provide some lateral resistance

Customer :

okay. I'll wait. Bigfork Montana. Lateral resistance?

Customer :

Are you still there?

Customer :

StructuralEng :

I apologize

StructuralEng :

I had a bit of an emergency come up.

StructuralEng :

Lateral resistance means you need some way to resist lateral forces. I will size these for gravity only. Is that reasonable?

Customer : That sounds reasonable. Would lateral resistance include using 6 x 6 corner posts imbedded in concrete instead of tree attachments? Like a free standing deck?

StructuralEng : Great. I'll get the sizes for you this morning.

StructuralEng : That could work for lateral, but would require a lot of movement and would probably engage the tree before the the posts. Adding diagonal braces between the posts would be the best way

StructuralEng : One last thought before I size things - using two trees could be tricky. You'll want to come up with some kind of detail that uses one of the for vertical support, but allLows slip horizontally, otherwise as the trees move independently (and differently) the tree house will slowly pull itself apart

Customer :

I see what you're saying on the lateral issues. I actually have something called a Garnier Limb for the tree attachment. It has a sliding brace allows the tree to sway without moving the rest of the tree house. I'll await your advice on the size of the beams. Thank you.

StructuralEng :

Great. I can size them now if you can hang out for a few minutes.

StructuralEng :

The joists can be 2x12 @ 9" o.c. Southern Pine No. 2

StructuralEng :

The main beams will have to be pressure treated glulam - 5-1/8" x 15" with a min Fb of 2400 psi and a min E of 1800 ksi.

StructuralEng :

If you've found my answer helpful, please click the green
"accept" button. I'll be happy to answer additional questions
on the topic. If you could provide feedback, I would appreciate it.

Customer :

Thank you.

Customer :

StructuralEng :

No problem. Best of luck with your project.