tree house build and lag screw strength

[diymirage]

morning guys

i have decided to finally build the kids a tree house

now, i understand there is all this fancy hardware out there, but it get pricey in a hurry, and quite frankly, i feel like its overkill


this will be a relatively small platform with an even smaller "house" on it
i have climbed in the tree yet to measure the actual possibilities

the tree in question has a rather low split into three lare branches
i intend to use those three branches to build my tree house on

now, i am open to any and all advice, but the main thing i want to know, right now, is if i use 3/4 x12 inch lag bolts, will that suffice?
(and i understand that this is a vauge question, so perhaps i should ask "what is the weight bearing capacity of a 3/4 x12 lag bolt)

in essence, the enter structure will be perched on 4 of these bolts so that is kind of a big deal

 

[diymirage]

if this chart is right, (and im imbedding the bolts deeper then the chart says) the sheer load for one bolt is 1168 pounds, correct?

in that case 4 of them would carry over 4600 pounds, that should be well enough for what im doing, i think

 

[68gtxman]

if this chart is right, (and im imbedding the bolts deeper then the chart says) the sheer load for one bolt is 1168 pounds, correct?

in that case 4 of them would carry over 4600 pounds, that should be well enough for what im doing, i think


View attachment 1716274382

Yes, you are reading the chart correctly. But, I would plan on doubling or even tripling the expected load to get a factor of safety. Good luck!

 

[Cuda416]

Not sure it applies, but with climbing equipment is usually rated for a working load of 10:1. If my 30Kn carabiner can hold 6750lbs, it means the working load is 675. Not sure how much you plan on putting up there, but keep in mind there is nothing keeping you from drilling all the way through and using a big *** bolt instead. You won't kill the tree since threes get there nutrients from the outer area, not the inner. Just don't "skirt" it and it will be fine. You could also put more than one bolt, lag or otherwise to increase the carrying capacity. Finally, if you really want to get nutz, put knee braces under connection points.

 

[diymirage]

so, this is totally in the planning stages, i have a very faint idea of what i might do, but like i said, if i cant get the 4 corner bolts figured out, the rest wont happen either


(ill grab some pictures of the tree i have in mind shortly, plus a backup one)


so far, the rough, rough idea is a 10x10 platform, with a 6x6 house on one corner, leaving a 4 ft "porch" on 2 sides



as far as weight goes, i went online and looked up a 10x10 wood shed, with floor on the lowes website and the claim it weights 1041 pounds
this is with a larger roof and wider walls then i intend to build, but much thinner floor joist, so i think its a bit of a trade off, and the treehouse might come in at 1100 pounds
add a few kids and i think i want to be able to hold up 1500 pounds

according to the principles laid down by @Cuda416 , i would want fasterners with a combined rating of 15.000 pounds

that would be 13 of those 3/4 lag bolts BUT everything i read online (and what i gathered from talking to my arborist buddy) tells me the lesser holes in the tree the beter
(people also seem to advise against drilling straight through and using a threaded rod)


so, i think id want to simply get a heavier rated mounting bolt
i found a vendor on ebay selling 1.25x12 lag bolts, im waiting to hear back from him what the sheer rating is

 

[Cuda416]

so, this is totally in the planning stages, i have a very faint idea of what i might do, but like i said, if i cant get the 4 corner bolts figured out, the rest wont happen either


(ill grab some pictures of the tree i have in mind shortly, plus a backup one)


so far, the rough, rough idea is a 10x10 platform, with a 6x6 house on one corner, leaving a 4 ft "porch" on 2 sides



as far as weight goes, i went online and looked up a 10x10 wood shed, with floor on the lowes website and the claim it weights 1041 pounds
this is with a larger roof and wider walls then i intend to build, but much thinner floor joist, so i think its a bit of a trade off, and the treehouse might come in at 1100 pounds
add a few kids and i think i want to be able to hold up 1500 pounds

according to the principles laid down by @Cuda416 , i would want fasterners with a combined rating of 15.000 pounds

that would be 13 of those 3/4 lag bolts BUT everything i read online (and what i gathered from talking to my arborist buddy) tells me the lesser holes in the tree the beter
(people also seem to advise against drilling straight through and using a threaded rod)


so, i think id want to simply get a heavier rated mounting bolt
i found a vendor on ebay selling 1.25x12 lag bolts, im waiting to hear back from him what the sheer rating is

Sounds like you're on a good path. Also great you were able to ask an arborist. It's always best not punch holes into trees but if you're going to, there are better ways. I also agree threaded rod would be a bad idea since It's not hardened at all isn't meant to hold much of a load. Also, stay away from screws if possible. Use ring shank nails. Screws aren't designed for any flex, whereas nails are. They are soft and can take much more movement. I got that from the designer of my barn/shop as well as a casual conversation from a structural engineer. They need to be ring shanks though or you risk them pulling out.

You gonna show us what it looks like when you're done? Tree houses are great!

 

[diymirage]

@Cuda416

i think im gonna move trees
this first one is the one i had in mind, but before those branches open up enough to build a platform in 25 feet up in the air

instead, i will use 4 out of this cluster of 5

the red beams will be 14 foot, the orange ones 8

it kind of changes the design, perhaps id build a 6 by 8 house leaving a 8 by 8 porch

the idea is it drill and cut a slot in the runners for the lagbolt to sit in, and not sinche the bolt down
this would allow for movement or growth in the trees

 

[jos51700]

Don't get me wrong, I'm all for massive factors of safety, but think about it like this: You're going to have maybe two adults and a kid up there, maybe three adults at most. Let's say they're all chubby, 250lbs ea. And the structure itself might weigh 1000 lbs (are you planning on windows and roofing?). That's 1750. One of those lag screws is close enough to that, so if you used 4 lag screws, you're looking at a factor of safety of less than 4, which is well stout.

A 14' span is going to be a long span and require a pretty large joist. If you're looking at 12" long lag bolts, I'd consider just going all the way through the tree and grabbing a board on the opposite side, across the long span, to spread that load out. I do NOT know how that affects trees. I'd consider stainless bolts, which will have different shear numbers but should be close.

Typically, tree houses are built where the tree is under the house and offers support in multiple places, versus building the equivalent of an elevated household deck. A deck calculator should help you approximate your needs here using those four trees, just think of it like a deck on posts. The slotted holes is a great idea.

 

[like_A_pike]

What species is the leaner? Any large branch scars or any other source of heart rot? How far down is the water?
How often do you get ice or sticky snow?

 

[fishmens67]

I question the foundation of the house.

 

[YY1]

Your car sits on 20 1/2 inch bolts.

...or 7/16 bolts if it still has factory A body parts.

 

[67Dart273]

The other issue is lag screw QUALITY and CORROSION.

The average lags you buy at the average Lowe's Depot are grade "junk." And even though maybe galvanized, trees are VERY corrosive.

 

[jos51700]

What species is the leaner? Any large branch scars or any other source of heart rot? How far down is the water?
How often do you get ice or sticky snow?

My assumption, and I knew I shouldn't have done it, was that the 'floor' would decent gaps to at least let out rainwater, similar to any other deck (and to save a few pounds).

I did NOT think about OP living in Michigan...

OP, build the floor at a 45 degree angle to the earth to allow the snow to slide off. Your kids will love it.

Seriously, Like a Pike brings up a legit point.

 

[diymirage]

What species is the leaner? Any large branch scars or any other source of heart rot? How far down is the water?
How often do you get ice or sticky snow?

Not a clue what species it is

I did have an arbolist look at it a few years ago and he noted that even though its leaning, it is still a healthy tree

No idea how deep the groundwater is

We get icy and sticky snow 3 -6 months out of the year

However, it has been brought to my attention that i want to build this in the side or backyard, so im back to looking for the right tree

 

[sireland67]

Don't get me wrong, I'm all for massive factors of safety, but think about it like this: You're going to have maybe two adults and a kid up there, maybe three adults at most. Let's say they're all chubby, 250lbs ea. And the structure itself might weigh 1000 lbs (are you planning on windows and roofing?). That's 1750. One of those lag screws is close enough to that, so if you used 4 lag screws, you're looking at a factor of safety of less than 4, which is well stout.

A 14' span is going to be a long span and require a pretty large joist. If you're looking at 12" long lag bolts, I'd consider just going all the way through the tree and grabbing a board on the opposite side, across the long span, to spread that load out. I do NOT know how that affects trees. I'd consider stainless bolts, which will have different shear numbers but should be close.

Typically, tree houses are built where the tree is under the house and offers support in multiple places, versus building the equivalent of an elevated household deck. A deck calculator should help you approximate your needs here using those four trees, just think of it like a deck on posts. The slotted holes is a great idea.

Typically stainless bolts are about 1/2 the strength of steel ones.