Shipping Container TreeHouse?

[cruzer076]

Hello guys, We just finished designing and building our first shipping container home using 2 shipping containers




This home is built on concrete piers (15 of them) 10' into the ground. We placed steel plates with jhooks into the concrete to weld the container to so they didn't go anywhere. The container is about 4' off the ground at its highest point. We haven't had any shifts or problems yet. It's only been 10 months so far.. I think that may be a overkill since a shipping container manages most of its weight on its own frame but my s/o feels safe so...




Now that we have finished, we are starting a new ambitious project...a shipping container treehouse...with a pergola and jacuzzi on top. (using (1) 40' container) 320 sq ft. 1bd/1ba
We have lots of elm trees but most are only 12-18 inches around...(I am unsure how much weight they could hold) so I am leaning towards using "stilts" and attaching a deck to the tree..
I would like the container about 12' off the ground.. I'm open to using tree's if you guys think that framing on a few 14-18inch trees would hold the weight.
To visualize we are thinking of something like this

or

Or


My idea is to drill (6) 10' holes, fill them with concrete, use Steel I-beams and set them inside the concrete coming up, then frame out the top square with i-beams as well. so we have 6 columns and a square i-beam frame. What I am unsure about is where I would need cross supports? Do I even need them? Would they go from bottom to top or just a foot or 2 down to the column?

I'm estimating a full shipping container would weight about 20-25k lbs full of furniture, people and with deck and jacuzzi...
My questions are:
1. What size i-beams can I use 3" 4"?
2. Do you have any other suggestions for a better foundation or framing system?
3. Would 6x6 posts work instead of steel beams?
4. Would you sink the i-beams into the concrete or bolt it at the bottom to some kind of brace?

The area where the posts will be may flood from time to time up to 3-4 feet high with water. just an fyi.

Looking forward to your opinions, thanks guys

==========
a 40' dry shipping container weighs 8,268 lbs
Payload capacity 55,126 lbs
Cubic capacity 2,389 cu ft
Internal length 12.03 m 39.5 ft
Internal width 7.7 ft
"In general, empty hot tubs can weigh anywhere from 400 to 700 pounds. A 700-pound hot tub is usually designed to hold about 600 gallons. When full, a hot tub of this size weighs about 6,000 pounds and has space for six average-sized adults."

[Dave Sparks]

Location of the project?  One always looks at the soil, wind, and snow loading requirements that are required for the area if it is going to last more than one winter. This is just for starting.

[cruzer076]

South East of Dallas about 30 miles,
The location is next to a dry a creek bed that fills up and sometimes floods during a rainstorm (Thus we want to have it high up)
The soil is seems to be some kind of black clay... It will be surrounded by trees and not an open field.
Average snowfall is 2inches a year.
Average rainfall is 39 inches a year


If you look at the second picture (The one with the dog) and you see the trees in the background, We want to build inside that wooded area about 300' behind the house into the woods. A very secluded area.

[UK4X4]

Your first issue to concider is your footing size...?

And the expected weight per leg........including the weight of the legs themselves....

With only 6 posts and clay silt soil, ground support is only arround 1500 to 2000#/ square ft....

Your center two posts if all the weight is evenly distributed......would be arround 6000lbs.......that means they would need a 3sq ft footing each
......thats just a quick rough calc, not including the frame weight...

FEMA does a whole range of stilt design guides.....which you may want to check.....

The higher you go the more lateral support is also an issue , bracing between posts would be very important at that height

[Dave Sparks]

Wind speed for an area that might have remnants of a  Hurricane / Tornado?
It is great to be up high but...

[NathanS]

Building way up off the ground, I think it's the lateral bracing that is the main challenge. When you're building on piers you are counting on dirt to be your lateral bracing, which is why piers are not really a 'prescriptive' building method and everyone is always warning against using them.

It looks like the first elevated shipping container pic you linked has the piers coming out of a slab, which is one way to provide a calculable lateral bracing.

Your house is really cool.

Because of the whole pier/dirt bracing thing, even for a regular old house you should probably talk to a soil engineer. When piers are that tall, you really might want to talk to engineer. If you want to use trees, I would look for the oldest engineer you can find. 

[Don_P]

I thought the main challenge would be getting the container 12' off the ground on a remote treed site 
Through interlibrary loan get hold of a copy of the "Manual of Steel Construction" you'll find the engineering info in there. Make sure your bracing doesn't catch that floating tree.  Building in a floodplain can get you into deep water, check the FEMA maps and your local rules, ours begin at the zoning dept.

Edit, more rambling;
Elm is not decay resistant, at all but for future ref. Depending on which one it can be quite strong. American and slippery (red) elm are the softer, weaker ones. Red elm is a beautiful furniture, cabinet, trim wood. Rock and winged elm (wahoo) are the high strength elms. In a column load of that length those diameters are more than enough in either. A column normally fails by crushing or buckling. A rough rule of thumb in wood, a square column that is an inch wide on each face for each foot it is tall, isn't going to buckle, all you need to check is the crushing strength. Or, a 12"x12"x 12' post isn't going to buckle, you'll smush it first. Another conservative rule of thumb, if you can inscribe the square shape engineering needs on the small end of a good log you're good. You can check allowable end grain compressive strength on the output of the spancalc at awc.org. This assumes a vertical load straight down the axis of the post, you still need to laterally brace it from swaying or it just became a beam/column and it can pop. Notice the X bracing in all of your examples. The pipe column house has cable or rod X bracing in most bays.

Notice their bracing runs in large X's from top to opposing post bottom. If the bracing lands somewhere in the middle of the post...Y braces, then that attachment point puts a bending load in the column when the building gets pushed on sideways by the wind, that is the reason for those long X's from top to bottom. As the brace moves up the post the post becomes a beam/column resisting 2 loads, one from above and one from the side, the rules of thumb are off.

Not to say that situation is insurmountable, the parts get heavier. You can open up a bay using heavier legs, TX, I'd use pipe. Then a portal frame by running a horizontal at ~8' and W bracing between 8 and 12' at about 45 degree angles. It creates a braced bay but requires enough leg strength to take an 8' cantilever at you lateral load. You're in an engineer's playground

[river place]

Around the Dallas area you have some of the most expansive clay in the world.  This is why so many houses built on slabs have so many foundation issues. 

If you went down 10 ft for your previous piers I would do the same but maybe do what they do near the coast.   You'd need to put in more of a piling type of foundation. You could tie them together with a concrete parameter or slab pour.  With that height I would think a rented crane would be required to place the container on top.  With the slow down in oil production you may find the cost to get a crane out there might be reasonable.