200 sqft treehouse

[brian7gv]

Well I have been lurking around this site for years now and i am finnaly going to post some of the work i have done. My wife and i finally purchase some property on the key penninsula in 2009. we wanted to build a house there but over time have moved the start date back and i have settled for a treehouse/shed/cabin. I have learned alot since i started but i think i need some critique from some people who know more. Here are some photos of the property and the start of the building process.

[brian7gv]

first stages

[phalynx]

I don't know what your design is but from what I can see, you need a LOT more bracing.  Here is a structure I built.  It isn't finished.  I have quite a bit of bracing and it does wiggle a bit.  I don't have any confidence problem with it though.   But you can see all the bracing I used and I used very large lag bolts to secure everything.  Nails will not do by themselves.  Just my two cents so far.

[brian7gv]

that looks really cool. how tall is it and what is the footprint? I did wind up bracing it some more. Ill post some pics and let me know what you think.

[brian7gv]

A lot of the lumber came from an old garage in Port Orchard that someone listed on craigslist for free. The teardown took me 3 days and some hard work. It wound up costing me $300 for fuel and the dump fee for the shingles. It was well worth it, i got alot of siding and sheating as well as 2x4 and 2x6. If only i had taken a picture of it before i tore it down.

[flyingvan]

  I haven't built a house that high, but I have built decks similar to that.  Don't mistake me for a real engineer or architect, please, but here's my concern----once you get some walls up and create a nice sail, I think your structure will twist in the wind.  You have good compressive strength with your posts and your cross bracing is good diagonal support, but if you imagine a giant hand grabbing the top of it and twisting it, the entire stilt structure will bend from a rectangle to a parallelogram.   Your floor you have down does provide some sheer against this but only if you are really, really secured down to those cross beams---more than just a couple of Simpson ties.  I would add a giant 'X' joining diagonal corners, or at least some 45 degree braces in each corner (as high as possible, just below the floor). 

[brian7gv]

Thanks flyingvan, you make a good point. That will be an easy fix and I will get right on it.

[MountainDon]

Frankly, the height of those posts scares me. Then I went back and read instead of just looking at pictures. I see Port Orchard mentioned. Port Orchard, WA? Earthquake country.

The USGS database shows that there is a 93.255% chance of a major earthquake within 50 kilometers of Port Orchard, Washington within the next 50 years.   ... note that probability is for a 5.0 quake; for lower intensity quakes the probability interval decreases and the percentage chance approaches 99%.   That probability risk is much higher than the area in NM where our cabin is located and I am having thoughts about it and it only sits on piers that extend 13 inches above ground level.

That data is pulled from this website which gets the data from the USGS


Let me add that I am not an engineer. I know one who would be quite concerned about that, to put it in the mildest possible language. If that was a simple uncovered deck, it would cause enough for concern, IMO. Erecting walls and a roof on top of that is going to greatly increase the effects of wind upon the structure, not to mention seismic activity. It is my belief that the plan needs some serious rethinking. That is my opinion, not an engineers opinion as I stated, but I believe a valid opinion.

Also note that even though the IRC allows a post size of 4x4, the current Prescriptive Residential Wood Deck Construction Guide recommends 6x6 as a minimum post size for decks.

If it were me, and I know it is not, I would consider enclosing that entire lower area with wall framing on 16" centers. Then nailing sheathing over the entire exterior, making a ground level shed out of that bottom. Framed and sheathed walls with the sheathing well nailed into the posts and the framing infill would make each wall able to resist much greater forces.

Anyhow that is one opinion. I don't want to appear to be a wet blanket, but I can not sit by without commenting on my perceptions.

[phalynx]

My structure is 17' fro ground level and is 12x24 in size.  I think there is a valid point about twisting at the bottom.  My posts are 3' in the ground and surrounded and supported with concrete to keep the legs from pulling towards each other.  In your case, a set of sturdy boards at the base surrounding the entire structure and then in the inside to keep every board from not only kicking outward, but also inward.  I am no engineer either, but this is what my work has taught me.  I believe my structure would be stronger if I put some cables going from the bottom of 1 corner to the top of another corner and then replicated on the other corners.  My structure doesn't wiggle a whole heck of a lot but it does wiggle. I would be concerned a little by your base not being in the ground but rather, setting on the ground.  There is nothing preventing it from tipping over in high winds.  All this in my opinion.  I had originally planned to have posts buried in the ground and attaching to the top of the base legs with "guy wires".  Ultimately, I don't believe it is needed in my case.  It might not be a bad idea in yours.

Just some food for thought.  There will be a few others chiming in, like MountainDon, who are far more smarter and "engineering wise" than I to offer more opinions. 

It is fun building though isn't it?

[flyingvan]

Just to tack on to the subject of earthquakes---I'm on a federal team and have responded to a few....If you have a brick structure, versus a tent, guess which is more likely to survive?  The stiffer the structure the more prone to damage it is.  Earthquakes seem to leave the rickety stuff alone (They leave them for the hurricanes) probably because they flex around some.
I like the cables and guy wires idea

[MountainDon]

I believe my structure would be stronger if I put some cables going from the bottom of 1 corner to the top of another corner and then replicated on the other corners.

That could help but would also take away from the use of the space under the floor.
Maybe that's a good thing (taking away from the usefulness) as then there woule be less chance of someone being under it when it collapses.

I had originally planned to have posts buried in the ground and attaching to the top of the base legs with "guy wires".

Guy wires from the top of each post down to some hefty concrete anchors could also help. As someone I spoke with about this said though... there in a chance for injury from running into a guy wire. He broke his nose as a kid by running into a guy wire.

[MountainDon]

There is no doubt in my mind that a tent would survive an earthquake better than most other structures. However, IMO, one can not extrapolate that data to a structure like this, and call it a safe structure.


I had another look at the images. Am I correct that the structure appears to be sitting on what are commonly referred to as deck blocks? The deck blocks appear to be simply sitting there on top of the earth? I think that must be correct as the ground is not disturbed enough to have made a hole in the ground and pour concrete. That did not register in my brain the last time I looked; I think the stilts got the best of me.

With a structure on top of that that becomes so easy to be overturned by strong winds. Do not count on the weight of the building counteracting lateral wind forces. This is especially a concern with a top heavy structure.

My earlier comment about building walls using the lower perimeter should now be modified... I was under the impression there was some concrete in the ground.  That does not seem to be the case.  A single storage shed can get by sitting on the ground or deck blocks. But a second floor, especially a highly raised second floor... ?  The shed could shift and maybe fall off it's blocks. But my impression here is that if the ground shakes the upper floor whips around and falls on whoever/whatever is on the ground.


Port Orchard is right in the worst seismic risk area in WA state.  That alone, IMO, should be cause enough to rethink what id being built here.


And of course, there is always the possibility that a quake or wind strong enough to cause severe damage might not come along in my lifetime, your lifetime, or the kids lifetime. At least things like tornados and hurricanes are usually given ample warning and people can stay away from dangerous areas. But nobody is good enough to predicting date and time of an earthquake or how strong it might be.

Anyhow that's what I have to say. There is information available about building in a seismic area. Pretty much all I have seen regarding construction is seismic zones centers around keeping all the parts together; keeping any one component from failing from too much flex. This is the world on the engineer or the world of following prescriptive solutions that have been derived from engineering analysis.

[brian7gv]

I appreciate all of your input on the structure as it sits right now. I do enjoy building but I wasnt really thinking about earthquakes as i have yet to experience one for myself. What sort of modifications would you suggest? I decided to use the deck blocks because of their ease of instalation and i had seen them used in the western wa area. the treehouse is 11x17 and it will be about 21 feet tall when finished. Any more insight would be greatly appreciated since i plan on it lasting a long time.

[Don_P]

I agree with the others.
I'd be looking to tower designs.
This is no endorsement just some quick searching.
http://www.water-towers.com/
http://www.fs.fed.us/database/acad/lt/

[Bob S.]

  Would it take care of most of the racking issues if you walled in the back bay to make a stogage area?

[Barry Broome]

Phalynx, do you have a thread on this forum which shows your structure being built in the above picture? I'm very interested to get ideas on this thread as I bought river property last year http://countryplans.com/smf/index.php?topic=10161

If and when I build it will likely be at least 12 feet or more above ground level (inside the flood zone on the river). I plan to overbuild (only do it once). I've given it a great deal of thought. Why drop time and money into something that might disappear with the first flood or hurricane. Even if I've only got $3,000 in the structure... and it goes down. That's still $3,000 I could have put into a $7,000 build that might last the rest of my life.

Don't take chances with mother nature. In the very least I'd say use 6X6's buried in the ground 3" supported beneath by concrete/gravel footer. Then fill hole with 2 feet of concrete. Then cross brace as recommended by mtnDon and others on here who've been around here for awhile.

When it comes to a structure like this. The most important part is the foundation IMO. In this case the posts/piers are part of the foundation.

Granted I'm still the village idiot when it comes to building. I'm still just too inexperienced.

Here's my shed I posted on here recently http://countryplans.com/smf/index.php?topic=9948

When I framed up the walls I failed to install a top plate. And I should have used 2X6 rafters. I'm still just a rookie, but I've spent a lot of time contemplating this type of build.

Some resources.

http://www.boardwalkbuilders.com/pages/art/art1.htm

http://amazingplans.com/styles/beach-pilings.html?plan_foundation=4550

http://www.topsider.com/Piling-pier-stilt-foundation-home-plans.asp

[brian7gv]

what do you think about building forms around the perimeter of the deck blocks and pouring a concrete pad up to the 4x4 posts? that would tie everything together but it still could move in the event of an earthquake. Do you think that enclosing the bottom area will still help or shoud i take it all down and pour some footings?  Im just not sure of how to attatch the house to the ground.

[brian7gv]

It gets worse

[phalynx]

Yes, it does....     Well, go ahead and post all of them..  Go ahead and take your licks now..   We need to know how far you got so we can see where changes can be made..  It won't be bad.  I have seen much much worse....  in fact, I may have built much much worse...

Let's see how far you got.

[UK4X4]

Ok fess up is it finished yet ?

here's a possible remedy

rent a hole auger dig 4 feet down between the existing pads ie 6 new holes 12" diameter site a paver or gravel in the bottom fit 6 off 6x6 treated posts into those holes running down from your beams and backfill with cement

wait for setting
remove the existing posts - dig out the 4 end positions and repeat.

spacing is uneven but you'll have a firm foundation -brace as per recomendations

[brian7gv]

Uh Oh. You guys are on to me. I have gotten alot further than these pictures show.

[brian7gv]

here are a few more. i had alot more pics but they were on my phone and it broke

[brian7gv]

Getting up to speed.

this tree fell 2 feet from the treehouse on the north side. scary

then i had to start cutting alot of them down since there was no root to them at all. the neighbor said they are prone to falling down so i have quite a few more to take down but i got all the ones on the west side so I should be good for a while.

[UK4X4]

"then i had to start cutting alot of them down since there was no root to them at all. the neighbor said they are prone to falling down"

This is what we've been trying to tell you - your tree house has no roots !

[Bob S.]

I would not let my children play under that tree house!!!