Tree House

[Epiphany]

How would one go about building a house in the shape of a giant tree trunk?  Frame, chicken wire, cement.....  Glenn would this be a good venue for cob?

(Picture My Side of the Mountain or Wilford Brimley's house in Star Wars - Ewoks...)

[Amanda_931]

Ferrocement might be the best way of all.  because it's thin-walled.

Although cob might be fun.  Most of the sculpture on cob is in a couple of inches of plaster coat as far as I can tell, so that's on top of a fairly thick structure.

Guy I knew eons ago once worked for a (the?) guy who was building houses by piling up dirt, putting a ferrocement layer on top, and then digging out the dirt.  It sounded wonderful!

[Epiphany]

Here's a link to some inspiration for a tree house...

http://www.toadhollowfarm.com/treetrunk.html

[glenn kangiser]

Actually cob is just modeling clay with sand and straw.  Becky Bee's book refers to it as sculpting your own house.  With cob plaster is optional - for the overly energetic or if you want a different color or a smooth finish or sacrificial finish for weathering.  Cob could be molded in the shape of a giant tree trunk or any other shape.  Smooth finished cob can be given a coat of concrete cure and seal after dry to keep you from getting your clothes dirty if you sit on it or brush against it.  It looks like it is varnished and can be re-coated if necessary as desired.  Clean up of your cob furniture is easy, using a product such as Pledge to clean the sealed surfaces.  Linseed oil also works and toughens the surface as for a floor use but does darken it.  Below is one of Becky and friends creations.  Many of her works are un-plastered.


With a minimun 6 inch rock base to build on (cobble rocks as a foundation - loose or mortared) and keep it dry it will last forever with minor maintenance (that is where a re-plastering would come in)..  The best mix for long lasting water resistant cob has about 70% sand.  The top should be covered with a roof or overhang.  

My clay oven, frog and conversation pit are all cob as is with no plaster coat.  It is fun to play in the mud and see what comes out.  The surface can be re-wet then troweled smooth with a steel trowel or my favorite for curved surfaces, a smooth firm rubber grout float for a very smooth finish.  A wood trowel works as a sander grabbing the high spots when wet and smoothing them off.  Dry cob will sand the wood trowel.

The difference between cob and ferro cement in heat transfer properties is very different.  Ferro cement being a thin wall like stucco but stronger, conducts heat fairly rapidly.  Cob is built in place adobe -monolithic curving walls being much stronger than adobe- the straw actually has silica in it making a strong reinforcement such as concrete with fibermesh added (great new modern idea-  The heavy walls give the thermal flywheel effect evening out the day and night temperatures.  Without insulation ferro cement would only have a slight lag.
Becky's book gives more detail and can be found at her site.

http://www.beckybee.net/

[Shelley]

Hey Glenn have you ever done this?

Never done cob, never seen cob and have never used this outside.

When I expose an interior adobe wall, I use lacquer thinner and styrofoam.  Chunk up an old cooler in the thinner til it looks like it's had enough.  Very scientific.

Brush it on.  Makes the adobe hard as a rock.  Only darkens it a few shades unlike the linseed oil.
Wonder if it works outdoors?

[glenn kangiser]

This is a new one to me, Shelly and I really appreciate you posting it.  You can bet I'll play around with it.  How long to dry and for fumes to dissipate?  Does it have better wear qualities -as in- would it harden a floor surface.  

Cob and adobe are very similar.  Adobe many times contains more clay necessitating drying the bricks before using them to cut down on excessive shrinkage.  Cob just adds up to the 70%sand to cut down on shrinkage and give the clay something to lock onto.  It locks onto the straw also as it shrinks making things tight like a drum head.  The whole assembly of dried clay, sand and straw is in tension making it very strong as long as it is dry, and not bad when only damp.  View each piece of sand as a mini-roof keeping the next piece or two below it dry, then the next piece or two keeping each one below them dry.  This is part of the reason that rain on the side of a cob wall doesn't immediately destroy it.  It takes a long time to dry thoroughly and a while to get wet.  Other references mention that the moisture only penetrates into a cob wall about 1/4 inch.  There are areas in England with cob houses around 800 years old.  

Below is a picture of the grandkids in the cob conversation pit.  

Thanks Shelly

[Shelley]

Well, as you know, lacquer thinner is pretty heady stuff.  But it evaporates quickly.  I'm doing it in an unfinished, unlived in house.  Let's say all gone in 4 hrs.

I've got a "truth hole" in one of my walls in my current house.  Like they do in straw bale.  If I scratch it with my fingernail, it's like scratching concrete.

Don't know how it would work on a mud floor.  Linseed oil is traditional if you're not into killing a calf every spring.

Read about it years ago.  Can't remember where.  Probably Earthbuilder.  Joe Tibbets lives here.

And, perfect adobe dirt is exactly 30% clay.  Go figure.

[Shelley]

Let's say 4 hours if the windows and doors are open and a breeze is blowing through....maybe.

[glenn kangiser]

The same formula is used in rammed earth construction with the exception that they don't usually add straw- it could be a good idea-  and if the clay is a bit weak they usually add 4 to 10 percent portland cement as a stabilizer - usually tractor or machine mixed on the ground -pretty dry mix and pneumatic or hand rammed into forms.

[Shelley]

Checked out Bee's site.  Cob is for people without an adobe yard and perhaps wanting a little more whimsy

May order her book and build myself a little hobbit house retreat.  Himself will never help me.  The sighs and the rolling eyes would be too much.
Maybe a hogan.  That would look good in NM.  Yeah, a hogan.

'Course that's after we put up the metal shop/temp living quarters and build the regular casita...which is after we get power, well and septic.  Maybe I'm getting ahead of myself.  She'll probably revise it 3 times b4 I'm ready.

[glenn kangiser]

Note:  Keep in mind that many alternative building methods are only accepted and approved by building officials if they feel it is 100% safe and that they have nearly no liability, in which case they usually will make you use the alternative material as an infill with some type of approved framing around or supporting it.  This could include concrete, wood and steel columns, beams and bond beams.  What you end up getting approved may not resemble what you wanted very closely.  

When they finish with you the alternative method may not be a cheaper building method, but may actually cost more.  You have to be willing to accept responsibility for your alternative building and you must know that it is safe because if it fails there is no one to blame but yourself- and others may blame you.  Even Mike Oehler's designs for the underground house were calced by an engineer to be sure they were safe.

If you want to be safe, energy efficient and approved by codes without having to worry about it, then one of John's plans is the way to go.

[Amanda_931]

Here's a cob-sculpted tree in a (SB) house in New York State.  Start at the bottom and work up.

http://www.potkettleblack.com/natbild/sarahtree/

[glenn kangiser]

That is a great link to a lot of other great links, Amanda.  Even if you have a conventional house, cob can be used for this type of decoration or built in furniture that is not something you will see very often.  Note that it is heavy - probably around 150 lbs per cubic foot so be sure you have adequate support.

Photo from site linked by Amanda showing a low cost decorative cob wall.  

[eddiescabin]

Sorry this is late...some guy just tried to get planning in Lafayette/Orinda (contra costa county California) to approve a $2 million+ tree house as you asked about.  The planners turned down the idea as the area is all $2 to $5 million dollar homes that did not want the attention, it should be available in any web search.

[glenn kangiser]

All the more reason to get out of so called civilization.

[Homesick Gypsy]

Couldn't access the article in the Contra Costa Times, except for a fee.  Darn, I'll bet it was good.