I'm guessing this balcony will be built and supported by wood...?  Will there be any heavy objects placed on the balcony...?  Large planters, furniture, hot tub, large grill, etc...?

It sounds like you're asking how far a balcony can cantilever before it needs to be supported by a column(s).  Using the widest typical lumber dimensions found at the usual hardware stores...I'm guessing that's a 2x12.  To take advantage of the structural integrity of the board, they should be placed with the long dimension standing vertically.  The denser the placement, the farther you can cantilever...but because it's wood, I wouldn't go beyond 5 feet.  If you do go to five feet, maybe place them at 1 foot on-center.

if one end is fastened to a house at the second floor against a rim joist or something, then you need a post or some other sort of structure to hold up the other end even if it's 4" wide.

if you have two support points holding a 2x12 beam/joist at the back, there is a rule of thumb that you can overhang about 1/3 of the member length.  if your beam is 15' long, then the back 10' has to be supported and it can overhang about 5'.

if it's wood, the post would be a 4x4, unless for some reason it was a 6x6.  if you cut a notch in the post to set a beam or joist on, you probably want a 6x6

draw a picture of what you're trying to figure out and post it.  it might help.

You should also consider Snow Loads, Drifting Snow loads, and comfort levels.

A deck can get kinda bouncy and well it might be safe but it doesn't feel that way due to the deflection.

Your balcony can be as cantilevered as your imagination will let it be! 

i raise your fancy cantilevers with a cantilevered balcony on a cantilevered building

I guess possibilities are endless in OKLAHOMA.

Will, what building is that?

Edit: Nevermind, MVRDV's Wozoco housing for whoever else is curious.  It's even cooler from the either side...

In this house that I'm planning, the balcony is 15-6 feet wide and 10 feet deep(It's a pretty big house), and I don't know much about cantilevers... Can someone fill me in...? What kind of support would I be needing?

i like the term overhanging beam.

http://www.aboutcivil.org/Determination-deflection-over-hanging-beams.html

this is what i think of as a cantilever:

http://emweb.unl.edu/Mechanics-Pages/Scott-Whitney/325hweb/Beams.htm

or, to simplify the illustration and give you a thing to test at home;

for more information:

http://faculty.arch.tamu.edu/anichols/index_files/courses/arch331/NS8-2beamdiagrams.pdf

If you look at the first of curtkram's diagrams above, you'll see the typical cantilever setup: a larger portion of a beam supported in two places ("developed length") with a cantilevered end. As a general rule, the ratio of the supported to unsupported parts of a cantilevered beam like that should never be beyond 1/3 cantilevered length for 2/3 supported length. That's true for slabs as well. Obviously, you can do otherwise with heroic structural engineering and more exotic systems or materials, but the 1/3:2/3 Rule will keep you in known territory until your cantilevered length gets beyond six feet in wood, 8 to 9 feet in concrete, or 10 feet in steel.

Beyond that, you need something special. Diagonal supports at least, or possibly high-strength materials and truss-work.

There's also a complication with using an embedded beam or slab this way as part of a cantilever system: leaks. Any time you have a beam or slab that extends continuously from interior to exterior like that, you've got a prime candidate for major water intrusion problems. Because of that, you'll usually see cantilevered slabs stepped at the boundary of inside to outside, and beams need to be extensively flashed around the hole they make in the building envelope.

So, not only are cantilevers more expensive because they require heavier structure to support them, they also require additional expense to keep the water out.

Currently, our bolt-on aluminum balconies can reach a maximum six of 6' depth x 20' width. These types don't require an embedded beam, or post beneath. The balconies basically attach with knife plates and sag rods. Here's an example of a large size bolt-on balcony

Cantilever barn in Cades Cove area of Great Smoky Mountains National Park.

Not sure if people are still active here, but wanted to check if approx 15' by 7'ft balcony is possible with just 3 columns (and beams) on 3 corners https://photos.app.goo.gl/OoNg...but without 4th column. I mean something like this:  

Thank you David and others. Yes, I am going to hire a local architect (and RCC consultant) who also will ensure setbacks, bylaws are met to get an approval from local authorities.

I wanted to model it beforehand to visualize, understand elevation and feasibility. 4th column can still be on the boundary wall w/o affecting parking width, but that may not be permitted due to bylaws and I personally would like to avoid a column on the boundary wall.

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what are the constraints of a cantilever balcony