I have a bungalow that I want to add a 2nd floor to. There is a knee wall that will come out & a new wall built at the front of the house. My question is, I have 2X8 joists 16oc that span 13' 6" from the front of the house to the back of the living room. Will they be strong enough for a 2nd floor? They are working now but the upstairs is only in the center of the house, knee wall to knee wall.

They should be fine if you have two (2) lines of solid bridging. Be sure that all the outside wall go to solid bearing(foundation) or support girder.

Chuck

The main exterior walls all rest on the basement walls, but I was planning on a cantilever of 14 inches,

They should be fine if you have two (2) lines of solid bridging. Be sure that all the outside wall go to solid bearing(foundation) or support girder.

Chuck

The main exterior walls all rest on the basement walls, but I was planning on a cantilever of 14 inches,

Getting a permit? They should tell you what is needed. Currently this is rated for a ceiling joist at 10-20# live load, not a floor joist. Span tables for FLOOR joists at 2x8" @16"Centers /40#live load, even with the strongest Modulus of Elasticity are maxed at 12'10". If they are bedrooms ONLY you can use 30# live load. You might need to double up every other joist. Span Tables Tutorial (http://www.awc.org/technical/spantables/tutorial.html)