I don't know enough about concrete to be able to tell you if doing such is a Good Idea.
I would think, unless there's an actual engineering reason for not mating old concrete to new, so long as you:

* Pre-build the rebar tie structure in ahead of time (rather than trying to go back and insert pins or epoxy in new rebar dowels after the fact)
* Use adhesion promoters to help mate the old and new concrete
* Use a concrete mix that's as close to an identical mix to what's in your original wall

Barring any technical issues beyond this (as I noted), you should be able to do it.

Why do you want to build a second story if you already have a house on a first story??

Posted By robinnc on 17 Dec 2018 06:44 AM
Why do you want to build a second story if you already have a house on a first story??

Dont have a house yet.  The concern is time and money.  If the divorce goes through and I get custody, my big concern is being able to get our daughter into a better school district then we are in now.  After all is said and done, I wouldnt be able to build the house I want right off the bat due to costs, so I was trying to think of a way to build one good enough to start in and then make the size I really want in 5-10 years when finances allow it.

Hi Redmst1969,

It can be done, bigger question is dose it make sense financially or logically.
In fact when traveling in Greece and Spain you will see concrete buildings with flat roofs and rebar sticking out from top of the walls all the time. Supposedly there are 2 reasons for it. One to allow future expansion, two reduced taxes as construction has not been completed yet.
I think it makes more sense if you could build part of the house and then add addition or build garage with above living space and then build your final home. Alternatively build both stories and just finish downstairs.
Building 1 story and adding second store on ICF home would be my last option. If this is must I would think about building 2x6 knee-wall on top of ICF to allow for rebar and other stubs in prep for second floor.
On other hand maybe just build short ICF wall right from beginning and build gables in the roof if cost is concern. Building second story from the beginning it is way more cost effective vs adding later.
Not sure if you planning to hire or diy but I have build my own home and I did second story wall in about 2 weeks just me working alone, by then I should have done it in 1 week.

Good luck.