I have been asked this question many times, and it is very hard to answer.
It depends on many factors. Past work experience can be used as a general guide line.
My builders and I came up with the 40% rule of thumb.
In general, the remodeling work should not exceed 40% of the house's total area.
There are different degrees of remodeling.
It makes sense to remodel an existing old house, when the work is primarily cosmetic (no structural work), even if the amount of work exceeds 40%.
It does not make sense, (unless the final cost will be less than the market value of surrounding homes)
when there is structural work involved, like a new addition greater than 40% of the existing house, or adding a second floor on top of the existing house, because the foundations are not strong enough to
support additional load.
Technically everything can be done. Keeping the project in the budget is a different matter, and there are too many variables to generalize. Each case needs to be evaluated in the proper context.
