This is just a very broad question. Let's take Case #1, a single-story
home addition of 36' x 16'. Case #2 would be an addition that's 50%
larger in area, at 36' x 24'.
So, would the cost of Case #2 be about 50% more than that of Case #1?
Does such a rough rule of thumb exist?
Most builders that I know base their ballpark estimates on a square footage
basis. A working estimate is usaully based a cost per linear or square foot
basis or per item on the items to be installed. They also factor in site
There are several factors that could kick it 10% up or down but your
statement is close enough for a general discussion.
Some factors that would affect the final tally include:
Crawl space or slab construction.
Perpendicular or parallel to existing structure.
The need for a center pier and beam on one and not the other.
Added windows or doors.
And probably a couple I did not list.
If Robert Allison choses to answer you post he would give you a more
accurate opinion than me.
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