I am in the process of finding a contractor to do a 1 story 10'X 20" addition plus remodel of area adjoining the addition.my question is how does a contractor decide what
type of foundation to build for this addition
what type is most cost effective? Will my local building code dictate what my options are?
If the existing house foundation meets the local building code he will likely match the existing. This will help to keep the floor levels the same elevation.
The building code does have some requirements to make certain the job is structurally sound but there should be quite a few choices as to the type.
All the codes I have dealt with require any new footings that are to be attached to an existing structure are to be identicle to the existing structure, or if the existing structure is not up to code, the foundation must be installed below the local frost line. I have seen footings that have been dug out and formed and I have also seen trenched foundations. This is where they basically make a trench and form 6" below grade and up to where the top of the foundation ends and pour into that. As long as it meets or exceeds the existing depth of the foundation it will be up to code. In any case expect to pay upwards of 2500 for the footings if you need to go below 42" in depth.