how can i find out if an address is a house or appartment building?

Answer 1

See if you can find a county website. If you can, type in the address and it will give you the classification/state code. If not, call zoning and they will tell you the type of house and the zoning for the area.
Apartments and even mail-boxes often have regular addresses with no designation for unit letters or numbers.

Answer 2

An apartment building will usually have some extra designation, such as Apt. # or a letter like A, B, or C, etc. House numbers are just the number and the street.