Apartment extention

[Douglas Tyrrell]

I am looking to extend a 24x40 ft rancher with an efficiency apartment. This would involve extending the foof 19 to 20 ft. It would be atached to the main house with it's own entrance from the outside. It would enclude a kitchen and bath with either one bedroom or a livingroom that can be converted. I would like to know if a perfab can be built and put into place. If so would this be less costly than constructing from the ground. I live in Bethlehem, Pa. where this is legal.