Expert: Dan Griffin - 1/1/2008

Question
I was thinking about buying a modular home which has been set on permanent foundation piers. The house is about 1,400sq ft. If I do get this home however I would like to add a complete basement underneath of it. So my question is: Is it possible to that on this type of home, what if any details can give me about doing it, like would i have to raise the home or could they do it without raising the house since it is already on the piers? Also do you have any idea about how much this would cost?

Answer
You sure are not the first person to ask the question.  I have already answered it on this forum twice.

I don't see any way to perform the basement without moving the existing house.  Your electricity, water, gas, and sewer system already exist.  It would be very difficult to maintain these services.  There have been basements dug under existing structures, but it would more than double the cost of the excavation just for the difficulty of removing the dirt, to say nothing of maintaining the structural integrity of the house, safety, and maintaining services.  YOu never tell how deep these piers are, but the basement will require digging about 10 feet below finish floor, if the piers are not this deep they are more of a hindrance than a help.  You are talking about removing about 350 cubic yards of dirt, about 30 large dump truck loads.

AS popular as this question is getting, perhaps someone should specialize in this process, but to my knowledge it would be unusual, but then, basements are quite unusual where I live.  If basements are common in your area, call a local contractor who specializes in basements and ask  them.  They may have some tricks I don't know about.