Approximately how much would it be per square foot to lower the floor in in our garage area and attached in law? The ceiling height is only about 7 feet right now. We’d like to lower the floor by 6 inches so that we can use the in-law as a legal rental property.
Assuming we have concrete slab foundation, what are options for lowering the floor?
To answer that question, you will first need to know how deep your footings are. I’m on the other side of the country from you, but knowing your climate is fairly mild year around, I would assume your building codes would not require footings to be much more than 12” deep. If that is the case, you really can’t go down very far because it could compromise the structural integrity of your foundation. Most codes will not permit you to excavate below the top surface of the footing. In the event you do go below that level, you can disturb the solid and it may not show up right away, but you will get settling in the foundation, and that’s not good for a lot of reasons. You can hire an engineer to design structural footings to go below that level, but I would guess your engineering costs and then the work to do that would be well over $10,000.00. You may have other options such as vaulting the ceiling or raising the roof. I suggest you reach out to a contractor in your area that can come up with some options and possible provide some design work for you. You should expect to pay a professional maybe $1,000.00 - $1,500.00 to provide this for you, but when your messing around with anything structural, I promise it is well worth the investment.
Joe Balich
Meridian DesignBuild, ltd.
