Building an addition, would a basement be sensable?

[ck 2]

I am getting ready to add a 20x26 addition to my ranch home. My home doesn't have a basement. But I was wondering would it make sense to put a basement under the 20x26 addition? I could use the extra space for storage or an extra bedroom.

Just wondered if anyone ever does this? Just put a basement under a small addition.

[Don_P]

You can but it'll take some reworking of the existing foundation unless you get away from it before you undermine.

[Richard A Hetzel]

What Don means is that for your new basement, you'll possibly, even probably, be digging below the bottoms of your existing footings. One should never excavate below an inaginary plane that extends out and down from footing bottoms at a 45-degree angle.

Therefore, if your existing footings are four feet below the ground, and your new basement floor will be seven or eight feet below the ground, either you'll have to end the basement three or four feet away from the existing foundation, or you will have to underpin the existing footings if you come closer than that. Underpinning is a costly and labor-intensive process.

Then you will have to decide if you want access to the basement from the inside of your home, and therefore, you'll have to plan a space of approximately 10 feet by 16 feet for a stair.

Folks often speak of a basement as "inexpensive space" because all it appears to cost are a few more courses of block, or a moderate amount of additional concrete. However, most builders will tell you that what they fear most is what they cannot see, and that's whatever is under the ground. There are a few more costs associated with a basement that it appears; however, it still costs less per square foot unheated and unfinished. If it's heated, air conditioned, and finished, other costs come into play, and the space there could well cost more per square foot than it would have to build the equivalent space above ground, and basement space will always be considered substandard compared to above-ground space.

[ck 2]

Thanks for the replies. Some more info for you.

My addition will butt up to the end wall of my house. My house is 30 ft wide, my addition will be 26 ft wide, stepping in 2 ft on the back and front. Roof line will also be different.

This end wall of my house is the only wall that will be affected. Almost half of this wall is consumed by a garage door and an entrance door right now.

It really isn't a load bearing wall since my house has a truss roof and the trusses rest on the front and back walls of the house.

So I understand what you are saying about the foundation and undermining. But am I wrong in thinking that my situation is not as critical as if it was on the front or back wall of my house.