You probably should check with a certified arborist. I'm a little confused by your description, though, because if you have a 10 ft side set back, then the tree must be at least 10 ft. from the house. If you're 10 ft away from the tree, and only taking out, say, 1/4 of the roots at that distance (I'm thinking a pie wedge out of the roots), you're probably going to be okay. Putting a slab over it will be worse, since if the roots ever do pull, they'll crack the slab. A tree person could tell you what will be safe, and how to do it.

FWIW, we confronted a similar issue and cut some large roots and put part of th ehosue up on piers/columns, rather than digging a foundation.

First you need to determine if it is your tree or your neighbor's tree. If it is your tree cutting it down is an option (maybe not the only option, but it is on the table). If it is the neighbor's tree you can cut out the roots up to the property line so long as it won't kill the tree. Only an arborist can tell you how many of the roots you can safely cut.

DH's rule of thumb when trying to protect trees was to not touch anything within the tree line - obviously an issue with a large oak. However, that is a builder being conservative to avoid calling an arborist. I imagine it varies by tree species as well.

Thanks guys. Heimert, you have it correctly. The tree is looks 15-18ft from the left front corner of the house if your facing it and I can't move the house back any further to pick up more room. I would like to dig straight down to put my basement walls but would be getting into the root system in a pie shaped way as you descibed. I'm quite sure it is on my neighbors property and I doubt the city arborist (Atlanta, they are impossible here) would let me cut into the roots very far. I definately have to have poured concrete walls to keep the water out (12" walls i'm doing). I am going to check with an arborist and hopefully they say I'm far enough away from it but the city may override them.

i would be doing some major checks to see whose tree it is. while i don''t like to just cut a tree down, you must realize that an oak tree, especially a large one, can send roots for quite a distance. you will run into roots almost as far out as the tree is tall, if not further. we have tons of oaks around here, and all over town you see sidewalks and driveway heaved up from oak roots from a tree 30+ feet away. imagine what that will do to your wall/slab over time.

i know of a couple people who put an underground wall a few feet away from their house just to divert the tree roots. in most cases this is not necessary, but in extreme cases it is that or do not build.
get a pro to evaluate before you go further.

I don't want to totally downplay the power of trees and the risk to a foundation but:

"you see sidewalks and driveway heaved up from oak roots from a tree 30+ feet away"

Sidewalks are typically 4" thick concrete, driveways are usually 6" thick concrete.

A residential slab should be a LOT more massive and MUCH stronger.

Only difference between a residential and sidewalk/driveway is that the residential has footings and typically more reinforcement( rebar, mesh) but is basically 4-6 " in the field of the pour. Residential usually has a higher p.s.i load requirement as well, but most use the equivalent for driveways. I cant speak for sidewalks as far as that goes.

I agree w/ the others to get a pros advise concerning the tree roots.

in my area slabs are the most common method of foundation due to high water table. it is not uncommon to see a tree root cause major slab damage. a good friend was renting a house down the road form my grandmother. it had 1 large oak in the front yard and one inthe back yard, and no other trees within 50' of it. the 2nd year they were there a hairline crack appeared in the kitchen tile. by the 4th year, the crack was 3" wide. the landlord finally sent soemone to fix it, they thought the ground had given way and were going to mudjack the house, and when they studied it they found it was a root from one of the oak trees. the house was 30 years old, the slab was 8" thick at the point of the break, AND this was 15 feet INSIDE the house, well beyond the footers.

although people don't think it can happen, a tree root will gradually crack concrete. the root exerts constant pressure on the concrete and as soon as it cracks, the gap starts to widen. the wider it gets, the less force it takes to spread it.

i would seriously consult a pro before i built this close to a large tree. it can be done but you have to make sure that you control the roots to minimize the damage they WILL cause.