I am far from an expert on this subject, but I have seen first hand the damage roots can do to a garage built on a slab. Over time, the entire floor was cracked and uneven. Above grade walls made from concrete block eventually cracked and tilted out of plumb breaking the pins that held the sills in place.

I think a lot depends on the construction. Slabs built with integral poured footings are probably not in great danger. On the other hand and in contrast to basements, the roots remain out of sight until the damage they're doing becomes obvious. If the area beneath the slab remains moist, it will attract roots.

I busted up the front porch slab of my rental house a few months ago and I was amazed at the amount of roots under there from a mature Slash Pine growing about 30' away. If they were under that porch I'm sure they are under the house as well, but I haven't noticed any cracks in the concrete. That house was built in 1962 and I'm sure the tree is at least 30 years old.

for the sake of discussion .....

the question is usually.. did the tree cause a given problem.. or take advantage of a pre existing problem ...

ken

Just my opinion... but trees that normally have exposed surface roots (sweetgum, maples, magnolia) are going to behave that way whether there's a slab over them or not.

I wouldn't plant any "bottomland" type tree near a slab, as those are typically the ones with the most surface roots.

Ken makes a good point. The ground can settle after the concrete is poured and then cracks can develop. Roots love cracks. They're a source of water and air. Good preparation before the concrete is poured makes all the difference.

Did you know a concrete truck delivering concrete will not drive on a concrete driveway unless a waiver is signed? They have no idea how thick it is, or if there are voids under it, compaction issues, etc.

I would only worry if there was a silver maple ;)