The root ball on most trees is about the same diameter as their canopy. If you can determine what the trees are, then you'll be able to gauge what the roots are going to do. There are some trees, such as a mulberry that can extend large roots beyond their canopy that can split foundations and cause all kinds of other problems.
I personally don't think that a dwarf/small tree should be any closer than 10' to a structure, larger trees should be at least 15' to 20' away. This allows mature trees to grow without impinging on the house and root systems should not be of concern. Another common problem is planting trees over sewer, water, or power lines. It's never a good idea to plant a tree where it can interfere with municipal systems or overhead power lines.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!