Question
I have 4 ash trees growing in my backyard ( not sure what the name is called but leaves are large upright) I do know they are ash. 3 of them are about 6 feet from the house and they are about 20 ft tall. I noticed this year the roots are all protruding above the ground they have already broken one sprinkler pipe.( which I repaired) and they seem to be folowing the curve of the concrete patio. The roots that are showing are about 8 inches in diameter. My question is should I be concerned that they will damage the foundation of my home. Should they be removed? I also should mention that I am in Las Vegas and its quite hot, they do provide great shade and I hate to remove them but if they will damage my home I have no choice.

Answer
The roots should not be as great a concern as the branches. If the branches grow to rub against the house, it will damage the tree and perhaps the house. The tree should be kept at least 20 feet from the house, this should be sufficient to avoid problems. This is farther than the branches will spread because this tree has a very upright growth form. The roots will extend much farther from the trunk than the branches; however, if your home has no leaks under the foundation, the roots will not grow in the dry soil under the house. The worst that would happen is that the roots will grow up to the foundation and then run parallel to the foundation.
Realizing the tree over time will get large as it grows and the limbs extend to the house the branches that touch the house will need to be pruned. This will be a future concern not one now.

The roots will grow toward water that is why the sprinkler system had a problem. Deep watering may help encourage the root system to be deeper in the soil. Roots will grow toward water so the % of roots should be deeper than only watering normally. There will still be lateral roots since these are needed to support the tree.  

The roots will grow in the lest resistance that is why they follow the patio cement--when and if they reach the foundation they will turn either to the side or go deep under the foundation and should not harm the foundation. I would leave them be and enjoy the shade they put out. But watch the limbs and keep them off the house. The rubbing can cause damage.