Why Trees & Slab-on-Ground Foundations Do Not Get Along

Why Trees and Slab-on-Ground Foundations Do Not Get Along

The presence of large deciduous trees near slab foundations can result in more distortion of the supporting soil   

Are some trees better than others?

Yes. Oak trees need a lot of room and are generally not compatible with the small lots you typically see in and around Houston.

Some better selections include lacebark elm trees

Lacebark elm in a brick planter. This tree does well in confined spaces.

Close up view of the distinctive bark on a lacebark elm.

An even closer look at the bark of a lacebark elm

Another good tree is a river birch. This tree does okay in a confined space. They have a distinctive bark. They tolerate poorly drained soil well. The major drawback is that they are shortlived.

Are some locations better than others

Yes, as far away from the foundation as practical. It is best that the drip line of any not be any closer to the foundation than 5-feet.

Do root barriers help?

In my experience, yes. But I would be the first to admit that other engineers may disagree. I generally recommend that new deciduous trees be planted so they will not overhand the roof during the life of the tree. Existing trees should be left alone unless it is obvious that the tree is a significant source of distress due to foundation distortion.  

The worst tree may be the tree that is missing

I have seen many situations where there was a large mature oak tree on the lot before the house was constructed and the tree was within the footprint of the foundation. A large oak can remove 150 to 200 gallons of water each day. Once the tree has been removed, the soil near the tree will begin to rehydrate causing the clay soil to swell. 

The only effective solution is to wait for some period of time to allow the soil to rehydrate before placing the slab. Virtually no builders are willing to do this. The same goes for buyers.  

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