Thursday, June 6, 2013

Trees, Trees, Trees

I read a report recently that roughly 90% of all foundation problems here in Houston are tree related.  The two big questions are 1) How do trees cause foundation movement? 2) What do you do with them?

Causes of Foundation Problems.

Trees drink water. I know this isn't mind blowing information, but trees drinking water is what causes the foundation to move.  As we discussed in earlier posts, moisture content in the soil is what causes foundation movement.  Trees cause one area to have a different moisture content than other parts of your lot, and a different moisture content than underneath the middle of your house as well.   Contrary to myth, trees are not pushing your foundation out of the ground.

There are however, two types of movement that are tree related: settlement, and heave.  The following is a slight explanation of each.

Settlement: Settlement occurs from the simple fact that trees are drinking water.  Being that the trees are usually located on one part of your lot, there will be more moisture removed from that side of the lot than in the other parts of your lot. Take my lot for example.....

See how all the vegetation is on one corner of my lot?  I have a 25 ft. pine tree, a 30 ft. sweetgum, a 12 ft. crepe myrtle, and a handful of red-tipped photinias around that side.  Each one of those is drawing moisture from the soil where that is not happening on the front right, back right, and back left sections of my lot.  So, the front left could dry out more, causing settlement on that side over time.  

Heave: Trees cause heave when they are removed.  Why?  Because they are no longer drinking water from soil that they have been drinking water from.  This will make the soil rehydrate, and therefore swell.  When the soil swells, it can create enough pressure to actually lift the foundation.  Go back to the picture of my lot.  If I removed all of that vegetation, 100's of gallons of water that used to be removed from the soil are now not being removed.  When the soil rehydrates,  the front left corner of my home would lift.

So what do we do about it?
The easy answer is water your trees.  I have a different philosophy on watering, and it's one that's worked very well for me.  I water what pulls moisture out of the ground.  I water my grass, and I run a soaker hose around my trees and photinias, and also run my sprinklers additionally on the front left section of my lot.  Where I water the back left, back right, and front right about 40 minutes per week, I run the front left about 60 minutes per week plus 20 minutes of soaking it with a soaker hose.  (I also have the advantage of having a compu-level, and the ability to shoot elevations across my home to make sure that it's working :p). I am not a proponent of removing trees.  Occasionally, when the home is directly against the house, I will recommend removing it.  For the most part, I say leave the tree and water it.  In the long term, it will be best for your house, best for you lot, and best for the tree.

I am also not a big proponent of root barriers.  To me, they don't make a lot of sense long term.  I've also heard the stories of "We installed this root barrier 4 years ago, and it worked really well for a while, but now it seems to be doing the same thing."

Look at the diagram above. The life of a root barrier  can only work as long as the barrier is as deep as the deepest that a tree can influence.  If the influence of the tree is beyond the root barrier, it's only a temporary fix.  Eventually diffusion will cause the moisture on the other side of the barricade to go to the tree. 

When that happens, the root barrier looses it's effect.  Also, most root barriers are made from rock, and some type of lining.  I've even seen them made from Steel I-Beams.  In Houston, steel will rust in the soil over time.

I say stop the shenanigans and tom-foolery and just water the trees.  I water my trees and yard almost exclusively, the only time I use a soaker hose next to the house is when/if I see the soil pulling away from the foundation due to lack of water.  If it rains, I don't run my sprinkler system. 

Once again, if you are seeing problems with your home, don't hesitate to contact us.  We are more than happy to help in any way possible.


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