Watering clay foundation in summer 1

[knowlittle]

I just moved to Dallas. My realtor said watering the house perimeter is necessary. According to him (and internet search) the clay soil in Dallas (north Texas) dries out in the summer (no rain, high heat) and contacts, putting a stress to the concrete slab foundation. Is this an urban myth?

 

[oldestguy]

I'd check with the City Engineer as to their experience with clays there. Some clays expand and contract significantly with moisture changes. Where summer drying results in settlement of the building, watering the soil counteracts that as a simple procedure.
Another factor might be the presence of trees nearby. They can withdraw lots of water, as much as several (even 50) barrels a day. Removing trees and watering might even be the best for these clay areas. Ask if the clay is montmorillonite or similar.
Edit:
Did a search for Dallas soils and , yes, there is plenty of expansive clay there. The effect can go well below foundations causing buildings to settle or raise depending on moisture conditions.

Look for cracks in the building and foundations, as well as uneven floor elevations due to settlements in the past.

 

[knowlittle]

Thank you for confirming house perimeter watering is not a myth. I will contact the city as advised. By the way, I have no big trees in my lot. Neither my next door neighbors. Montmorilonite is a bad clay?

 

[oldestguy]

Well clays that expand and contract significantly can be troublesome as a result, yet you can build on them as long as you take into account with the building what can happen. For example an engineer I know lived in Colorado where the clay there is highly sensitive to moisture changes and his house interior moved up and down with the seasons not equally as the outside walls (inches). He recognized this and each spring would adjust the interior columns in his basement and reverse that in the fall. No big problem. I suspect your situation has been taken care of by that summer watering. For a school in Appleton Wisconsin an outside wall of an auditorium had a significant settlement in just one area. Just outside that wall there were fast growing elm trees. Instead of cutting them down they just keep a small ditch alongside the wall with water dribbling in. Wall came back up and all is fine. I saw the same treatment done in Lansing IA at a nursing home where one unit was not livable due to the wall settling and a tree outside. Watering the tree made the unit livable again.

 

[chicopee]

Great information from as my son and his family are being transferred to Colorado Spring. Interestingly enough, in Colorado Spring, insurance companies will not cover destroyed homes from landslides as informed by a realtor in that city.

 

[Lomarandil]

Chicopee --

1) That's hard for me to believe (the insurance, not that your son is moving!). If this were a concern, I'd ask another source.
2) Only a miniscule percentage of houses in Colorado Springs would be at any risk of landslide. Manitou Springs, sure.

----
just call me Lo.

 

[emmgjld]

Information from realtors ... Usually a good place start a conversation or investigation.
Yes, there are a few select areas of the greater Colorado Springs Area, that were built upon and have very interesting risks. I could believe that a very few areas, probably on the east, northeast slopes below Cheyenne Mtn. have the geology which could could even cause an insurance agent to stop trying to sell.

 

[Agent666]

We have expansive clays in the area I'm in, its not out of the question to get +/-100mm of heave in highly expansive clays.

I've heard of instances where the site is stripped and left for a few months in summer and its dried out too much beyond the natural equilibrium point of the soil water content. Then they build, and the first winter comes along and the ground re-hydrates back to its natural state around the perimeter but no water can get to the interior protected by the slab and sees the entire like 150mm of heave from internal to external and it basically wrecks the house. Sometimes I see if a site is left exposed for some period of time that the geotech requires the building platform to be flooded to restore the lost water content prior to starting construction.

Its mostly dealt with by making sure your foundations go deeper than the surface clays, usual advice in these parts for moderately expansive clays is to ensure you are 600mm below finished ground for your footings, this maintains the water in the soils under the slab making it less susceptible to seasonal variations

 

[knowlittle]

Thank you for confirming house perimeter watering is not a gimmick.