Water your foundation?

H

Homebrew

25+ Posts
I'm looking for opinions from the Horn Fans nation. Mrs. Homebrew spoke to a friend this weekend who was simply aghast that we were not "watering our foundation." Said friend advised circling the foundation with soaker hoses or risk catastrophic damage to our house. A quick review of sources on the interwebs reveals wildly divergent opinions. Some say it's a homeowners responsibility to _constantly_ water a foundation to keep it stable while others dismiss this notion as a concerted effort by the Texas construction industry to shift blame for substandard or inappropriate building practices.

It strikes me that you'd have to pump thousands of gallons into the ground to penetrate very far at all beneath a foundation. I'm averse to pumping precious drinking water into the ground during a drought without a pretty good rationale.

What's your take on the issue?
 
Far from bogus, but believe what you will. The soils in Texas are some of the most expansive in the United States. Be careful of those "angry homeowner" websites. These people are just pissed at their tract builders and are not engineers or architects.
 
I have heard this too, and there are divergent opinions on the practice. Apparently it all depends on your soil type.
Sometimes watering the foundation can be bad, I'm told. Sometimes it is necessary. I don't have a straight answer, except the house may have to be analyzed by an expert of some sort.
 
I've done it.

I guess you don't want to "over-water" it, as if there's a way to tell. If there is a way, tell me. Over-watering will weaken the soil, or reduce its load bearing capacity. This is also not good. I'd say just stick a hose next to the house on one side, let it run for a bit, then move the hose. Rinse and repeat.
 
My thought on what it meant to water the foundation was just to water the grass as normal. And that watering the soil near the foundation is what is needed to prevent soil from drying up.
 
My wife's granddad's house is a pier-and-beam house that leans slightly sometimes - bad enough that doors won't close in their frames. Apparently he would use soaker hoses on one side and the house would right itself.
 
I could write for days on the subject. Almost all residences (in TX anyway) are built using "floating" slabs that are stiffened with beams. They sit on top of dirt (and slightly into dirt as far as the beams are concerned) and they respond to the expansion and contraction of the soil. Dirt goes up, house goes up. Dirt goes down, house goes down. We've all seen dry "cracked" soil. That is dirt that has dried and contracted to the point that it has cracked, You've never seen cracked mud.

The problem comes in when you have dirt expand and contract in an uneven manner. Left side goes up and right side does not. If the beam is deep enough and/or thick enough, the slab will be stiff enough to withstand the differential movement of the soil. A lower end home will probably not have a stiff enough slab. Particularly homes built by big builders in big brown subdivisions.

When you have a sever drought like the one we have just started (yeah, just started), the edges will dry out, but the center of the house will dry out at a MUCH slower rate, if at all. I **** you not, there really haven't been any good studies of this. Anyway, "watering the foundation" is theoretically an effort to keep the soils stable and moist and happy. The problem with this idea is that you need to have soils that have PVR's of a couple of inches over many feet. (potential vertical rise - measures expansiveness capability of soil). Soils with high PVR's don't really soak up the water. They tend to get slick. If you have the worst kind of soils (high PVR's) and shallow beams you would do well to have the dirt under the middle of your house have the same moisture content as the dirt under the edges. The problem is how do you water these slick soils deep enough to make a difference. Well, you can't really imo. Note that I said imo. You might be able to water the top soils enough to make them slick and prevent more evapotranspiration from the deeper soils. Sort of a tarp or saran wrap if you will. One those soils have become drier that normal (and normal means the day your slab was poured) I do not personally believe there is much you can do to affect the moisture content of the soils deep under your home. It's not going to hurt anything to water, it's just probably not going to do much good. It's kind of like a wood window. Keep the wood clean and painted and repaint when the paint needs it. If you let the paint crack and peel and and then wait another year or so, you may very well need to replace the window. If you keep after it every year, you will probably have a window that will last for decades. Same thing with your foundation, if you make sure that it never gets abnormally dry under your house, you will probably never have any problems.

Commercial building are built using deep drilled piers. They typically are not soil supported. Moisture of the soils can affect them, but it's pretty rare.
 
I speciafically stated those with concrete foundations. I know that some commercial buildings have drastically different foundations (high rises/scyscrpers, etc). But, I'm thinking of a slab strip center or these metal buildings that have concrete foundations. Here, we can make comparisons. And if they are similarly constructed, I still ask, "Do commercial buildings have this problem"?

Also, I have heard the hill country has the most stable soil (the rock). If so, do those houses have to worry about soil moisture?
 
You're on the right track Holden. Many strip centers are built with a deep perimeter beam and a floating slab inside that perimeter. The interior partition walls often do not support or exert pressure on the roof structure. They have movement, but it's usually imperceptible. The perimeter beam is deep enough that it is stiff enough. It still moves, but it doesn't bend. Many soils in Texas have the ability to exert pressures FAR in excess of the weight of the structure that sits on top of it. For example, in the Las Colinas area there are soils that can exert pressures so high that it's unfathomable. A typical house weighs about 150 lbs/sq. ft. Let's say that the house is 2500 sq feet. That means the house weighs around 37,500 pounds. There are soils that exert that much pressure per square FOOT! In short, if the soils wants to move, the house IS going to move if it is a soil supported slab. Sometimes as much as 8 inches.

The Hill country is a little more complex than you may think. Rock is pretty ******* stable around here and is not affected by moisture changes, but it's pretty rare to find a lot that has a flat rock to put a house on. There is almost always some soil involved and the soil is usually expansive. A common technique used was a cut and fill technique. Cut into the side of a hill and take the stuff cut out and push it downhill to make a flat area that is hald undisturbed native condition and half that is granola. With proper compaction (rarely done) it should not cause a problem. Those are the soils that frequently "settle" as they are slowly compacted. The Hill country was under an ocean for millions of years and it compacted **** pretty well. Once it is disturbed, who knows?

I've seen houses in South Austin that were 13 inches out of level. You could roll a marble down the sculptured oranged carpet and it would look like a pac man. The cut side was the high side and it is my opinion that the cut side had increased its moisture content over the years and the fill side had compacted. The high side also had major plumbing leaks under the slab which act much like pebbles in a shoe at the least and can cause more pervasive damage if they get under a beam and lift a stiffened beam.

People talk about "settling" foundations and the vast majority of them - homeowners, builders, engineers and adjusters are just plain talking out of their ***, but not many people know enough to call their ****.
 
Just a btw, the material used (concrete or other) is not really the issue. Its the philosophy of the construction, not the materials in most cases.
 
i was always assumed pier and beam residential construction was more susceptible to the effects of expansive soil. Of course, fixing the problem is also easier with pier and beam construction, because you are more than likely not even dealing with a slab.

My house is unlevel, doors don't shut, etc. I figured unprofessional watering of the foundation by me would just exacerbate the problem. Plus, i didn't want to get into a situation where i always had to have wet soil, constantly having to maintaining some consistent level. It's hard enough trying to keep my lawn from dying.

Texas is more dry than wet. I figure dry is the more constant condition, but obviously i am monday morning quarterbacking here.

I figure when it gets bad enough, i will have the skirt ripped out and all the piers tweaked or worse, replaced.
 
It depends on how deep and how big your piers are. People think a pier needs to go down to bedrock and that's just not the case. It's a matter of surface area and friction. A shallow, thin pier can get squeezed out of the soil as it expands, but a deep and wide pier has enough surface area to resist movement because of friction.

Pre- WW2 most houses were built using wooden piers and beams. They rocked and rolled all over the place, but if you think about it did they have sheetrock? No. They had wallpaper that floated on a gauze backing. Hence, no cracks. The plaster houses usually had cracks.

Texas is generally a dry place, true enough, but it's not how dry it is generally, but how dry (or wet) it is today in comparison to the day your foundation was built. Even though we are in the beginning of a cataclysmic drought (my opinion, shared by others who I trust) your soils could be wetter today than when your house was built.
 
nick made a minor error...at 150 lbs/sq ft. his hypothetical house would weigh 375,000 lbs.

personally, I tend to believe it's closer to 200 lbs/sq ft. but that's really beside the point.
 
****

It was a great example albeit wrong.

Btw, I was learned that dead loads were around 146-149. Is that incorrect as well?
 
nick, in the cases I've been involved with (all socal) most engineers assumptions have been around 180-200.

I think tile roofs are much more common here, and we use more stucco, which is much heavier than siding. That probably explains the difference.

BTW: I was sincere when I wrote "minor error" because it really didn't take away from your argument.
 
Nick - whats' your opinion on watering a post tension slab in Northwest Austin (Avery ranch). It's on rock but there is still dirt. I don't have issues after four years but don't to cause them by sudenly watering. Also is there a service that can help me decide?
 
I rarely came across any post-tensioned slabs. I don't think they use them any more, but I could easily be wrong. The theory behind them as I understand it is that the network of cables, when tightened, gives the slab its stiffness needed to keep from bending in response to moisture induced volumetric changes. Once they get far enough out of whack they can literally explode. Happened to a friend of mine who poured them for his job while at UT. His father was supposedly the main guy behind their use. Dick Martter out of Dallas.

They are REALLY hard to repair once they bend out of tolerance. Unless they are really a lot stiffer than your normal raft mat slab, I would think the watering issues would be the same. If there isn't a lot of soil under the slab then there isn't going to be much movement. The PVR of clay soils (potential vertical rise) has to be multiplied by the depth of the soil. If a clay has a PVR of 1/2" per foot, but there is only a foot of soil that's not going to be a big deal most probably. If that clay extends down 8 feet, then the PVR would be 4" and that's a big deal. The soils are pretty much never homogeneous for a depth of 8' so it's all theoretical, but I think you get the picture.
 
I was typing while you were. I think if you maintain a watering regimen year round for years, your are probably doing a good thing, but I don't think you can start in July of an already fairly significant drought and do much to make up for the years you didn't water.
 
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