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Why Are Texas Homeowners Told That They Need To Add Water to the Soil Around Their Foundation? Part 2

In my previous blog (Part1), I discussed the “requirement” for Texas homeowners to add water to the soils around their slab foundation. This is being done to attempt to limit foundation movement caused by clay soils drying out.

Slab foundations in North Texas are usually not installed in a stable bearing stratum (like rock) but are installed on the surface of expansive clay. Being installed on the surface ensures that the foundation is in (and on top of) the Active Zone. The Active Zone is that depth below the ground surface where the moisture content does not vary. The soil below this Active Zone is reasonably stable, but the soil above the Zone contracts and swells in a cyclical manner, depending on the season (wet/dry). This shrink / swell can push a slab foundation around.

So the goal of adding water to the clay soils around the foundation is to attempt to keep the moisture content of the clay in the Active Zone as constant as possible. Doing this minimizes (but does not necessarily eliminate) the potential for slab settlement. at least the settlement that is caused by the soils becoming desiccated. (Slabs settle for reasons other than desiccation.)

There are three methods commonly used by homeowners to add water to the clay.

Soaker Hoses
The most common method of maintaining the soil moisture is by laying soaker hoses on top of the ground around the foundation. Even though this technique has its difficulties, it is the simplest and least expensive. It also makes it easy to see if the hoses have been damaged and need replacement. It is usually recommended that the hoses be placed 18” to 24” from the foundation.

One problem with soaker hoses laid on top of the ground is that a lot of the water can be lost to evaporation or run off. Another problem is that they get kicked around and cut up by the landscaping crew.

Some homeowners bury the soaker hose which protects them from lawn mowers, but this makes it more difficult to see if they have been cut, damaged, etc.

Automatic Lawn Sprinkler (Irrigation) System.
If a homeowner is planning to have an irrigation system installed, here are a few things to discuss with the irrigation (licensed) specialist:

• If I were going to have a sprinkler system installed, I would have a supply line installed parallel to and about 4 or 5 feet from the foundation (to minimize the bad effects if a leak developed in the system). I would then install short radial lines to reach the foundation area (with the sprinkler head about 6” or so from the foundation).
• I would not install the water supply line only a few inches from the foundation.
• Regularly check the sprinkler system for leaks, including at the valves.
• In the Dallas / Ft. Worth area, I would install the irrigation pipes at least 12” below the surface to minimize the danger of an extended period of freezing weather. However, the irrigation technician will know the minimum depth. I had a neighbor whose new sprinkler system was buried only 8” and portions of it froze during a particularly cold winter. Your local city building code department probably has minimum guidelines on this.
• If the purpose of the irrigation system is to keep the soils near the foundation at a constant moisture content, then there should be 3 or 4 zones dedicated to the foundation only (possibly more depending on the size of the house). This way, it is not necessary to water the entire yard when the foundation soils need water.
• Do not allow the sprinklers to spray water on the brick/siding.
•DO NOT suddenly begin an aggressive watering program if the clay soils are in a desiccated state (like during a drought or in the dry summer months). In other words, do not suddenly put a lot of water into the clay soils around your foundation. To do so, can cause upheaval of the slab. It is best to allow Mother Nature to rehydrate the soils during the winter/spring months and then start a watering program prior to the summer drought kicking in.
• Too many homeowners water only enough to keep the upper few inches of soil moist; this is inadequate.
• One typical indicator that the soil around a foundation needs moisture is that the soil begins to pull away from the foundation. When this occurs, moisture is needed: do not pour water into the gap!
• During the prolonged summer drought, it may be necessary to water the soil around the foundation several times a week. A word of caution though – do not suddenly overwater dry expansive clays! The goal is to keep the soil near and under the foundation at a consistent moisture content (neither wet and/or muddy nor dry and cracked).

I  have seen homeowners who had just purchased their homes and began their watering the soil program only to cause the clay to expand, heaving their foundation upwards. They later found out that the soils around the foundation had not been “watered” for months and were in a desiccated condition. I do not have an answer to this dilemma. My advice is to be careful and be gradual in your watering program. As stated elsewhere in this blog, if it is new home, talk with the builder and/or his engineer about their recommended watering  guidelines. If an older home, let Mother Nature rehydrate the soils, then you start your watering program.

In the next blog, I will discuss the pros and cons of a buried drip irrigation system.

For additional information, go to  http://www.GeoDFW.com.

 
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Posted by on February 13, 2015 in foundation repair

 

Why Are Texas Homeowners Told That They Need To Add Water To The Soil Around Their Foundation? Part 1

Background
As is well known by most homeowners in North Central Texas, the foundations for our homes are many times constructed on expansive clay soils. The problem is that clay soils shrink when they dry out and swell when they experience an increase in its moisture content and this shrink / swell of the soils can easily push a slab foundation around. This has cost Texas homeowners millions and millions of dollars in repairs.

In the North Texas area, the soils tend to become desiccated in the dry summer months. There is a depth below the surface which is called the “Moisture Active Zone”. This zone is typically considered to be about 15 (or so) feet deep but the actual depth varies depending on many factors (soil conditions, rain, drought, trees, exposure to sun/wind, etc.).

Below the active zone, the moisture content of the soil generally does not change. However, above the active zone, it does. As the soil moisture changes, so does the volume of the clay soils and a structure built in (or on top of) the active zone is prone to move. This includes almost all slab foundations.

So, in much of Texas, it is commonly said that to prevent (at least minimize) the movement of a slab foundation, a homeowner must maintain the soil moisture content around the slab foundation at a constant rate (year around). This means attempting to replace the moisture in the active zone that was lost because of desiccation caused by environmental influences. This is done in the dry seasons by adding water to the soils. Maintaining the soil moisture content at a constant value is an easy thing to say but is difficult to do, especially during times of extended drought.

One difficulty for homeowners is that there is no “formula” available to tell them how much water they need to add per day/week to keep the soil stable, i.e., to keep the soil volume constant. There are too many variables.

This is because environmental and soil conditions vary from neighborhood to neighborhood. Also, the rigidity of one slab is typically different than another. The more rigid a slab is, the better able it is to overcome the movements of the soils caused by the variations in the seasonal moisture conditions (rainy season vs. dry season).

I am asked regularly: “can the builders build a slab that does not move”? The short answer is yes. The basic reason most slab foundations in North Texas move is that they are not founded in a stable bearing stratum which is below the moisture active zone. (There are other reasons a slab foundation move but moisture variation is the subject of this blog.)

So, to answer the primary question posed in the title of this blog: homeowners are told to add water to the soils supporting their foundation because most slab foundations are based in the active zone where the soil moisture content varies because these soils are susceptible to desiccation during the hot, dry summer months (and during other periods of drought).

I should say that I have observed a few homes with slab foundations where the homeowners appeared to be very diligent about applying water to the soils, but their foundations still moved and further (and more expensive) remedial efforts were required. Also, a word of caution: I have also seen homes where the homeowners started a vigorous watering program when the soils supporting his foundation were dry, expansive clays and the sudden increase in the moisture content of the clays caused the clay to expand and pushed (heaved) the slab up significantly. This upheaval is a problem.

The next blog will discuss the various methods commonly used to add water to the soils around the foundation.

http://www.GeoDFW.com

GeoDynamics Engineering

 
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Posted by on February 1, 2015 in foundation repair

 

House “Flippers”

Over the years, I have inspected the foundation of homes that had been purchased by investors. The investors remodeled the interior / exteriors and brought them up to a “new car smell” standard and sold them. Obviously, I am somewhat jaded by some of the things I have seen “flippers” do. However, on the other hand, I have seen some investors who not only do a wonderful job on the “new car smell” upgrades but  also do a good job on repairing the foundation (if needed).

Since I get involved in only foundation problems (in North Texas), my comments will center around the Good, Bad and the Ugly aspects of buying a home that has foundation problems from an investor. (I should also say that I have also seen some long time homeowners / occupants of a home act the same way as the “flippers” do – see the last example of “The Ugly”.)

The Good

One home I inspected was owned by an investor who recognized that foundation repair was needed on a home she was going to “flip”. She contacted an engineer to design the foundation repairs. She hired a reputable foundation repair company to do the work. Once the foundation work was completed, she had the engineer return and review the work and write a compliance letter to pass on to a prospective buyer.

Included in her sales package to any prospective purchaser was a copy of the engineer’s reports, the foundation repair company’s warranty documents and a copy of the sub slab plumbing leak test (done after the foundation work was completed).

She then installed new floors and remodeled the kitchen and baths.

The home rapidly sold at the asking price.

The Bad

Several months ago, I inspected the foundation of a 1500 sq ft home with a slab foundation. The buyer (my client) loved the home because the investor had installed new wood floors, new kitchen granite counter tops and removed some walls to make an open interior living room/dining room and kitchen. He had also recently had foundation work performed. The investor had retained an engineer to design the foundation repair. The engineer had recommended the installation of numerous piers around the exterior and throughout the interior.

He also specified that the foundation be raised to within a specific range.

The investor hired a foundation repair company to install the piers supposedly in accordance with the engineer’s specifications. (It was later determined by my client that the foundation repair contractor did not obtain a building permit as required by the city.) Once the foundation was “repaired” the owner completely remodeled the two bathrooms and installed new wood floors.

My inspection found that the foundation in several of the rooms was still significantly out of level, with some doors so much out of level that they could not be closed. Also, there was no evidence that the foundation repair engineer had ever reviewed the foundation repairs as they was being done or afterward.

I advised my client to have the owner (investor) get his engineer to issue a letter certifying that the foundation work was done to his specifications or if not, describe what needed to be done to make it so. I also advised my client that to attempt to raise the foundation up to an acceptable level would probably damage the remodeled bathrooms (including the shower tile walls); so some cosmetic repairs would need to be done after the foundation was lifted up.

The owner was not willing to do these things so my client wisely backed out of the deal.

The Ugly

I once inspected a small home for a young couple who had just purchased their first home and within a few weeks after they moved in, large cracks began appearing in the sheetrock. In my inspection I found that the doors were generally level but that the slab was over 6″ out of level. It was obvious that the foundation was (and had been) unstable.

I asked them if they had a copy of the report from their General Home Inspector, made prior to purchasing the home. They said that their realtor told them that an inspection was not necessary so they did not have the home inspected. (The realtor had them sign a document that said they did not want an inspection.)

They found out by talking to a neighbor that the previous owner was a professional painter and that he would completely paint the interior of the home two times a year and had done so prior to putting the home on the market. (He also had rehung the interior doors.)

To repair the foundation would require about $25k of piers which they could not afford.

My Advice To a Buyer of a Home in North Texas

Get all documents from the seller that concern foundation problems. If the owner says that there has not been any foundation work done or an engineering inspection done on the foundation, then I would also ask if he has ever had the foundation inspected by a foundation repair company (who probably would not be an engineer). If so, who was it and what did they recommend? I would also ask if the seller if he has ever had any problems with the operation of any doors (sticking) or made cosmetic repairs to the sheetrock or brick cracks. Call the city Building Inspection Department and ask if there have been any building permits issued for foundation repairs. If so, get the documents.

Retain an engineer to inspect the foundation prior during the option period. The engineer should also take elevations as a part of his inspection.

Many times, if a foundation has been repaired, the foundation repair contractor will have retained an engineer to review and sign off on the repairs. This engineer is the engineer-of-record for the foundation repairs. It may be possible to get this engineer involved in the inspection of the current condition of the foundation. If so, he should issue a written report of his findings.

 
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Posted by on December 29, 2014 in foundation repair

 

Building a Home on a Hill

Over the years, I have inspected numerous foundations of homes that are constructed on severe topography, i.e., where the ground surface slopes significantly, such as on the side of a hill or on a creek lot. Generally speaking, what I find is that portion of the foundation that is downhill, has settled. This settlement occurred because the builder/developer brought in fill material to level the lot prior to installing the foundation and the fill dirt consolidated (compressed) over time and allowed the slab to settle. Also, dirt located uphill will tend to move downhill (because of gravity). This action is called “soil creep”.” Soil creep” is a slow gradual action that usually occurs over a several year period.

Obviously, it is possible to design/construct a stable foundation for these types of conditions, however, the design needs to be well thought out. It is recommended that a site specific soil report be obtained that determines the soil properties & characteristics. The design engineer will then use the soil data to design the foundation. Many times, a foundation located on the side of a hill should include piers that are founded in a stable bearing stratum.

Usually, these piers are drilled concrete piers, preferably installed into a stable rock formation or if rock is too far down, the pier shaft is belled at the bottom to a diameter of 2.5 to 3 times the diameter of the pier shaft. In other words, if a 12″ diameter pier shaft is specified, the bell diameter will be 30″ to 36″ diameter (depending on what the design engineer determines).

Yes, this is expensive, but it is usually not as expensive as trying to install piers after the home is built and the foundation moves.

Also, when a home is being constructed on a severe hill, it is many times, advisable to install a retaining wall. I have seen many homes where the soil is moving downhill and causing a void space to appear under the slab. The only way to stop this “soil creep” downhill is to have a stable retaining wall stopping the soil. The foundation design engineer can determine if a retaining wall is necessary.

The object of this blog is to caution folks who are going to build a slab foundation on the side of a hill to be cautious AND obtain the proper engineering advice.

 
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Posted by on November 16, 2014 in foundation repair

 

Buyers Beware – Part 2

I once inspected a slab foundation of a residence for a lady who had owned a home for 15 years and was in the process of selling it. The home was about 2 years old when she purchased it from the original owner. It is located in a suburb of Dallas well known for having highly expansive clay soils. (This means that when the clays experience an increase in moisture content, they can expand significantly.)

She told me that she had a contract on the house but the buyer backed out after his general inspection reported that foundation movement had occurred. She did not understand why the inspector would come to that conclusion since, in 15 years, she had not had any sheetrock cracks, brick cracks (except for one minor crack) nor experienced any problem with any of the doors.

My investigation showed that the foundation was over 6” out of level and I concluded that the back of the foundation had heaved upward because of soil expansion. Furthermore, all of this occurred prior to her buying the home.

I suspect that the original owner knew about the problem and made cosmetic repairs and dumped the property. Unfortunately, when she bought the home (15 year ago), her general inspector did not warn her about the condition of the foundation.

The good news was that there had not been any significant foundation movement since she purchased the house; the bad news was that prior to her purchasing the home, it had heaved upwards and was 6” out of level.

If a problem with a foundation is defined as it being significantly out of level because of upheaval, then the logical remedy would be to lower the heaved portion. This can be done, but it is outrageously expensive and is therefore done infrequently. Because of the expense, this was not an option for her.

However, if a foundation problem is defined as having recent foundation instability, then she was in good shape because the home had not moved noticeably for 15 years. However, the big problem was that the foundation was over 6” out of level.

There was no financially reasonable remedy for solving her foundation problem. So, because the seller had covered up defects and she was not properly advised when she purchased the home, she was stuck with a nice home in a nice neighborhood that she could not sell at the going market value.

In a defense of her general inspector, the original seller of this home had the cosmetic damages repaired prior to putting the home on the market. If a seller of a home hires a professional painter and brick mason, they can make most defects in the sheetrock and brick disappear. And if a general inspector does not see cosmetic defects normally associated with foundation movement, they (at least some of them) assume that the foundation is ok.

So, could this have been prevented? Yes. The key is to either hire a very detailed general inspector who can look beyond the obvious (and possibly a structural engineer that will take slab elevations).

When she purchased the home, her general inspector (and her realtor) should have noticed the slab diselevation (I do not know how they missed noticing that the master bath was over 2” out of level). Nor did they notice that the kitchen base cabinets, the hall bathtub, the fireplace hearth and the fireplace mantle were all noticeably out of level.

To repeat, a buyer’s first line of defense against buying a house with a damaged foundation is to hire a competent, detailed-oriented general inspector. If there are indications of unusual foundation movement, he may recommend hiring an engineer to do a more detailed inspection of the foundation.

 
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Posted by on October 1, 2014 in foundation repair

 

Buyers Beware

Recently, I have seen a few sellers of a home either not disclosing existing foundation problems or purposely hiding critical information about it. One example follows:

The seller (a house investor aka “flipper”) provided documents to the buyer that showed that 35 piers had been installed under the front portion of the foundation, including in the interior. The documents also showed that the foundation had been 8 inches out of level (prior to the foundation repairs). The home had been extensively remodeled after the pier installation.
The prospective buyer retained me to inspect the foundation. I determined that the house was still over 3 inches out of level and that the front portion of the foundation had been lifted about 5”. I recommended that the buyer ask if the seller had had the sub slab plumbing tested after the lift. The seller said that the foundation repair company told him that it was not necessary so no test had been conducted.
I advised my client to insist that the plumbing be checked. A few days later, the seller sent a copy of an invoice from a plumber that stated there were no plumbing leaks. However, the address on the invoice did not exist, the plumbing company did not exist and the plumber who reportedly did the test was not a licensed plumber. The invoice was obviously a fake.
The buyer backed out of the contract

 
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Posted by on September 15, 2014 in foundation repair

 

Miscellaneous Surface Drainage Comments

Too many times, I see inadequate surface drainage conditions around a foundation that can potentially cause foundation movement. Because of the presence of expansive clay soils, poor drainage conditions around a foundation in North Texas can increase the likelihood of soil expansion (with the resultant upheaval of a slab foundation). The expansion of clay soils is caused by an increase in the soil moisture content.

Some clays in North Texas are highly expansive while others not so much. In areas that have highly expansive clays, soil expansion can cause a slab to heave upwards several inches (I have seen 12” of upheaval in Irving, Texas). However, in other areas, having water ponding near the foundation does not cause a noticeable foundation problem but the water is more of a nuisance. It is a good practice to always maintain excellent drainage conditions around a foundation, regardless of what the problem is.

Some builders make it nearly impossible to have good drainage conditions because they did not install the slab foundation high enough around the ground surface. This seems to be especially the case in many rural areas.  

Rural Residential Developments

I got a call from a homeowner in a rather rural community (a few dozen homes in a non-incorporated area) that said he had a drainage problem and asked me to inspect it and design a repair. Once at his house, I noticed that not only was the ground surface around his home flat but so was the entire neighborhood, so there was no place for the water in his yard to drain. He then showed me photos of his neighborhood after a heavy rain and there was a foot or so of water in the streets (the streets were somewhat lower than the front yards) but the water came up very close to his house (and his neighbors). I told him (the obvious) that improving the drainage conditions around his home was meaningless until the neighborhood drainage was repaired.

The homeowner ended up suing the builder and the developer (who installed the streets, water, lots, etc.). Both the builder and developer took bankruptcy and the homeowner took a real bath on the house value.

 Flower Beds

The foundation should be installed high enough so that when (if) a flower bed is installed adjacent to the house, the ground surface can still slope enough so water can run rapidly away from the foundation. (Refer to the Drainage Guidelines below).

Swimming Pool Drainage

If I were to build a swimming pool, I would specify that any drainage catch basins or drainage channels had to be a minimum of 9” diameter for the catch basins and 4” wide for the drainage channels. Not the absurdly small drainage systems normally used that get clogged up easily.

 French Drains

Over the years, I have seen several french drains situated immediately adjacent to the foundation. Depending on the drainage system construction and soil characteristics, it is possible that the soil moisture content can be increased because too many times, water pools around the drainage pipe. This can be like a sub slab plumbing leak and under the “right” soil conditions can actually cause a slab to heave up. To prove this would require some geotechnical testing. But to be safe, the drain system should be installed a few feet away from the foundation.

Engineering Drainage Guidelines

The “Guidelines for the Evaluation and Repair of Residential Foundations” adopted by the Texas Section of the American Society of Civil Engineers (ASCE) in 2002 with an effective date of January 2003, states the following concerning the drainage conditions around a foundation: “Where practicable, for adjacent ground exposed or vegetative areas, a minimum slope of 5% (i.e. 6 inch drop over a 10 feet distance) away from the foundation should be provided for the first 5 feet all around (the foundation). (Drainage) swales should have longitudinal slopes of at least 2% (i.e. 6 inches over a 25 foot distance), if practicable, and 1% (3 inches over 25 feet) at a minimum.”

 The ASCE also developed a guideline for the “Recommended Practice for the Design of Residential Foundations”. In that document, they state the following concerning drainage: “For adjacent ground exposed or vegetative areas, provide adequate drainage away from the foundation (minimum five percent slope in the first ten feet and minimum two percent slope elsewhere). The bottom of any drainage swale should not be located within four feet of the foundation. Pervious planting beds should slope away from the foundation at least two inches per foot. Planting bed edging shall allow water to drain out of the beds.”

 

 

 
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Posted by on January 1, 2013 in foundation repair

 
 
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