Coyle Inspection Engineers, Inc.'s Fan Box

Tuesday, July 18, 2006

Expansive Soil - Bentonite

If you currently own a home in Colorado, or are planning to purchase one soon, especially along the Eastern "front range", the subject of expansive soils should be of primary concern. Expansive soils cause millions of dollars in damage annually. It is estimated that 50% of the land in the United States has expansive soil, but it is in the populated areas that the effects become most apparent. Colorado & Texas are the two areas of the country most significantly affected by this condition.
With significant real estate development along the Colorado front range in the past 30 years, the problems caused by expansive soil have become painfully obvious. Many people have literally lost their homes due to extensive damage and the high costs of repair. In some cases, class action lawsuits have been brought against builders and/or developers for failure to follow the recommendations of their soils engineers, or for failure to properly disclose the potential risks associated with purchasing a home built on expansive soil."Bentonite" is a term commonly used to describe expansive soil. Expansive soils such as clay, claystone, and shale will "swell" in volume when wetted and will shrink when dried. This volumetric expansion and contraction can cause houses and other structures to heave, settle, and shift unevenly, resulting in damage that is sometimes severe.Minor damage from expansive soil movement can sometimes be repaired for less than $5,000. However, major damage can cost $30,000 to $50,000 and occasionally up to $100,000 or more to repair!
Geotechnical engineering and structural engineering have come a long way in the last 30 years, and specific foundation systems have been devised to help counteract some of the problems inherent with expansive soils. However, the risk of damage to homes can be minimized but cannot always be eliminated.

Here are several good reasons for having your home inspected by a trained professional:
  • Not all homes in Colorado are built on expansive soil. A trained professional knows what to look for to determine if expansive soils are potentially present.
  • Expansive soil can vary significantly in its destructive potential from one area to another, even from lot to lot! An experienced professional can help project the potential future impact of expansive soil on a given home.
  • Some types and styles of construction are more susceptible to damage from expansive soil than others. A professional can counsel you on the home in question, to better understand the risks.
  • Expansive soils can be expected to eventually "stabilize" under certain conditions, but will not stabilize under others. A professional will discuss low cost improvements that will help promote stability.
  • The beginnings of expansive soil related movement can be difficult for the untrained eye to recognize. The experienced professional is trained to recognize "early warning signs" that foretell of future problems.

Invitation for Testimonials

In the past, testimonials have traditionally been written and mailed. Then e-mail became a common avenue for expressing your experiences. But now, in the up and coming blog-a-thon world you have the option to post your experiences here. Simply post a comment to this message and feel free to link back to your own web-site or blog if you choose.
Having a great day, and hope you are too!
Mike Coyle

Thursday, July 13, 2006

EcoEnovation - Denver: Good News and Bad

EcoEnovation - Denver: Good News and Bad
Here is a very interesting blog showing a home renovation project being done in an environmentally friendly way. My hat's off to Jonathon and Hanna for their enlightened thinking and conviction to make this a reality!

Wednesday, July 12, 2006

Drought causing structural damage

I wrote this article in 2003 and it is still valid today.
Mike

Is the drought affecting your home’s foundation?
by - Michael D. Coyle, P.E.
Coyle Inspection Engineers, Inc.
January 27, 2003

RECENT MOVEMENT: As a professional engineer specializing in home inspections and structural repair design, I have seen a dramatic increase in structural movement over the past year, especially in urban area housing. But why now? Could it be the drought? At first this seems to befuddle common engineering logic. After all, the dictate for construction in expansive soil areas has always been - "keep the drainage away from the foundation and do not place landscaping near the foundation that requires water." All the engineering and real estate literature emphasizes this requirement. However, with the drought there has been very little drainage to speak of, and with the watering restrictions our foundations have been high and dry. So what gives? Have the engineers been wrong all these years?

EXPANSIVE SOIL BEHAVIOR: You are probably familiar with the term "expansive soil." It is prevalent along the Colorado Front Range and by some estimations is present in 50% of the land in the USA. In brief, when the moisture content of expansive soil increases, the soil swells, or increases in volume, hence its name. This can result in upheaval of foundations built on the expansive soil. With development of raw land into housing developments, the pre-existing drainage and soil characteristics are altered by the introduction of "hard surfaces" (roofs, driveways, etc.) and landscape irrigation. In semi-arid climates like Denver, this change from historical conditions to "developed" conditions almost always results in an increase in moisture content in the soil at foundation depths. And with the increase in moisture content the potential for structural movement/upheaval increases. Hence the logic of keeping drainage away and minimizing irrigation is sound and the engineers have been correct in this approach. But drought conditions have not been part of the equation - until now.

THE EFFECTS OF THE DROUGHT: We are now into a new cycle in the life of foundation soils in developed areas. Originally (prior to development) the native soils were fairly dry. However, development resulted in elevated moisture levels that stabilized over time at the elevated levels. And as long as that stable moisture content was maintained, all was well. But along comes the drought, and the resulting watering restrictions, and our foundation soils are now drying out. Well, the devious nature of expansive soil is that it will shrink if it dries while under a heavy load (such as a house), causing settlement. This is especially true when a home is built on a spread footing foundation (most homes built prior to 1970), as opposed to drilled piers (caissons). Homes on caissons are typically anchored into deeper bedrock and therefore are less effected by the drought. Homes on footings, however, typically bear onto the soils above bedrock and tend to "float" with the changing moisture conditions of those soils. And as the soils have been drying recently, the homes have been settling. In almost every inspection I hear the following, "this home hasn’t moved in 30 years and now all of a sudden..."

SYMPTOMS OF MOVEMENT: Look for cracking in exterior brick walls and interior plaster/drywall. Cracks tend to develop first at window and door corners. Sloping floors, and binding doors are also indications of movement. Most lots are naturally sloped and settlement frequently occurs at the downhill side of the home. Of particular interest is the degree of cracking and floor slope and the rapidity of its development. Any new cracks of 1/8" or more indicates trouble. Homes with crawlspace depth foundations are particularly susceptible as the foundation is shallow relative to the ground surface. These soils dry out faster than basement depth soils. If the drought continues, however, I would expect basement depth foundations to become increasingly affected.

SOLUTIONS: Depending on the magnitude and rapidity of the movement, it may become necessary to underpin the foundation with steel piers to prevent further settlement. Minor movements however, can be monitored and addressed on an as-needed basis. With a return to more normal climatic and landscape watering conditions, some minor settlements may actually reverse themselves, at least to some degree. This is hopeful thinking however, and I would not count on it, especially if the drought continues for the next year or more. The longer the drought lasts, the greater our problems will become as settlement will continue and damage will progress. The first step is to have a professional engineer assess the current condition of the home, to determine if monitoring is a legitimate option at this time, or if underpinning is necessary to minimize further damage. If underpinning is warranted, the engineer will need to prepare a structural repair design for use by a structural repair contractor. Make sure to use an engineer with specific experience in residential structural inspection and repair design. In the meantime... pray for rain!

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On this blog you will be able to read articles and helpful information about the home inspection industry, structural issues facing owners/buyers, words of wisdom from our engineers, answers to your questions, and hopefully it will be entertaining as well as informative. So please do not be shy!

At your service!
Mike Coyle