Thoughts on the Engineering Industry

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Archive for the tag “foundation”

Three Common Causes of Differential Foundation Movement

Hello everyone, I hope you guys have been doing well. I’ve been a bit busy lately, but now that I’m caught with my work and various other stuff, I have decided to continue with the theme of foundation movement.  Last time, we talked about cracks in the finishes of the house – I would like to now move onto some of the root causes of the foundation movement.

At its most basic level, most foundation movement is caused by change in the moisture content and resulting expansion/contraction of the soil supporting your house foundation.  Depending on the amount of clay or fill soil on your property, the resulting differential movement can vary by location and magnitude.  In some other cases, it is a failure of the foundation structure; it is far less common and in most cases associated a pier and beam foundation.  Even then, most of those failures I’ve seen were affected in some way by moisture content of the air/soil within the crawlspace.  Having said all that, today I will discuss the effect of soil moisture content as it is the prevalent cause of foundation movement.

Tree Roots within the Vicinity of the Foundation

The most common cause of foundation movement I see is the result trees affecting the moisture content of the surrounding soil.  In times of relative drought, the tree roots will absorb more water in the soil and decrease the relative moisture similar to surrounding areas.  In times of more rainfall, the dry soil will then expand and change the relative soil level again.  In general, tree roots extend an additional 50% further from the trunk than the outer canopy.  If the tree roots extend under your foundation, the soil under your foundation will expand differentially to surrounding areas depending seasonal rains.  The cracks resulting from this foundation movement will typically expand and contract, or reopen when patched.  Differential movement associated with tree roots can be reduced by placing a root barrier around your foundation and maintaining a regular watering program around your house.

Site Drainage

As with the trees, various site drainage conditions can cause water ponding and result in different soil moisture contents around your foundation.  As a result, the soil in areas with increased amounts of water will expand more than the soil in other areas.  Similar to the tree rot conditions, the level of the foundation and resulting cracks will fluctuate depending on the amount of seasonal rains.  Differential foundation movement associated with site drainage can be reduced by maintaining an adequate slope around the perimeter of the foundation so that the site drainage will allow water to flow around and away from your house.

Plumbing Leaks

Water from plumbing leaks can also cause the expansion of soil, typically within an isolated area.  Depending on the size and frequency of the leaks, the leaking water can cause differential foundation movement and result in interior distress associated with that movement.  In most cases, the soil expansion and differential movement does not extend far from the leak location and will not result in wide spread foundation movement.  In addition, the soil will typically contract back to it’s original volume once the leak is repaired.

Given this short outline, I hope that you can get a basic idea of what is causing the differential foundation movement you are having and how to address the issue.

What has been your experience been like in dealing with differential foundation movement?  For the people inspecting foundations, I’d be interested in hearing about your stories as well, since I still definitely have a lot more I could learn on the topic.  If you enjoyed my post, hit the like button, follow my blog for updates and share this post with your friends.  Thanks for reading and have a good week!

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Using Cracks in Gypsum Board to Assess Foundation Movement

Hello everyone – I hope you have been doing well. I know I’ve been away awhile but I plan on doing more these blog post again.  The truth is that I got away from it because I wanted to rethink my blog goals, topics, and general post structure and scope. I’ve decided that I would like to refocus my blog on topics I deal with as a forensic engineer, and keep the blog posts simple and focused on a specific topic.  We’ll see how this new blog structure works out in the next month – feel free to leave some comments on how you like it.

With that update out of the way, I would like to jump into our topic for today – gypsum board cracks in a house and how it relates to foundation movement.  A fair number of the house inspections I do involve assessing these conditions and determining if there is a correlation to any possible foundation movement.

In my experience, cracks in the gypsum board finishes of a house fall under two categories – tapered cracks, and expansion/contraction cracks at gypsum board joints.

Expansion/contraction cracks are visible in most houses – most commonly in the garage due to increased outside exposure along with the relatively less insulated and/or finished conditions.  However, these cracks can occur in other areas of the house as well.  These cracks will typically be horizontal or perpendicular in orientation, have an even gap across the length, and be patterned at typical lengths/spaces of gypsum board joints or at wall-to-ceiling and wall-corner joints.  These cracks are not directly correlated to foundation movement in most cases and are instead the result of the expansion and/or contraction of the gypsum board.

Tapered cracks, usually at doors, windows, and ceiling and wall joints, are visible in most houses as well.  These cracks typically extend diagonally at susceptible areas when not at wall or ceiling joints and are indicative of some form of foundation movement.  It is more common to see these tapered cracks in houses with a concrete slab foundation due to the foundation resting directly on ground which makes them susceptible to seasonal fluctuations of supporting soil.  However, these cracks can be present in any house depending on their construction and conditions of the surrounding lot.

When discerning the cause of the gypsum board cracks, these inspections also require the correlation of the location and relative age of the cracks to measured low spots or high spots.  When my company performs these foundation inspections, we use a compulevel to determine relative differential movement of the foundation.  If a crack is located away from a high spot or low spot, it typically indicates that it is either expanson/contraction related or the result of foundation movement that has occurred previously and has since leveled again.  In addition, if paint or significant amounts of dust/debris are present in the cracks, it usually indicates that the crack has been present for a relatively longer period of time (depending on when the interior finishes were last painted).   Using the above information, we can determine which cracks are the result of relative foundation movement and how long the possible foundation movement has been occurring.

While most of you probably don’t have access to the equipment to find a relative floor elevations and measure differential movement, this information should help when initially assessing the cause of gypsum board cracks, and also help in understanding the foundation inspection process.  I will probably write a few more blog posts covering the basics of foundation inspection, so feel free to ask me any questions you have and I will answer them if I can.  I would also like to hear from people in the inspection business as well.  For those with inspection experience, how do you assess gypsum board cracks in relation to foundation movement?  If you enjoyed my post, hit the like button, follow my blog for updates and share this post with your friends.  Thanks for reading and have a good week!

High Performance Energy Saving Design for the Karuna House Part 1 – Foundation Design

     Hello everyone! I hope your holiday break went well.  I had a fun time with my family and definitely felt like I recharged my batteries as well. Hopefully you guys could do the same.  Today I want to start a series of blog posts on a detailed overview of the high performance systems used in the Karuna House created by Holst Architecture and Hammer & Hand.

The Karuna House is a house designed to meet Passive House standards, Minergie-P-ECO, and Platinum LEED Home Standards.  The client is a leading proponent of high performance design technology for climate control.  This house is intended to be a case study in the usage of the current technology on the market today.  In the first part of this blog post series, I am going to discuss the design of the foundation and the energy saving technology applied in that part of the design.

The main concern for the foundation involved insulating the basement and foundation.  With that in mind, most of the technology focuses on maintaining a good quality building envelope that insulates well.  The first step was the cut and fill for the excavation.  In this step, the cut was balanced with the fill to ensure that there wasn’t a need to haul around aggregate to complete the fill process.  For the next step, an Expanded Polystyrene (EPS) geofoam foundation insulation was placed around the cut and fill earthwork before the concrete foundation was constructed.  Next, the footings beneath the structure were placed and a moisture blocking capillery break material was placed on top of that.  Once the footings were in place, gravel fill was placed for the foundation base and the basement foundation wall was constructed with a vapor barrier extending to both sides of the wall.  The concrete mix used in the basement foundation wall consisted of 30% fly ash and used locally sourced aggregate.  In order to obtain better energy efficiency, EPS was placed in critical thermal bridge sections.  Along the foundation walls, a product called a drain board was applied to it’s surface as well to allow water to flow down the foundation walls and past the footings.  Once all that was completed, they applied the vapor barrier over the gravel base and laid some more EPS foam before they constructed the slab portion of the foundation.

My take away from reading the article and watching the videos is that there are two critical issues that affect house foundations – moisture control and thermal bridging.  The designers used the EPS and vapor barriers to address these issues.  Along with that, methods of construction were used that reduce the use of energy/material in construction as well.  Overall, I think this was a good application of some practical design ideas.  A lot of designs like this get caught up in following the latest complex and cool looking trend instead of finding a solid and fundamental solution to the problem – this design avoids that fairly well.

What are your thoughts on the design?  Does it seem like a practical application to use for increased energy efficiency?  Any issues you worry about over it’s life cycle?  Thanks for your time and have a good week! 🙂

Source:

Hammer and Hand, “The Karuna House: Foundation System”, http://goo.gl/C9Hccu

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