Armchair Builder

House Foundation Excavation: High Water Table Issues

Excavation for House Foundation

It’s a great time of year to install your new house foundation.  Starting construction in the spring allows you to maximize the building season for your schedule and budget.  It can however create problems with high water tables.  Here we will discuss a few builder tips for dealing with water in your new home excavation.
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Why Do I Have a High Water Table?

The water table typically rises in the spring in many parts of the U.S. due to higher amounts of precipitation and runoff from melting snow.  Just as the level in the rivers, ponds and lakes rise, the ground water table rises.  As more and more water filters down into the ground, the level of the ground water table rises.

A House Foundation Excavation and Water…Not the best combination.

High water tables aren’t a big issue until you dig a hole for a foundation or a trench for utilities.  When you dig down near the level of the table, water will fill the bottom of your new excavation.  This creates two big problems relating to safety and quality.
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First, when water enters an excavation it has a tendency to destabilize the sides of the hole and cause cave-ins.   Not only does this create more work for the company digging the hole, but it also creates a dangerous condition for any workers down inside.    There are typically no workers in the house foundation excavation while digging, but they will eventually arrive to install footing and foundation forms.
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Cave-ins can also cause damage to occur to form work and drainage systems.  If the hole caves in while the foundation is in process, the dirt can crush forms, tools, pipe…etc.  And as mentioned above, each time a cave-in occurs, the dirt will need to be removed to resume work.  This can get costly when a backhoe and operator can cost $100+ per hour!
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The other problem with water entering your new house foundation excavation relates to quality.  If you are forming up the footings, you want the area to be as dry as possible.  Most inspectors in the midwestern states will fail your footing inspection if there is a significant amount of water between the forms.  Why?  It’s not that water is bad for curing concrete…quite the contrary (water actually helps strengthen the concrete after it sets up).
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The issue with water under the  footing forms for your house foundation involves the possible contamination of the concrete mixture.  Water and dirt create mud.  If the mud gets mixed in with the concrete as it is placed, it can lead to the weakening of the footings.  And since your entire house rests on the footings, we don’t want to take the risk.
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The other problem with water under the footing forms involves the possibility of settlement after the hole dries out.  Some soil types expand when mixed with water.  If your footings are poured on top of the expanded wet material, your footings may settle when the water goes away.  This can lead to future foundation problems.
Excavation for House Foundation

Dry House Foundation Excavation

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Builder Trick to Remove Water from House Foundation Excavation

One way to solve the high water table issue is to over-excavate a small hole next to your house foundation excavation.  You will dig this adjacent hole 1.5 to 2 feet deeper than the main excavation (and approximately 3 feet in diameter).  You will then place a water pump down into the small hole.  As long as your pump can keep up with the water entering the house foundation excavation, it will stay dry.  It’s best to get the biggest pump you can handle that will fit into the hole.  Most rental companies supply what they call trash pumps…let them know what you are using it for and they can help you.

Have you ever thought about building your own home?  Be sure to stop by the Armchair Builder How to Build Your Own Home resource page.

Safety with Excavations

Your house foundation excavation, as well as utility trench excavations, require special treatment to remain safe.  For the house foundation, sloping or benching the excavation is necessary to help prevent cave-ins.  For more information on how to slope or bench an excavation and for other useful safety tips, check out OSHA’s (Occupational Safety and Health Administration) guide to safety with excavations.

Here are some additional resources you might find helpful to you when planning a new foundation project.

Drain Tile and Your Basement  This video talks about the role drain tile plays in a properly built basement foundation.  We cover the basics and offer up builder tips for proper installation.

Your Home Foundation:  Frost Protection  This article talks about the importance of protecting your foundation from frost when installing in cold weather.  It can be tricky to pour of foundation in below freezing temperatures…so we give you some tips to get a quality job

Structural Problems:  What are Your Chances?  In this article we discuss the percentages of structural problems in homes.  We also talk about how foundations are the big ticket for prevention.  With proper building methods, you can avoid these major issues with your new home.

Preventing Home Foundation Problems   We offer up typical foundation installation quality problems and talk about how you can avoid them in your new home or addition.

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4 Comments for House Foundation Excavation: High Water Table Issues

How to Build a Home, Step 21: Excavate for Foundation - Armchair Builder :: Blog :: Build, renovate, & repair your own home. Save money as an owner-builder.- Armchair Builder :: Blog :: Build, renovate, & repair your own home. Save money as an own | March 12, 2013 at 1:04 pm

[...] For some tips on how to deal with a high water table when excavating for your new foundation, check out this article, House Foundation Excavation:  High Water Table Issues. [...]

Footings are the next step in our How to Build a Home Blog Series.- Armchair Builder :: Blog :: Build, renovate, & repair your own home. Save money as an owner-builder. | March 19, 2013 at 3:11 pm

[...] If you are having issues keeping the excavation for your dream home dry, check out this article, House Foundation Excavation: High Water Table Issues. [...]

Foundation Waterproofing: How to keep water out of your new home.- Armchair Builder :: Blog :: Build, renovate, & repair your own home. Save money as an owner-builder. | March 27, 2013 at 11:41 am

[...] Dry – The wall and footing should be dry before application.  So check the weather to make certain rain is not in the forecast.  If there is water in the hole, you will want to remove it. Check out this article for tips to deal with high water tables issues. [...]

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