If you plan to build a basement in an area that has clay in the ground, you must take precautions to avoid structural damage to your home. So here are a couple of tips to consider before starting basement construction in clay soils.
Before starting the construction of the basement, you need to know what type of flooring you are building on. The United States Department of Agriculture has information on soil for most of the United States. Soil tests can also be done so you know what you are working with. Another important step is to make sure the soil is compacted. Not compacting the soil properly can also cause problems in the future.
Expansive clay soils, such as bentonite and montmorillonite, can cause structural damage to basements and home foundations when proper precautions are not taken during construction. When you decide to build a basement in an area that has clay soil, you need to take into account the nature of the soil you plan to build on. Clay retains moisture, and as the seasons change, the amount of moisture in the soil also changes.
Building on clay when it contains large amounts of moisture can cause your basement to sink as the moisture content of the soil decreases. If you build while the moisture content is low, your basement can be pushed up when the moisture content increases. This can end up causing structural cracks. There are several ways to deal with seasonal changes in clay’s moisture content when building a basement.
Before installing the basement, you must be building on stable ground. With clay in particular, it is important to ensure that the soil is well compacted so that the soil does not shift under the weight of your house. The soil can be treated with a lime mixture to increase stability and control swelling. This is done by removing a layer of soil and adding several trenches under the area where you want to build your basement or base. Once you have the trenches in place, fill them with a lime mixture. This treatment adds about a month to the time you will need for construction.
Basements that are built on clay soil must be able to breathe or move slightly up and down with the groundwater in the soil. The concrete floors are not attached to the concrete foundation so that this movement does not cause structural damage. To allow for this movement, all internal basement walls must be “floating walls” or raised walls. Floating walls are suspended from the first floor and have a gap between the wall and the concrete floor slab. When you build in some areas, you are actually required to use floating walls in basement construction. When you get your building permit, you need to find out if this is a requirement for your area.
When the basement construction includes plumbing, a reverse process to that of the floating wall is required. The floating walls are attached to the floor to create a solid base and the space is at the top of the wall in these cases. Expansion joints and flex lines are used for basement plumbing when working in clay soil to allow natural movement with changes in soil moisture. Space should be left for pipes to reduce the risk of pipe breakage.
US Department of Agriculture
http://websoilsurvey.nrcs.usda.gov/app/