When it comes to finding the ideal lot for building a home, location isn’t the only factor. Soil quality can be just as important.
The stakes are high, no pun intended. A site could harbor dangerous toxins like lead, zinc, mercury, or cadmium. A parcel could have soil that’s not suitable for construction, leading to a home that leans or even collapses.
If you’re looking to build a new home, it’s essential that you test or sample the soil first, ideally before purchasing a parcel of land. Here’s what you need to know about this critical first step in construction planning.
What is soil sampling?
Soil sampling (sometimes known as soil testing) is the process of taking soil from a parcel of land to determine its composition. The process is conducted by a soil engineer, who will visit the site, collect several soil samples at different levels, and then assess them on-site or in a lab. The soil engineer will bore several holes at varying depths (“core down”) for an in-depth look at what’s happening at each level sampled. The results will reveal how reactive the soil is and classify it so the structural engineers are fully informed.
Who performs soil sampling?
A homebuyer, real estate agent, builder, general contractor (GC), or architect will contract with a soil engineer to assess the soil on a parcel of land (average cost $1,410
). Look for a soil engineer who’s licensed and professionally registered by your state.
When does soil testing happen?
Soil sampling usually occurs before the builder, GC, or homeowner files for building permits. The process may be conducted both during and after construction. If the test is conducted during construction, the soil engineer will make sure conditions continue to be compatible with the initial construction recommendations and if the soil changes, they’ll likely modify them. If conducted after, they’ll evaluate whether construction followed their guidance.
What are the different types of soil tests for building construction?
Soil engineers carry out multiple tests depending on the nature of a piece of land. In general, they determine soil’s physical and chemical composition to determine whether it’s free of contaminants and whether the texture can properly support structures.
When assessing soil’s ability to handle heavy loads, they’ll test its moisture content (Atterberg limits test
), specific gravity, dry density, compaction (Proctor’s test), and more. Among other factors, they’ll determine how expansive soil is, which indicates how much it will expand in volume when wet and how much it will shrink when dried.
For homebuyers planning to add a septic system or a well, they’ll also assess soil’s permeability and drainage capabilities via perc (percolation), deep hole, or seasonal high water table tests.
What to do with the findings of soil testing?
Fortunately, soil engineers make this part simple. After they summarize their findings, they provide an interpretation of the data and recommendations for your architect, structural engineer, builder, and GC.
The bottom line indicates whether you should move ahead with the purchase of a parcel of land. Beyond that, it’s up to your architect, structural engineer, builder, or GC to follow the detailed suggestions when designing and building your home.
Why is soil testing important for new homes?
Most municipalities require a soil test before awarding building permits, for good reason. Soil engineers determine whether a parcel is sufficiently low in toxins and safe to build on. If it is not safe, they’ll recommend against developing that land.
They’ll also evaluate the soil’s bearing capacity, meaning how much load it can support. Depending on their findings they may suggest ways to work with less ideal soil. This may mean building a wider or deeper foundation, draining the land more, grading the land, or including earth supports. For example, if you’re buying a hillside property, they’ll likely recommend methods for preventing or managing erosion, gullies, mudflows, and landslides.