Get the Dirt on Compaction Tests!

Get the Dirt on Compaction Tests

When building in Southwest Florida you most often need to bring in yards of fill dirt to your property to meet elevation and drainage code requirements. The amount of fill dirt needed heavily depends on your lot specific characteristics, like the flood zone it resides in and its current elevation. (Learn more about virgin ground and Finished Floor Elevation (FFE) here).

The dirt used in home construction comes from a dirt mine. The dirt product can’t be too wet or too dry and must pass a soil test showing its properties are suitable for construction. In Florida with severe heat and a rainy season it’s very important your builder uses dirt from a mine supplying quality dirt.

Foundation Construction

One of the very first steps in your homes building process is the piling of the house pad whether you are building a stem-wall or monolithic foundation. Learn more about the differences here. 

The fill dirt brought in is dropped in the location where your home will reside on the property. From there they build out the house pad. The pad consists of yards of fill dirt that is leveled, compacted as well as sloped to establish proper drainage away from your home’s foundation.

The building of the foundation goes through several inspections and one element of those inspections is a passing compaction test. The soil strength of the dirt surrounding the footer of your home is imperative to its performance so it’s tested during two stages. Once prior to the concrete footers being poured and again at the backfill of the stem wall stage to ensure suitable compaction prior to the pouring of the concrete slab.

Who performs the test?

A licensed engineer performs the compaction test on site with a tool that has a probe and electronic reader. The device is pushed into the soil to obtain a sample. The operator enters the depths of the sample and a reading on the moisture and density detected is given. Soil samples are taken from the center and four corners of the house pad. These samples are taken after every 12 inches of dirt. This ensures each level of the fill dirt has been properly compacted to give the house pad stability throughout.


The results are provided via a compaction test report that states the location in which the sample was taken and reading for the moisture level (pcf), the optimum moisture percentage, the field dry density (pcf), the field moisture percentage, and the soil compaction percentage those results calculate to.

A passing compaction test is 95% or greater from all samples taken. At this rating the dirt has acceptable amounts of moisture and is displaying density in line to not excessively expand or contrast under the weight needed to be borne. Example


Without proper compaction tests at critical steps in the building of your homes foundation you could experience settling. The dirt will expand and contrast if not compacted correctly which may cause cracks in the walls and foundation. Using quality dirt, proper materials, equipment and passing inspections during the construction of your home’s foundation is critical.  Learn more about Sposen Homes through our comprehensive blogs posted here.