Engineering slab foundation investigations for real estate transactions are almost always described as preliminary or as based on a first impression
There are several reasons for this:
In the engineering world, any investigation of how a structural element is performing is considered “preliminary” unless material samples are made and analyzed in an engineering laboratory. That is never going to happen in a normal real estate transaction. There is no time and there are literally dozens of tests that could be performed.
The performance of a foundation should be ideally based on several investigations taken over a period of time as the foundation distorts in response to changes in the moisture content of the supporting soil. The time span should be at least six months and can easily be two years. This alone precludes making a foundation performance evaluation of how well or poorly the foundation is performing for a real estate transaction.
There are rarely plans available. I once made an investigation for a house owned by an attorney. There were extensive and severe problems with the floor tile. There were loose tiles that no longer bonded to the slab surface and there was well-bonded tile that was cracked. The tile has clearly not been applied right using a flexible thinset mortar and an isolation or decoupling membrane but that could not be a full explanation.
The attorney wanted me to design a repair. I told him that I did not design repairs. He pressured me and I told him that I might reconsider if I was provided a soil report and sealed and signed drawings of the foundation design. I never saw a soil report. The builder explained that he saw what builders were doing on nearby lots and copied their “design” modifying it by adding 6-feet piers.
What other types of investigations are there from an engineering perspective?
There are three types of investigations recognized by the American Society of Civil Engineers.
This is a visual overview of the general condition of the building envelope. It is used to screen houses with a view of setting priorities for maintenance, repair or further study. It may or may not include a site visit. A site visit might not be necessary depending on the needs of the client.
This investigation includes a site visit to identify problem areas, review available documents such as plans, an interview of any parties who might have special knowledge of previous repairs, etc.
In a detailed assessment, the number of tests and other activities involved in the investigation can be open-ended. In any case, a detailed investigation can involve material tests, monitoring the finish materials like floor tile, and brick veneer for distress/damage consistent with foundation distortion. A series of elevation measurements can be made to monitor foundation movement.
Detailed investigations usually are used where the construction of the house is subject in litigation.