Every project comes with at least one unexpected incident, sometimes multiple. I would say less than half of our projects (probably even close to only 1/3 of our projects) have a soils test involved. Generally speaking, soils reports are to be expected for sloping sites, sites in known hazardous soils conditions, and when building taller than a single story. This isn’t to say soils reports aren’t important. Designing for the proper soil is critical. it will determine how your building connects to the earth and ensure your house remains level.
Soils tests are important because they provide an analysis of the soils on the specific site so that the structure can be engineered to endure the soils conditions. The foundation design can be impacted by the soils report along with several other factors that could affect the overall structural design. When a soils report is not required, the structural engineer will use the up to date California Building Code geotechnical specifications for the particular area and design conservatively for those found conditions.
In our latest tale of unexpected circumstances, we have been designing a new single story house in a particular Bay Area city along the Peninsula. There is an existing single story house to be demolished (it’s over 60 years old) and our site is basically flat, and confirmed not be in any kind of hazardous geotechnical area. Very often the city will remind you if a soils test will be required early on in the process. For most new construction projects, there is an entitlement process that will bring up any red flags so you can plan for what’s to come. In this project’s case, we were specifically told that a soils report was not required during the planning design review, it was a surprise for us when the building department plan check comments came back and asked for our soils report.
This isn’t a big deal from a design point of view – at least it shouldn’t be since the structural design is fairly conservative. It may alter the depth of the footing to be embedded, or possibly affect the concrete mix, but we most likely have already gone overboard with the assumptions. The kicker here is that soils reports take time and money. Luckily, the local building trend tends to be such that it’s not peak busy time, but it also doesn’t mean a soils engineer can go bore and write up a report in less than three weeks.
Fortunately for us, we’re still waiting on formal approval of the planning part of our project that is in the last stretch of public comment period, and we have initial plan check comments to take care of in the meantime so it shouldn’t slow down the overall timeline of the project permitting, but it just goes to show that with every project, “expect the unexpected.”