Survey or soils report? You need both, and here is why

By Ram Gabay, DVLP Construction  ·  3 minute read

Yes, you need both, and you should order both the week you get the lot. The survey tells your architect what is on top of the ground. The soils report tells your structural engineer what is underneath it. Neither one can stand in for the other, and neither one waits for the other.

The survey: what is on top

A licensed land surveyor measures the lot as it actually is: property lines, grades and contours, existing structures and walls, trees, curbs, easements. What you get back is a stamped drawing, often a single sheet.

Your architect draws on that sheet. Without it he is designing off a parcel map, guessing at where the lines are and how steep the ground is, and those guesses come back later as setback problems and redesigns. Of the two reports, the survey is the quick one.

The soils report: what is underneath

A geotechnical engineer, the soils engineer, drills borings or digs test pits, logs what comes out of each hole, sends samples to a lab, and writes up what the ground can carry and what has to happen to it before you build. That might mean removing and recompacting the dirt under the house, footings that go down into rock, or drilled piers.

From drilling to report in hand, four to eight weeks is normal. Good engineers also have a waiting list before they can get a rig to your lot, and that list has been longer since the Palisades and Eaton fires.

One thing people get wrong: the soils engineer does not design your foundation. He gives the structural engineer the recommendations, and the structural engineer designs from them.

Who needs which

• Your architect needs the survey. He does not need the soils report. What is underground does not change the floor plan.
• Your structural engineer needs both the finished architectural design and the soils report. He cannot design the foundation without the report.

Why you order them together

Because they do not depend on each other, there is no reason to wait on one to order the other. The expensive mistake is ordering the soils report after the design is finished. The architect hands off, the structural engineer has nothing to design the foundation from, and your permit sits for a month or two while a lab works through its queue. Ordered on day one, the report is back long before the architect is done.

One thing to say before anyone drills

If there is any chance you want a pool, tell the soils engineer before he drills, and roughly where it would go. A pool is a deep hole next to your house. It changes where he puts his borings and what he recommends, and a report that never planned for one can mean paying for a second visit.

Together with a civil engineer, these reports usually run into the tens of thousands. That is small next to the cost of a design that has to be redrawn, or a permit that waits on paperwork you could have had months earlier.

Want the whole sequence, including where the civil and structural engineers fit?

How long a soils report really takesHow we run preconstruction