What's Under Your Feet
The soil report that changed our foundation plans and why every builder needs one
Why Soil Matters
Before you pour concrete for a building, you need to know what's underground. Different types of soil act differently. Some are strong. Some shift and expand when wet. Some can't hold the weight of a building at all.
We hired Fenagh Engineering to test the soil at 3312 Luna Ave. Jason Meares, their engineer, dug three test pits by hand in different spots on the property.
What They Found
The ground had three layers:
- Top layer (1-2 feet deep): Clayey sand fill soil. This is loose material that someone dumped there at some point. Not natural ground.
- Middle layer (in some spots): Clayey sand with lean clay. This layer swells when it gets wet. That's bad for buildings.
- Bottom layer: Very Old Paralic Deposit sandstone. This is the good stuff. It's been here for thousands of years and is very strong.
The fill soil on top? Not strong enough to build on. The clay layer? It has "medium to high expansion potential." That means it swells and shrinks with moisture. Put a building on expanding soil and you get cracked foundations and uneven floors.
What They Told Us to Do
Fenagh's instructions were specific:
- Remove and repack all loose soil. Dig down 1-3 feet and compact the soil to 90% maximum density. Think of it like packing dirt really tight so it can hold weight.
- Dig at least 5 feet past the building edges. The packed zone has to extend beyond the building on all sides.
- Be careful near the existing duplex. Where new digging gets close to old foundations, work in small sections. Dig and fill one 5-foot strip at a time so the old building stays stable.
- All new footings must sit 6 inches into the sandstone. In some spots, foundations will need to go deeper than the plans show.
Extra Tests Needed During Construction
Fenagh would need to come back during construction for:
- Checking the bottom of every hole before we pour concrete
- Testing that the repacked soil is tight enough
- Collecting soil samples to check expansion and sulfate levels
- Watching foundation digs to make sure they're deep enough
The Surprise With the Neighbors
While Fenagh was on site, the surveyors ran into a problem. They found the front property corners but couldn't find the rear corners. The marker was probably on the neighbor's property near a power pole.
A worker tried to contact the neighbor but nobody was home. Meanwhile, a neighbor named Anne came by, asked the surveyors questions about the trucks, and took a picture of their truck. This wasn't the first time she'd been near the property asking questions.
The survey delay cost us 1-2 days while the team went back to the office to do calculations.
What This Cost
The soil work added cost in several ways:
- Fenagh's testing and inspection fees for multiple site visits
- Deeper foundations in some areas (more concrete and rebar)
- Extra excavation to remove and repack 1-3 feet of soil across the site
- The expansion test could require thicker concrete slabs or more rebar
The Lesson
Never skip the soil report. It's easy to think of it as just another fee. But finding out your soil is weak after you pour foundations is a nightmare. Fenagh's early findings let us plan for deeper footings and proper soil prep from the start. It saved us from much bigger problems later.