If you are building a new home, an addition or an ADU in Los Angeles, one of the first structural decisions is the type of foundation. Most residential projects here use one of two systems: a slab on grade or a raised foundation with a crawlspace. Your engineer will make the final call, but understanding the difference helps you ask the right questions.
What is a slab on grade?
A slab foundation is a single layer of reinforced concrete poured directly on prepared ground, with thickened edges or footings around the perimeter and under bearing walls. The floor of the building sits right on the concrete.
- Usually faster to build and often lower in cost
- Common for ADUs, garages and many new single-story homes
- No crawlspace, so plumbing is set in place before the pour
What is a raised foundation?
A raised foundation uses concrete perimeter footings and interior piers that hold a wood floor system above the ground, leaving a crawlspace underneath. Many older Los Angeles homes, especially craftsman bungalows, are built this way.
- Works well on sloped lots
- Easier access to plumbing and wiring later
- Matches the floor height of many older homes, which matters for additions
How to decide
For an addition, the existing house often decides for you. If your home sits on a raised foundation, a raised addition keeps the floors level and the transition seamless. For a detached ADU on a flat lot, a slab is often the simpler and more economical choice. Hillside lots usually point toward raised or stepped foundations designed by an engineer.
Soil conditions, drainage, the design of the building and your budget all play a part. A soils report, when required, gives your engineer the information needed to size the footings correctly.
Why the builder matters as much as the type
Either foundation will perform well when it is built right. That means accurate layout, footings dug to the specified depth, rebar placed and tied per the drawings, and anchor bolts and hold-downs set exactly where the framing needs them. Mistakes at this stage are expensive to fix once the walls go up.
GTKN builds both slab and raised foundations across Los Angeles, and because we frame too, we make sure the foundation is ready for the next stage. Have plans in hand or just starting to plan? Call us at (323) 253-4423 for a free estimate.
Get a Free Estimate