By LE Construction · Published October 6, 2026
Most Ventura County houses sit on one of two kinds of foundation: a concrete slab on the ground, or a raised wood floor over a crawlspace. The type affects how remodels, repairs and earthquake upgrades work, and it is one of the first things we check at an estimate.
How to tell which you have
- Raised foundation: foundation vents along the base of the outside walls, a crawlspace access hatch, and usually a few steps up to the front door.
- Slab: no crawlspace, no foundation vents, and floors close to ground level.
Older homes near the downtowns of Santa Paula, Ventura, Ojai and Fillmore are mostly raised. Post-war tracts in Oxnard, Camarillo, Simi Valley and the Conejo Valley are mostly slab.
Remodeling differences
Plumbing
On a raised foundation, drains and supply lines run through the crawlspace. Moving a sink, toilet or shower is usually easier. On a slab, moving a drain means cutting and patching concrete, which adds cost. In many tract homes, the slab is post-tensioned and must never be cut without locating the cables first.
Floors
Raised floors can sag or bounce with age and may have rot near bathrooms and kitchens. Slabs can crack and, on expansive soils, move with moisture.
Curbless showers
On a raised floor, the framing can often be lowered for a curbless shower. On a slab, the concrete may have to be recessed.
Earthquake differences
Older raised foundations often have short cripple walls and few anchor bolts. In a strong earthquake, those walls can collapse and the house can slide off its foundation. A brace-and-bolt retrofit addresses both, and California’s Earthquake Brace + Bolt program offers grants for eligible houses. Slab houses do not have cripple walls and do not need that retrofit.
Repairs and maintenance
- Raised foundations: check the crawlspace for water, rot, pests and ventilation.
- Slabs: watch for slab leaks (warm spots, unexplained water use) and drainage against the foundation.
Additions
Additions usually match the existing foundation type so the floors line up: a raised addition on a raised house, a slab addition on a slab house. The engineer designs the new foundation for the soil.
See our pages on seismic retrofitting, foundations and signs of foundation problems.
Frequently asked questions
How can I tell if my house is on a slab or a raised foundation?
Look for foundation vents near the ground on the outside walls, or an access hatch in a closet or outside. Those mean a crawlspace and a raised floor. If the floor sits only a step or so above the ground with no vents or crawlspace access, it is likely a slab.
Is a raised foundation better in an earthquake?
Not inherently. A well-built raised foundation that is bolted and braced performs well. Older raised foundations with unbraced cripple walls and few anchor bolts are vulnerable, which is why the brace-and-bolt retrofit exists. Slab homes do not have cripple walls to fail.
Can a bathroom be moved more easily on a raised foundation?
Generally yes. Drains and supply lines run through the crawlspace, so relocating them does not require cutting concrete. On a slab, moving a drain means cutting and patching the slab.
What is a post-tensioned slab?
It is a slab reinforced with steel cables tensioned after the concrete cures, common in Southern California tract homes. It must not be cut or drilled without first locating the cables, because damaging one is dangerous and costly.