Space without height
Where height limits, view protections, or neighborhood character make a second story difficult, a basement adds square footage below the roofline.
New custom homes
One-story homes with a basement.
A single-story house keeps every everyday room on one level, which suits young families and homeowners planning to stay for decades. A basement adds the rooms that don't need a view, such as a media room, gym, storage, wine room, or guest suite, without a second story. ROAM Design Studio LLC designs and permits these homes, and ROAM Builders Inc. (CSLB Lic. #1151324) builds them, across Pasadena, Altadena, and the Los Angeles foothills.
Why this layout
What a basement does for a one-story home.
One level for daily life
Kitchen, living areas, and bedrooms on the main floor, with no stairs in the daily routine, whether you have toddlers now or want to age in place later.
Rooms that work below grade
Below-grade rooms stay cooler and quieter, which suits home theaters, gyms, studios, and wine storage.
Check these first
Five things that decide whether a basement works on your lot.
- Soils and groundwater. LA County requires a soils report for basement walls, and other agencies may too. The geotechnical engineer's findings set the wall design, waterproofing, and drainage.
- Grading. Excavating for a basement moves a lot of soil. Whether you need a grading permit, and on some sites a haul route, depends on how much soil is removed or backfilled and on the site conditions.
- Slope and geology. Hillside lots can make a basement easier, with one wall opening to daylight, or harder, with shoring and geology review. In unincorporated LA County, projects in hillside, liquefaction, or landslide areas cannot use the self-certification fast track.
- How floor area is counted. Zoning codes define when a basement counts toward the floor area limit, usually based on how far it rises above the surrounding grade. That definition shapes the depth and the window wells.
- Septic and utilities. Some foothill lots, including many in Altadena, still use septic systems. The location of the septic field, sewer lateral, and utilities affects where a basement can go.
Fire rebuilds
Basements in Altadena and Palisades fire rebuilds.
Many homeowners rebuilding after the January 2025 fires want more space than they had without giving up a single-story house. A basement is one way to get it, but the rules differ by jurisdiction:
- City of Los Angeles (most of Pacific Palisades): the implementation guidelines for the Mayor's Executive Order No. 1 allow adding a new basement or enlarging an existing one on a like-for-like project, provided the basement does not exceed 110% of the existing building footprint. Under Executive Order No. 8, a new basement is allowed when the home complies with current zoning. See our Palisades fire rebuild guide.
- Unincorporated LA County (Altadena): the like-for-like pathway allows growth of up to 10% or 200 square feet, whichever is greater. The County's guidance doesn't address basements directly, so we confirm with County Planning for your parcel before committing to a basement on a like-for-like rebuild. See our Altadena fire rebuild guide.
Sources: LA County like-for-like rebuild, LA County fire rebuild FAQ, LA County self-certification, the City of Los Angeles EO1 Implementation Guidelines (version 4.0, June 11, 2026), and the City of LA recovery FAQ, reviewed October 2026. Rules change; confirm current requirements with the agency for your property.
ROAM is not affiliated with Los Angeles County or the City of Los Angeles. This page is general information, not legal, engineering, or permitting advice. See our legal notices.
Common questions
Basement questions, answered.
Can you build a house with a basement in California?
Yes. Basements are less common in Southern California than in colder regions because footings don't need to go below a frost line, but they are allowed and built regularly. What it takes is a soils report, a basement designed for the soil and groundwater conditions, waterproofing and drainage, and, depending on how much soil is moved, a grading permit.
Can I add a basement to an Altadena fire rebuild?
LA County's like-for-like pathway for the Eaton Fire area allows a rebuild to grow by up to 10% or 200 square feet, whichever is greater. The County's like-for-like guidance does not address basements directly, so whether a new basement keeps your project on the like-for-like pathway is a question to confirm with LA County Planning for your parcel before design is finalized. Rebuilds outside like-for-like follow standard zoning and the Altadena Community Standards District.
Can I add a basement to a Palisades fire rebuild?
In the City of Los Angeles, yes, within limits. The City's current implementation guidelines for the Mayor's Executive Order No. 1 (version 4.0, June 2026) say adding a new basement or enlarging an existing one qualifies as a like-for-like project as long as the basement does not exceed 110% of the existing building footprint.
Does a basement count toward my home's floor area?
It depends on the city and how far the basement sits above the surrounding grade. Many codes, including the City of Los Angeles hillside rules, exclude a basement from floor area when it stays mostly below grade, and count it once enough of its walls are exposed. We check the definition in the zoning code that applies to your lot before setting the basement depth and layout.
Is a one-story home with a basement more expensive than a two-story home?
Per square foot, basement space usually costs more to build than above-grade space because of excavation, shoring, concrete walls, and waterproofing. In exchange you keep a single-level main floor, a lower roofline, and quieter rooms below. Whether it pencils out depends on the lot, the soil, and how much of the program has to go below grade, so we price both options when the comparison matters.