Home Additions and Second Stories

A new room is the smallest part of an addition. The moment floor area is added, the city measures the whole house again: setbacks on every side, floor area against the lot, height, parking, and in hillside areas the slope and the soils under the new foundation. The existing structure has to carry the new loads, the energy documents have to cover the combined building, and a wall near a property line may need a fire rating it never had. In cities with design review, the elevation goes to a planner before it goes to a plan checker. Design 1 Studio has designed additions and second stories in more than two dozen cities across Los Angeles County and Orange County since 2015, every set coordinated with a licensed structural engineer and managed through permit issuance. Our work is residential, up to two stories.

The family room was small. The lot was not simple: a flag lot in the Altadena Community Standards District where the house and garage already sat close to the west property line. Applying the current side setback would have left a room too narrow to use. In August 2020 the County planner required relief from an 11-foot-4-inch side yard down to five feet, and questioned a rear yard shown under 25 feet. The route was a modification of the Community Standards District setback under County Code section 22.306.090, approved by the Hearing Officer on April 20, 2021, with the affidavit recorded and the plans approved that August. The building permit issued November 2, 2022. On June 10, 2025 the County marked the building final passed and wrote “Addition complete.” A 307-square-foot room, five years from first comment to final, because the lot decided the setback and the setback decided the room.

A 966-square-foot house, a 208-square-foot addition at the rear and 193 square feet of interior remodel. Lakewood reviews the design; Los Angeles County reviews the building. Lakewood’s planning corrections came September 3, 2024 and its approval October 8. County Building and Safety then needed that approval, the owner information and the Title 24 sheets before it would review, and approved the plans on December 30, 2024 subject to the planning restamp, the construction-waste plan and the remaining referrals. The ready-to-issue package went to the owner’s contractor on January 22, 2025, and the permit was pulled that April. Nothing about this project was contested. It is what most additions are: two agencies, five document sets, and someone keeping them in order.

The owner wanted a home of about 2,800 square feet, which meant a second story on a hillside lot in the City of Los Angeles. Upstairs area is never only upstairs. The design pulled in foundation and first-floor structural work, soils and grading review, sewer clearance, and the City’s requirement for a third parking space once a hillside home passes 2,400 square feet of residential floor area. The scheme at 2,798 square feet of floor area kept the third space with a car lift, which raised the garage and its framing. Reducing the house by 247 square feet would remove the third-space requirement, and if the whole reduction came upstairs the second floor would fall from 1,123 to 876 square feet. We put both schemes in front of the owner with the contractor’s pricing, so the decision between size and cost is made on paper before another round of engineering. The project is in design and pricing as of October 2026.

• The house and the lot read first: zone, setbacks on every side, floor-area limits, height, parking, slope, any design-review district, and what the existing permits say the house already is.
• The size question settled early, with the thresholds that change the rules marked on the plan: floor area, parking, hillside, fire separation.
• Structural coordination with a licensed engineer for the foundation, the new loads on existing framing, and shear.
• Energy documents for the combined building, not only the new room.
• Plan check managed to issuance, with any correction the code does not support answered in writing.

Does a small addition need planning approval?

It depends on the lot, not the size. A 307-square-foot room in Altadena needed a hearing because the existing house sat inside the current setback. The same room on a wide lot is a building permit.

Can I add a second story to my house?

Usually, within the zone’s height and floor-area limits and with the structure to carry it. In hillside areas of the City of Los Angeles, passing 2,400 square feet of residential floor area adds a third required parking space, which often decides the size.

Will the addition trigger upgrades to the rest of the house?

The energy documents cover the combined building, and the structure has to carry the new loads. Beyond that, upgrades depend on what the existing permits show and on the city.

How long does an addition take to permit?

A rear addition in Lakewood went from planning submittal to approved building plans in about four months. A hillside second story or a setback modification takes longer, and the lot decides which one you have.