Room Additions

Room Addition Contractor in Los Angeles

Adding square footage to your home, whether that's a bump-out off the kitchen, a full second story, or a new master suite, is a bigger structural undertaking than a remodel of what's already there. Apex Build handles Los Angeles room additions from design through LADBS permit approval to final walkthrough, and we quote by addition type instead of one blended number that hides what your project actually costs.

Licensed, bonded, and insured

Apex Build is a licensed, bonded, and insured general contractor serving Los Angeles and the surrounding communities. We handle LADBS plan check and permitting directly for every addition we build, so you're not the one standing in line at the counter.

Serving: Los Angeles city and the greater LA area, including the San Fernando Valley, Westside, and surrounding LA County communities. See the service area section below for the full list.

What's included in a room addition project

A room addition covers a wide range of scopes, and the right approach (and the right cost) depends heavily on which type you're building. Apex Build builds all of the following in Los Angeles:

• Bump-out — a small footprint expansion, typically 50-200 sqft, added onto an existing room such as a kitchen or bathroom

• Ground-floor extension — a larger addition, typically 200-500 sqft, that extends the home's existing footprint

• Family room or bonus room — including bonus rooms built over an existing garage

• Master suite addition — a new primary bedroom, often with an attached bathroom and closet

• Kitchen extension — expanding an existing kitchen's footprint, including plumbing and electrical relocation

• Bathroom addition — a new full or half bath added to the home

• Second-story addition — building up rather than out, which adds structural and foundation scope not present in ground-floor work

• In-law or multigenerational suite — a self-contained living space added to the home for extended family

This page is scoped to additions that add new square footage to your home's existing structure. If you're converting an existing garage into a rentable unit, that's a different project with its own permit path. See our Garage-to-ADU conversion page. If you're renovating space you already have without adding square footage, see whole-home remodeling. If you're building an entirely new structure from the ground up, see new construction.

How much does a room addition cost in Los Angeles?

Cost varies significantly by addition type because each one carries different structural, plumbing, and framing complexity. The ranges below come from a cost breakdown specific to the Los Angeles market, published by NPLine Design.

Bathroom additions run highest per square foot because of the plumbing, waterproofing, and ventilation work packed into a small footprint. Second-story additions carry the widest total-cost range because they bring in foundation and structural work that ground-floor additions don't need. Across the broader LA market, Angi's home addition cost data for Los Angeles puts the average total investment for a home addition project at roughly $102,994, with most projects landing between $59,907 and $156,853. That figure blends every addition type together, so treat it as a general market backdrop rather than a quote for your specific project.

We'll give you a real number for your addition type and lot after a site visit. No project on this page gets built off a phone-quoted range.

Second-story additions: the structural cost most pages don't mention

Building up costs more than building out, and the reason is foundation and structural work, not finish materials. A lot of Los Angeles room-addition pages quote a second-story addition at close to the same per-square-foot rate as a ground-floor addition. That's not accurate, and it's not what you'll pay once your structural engineer looks at the plans.

Before any second-story framing starts, your existing foundation needs a structural assessment. That assessment runs $3,000-$8,000. If the foundation needs strengthening to carry the new load (which is common on older LA housing stock), that work runs $20,000-$80,000 or more, broken into conventional underpinning ($500-$1,000 per linear foot), micropiles ($800-$1,500 per linear foot), or helical piers ($1,500-$3,000 per pier) depending on soil conditions and what your engineer specifies. These figures come from NPLine Design's Los Angeles cost breakdown.

Because Los Angeles sits in Seismic Design Category D, seismic compliance work (shear walls, hold-down anchors, moment frames running $5,000-$15,000 each, and continuous load paths through the structure) typically adds another 10-15% on top of standard structural costs. Your existing first-floor walls also need to be assessed and often reinforced, since the ceiling of your first floor becomes the floor of your new second story and needs added beam or post support to carry it. Homes on hillside lots need an additional soil-engineer evaluation before any of this can be designed, per Sweeten's second-story addition guide for Los Angeles.

If your second-story addition is a bonus room built over an existing garage, add foundation reinforcement (roughly $10,000-$30,000) plus a new staircase ($5,000-$15,000) on top of the base construction cost.

As a rough rule of thumb, second-story work tends to run about double the per-square-foot budget of a comparable ground-floor addition once structural costs are factored in, according to Structura Remodeling's Los Angeles cost analysis. We'd rather tell you that upfront than hand you a teaser number that falls apart once the structural engineer gets involved.

Our process

1. Consultation and site visit. We walk your property, talk through what you're trying to add, and give you an honest first read on scope, structural feasibility, and rough budget range.

2. Design and engineering. We develop plans for your addition, bring in a structural engineer where the project requires one (which is standard on any second-story project), and finalize the scope you're approving.

3. LADBS plan check and permitting. We file your building plans with the LA Department of Building and Safety and manage the plan check process through to permit issuance. More detail on this step below.

4. Construction. Our crews build the addition, from foundation and framing through electrical, plumbing, insulation, drywall, and finishes.

5. Inspections. LADBS inspects at required stages throughout construction to confirm the work matches approved plans.

6. Final walkthrough. We walk the finished addition with you, address any punch-list items, and close out final inspection and permit sign-off.

Permits: what LADBS requires for a room addition

Any project that adds square footage to your home needs a permit from the LA Department of Building and Safety before construction can start. LADBS categorizes room additions and second-story additions under its "Addition to building" permit type, and your plans need to go through Building Plan Check and be approved before a permit is issued, per LADBS's building permit requirements. LADBS offers three plan check pathways: Express Permit for qualifying smaller projects, Counter Plan Check for in-person review, and Regular Plan Check for standard projects. Which pathway applies depends on your project's size and complexity, and we'll tell you which one your addition falls under once we've seen the plans.

As part of plan check, LADBS reviews your addition against setback, height, and lot coverage requirements to confirm it fits the character of your neighborhood. LADBS publishes a Yard Setback Calculator that homeowners and contractors can use as a starting reference, though your final numbers get confirmed during plan check itself.

Permit and plan-check fees vary by project scope, permit type, and how many trades are involved (electrical, plumbing, mechanical each carry their own permit on top of the building permit). Across the sources we've reviewed for the LA market, total permit and fee costs for a room addition commonly land somewhere between $3,000 and $25,000 or more, according to Structura Remodeling's fee breakdown. There's no single published fee schedule that covers every scenario, so we won't quote you an exact permit total until we know your addition's square footage, trades involved, and which plan check pathway applies. If you're building a large addition, note that the LA Unified School District also charges a school impact fee of roughly $4.79 per square foot on qualifying projects.

A note on jurisdiction: everything above applies to properties inside the City of Los Angeles, where LADBS is the governing authority. If your property sits in a different LA County city or an unincorporated area, that city's own building department, not LADBS, handles your permit. Tell us your address and we'll confirm which department has jurisdiction over your project.

Zoning limits on room additions

Most single-family lots in Los Angeles fall under the Baseline Mansionization Ordinance, which regulates the size, height, and mass of additions and new construction on R1 and related single-family zones outside hillside and coastal areas, according to the LA Conservancy's overview of the ordinance. It sets a floor-area ratio limit tied to your lot size, and that limit has been adjusted since the ordinance first passed in 2008. Hillside lots fall under a separate ordinance, the Baseline Hillside Ordinance, with its own size and coverage limits.

We're not going to quote you one FAR number here and call it universal, because the actual limit depends on your specific lot size, zone, and whether any design-compliance bonus applies, and it gets confirmed during LADBS plan check regardless of what any website says in advance. What we will do is pull your lot's zoning during the design phase, before you've committed to a floor plan that doesn't fit.

How long does a room addition take?

Timeline depends heavily on addition type, same as cost. Based on NPLine Design's Los Angeles project data, bump-outs typically run 2-4 months, ground-floor extensions and master suites typically run 4-8 months, and second-story additions run 8-14 months, including 2-4 months for design and engineering and 2-4 months for permitting before construction even starts. Most room addition projects overall fall in a 3-9 month range from start to finish.

Timing matters for second-story work specifically, since it involves an open roof for longer stretches of the build. Sweeten's second-story renovation guide recommends starting construction in early spring so the project wraps before the rainy season affects framing.

Do I need to move out during a room addition?

For most ground-floor additions and bump-outs, you can typically stay in your home throughout construction, as long as the crew sets up proper containment, like floor-to-ceiling dust barriers, between the work area and the rest of the house. You may need to vacate temporarily if the work directly affects an occupied structural area, or if lead or asbestos abatement is required before demolition can start, per general renovation guidance from Dalinghaus Construction and HomeAdvisor's addition prep guidance. We'll tell you upfront during design if your specific project is one that requires temporary relocation.

Does a room addition add value to my home?

Bathroom additions tend to show the strongest return among addition types in the LA market, recouping roughly 65-75% of project cost at resale according to NPLine Design's cost and ROI data. Looking more broadly across the market, room additions in general tend to recoup somewhere in the 50-70% range, with kitchen and bathroom-focused additions trending higher and second-story additions that add a primary suite tending to land among the highest-return addition types. Treat these as directional guidance rather than a guarantee. Resale value depends on your neighborhood, comparable sales, and how the finished space integrates with the rest of the home.

Why homeowners choose Apex Build

• We separate cost and timeline by addition type. A bump-out and a second story are different projects with different budgets. We won't quote you one blended number that hides which one you're actually building.

• We don't hide second-story structural costs. Foundation assessment, seismic compliance, and load-bearing work get priced upfront, not discovered mid-project.

• We handle LADBS permitting directly. From plan check through final inspection, we manage the permit process so you're not learning it yourself.

• Licensed, bonded, and insured. Apex Build carries the licensing required to pull permits and build in the City of Los Angeles.

• Local crews who know LA housing stock. Older LA homes often carry structural quirks that only show up once walls open, and our crews have seen the common ones before.

Service area

Apex Build builds room additions across Los Angeles and the surrounding LA County area, including the San Fernando Valley, the Westside, Central LA, and neighboring communities. Every project starts with confirming which building department, LADBS or another city's own department, has jurisdiction over your address, since permit requirements differ outside the City of Los Angeles.