A home addition in Los Angeles costs roughly $300 to $500 per square foot for a single-story build-out, and $400 to $600 per square foot to build up a second story. For most homeowners that works out to $125,000 to $250,000 for a 500-square-foot addition, though the final number depends on the type of room, your finishes, and your lot.
Here at GreatBuildz, a free service that connects homeowners with reliable, pre-screened room addition contractors, we talk with people every day who are weighing a home addition instead of buying a bigger house. Below are current LA costs, a simple way to estimate your own project, what the permit process looks like, and where you will actually live while the work happens.
Key Takeaways: Home Addition Costs in Los Angeles
- Single-story addition: about $300 to $500 per square foot. Complex or high-end projects can run $600+.
- Second-story addition: about $400 to $600 per square foot, because the first floor and foundation usually need reinforcing.
- Master suite (400 to 500 sq ft): roughly $150,000 to $250,000.
- Bathroom addition: about $40,000 to $90,000. Plumbing and waterproofing make it pricier than a bedroom of the same size.
- Bedroom or office addition: about $50,000 to $100,000. The simplest room to build, since it needs no plumbing.
- Permits and plan check: LA review commonly takes 2 to 8 weeks for a standard addition, longer for hillside or historic lots.
How much does a house addition cost per square foot?
Most single-story home additions in Los Angeles cost $300 to $500 per square foot. Ground-level additions on the simpler end land near $250 to $350, while larger or higher-finish projects reach $500 or more.
Home addition costs vary a lot depending on what you are building. A basic bedroom is far cheaper per foot than a kitchen or bathroom because it needs no plumbing, gas, or specialty finishes. Prices below are specific to Los Angeles and Southern California, where labor and materials run above the national average. Building costs also shift by neighborhood, so treat these as planning ranges and confirm with a couple of local contractors.
Cost to add on to your house, by room type
Master suite addition: $150,000 to $250,000. A master suite floor plan can be as small as 300 square feet, but most run 400 to 500 square feet or larger. A common footprint is 20×20 or 20×25 feet, and the price is similar for a full guest or in-law suite. This assumes a single-story addition. See our master suite addition cost guide for details.
Bathroom addition: $40,000 to $90,000. The price depends on size and fixtures. A half-bath with just a toilet and sink costs less than a full bathroom with a tub or shower, and a luxury primary bathroom sits at the top of the range. Cost also climbs the farther the new bathroom is from existing plumbing lines. Here is our full bathroom addition cost breakdown.
Kitchen addition or expansion: $100,000 to $150,000. A kitchen addition means demolishing the old space and building a new kitchen in the expanded footprint. Kitchens are expensive on their own because of cabinets, countertops, and appliances, and an addition adds new plumbing, electrical, and gas on top of that.
Bedroom, office, or bonus room addition: $50,000 to $100,000. This is the simplest and cheapest room to build because it is a “dry” room with no water or gas connections. Costs rise if you add built-in cabinetry, a closet system, or high-end finishes.
Second-story addition: $400 to $600 per square foot. Building up always costs more than building out. The crew often has to reinforce the foundation and first-floor walls, add beams, tear off and rebuild the roof, and frame a new staircase. Most homeowners also end up reconfiguring part of the first floor to fit the stairs, which adds cost. Our second-story addition guide covers the process.
Estimate your home addition cost in two steps
You do not need a calculator to get a rough budget. Take your planned square footage and multiply it by a per-foot figure for your project type:
- A simple single-story room: square footage x $250 to $350.
- A kitchen, bathroom, or high-finish space: square footage x $400 to $500.
- A second-story addition: square footage x $400 to $600.
A 400-square-foot bedroom addition, for example, lands around $100,000 to $140,000. Treat the result as a starting range, then get real numbers from contractors who can see your home and plans. Every project is different, and an online cost calculator cannot account for your foundation, access, or finish choices.
What is the cheapest way to add on to a house?
The cheapest addition per square foot is a single-story “dry” room, such as a bedroom, office, or bonus room, built on an accessible, flat part of your lot. You keep costs down by avoiding plumbing and gas, keeping the roofline simple, choosing mid-range finishes, and building out rather than up. Converting existing space, such as a garage, is often cheaper still than adding new square footage, if that fits your needs.
Where will you live during a home addition?
For a small, single-story addition that is sealed off from your living space, most families can stay in the home during construction. For a major project like a second-story addition, plan to move out for at least part of the job.
This is one of the most common questions we hear, and the honest answer is that it depends on scope. A bedroom or bathroom addition at the back of the house is usually livable, though noisy and dusty. A second-story addition is different: the contractor has to tear off part of the roof and do heavy work on the first floor early on, so the home can be unlivable for weeks. Once the framing and new roof are done, moving back in gets easier. Budget for a few weeks of a rental or a stay with family so the timeline does not catch you off guard.
How long does a home addition take?
A typical single-story home addition takes about 3 to 6 months from permit to completion, and a second-story addition often runs 6 to 12 months. The build is only part of it: design and engineering usually take 1 to 3 months before that, and plan check adds several more weeks on top. Timelines stretch with permit corrections, custom materials, and weather. Ask any contractor you interview for a realistic schedule tied to your specific plans.
Is a home addition worth it in Los Angeles?
A well-planned addition usually returns a meaningful share of its cost at resale and adds day-to-day livability on top of that. In Remodeling magazine’s Cost vs. Value report for the Pacific region, which includes California, additions tend to recoup roughly half their cost at resale, and projects that add a bathroom or an in-demand bedroom sit toward the higher end. In a high-priced market like Los Angeles, adding functional square footage is frequently cheaper than buying a bigger house, which is why many homeowners build instead of move. If you are weighing an addition against a separate rental unit, compare it with an ADU (accessory dwelling unit), which can add rentable space and income.
How to start planning a home addition
Once you have a rough budget, the next step is deciding the size and location of the new space. Think about how it will work for you now and for a future buyer later. A functional, well-built addition adds real resale value, but you do not want to “overbuild” for your neighborhood with too many bedrooms or too much square footage.
You will also need to understand your zoning and whether there is room on your lot to build. Most cities require a “setback,” an area near your property lines where you are not allowed to build, so that limits where an addition can go. Two good ways to learn your options: visit your city building department and ask for guidance, or hire a local architect or designer to review your property. A good general contractor can also help at this early stage and give you realistic budgets from recent projects.
Single-story additions and setbacks
For a one-story addition, the likely spot is the front or back of the home, since side yards are rarely wide enough. That means you need room in a yard after accounting for the required setback. You will also want the new space to connect naturally to the rest of the house. Early on, have an architect draw your existing layout and figure out how the addition ties in, because reconfiguring existing rooms to make it flow is an added cost.
Second-story additions
A competent architect is a must for a second-story addition, and they will bring in a structural engineer to determine how to brace the first floor for the added weight on top. The design has to fit a staircase somewhere on the first floor while keeping that floor functional. This is a major project that takes months and makes it hard to live in the home during the early phase.
Thinking about two primary suites?
Multigenerational households sometimes add a second primary suite so two adults or an adult and an aging parent each have their own bedroom and bathroom. If a two-master layout is your goal, plan it with an architect early, since a second suite means more plumbing and often points toward a second-story addition to fit the square footage.
Do you need a permit for a home addition in Los Angeles?
Yes. Any home addition in Los Angeles requires a building permit, along with plan check review before work starts. Plan check for a standard residential addition commonly takes 2 to 8 weeks, and 8 to 16 weeks for hillside, historic (HPOZ), or coastal lots, plus one to three rounds of corrections if the reviewer asks for changes.
“Plan check” is the city’s review of your drawings for structural, electrical, plumbing, and zoning compliance before it issues the permit. California updated its building codes effective January 1, 2026 (the 2025 California Building Standards Code), which added review for Title 24 energy efficiency, seismic, and fire-resistant standards, so budget time for that. Permit and plan-check fees are separate from construction and are set by your city, so confirm the amount with your local building department.
What is the process to build a home addition?
Once you decide to move forward, meet with both architects and contractors to find the right fit. Sometimes it is smart to start with contractors, and the one you choose brings in an architect they already work with. Starting with an architect alone can backfire: when the plans are done, the construction bids may come in over budget and you have to redesign.
To keep costs reasonable, keep at least one contractor involved throughout the design process so the plans match your budget from the start.
A few home addition tips before you start
- Budget for city plan check, permit, and any impact fees your city charges on top of construction.
- Set aside a 10 to 20 percent contingency above the contractor’s estimate. On most projects, something unexpected comes up, and if it does not, you are pleasantly surprised.
- Be detailed upfront about your scope and materials. The fewer “change orders” (formal mid-project changes to the contract) you make during construction, the fewer delays and extra charges you face.
- Add the new space to your homeowner’s insurance when the project is done, and tell your agent before you start so you are covered during construction.
How to finance a home addition
Because additions are expensive, many homeowners finance rather than pay cash. Common options include a home equity loan or line of credit, a cash-out refinance, a renovation loan, and a construction loan. Each works differently, so compare terms before you commit. Our guide to renovation financing options walks through them in detail.
How do I find a home addition contractor near me?
Only a licensed general contractor is qualified to build a home addition, and you should never hire an unlicensed or uninsured contractor for a project this size. The best way to find a good one is a referral from friends or family who had a good experience. If you cannot get a solid referral, GreatBuildz can connect you with reputable, local home addition contractors in your area.
Before you sign, check the contractor’s license on the California State License Board (CSLB) website, confirm it is active with no complaints, and ask for proof of both general liability and workers’ compensation insurance. Have their insurance broker add you to the policy as “additional insured.” It is also worth calling your home insurance agent before construction so they can advise on any coverage changes.
Home Addition FAQs
How much does a home addition cost in Los Angeles?
Most additions run $300 to $500 per square foot for a single-story build-out and $400 to $600 per square foot for a second story. A 500-square-foot addition typically lands between $125,000 and $250,000, and a 1,000-square-foot addition between $250,000 and $500,000, depending on room type and finishes.
What types of home additions are common in Los Angeles?
The most common are single-room additions (bedroom, office, or bathroom), master suite additions, second-story build-outs, and accessory dwelling units (ADUs). Which one fits depends on your lot size, budget, and zoning.
Do I need a permit for a home addition in Los Angeles?
Yes. Every addition needs a building permit and plan check approval before construction. Standard plan check commonly takes 2 to 8 weeks, longer for hillside, historic, or coastal properties.
Where do I live during a home addition?
For a small single-story addition sealed off from your living space, most families can stay home. For a second-story addition, plan to move out for at least the early weeks, when the roof is open and heavy first-floor work is underway.
What is the cheapest way to add on to a house?
A single-story “dry” room with no plumbing, such as a bedroom or office, built on flat, accessible land, is the cheapest per square foot. Converting existing space like a garage is often cheaper than adding new square footage.
How long does a second-story addition take?
Second-story additions usually take several months. Timelines stretch with structural upgrades, permit corrections, and the work of tying new framing into the existing house. An experienced contractor keeps the disruption to a minimum.
How do I choose the right contractor for an addition in LA?
Hire a licensed, local general contractor with a track record of completed additions and experience with Los Angeles permitting. Verify the license on the CSLB site and confirm liability and workers’ compensation insurance before signing.
How long does a home addition take?
A single-story addition typically takes 3 to 6 months from permit to completion, and a second-story addition often runs 6 to 12 months. Design and engineering usually add 1 to 3 months before the build, and plan check adds several more weeks.
Is a home addition worth it in Los Angeles?
A well-planned addition returns a meaningful share of its cost at resale and adds everyday livability on top of that, and additions that add a bathroom or an in-demand bedroom tend to recover the most. In a high-priced market like Los Angeles, adding square footage is often cheaper than buying a bigger house.
When it comes to planning and coordinating a home addition, you should not have to go it alone. GreatBuildz is a free service that connects homeowners with reliable, thoroughly screened general contractors and provides project support from start to finish. Call now (888.668.2454) to talk with a real person about your project, or visit www.greatbuildz.com for more information.
