How much does it cost to add a second story in Los Angeles?

Adding a second story in Los Angeles costs $250–$600 per square foot in 2026. A 600 sqft second-story master suite (bedroom + bathroom + closet) typically costs $200K–$350K. The premium over ground-floor additions comes from structural engineering, temporary shoring, and extended construction timeline.

How much does room additions cost in Los Angeles?

Room Additions in Los Angeles typically runs 5–15% above the greater LA average due to local labor market conditions and LADBS permit processing. Get 3 competitive bids from CSLB-licensed contractors who have completed recent projects in Los Angeles or adjacent neighborhoods for the most accurate pricing.

Do I need a permit to add a room to my house in LA?

Yes. Any room addition in Los Angeles requires LADBS building permits including: structural plans stamped by a licensed engineer, foundation permits, electrical/plumbing/HVAC permits, and fire/life safety review. The plan check process takes 6–12 weeks depending on complexity.

How long does room additions take in Los Angeles?

Project timelines for room additions in Los Angeles depend on LADBS permit processing time (4–16 weeks for most residential projects) plus construction duration. Total timeline from first contractor meeting to project completion: 3–9 months for most residential scopes. Projects in fire zones or on hillside lots in Los Angeles may run 20–30% longer due to additional permit review.

Room Additions & Expansions Los Angeles

Room Addition & Expansion Services

Room additions in Los Angeles cost $200 to $500 per sqft in 2026. A 400-sqft bedroom addition runs $80,000 to $200,000. A second-story addition costs $250 to $500 per sqft due to structural reinforcement. NP Line Design handles additions under CSLB #1105249.

How much does a room addition cost in Los Angeles?

Room additions in Los Angeles cost $250 to $550 per square foot in 2026 depending on type and scope. Second-story additions run $350–$550/sqft ($150K–$500K+), ground-floor extensions $250–$450/sqft, and bathroom additions $400–$700/sqft. The Baseline Mansionization Ordinance limits R1 lots to 0.50 FAR. Foundation assessment ($3K–$8K) is required before any second-story project.

Second-Story Addition — $350–$550/sqft ($150K–$500K+). Foundation assessment, structural engineering, shear walls, new roof system. Timeline 8–14 months. Most families relocate during construction.

Ground-Floor Extension — $250–$450/sqft ($80K–$225K). New foundation, roofline integration, utility extension. 4–8 months. Can often remain in home.

Master Suite Addition — $300–$500/sqft ($125K–$300K). En-suite bathroom, walk-in closet, premium finishes. 55–67% ROI at resale.

Kitchen Extension — $350–$600/sqft ($75K–$200K). Open-concept expansion. Plumbing, electrical, HVAC redistribution. 60–70% ROI.

Bathroom Addition — $400–$700/sqft ($35K–$90K). HIGHEST ROI addition at 65–75%. Adding a second bathroom (1BA→2BA) is the single most impactful upgrade for LA home value.

Bonus Room Over Garage — $200–$400/sqft ($60K–$150K). Existing garage foundation usually needs reinforcement ($10K–$30K). Staircase $5K–$15K.

In-Law / Multigenerational Suite — $300–$500/sqft ($100K–$300K). Separate entrance, kitchenette, full bathroom. 60 million Americans now live multigenerational.

What’s Included

Feasibility study
Zoning & BMO analysis
Architectural design
Structural engineering
Foundation assessment
LADBS permits
Foundation work
Framing & construction
Roofline integration
Finish matching
Final inspection & warranty

2026 Los Angeles Room Addition Costs

Room additions in Los Angeles cost $200 to $500 per sqft in 2026. A 400-sqft bedroom addition runs $80,000 to $200,000. A second-story addition costs $250 to $500 per sqft due to structural reinforcement. NP Line Design handles additions under CSLB #1105249.

What is the most expensive type of room addition?

Second-story additions are the most expensive at $350–$550 per square foot in Los Angeles due to foundation strengthening ($20K–$80K+), structural engineering for seismic compliance, temporary shoring, new roof construction, and 8–14 month timelines. However, in neighborhoods where larger homes command significant premiums, a second story can add $200K–$400K in value.

Room Addition Costs in Los Angeles (2026)
Scope	Cost Range	Timeline
Ground-Floor Bump-Out (50-200 sqft)	$20K – $100K	2–4 months
Bathroom Addition	$35K – $90K	2–4 months
Bonus Room Over Garage	$60K – $150K	3–6 months
Ground-Floor Extension (200-500 sqft)	$80K – $225K	4–8 months
Master Suite Addition	$125K – $300K	4–8 months
In-Law / Multigenerational Suite	$100K – $300K	4–10 months
Second-Story Addition	$150K – $500K+	8–14 months

Ground-Floor Bump-Out $20K–$100K

50–200 sqft expansion. New foundation, roofline tie-in. 2–4 months. $300–$500/sqft. Can often remain in home.

Bathroom Addition $35K–$90K

HIGHEST ROI at 65–75%. Adding a second bath (1BA→2BA) is the most impactful upgrade. $400–$700/sqft. 2–4 months.

Bonus Room Over Garage $60K–$150K

Garage foundation reinforcement $10K–$30K. Staircase $5K–$15K. $200–$400/sqft. 3–6 months.

Ground-Floor Extension $80K–$225K

200–500 sqft. New foundation, roofline integration, utility extension. $250–$450/sqft. 4–8 months.

Master Suite Addition $125K–$300K

En-suite bathroom, walk-in closet, premium finishes. $300–$500/sqft. 55–67% ROI. 4–8 months.

In-Law / Multigenerational Suite $100K–$300K

Separate entrance, kitchenette, full bathroom. $300–$500/sqft. 60M Americans live multigenerational. 4–10 months.

Second-Story Addition $150K–$500K+

Full second floor: foundation assessment, structural engineering, shear walls, new roof. $350–$550/sqft. 8–14 months.

Room addition costs vary by scope, structural requirements, site conditions, and finishes. Foundation strengthening, if needed, adds $20K–$80K+. All estimates subject to feasibility assessment and engineering review.

BMO & BHO Zoning Guide for Room Additions

Room additions in Los Angeles cost $200 to $500 per sqft in 2026. A 400-sqft bedroom addition runs $80,000 to $200,000. A second-story addition costs $250 to $500 per sqft due to structural reinforcement. NP Line Design handles additions under CSLB #1105249.

Can I add a second story to my Los Angeles home?

Whether you can add a second story depends on the Baseline Mansionization Ordinance (BMO). In R1 zones, your total floor area (RFA) cannot exceed 0.50 times your lot size. For a typical 6,000 sqft LA lot, the maximum is 3,000 sqft total. If your existing home is 1,800 sqft, you could add up to 1,200 sqft. Height is capped at 33 feet and 2 stories. A foundation assessment ($3K–$8K) determines if your existing foundation can support the additional load.

Baseline Mansionization Ordinance (BMO) — R1 Zones

Rule	R1 Requirement	Example (6,000 sqft lot)
Max FAR	0.50	3,000 sqft total
Height limit	33 ft / 2 stories	—
Encroachment plane	20 ft at side setback, 45° inward	Limits bulk near property lines
Front setback	20% of lot depth (min 15, max 20 ft)	~20 ft typical
Side setback	5 ft min (+1 ft per 10 ft height >18 ft)	5–7 ft
Rear setback	15 ft minimum	15 ft
Garage exclusion	Up to 400 sqft	Does NOT count toward FAR
Lot coverage	50% maximum	3,000 sqft of footprint

Baseline Hillside Ordinance (BHO)

Rule	Hillside Requirement
FAR	0.30–0.45 (varies by lot/slope)
Height	36 ft max (28 ft for >50% slope)
Grading	Limited quantities
Additional review	Neighbor notification required

      The Baseline Mansionization Ordinance (BMO) is the #1 constraint on room additions in LA’s R1 neighborhoods. It limits your total Residential Floor Area (RFA) to 50% of lot size. Garages up to 400 sqft are excluded from this calculation. Before planning any addition, we calculate your available RFA to determine exactly how much you can build.
    

Second-Story Additions Deep Dive

How much does a second-story addition cost in Los Angeles?

A full second-story addition in Los Angeles costs $350 to $550 per square foot in 2026, totaling $150,000 to $500,000+ for a typical 800–1,200 sqft addition. This includes foundation assessment ($3K–$8K), potential foundation strengthening ($20K–$80K+), structural engineering, shear walls, new floor and roof framing, and all finishes. Timeline is 8–14 months from design through completion.

Full vs Partial Second Story

Factor	Full Second Story	Partial / Pop-Up
Cost/sqft	$350–$550	$300–$500
Typical scope	800–1,200+ sqft	200–600 sqft
Foundation work	Extensive	Moderate
Timeline	8–14 months	4–8 months
Relocation needed?	Usually yes	Often no
BMO impact	Major (large RFA increase)	Moderate

Foundation Assessment ($3K–$8K)

A structural engineer and geotechnical consultant evaluate your existing foundation to determine if it can support a second story. The assessment includes soil testing, foundation inspection, and load calculations. Common findings by era:

Home Era	Foundation Type	Strengthening Needed?
Pre-1950s	Unreinforced masonry / shallow footings	Almost always
1950s–1970s	Perimeter footings, slab-on-grade	Depends on condition and soil
1980s+	Engineered foundations	Usually adequate

Foundation Strengthening Costs

Method	Cost	Application
Conventional underpinning	$500–$1,000/LF	Deepening existing footings
Micropile	$800–$1,500/LF	Poor soils, limited access
New parallel footings	$300–$600/LF	Adding alongside existing
Helical pier	$1,500–$3,000/pier	Point loads, unstable soils

      Temporary relocation: For a full second-story addition, most families need to relocate for 5–7 months during construction. Budget $2,000–$5,000/month for temporary housing, totaling $10,000–$35,000. Factor this into your overall project budget from the start.
    

Foundation & Structural Engineering

Can my foundation support a second story?

A structural engineer must assess your foundation ($3,000–$8,000 including geotechnical investigation). Pre-1950s homes almost always need strengthening. 1950s–1970s tract homes may or may not be adequate. 1980s+ homes usually have engineered foundations that can support additions. Foundation strengthening costs $20,000–$80,000+ if required.

Los Angeles is in Seismic Design Category D (high seismic). All additions require engineered shear walls, hold-down anchors, and continuous load paths from roof to foundation. Steel moment frames ($5,000–$15,000 each) may be needed where large openings don’t allow enough shear wall length.

Seismic Requirements for Additions

Requirement	Description	Cost Impact
Shear walls	Plywood-sheathed walls resisting lateral forces	Included in framing
Hold-down anchors	Simpson HD series connecting walls to foundation	$200–$500 each
Moment frames	Steel frames for large openings (garage, great room)	$5,000–$15,000 each
Continuous load path	Roof-to-foundation connection chain	Engineering cost
Foundation bolting	Retrofit bolts for pre-1980 homes	$3,000–$7,000
Cripple wall bracing	Bracing short walls between foundation and floor	$3,000–$5,000

      Seismic engineering adds 10–15% to structural costs but is non-negotiable in LA. All additions must meet current California Building Code seismic provisions regardless of the age of the existing structure. The addition triggers a “substantial alteration” review, which may require seismic retrofitting of the existing structure as well.
    

Room Addition vs ADU Decision Guide

Room additions in Los Angeles cost $200 to $500 per sqft in 2026. A 400-sqft bedroom addition runs $80,000 to $200,000. A second-story addition costs $250 to $500 per sqft due to structural reinforcement. NP Line Design handles additions under CSLB #1105249.

Should I build a room addition or an ADU?

Choose a room addition to expand your main home (more bedrooms, bigger kitchen). Choose an ADU for rental income, multigenerational living with privacy, or if you have hit BMO FAR limits. ADUs are exempt from many R1 zoning restrictions and can now be sold separately under AB 1033 (2025). Room additions count toward BMO FAR limits; ADUs do not.

Factor	Room Addition	ADU
Purpose	Expand main home	Separate dwelling
Cost/sqft	$250–$550	$250–$450
BMO/FAR	Counts toward limits	Exempt from FAR
Rental income	No	Yes
Separate sale	Not possible	Yes (AB 1033, 2025)
Setbacks	Standard (5 ft side, 15 ft rear)	4 ft all sides (state)
Kitchen required	No	Yes (complete dwelling)
Permit complexity	Standard	Streamlined per state law

      When a room addition is better: You need more bedrooms for your family, want a larger kitchen or living space, prefer one unified home, or the addition complements your home’s layout. When an ADU is better: You want rental income ($1,500–$3,500/mo in LA), need multigenerational living with privacy, have hit BMO FAR limits on your main home, or want an asset you can sell separately under AB 1033.
    

Ground-Floor Extensions & Specialty Rooms

Bump-Outs (50–200 sqft) $300–$500/sqft

Small expansions to enlarge a single room. New foundation pour, roofline tie-in, finish matching. 2–4 months. Often no relocation needed.

Kitchen Expansion $350–$600/sqft

Open-concept conversion. Plumbing, electrical, HVAC redistribution. Structural beam for load-bearing wall removal ($5K–$15K). 60–70% ROI.

Home Office Addition $30K–$80K

Dedicated workspace with separate HVAC zone, sound insulation, dedicated electrical circuit. 28% of workers now hybrid, 12% fully remote.

Sunroom / Four-Season Room $30K–$80K

Glass-enclosed living space. Insulated glazing for energy efficiency. HVAC extension. LA’s 284 sunny days make sunrooms exceptionally popular.

Critical Integration Costs

Integration Item	Cost	Notes
Roofline integration	$5,000–$15,000	Matching existing roof pitch, materials, and flashing
Finish matching	$5,000–$15,000	Matching flooring, trim, paint, and textures to existing home
Utility extension	$8,000–$20,000	Extending electrical, plumbing, and HVAC to new space
Load-bearing wall removal	$5,000–$15,000	Structural beam (LVL or steel) to open floor plan

LADBS Permits for Room Additions

Room additions in Los Angeles cost $200 to $500 per sqft in 2026. A 400-sqft bedroom addition runs $80,000 to $200,000. A second-story addition costs $250 to $500 per sqft due to structural reinforcement. NP Line Design handles additions under CSLB #1105249.

Permit / Fee	Cost	Notes
Building permit (500 sqft addition)	$3,000–$15,000	Based on project valuation
LAUSD school fee	$4.79/sqft	Required for all new habitable space
Electrical permit	$500–$2,000	Per circuit count
Plumbing permit	$500–$2,000	Per fixture count
Mechanical (HVAC) permit	$500–$1,500	New or extended HVAC system
Plan check fee	65% of permit fee	4–8 weeks standard, expedited available (50% surcharge)
Green Building fee	Varies	CALGreen compliance review
Total (typical 500 sqft addition)	$8,000–$25,000	All permits and fees combined

Permit Timeline & Process

Stage	Duration	Notes
Plan check (standard)	4–8 weeks	LADBS review of structural, electrical, plumbing, mechanical plans
Plan check (expedited)	2–4 weeks	50% surcharge on plan check fees
Corrections	2–4 weeks	If LADBS requests plan revisions
Permit issuance	1–2 weeks	After plan check approval

      ALL room additions in Los Angeles require LADBS building permits. There is no size threshold below which a permit is not required for structural additions. Title 24 energy compliance is mandatory. Fire-rated separation may be required depending on setback distance to property lines. CEQA exemptions apply to most residential additions under 10,000 sqft.
    

2026 Room Addition Trends in Los Angeles

Room additions in Los Angeles cost $200 to $500 per sqft in 2026. A 400-sqft bedroom addition runs $80,000 to $200,000. A second-story addition costs $250 to $500 per sqft due to structural reinforcement. NP Line Design handles additions under CSLB #1105249.

Multigenerational living: 60 million Americans now live in multigenerational households, the highest number ever recorded. In LA, soaring housing costs drive families to add in-law suites ($100K–$300K) rather than purchase separate homes. Separate entrances and kitchenettes are standard.

Home office permanence: 28% of workers are hybrid and 12% fully remote in 2026. Dedicated home office additions ($30K–$80K) with sound insulation, separate HVAC zones, and dedicated electrical circuits have become a top-3 addition request in LA.

Indoor-outdoor flow: NanaWall and similar multi-slide door systems ($800–$1,200/linear foot) are increasingly specified in ground-floor extensions. LA’s 284 sunny days per year make seamless indoor-outdoor transitions particularly effective for kitchen and living room expansions.

Modular / prefab additions: Factory-built room additions are 30–50% faster than traditional construction with tighter quality control. Costs are comparable to conventional framing ($250–$450/sqft) but timelines shrink from 6–14 months to 3–8 months. Growing in popularity for ground-floor extensions.

Smart home integration: Building an addition is the optimal time to install whole-home smart systems. Structured wiring ($3K–$8K), smart HVAC zoning, automated shading, and integrated lighting control add 5–10% to project cost but deliver a future-proofed home.

ADU vs addition market: California’s AB 1033 (2025) allowing ADU separate sale has shifted the calculus for many homeowners. When FAR limits constrain room additions, an ADU (exempt from FAR) may be the better investment — especially with LA rental income potential of $1,500–$3,500/month.

ROI by Room Addition Type

Room additions in Los Angeles cost $200 to $500 per sqft in 2026. A 400-sqft bedroom addition runs $80,000 to $200,000. A second-story addition costs $250 to $500 per sqft due to structural reinforcement. NP Line Design handles additions under CSLB #1105249.

65–75% Bathroom ROI

$350–$550/sqft Second Story Cost

8–14 mo Timeline

0.50 FAR BMO Limit

Addition Type	Cost Range	ROI at Resale	Best For
Bathroom addition (1BA→2BA)	$35K–$90K	65–75%	Highest percentage ROI
Kitchen extension	$75K–$200K	60–70%	Open-concept living
Master suite	$125K–$300K	55–67%	Primary bedroom upgrade
Second story (full)	$150K–$500K+	55–65%	Maximum absolute value gain
In-law suite	$100K–$300K	50–60%	Multigenerational + rental potential
Bonus room over garage	$60K–$150K	50–60%	Additional living space

      Neighborhood break-even analysis: In LA neighborhoods where larger homes command $600–$1,000+/sqft (Brentwood, Studio City, Sherman Oaks), a second-story addition costing $350–$550/sqft can create significant equity. In areas where home values are $400–$500/sqft, ground-floor extensions and bathroom additions offer better ROI per dollar invested. We provide a neighborhood-specific ROI analysis with every feasibility assessment.
    

More space, same home

Room Addition Portfolio

NP Line Design project in Los Angeles (CSLB #1105249)

Free Addition Estimate Call Text Fire Rebuild · Permit Hold — Expedited Services

Frequently Asked Questions — Room Additions in LA

Room additions in Los Angeles cost $200 to $500 per sqft in 2026. A 400-sqft bedroom addition runs $80,000 to $200,000. A second-story addition costs $250 to $500 per sqft due to structural reinforcement. NP Line Design handles additions under CSLB #1105249.

How much does a room addition cost in Los Angeles?

Room additions in LA cost $250–$550 per square foot depending on type. Second-story additions run $350–$550/sqft ($150K–$500K+). Ground-floor extensions cost $250–$450/sqft. Bathroom additions are $400–$700/sqft. Master suites run $300–$500/sqft ($125K–$300K).

Can I add a second story to my LA home?

It depends on the Baseline Mansionization Ordinance (BMO). In R1 zones, your total floor area cannot exceed 0.50 times your lot size. For a 6,000 sqft lot, the max is 3,000 sqft. If your current home is 1,800 sqft, you could add up to 1,200 sqft. Height is capped at 33 feet / 2 stories. A foundation assessment ($3K–$8K) determines structural feasibility.

What is the Baseline Mansionization Ordinance?

The BMO (LAMC Section 12.08 C) limits residential floor area in R1 zones to 50% of lot size (0.50 FAR). Height is capped at 33 feet / 2 stories. An encroachment plane starts at 20 feet at the side setback and angles inward at 45 degrees. Garages up to 400 sqft are excluded from the FAR calculation. The BMO is the #1 constraint on additions in LA.

How much does a second-story addition cost?

A full second-story addition in LA costs $350–$550 per square foot, totaling $150,000–$500,000+ for 800–1,200 sqft. This includes foundation assessment ($3K–$8K), foundation strengthening if needed ($20K–$80K+), structural engineering, shear walls, new roof, and all finishes. Timeline is 8–14 months.

Do I need permits for a room addition?

Yes. ALL room additions in Los Angeles require LADBS building permits. There is no size threshold below which a permit is not required for structural additions. You will also need separate electrical, plumbing, and mechanical permits. Total permit costs for a 500 sqft addition: $8,000–$25,000 including all fees.

Room addition vs ADU — which should I choose?

Choose a room addition to expand your main home (more bedrooms, bigger kitchen). Choose an ADU for rental income, multigenerational living with privacy, or if you have hit BMO FAR limits. ADUs are exempt from many R1 zoning restrictions and can now be sold separately under AB 1033 (2025).

Can my foundation support a second story?

A structural engineer must assess your foundation ($3,000–$8,000 including geotechnical investigation). Pre-1950s homes almost always need strengthening. 1950s–1970s tract homes may or may not be adequate. 1980s+ homes usually have engineered foundations that can support additions. Foundation strengthening costs $20,000–$80,000+ if required.

How long does a room addition take?

Ground-floor bump-outs: 2–4 months. Extensions and master suites: 4–8 months. Second-story additions: 8–14 months (including 2–4 months design/engineering, 2–4 months permitting, and 4–7 months construction). LADBS plan check adds 4–8 weeks; expedited plan check cuts this roughly in half.

Which room addition has the best ROI?

Bathroom addition has the highest ROI at 65–75% — adding a second bathroom (1BA to 2BA) is the single most impactful upgrade for LA home value. Master suite additions return 55–67%. Kitchen extensions return 60–70%. Second-story additions return 55–65% but add the most absolute dollar value in high-priced neighborhoods.

Do I need to move out during construction?

For a full second-story addition: usually yes (5–7 months, budget $2,000–$5,000/month for temporary housing). For ground-floor extensions: often no, especially if the work area can be isolated from occupied spaces. For bump-outs under 200 sqft: rarely necessary.

What about seismic requirements for additions?

LA is in Seismic Design Category D (high seismic). All additions require engineered shear walls, hold-down anchors, and continuous load paths from roof to foundation. Steel moment frames ($5,000–$15,000 each) may be needed where large openings don’t allow enough shear wall length. Seismic engineering adds 10–15% to structural costs.

How much are LADBS permits for an addition?

Total permit and fee costs for a 500 sqft addition: $8,000–$25,000. This includes building permit ($3K–$15K based on valuation), LAUSD school fee ($4.79/sqft), electrical/plumbing/mechanical permits ($500–$2K each), plan check fees, and Green Building fee. Expedited plan check adds a 50% surcharge.

What are the 2026 trends for room additions?

Top trends: multigenerational living suites (60 million Americans in multigenerational households), permanent home office additions (28% of workers hybrid, 12% fully remote), indoor-outdoor flow with NanaWall folding glass, modular/prefab additions (30–50% faster), and smart home integration during construction.

Why hire a GC instead of managing subcontractors myself?

Room additions involve 8–12 trades (foundation, framing, roofing, electrical, plumbing, HVAC, drywall, painting, flooring, finish carpentry). A GC coordinates all trades, manages LADBS permits, navigates BMO/BHO zoning, handles structural engineering, and provides a single warranty. This saves 15–20% versus self-managing separate contractors.

Get Your Free Feasibility Assessment

Share your room addition project details. A project specialist will review and respond with a custom feasibility assessment within 24 hours.

Why NP Line Design for Room Additions

Room additions in Los Angeles cost $200 to $500 per sqft in 2026. A 400-sqft bedroom addition runs $80,000 to $200,000. A second-story addition costs $250 to $500 per sqft due to structural reinforcement. NP Line Design handles additions under CSLB #1105249.

Licensed General Contractor

CSLB #1105249 B-license — active and clean
$25K contractor surety bond + GL + workers’ comp
10+ years serving Los Angeles communities
Verify at cslb.ca.gov

LADBS Permit Expert

In-house permit management for all additions
Building, electrical, plumbing, mechanical permits
Plan check expediting available
Inspection scheduling and compliance

Structural Engineering

Foundation assessment and analysis
Seismic design (Category D compliance)
Shear walls, moment frames, load paths
Foundation strengthening when required

BMO/BHO Zoning

FAR calculation and available RFA analysis
BMO encroachment plane compliance
BHO hillside requirements
Zoning variance guidance when needed

BBB A+ Accredited

Better Business Bureau A+ rating
Zero unresolved complaints
Transparent pricing and contracts

Full Insurance Coverage

General liability insurance
Workers’ compensation for all crew members
Certificates of insurance available on request

Tier	Cost Range	What’s Included
Bump-Out	$50K–$100K	100–200 sqft kitchen/bathroom expansion, foundation extension, roofline match
Ground-Floor Addition	$100K–$200K	300–500 sqft bedroom/family room, full foundation, HVAC extension
Second Story	$200K–$400K	600–1,200 sqft upper level, structural reinforcement, new staircase
Major Wing	$300K–$600K+	1,000+ sqft multi-room addition, new systems, separate entrance option

Room Additions & Expansions Los Angeles — Second Stories, Extensions, Master Suites & Bonus Rooms

Free Room Addition Estimate

Room Addition & Expansion Services

What’s Included

2026 Los Angeles Room Addition Costs

BMO & BHO Zoning Guide for Room Additions

Baseline Mansionization Ordinance (BMO) — R1 Zones

Baseline Hillside Ordinance (BHO)

Second-Story Additions Deep Dive

Full vs Partial Second Story

Foundation Assessment ($3K–$8K)

Foundation Strengthening Costs

Foundation & Structural Engineering

Seismic Requirements for Additions

Room Addition vs ADU Decision Guide

Ground-Floor Extensions & Specialty Rooms

Critical Integration Costs

LADBS Permits for Room Additions

Permit Timeline & Process

2026 Room Addition Trends in Los Angeles

ROI by Room Addition Type

Frequently Asked Questions — Room Additions in LA

How much does a room addition cost in Los Angeles?

Can I add a second story to my LA home?

What is the Baseline Mansionization Ordinance?

How much does a second-story addition cost?

Do I need permits for a room addition?

Room addition vs ADU — which should I choose?

Can my foundation support a second story?

How long does a room addition take?

Which room addition has the best ROI?

Do I need to move out during construction?

What about seismic requirements for additions?

How much are LADBS permits for an addition?

What are the 2026 trends for room additions?

Why hire a GC instead of managing subcontractors myself?

Explore More Room Additions Resources

Get Your Free Feasibility Assessment

Why NP Line Design for Room Additions

Licensed General Contractor

LADBS Permit Expert

Structural Engineering

BMO/BHO Zoning

BBB A+ Accredited

Full Insurance Coverage

Related Services

How Much Does Room Additions & Expansions Cost in Los Angeles? (2026)

Ask a Contractor: Room Additions & Expansions

Frequently Asked Questions: Room Additions & Expansions in Los Angeles

How much does a room addition cost in Los Angeles?

How much does it cost to add a second story in Los Angeles?

Do I need a permit to add a room to my house in LA?

Common Mistakes to Avoid

Frequently Asked Questions

How much does room additions cost in Los Angeles?

How long does room additions take in Los Angeles?

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