Free · About 60 seconds · No obligation

Find out what ADU your lot allows, and how to pay for it.

Answer three quick questions. See what an ADU on your property could cost, what it could rent for, and what the monthly payment might be.

  • One team for the lot check, the loan and the build
  • Keep your low first-mortgage rate with an ADU HELOC
  • We draw the plans and handle the city permits
Modern detached ADU with a flat roof, cedar accents and glass sliding doors
A modern detached ADU (illustration)

Where is the property?

We serve Los Angeles, Orange, Riverside, San Bernardino, San Diego and Ventura counties.

What's the ADU mainly for?

No sign-up needed to see your numbers.

See it before you build it

What could your property become?

Pick what you have today, then drag the slider. Under each one you'll see what's usually allowed, what it could cost and rent for, and how we build it.

The same backyard with a new detached ADU cottage, lawn and paver path Empty backyard with dry patchy grass and an old wood fence

Detached ADU

1Check it

2Pay for it

3Build it

Estimates for a typical size, not a quote. Photos are AI-generated illustrations of typical projects, not actual MARS work.

Why homeowners choose us

One team. Three jobs. No running around.

Most people talk to an architect, a bank and a contractor who never talk to each other. With Let's Talk ADU, the people who check your lot, set up your loan and build your ADU work together.

1

Check your lot

We find out what your city allows on your property before you spend money on plans.

  • Size limits and setbacks
  • Garage, backyard or attached options
  • Electrical and sewer needs, on a free site visit
2

Pay for it

Compare ways to fund the build with our licensed lending team, E Mortgage Capital.

  • ADU & Renovation HELOC
  • Cash-out refinance
  • Renovation or construction loans
3

Build it

MARS Construction designs, permits and builds your ADU with its own crews.

  • Plans drawn for your lot
  • Structural and energy engineering
  • City permits and corrections
How it works

From "Can I?" to move-in, in four steps

1

Free lot check & visit

Tell us about your property. We look at your city's rules, then visit to check the yard, the electrical panel and the sewer line.

2

See your financing options

Compare a HELOC, a cash-out refinance and construction loans side by side. Pick what fits your budget and goals.

3

Design & permits

We draw plans with you, handle the engineering and submit everything to the city, including any changes they ask for.

4

Build & move in

MARS crews build your ADU and see it through final inspection. Then it's ready for family or a tenant.

Financing, built in

Pay for your ADU without giving up your low rate

If you locked in a low mortgage rate, you probably don't want to lose it. An ADU HELOC is a second loan on your home's equity, so your first mortgage stays exactly as it is.

Simple version: your current mortgage stays put. The HELOC pays for the ADU. Once the ADU is rented, that rent can help cover the payment.

Talk to a Loan Officer

Loans offered by E Mortgage Capital Inc., NMLS #1416824. Pat Collins, NMLS #1628553, DRE #02143449. Not a commitment to lend. All loans subject to credit, income, property and underwriting approval.

ADU & Renovation HELOC Most popular

A credit line on your home's equity. Draw what you need, and draw again as you repay. Apply online, with no in-person appraisal.

Good fit if you have a low first-mortgage rate you want to keep.

Cash-out refinance

Replace your current mortgage with a larger one and take the difference in cash. Closing costs apply.

Good fit if your current rate is already higher than today's rates.

Renovation or construction loan

Based on the project itself. Some programs can fund a new ADU when you buy a home or refinance.

Good fit if you're buying, or have little equity today.

Primary homes and rentals. Self-employed and retired borrowers welcome. Future ADU rent can sometimes help you qualify, depending on the program.

Payment calculator

Can the rent cover the payment?

Move the sliders to see how an ADU could pay for itself. These are simple estimates to help you plan, not a quote.

Set it to what similar units rent for near you.
Example rate only. Your real rate depends on credit, equity and the program.

How will you pay down the loan?

Left over each month —

Monthly payment—
Rent after upkeep—
Rent per year—
Interest per year—

"Rent after upkeep" sets aside 15% of rent for taxes, insurance, repairs and empty months. Interest-only payment assumes the full amount is drawn.

Get Numbers for My Lot
What the numbers can look like

Two common ADU projects, in plain dollars

Example math to show how an ADU can pay for itself. Your costs and rent will depend on your lot and neighborhood.

Pre-approved city plans

Your city may already have a plan approved

Many SoCal cities offer ADU designs they have already reviewed. Building one can save time in plan check and cost less than a fully custom design. Pick a plan and we'll tell you if it fits your lot.

AnaheimStudio · Plan 001 · 224 sq ft
PasadenaStudio · Prototype A · 374 sq ft
Santa AnaStudio · Studio plan · 399 sq ft
BurbankStudio · BPAP 24001 · 432 sq ft
Faster permitsThe city has already reviewed the design.
Lower design costLess custom drawing work up front.
We do the restSite fit, permits and the build.

Plan details come from each city's program and can change. We confirm current details for your address.

Questions

Straight answers to common questions

Updated

California ADU rules at a glance

  • Detached ADU: up to 1,200 sq ft on a single-family lot.
  • Attached ADU: up to half the size of the main home, capped at 1,200 sq ft.
  • Junior ADU: up to 500 sq ft, inside the existing home.
  • Impact fees: ADUs under 750 sq ft are exempt from city impact fees.
  • Garage conversions: cities generally can't require replacement parking.
  • Financing: an ADU HELOC is a second loan, so your first mortgage and rate stay in place.

Local rules vary. We confirm what applies to your address during the free lot check.

What is an ADU, exactly?

An accessory dwelling unit is a second, self-contained home on the same lot as your house. It has its own entrance, kitchen and bathroom. It can be a backyard cottage, a converted garage, an addition to your house, or a junior ADU inside it.

How much does an ADU cost in Southern California?

It depends mostly on the type and size. A garage conversion or junior ADU usually costs less than a new detached ADU, because part of the building already exists. Use the free lot check at the top of this page for a planning estimate. We give exact pricing after a free site visit.

Will I lose my low mortgage rate?

Not with a HELOC. A HELOC is a second loan, so your first mortgage and its rate stay in place. A cash-out refinance is different: it replaces your current mortgage with a new one.

Why does 749 square feet come up so often?

Under California law, ADUs under 750 sq ft are exempt from city impact fees. A well-designed 749 sq ft unit can fit two bedrooms and avoid those fees. We confirm the details with your city.

If I convert my garage, do I need to replace the parking?

In California, cities generally can't require you to replace parking when you convert a garage into an ADU. We check your city's rules during the free lot check.

Can the future ADU rent help me qualify for the loan?

Sometimes, depending on the loan program. Our loan officer will tell you which programs can count projected rent for your situation.

Do I need an appraisal for the HELOC?

Our ADU & Renovation HELOC uses an automated home valuation, so there's no in-person appraisal in most cases.

Do you handle the permits?

Yes. We draw the plans, handle the structural and energy engineering, submit everything to the city and make any corrections the city asks for.

Who actually builds it?

MARS Construction Industries Corp, CSLB #1138550, with its own crews. MARS is licensed A, B, C-36 and C-20, and is bonded and insured.

Can I rent out my ADU?

Yes. California lets homeowners rent an ADU long term. Cities can require rentals to be longer than 30 days, so short-term vacation rentals are often not allowed.

Do I have to live on the property to build an ADU?

Not for a regular ADU. California no longer requires the owner to live on the property. A junior ADU is different: the owner usually has to live in the main house or the junior ADU.

Which areas do you serve?

Los Angeles, Orange, Riverside, San Bernardino, San Diego and Ventura counties in Southern California.

What documents will I need for financing?

Usually proof of income (W-2s or 1099s, tax returns or transcripts) and recent bank and asset statements. We'll send you a simple checklist for your situation.

Free property visit

Not sure your lot can handle an ADU? Let's take a look.

Book a free, no-obligation visit. A construction lead and a loan officer will look at your property and your numbers together.

  • Where an ADU fits on your lot, and how big
  • Your electrical panel and sewer line
  • A budget and the loan options that fit it

Request my free visit

A team member replies within 1 business day.

By submitting, you agree to be contacted about your project by phone, text or email.

Call Check My Lot