In-law suite
$60k–$95k
- Bedroom with an egress window
- Full bathroom with a low shower
- Kitchenette with sink and fridge
- Sitting room and closet
- Linked smoke and CO alarms
- Permits and inspections
Basement apartment conversion · Licensed & insured · Zoning checked first
Basement apartment conversion that passes inspection, not just one that looks finished.
A basement becomes a legal apartment when it meets the rules for a separate home: ceiling height, a way out in a fire, a fire-rated ceiling, its own kitchen and a permit that says so. We check your zoning before anything else, then price three routes from an in-law suite to a unit with its own door.
Text your town and a photo of the basement. A supervisor who builds basement units replies within 5 minutes during business hours.
- $100–170kTypical legal unit
- 12–16 wksLegal unit build time
- 4.9410 reviews
- 24hWritten estimate
What happens after you text us
We ask for your town first, because zoning decides what is allowed.
Some towns welcome basement units and some forbid them. The supervisor asks where the house is and who will live there, checks the local rules before the visit, and then measures the ceiling and the windows.
- Zoning is checked before anyone quotes a kitchen
- Who will live there changes which code rules apply
- Ceiling height and exits are measured at the first visit
My mother is moving in with us next spring. We would like to make the basement a small apartment so she has her own space and kitchen.
Hi Nicole, this is Rachel, I plan our basement apartments. That is a lovely plan. Which town is the house in? I will check the local rules on second units before we talk layout.
We are in the town limits, on a regular single-family street.
Thanks, I will look up your zoning today. Could you also send a photo of the basement windows and measure from the floor to the bottom of the joists?
Seven feet two. The windows are small, near the ceiling.
Seven two works. The bedroom will need an egress window. I can visit Tuesday at 3, and you will have written prices for a suite and a full apartment by Wednesday night.
What a basement apartment costs
A basement apartment costs $60,000 to $250,000. The kitchen and the entrance set the tier.
Ranges are for 700 to 1,100 square feet with ceilings already near 7 feet. Most homeowners choose the legal apartment, because a full kitchen, fire separation and a certificate of occupancy let the unit be used by anyone later.
Legal apartment
$100k–$170k
- Everything in In-law suite
- Full kitchen with a range
- Fire-rated ceiling and door
- Separate heat and cooling
- Sound insulation overhead
- Certificate of occupancy
Unit with own entrance
$175k–$250k+
- Everything in Legal apartment
- Foundation cut for a new door
- Exterior stairwell and drain
- Separate electric meter
- Laundry inside the unit
- Engineering for the opening
Run the numbers on a basement unit
Choose the route, the square footage and the house type. The range shifts with every pick, using the same tiers our conversion supervisors quote.
A range, not a quote. Your written estimate comes after the visit and does not change once you approve it.
Typical range for your answers
Turn this range into my written unit priceWhere the money goes
The kitchen and bath take a third of the budget. Safety rules take more than most people expect.
Averages from our recent legal basement apartments. Egress windows, fire-rated ceilings, linked alarms and separate heat are what make a unit legal, and together they cost about as much as the kitchen.
Get my itemized apartment estimate
In-law suite or legal apartment
Build an in-law suite for family. Build a legal apartment if anyone else may live there.
An in-law suite shares the house and has no full kitchen, so many towns treat it as part of your home. A legal apartment is a separate dwelling with stricter rules and a higher price. We check six things and write down which one fits your plans.
| If this is true | We recommend |
|---|---|
| A parent will live there and share meals upstairs | In-law suite |
| You may rent it to a tenant in the future | Legal apartment |
| Your town bans second kitchens in single-family homes | In-law suite |
| Your town allows accessory dwelling units | Legal apartment |
| The occupant needs their own cooking and laundry | Legal apartment |
| Your budget for the conversion is under $100,000 | In-law suite |
How long it takes
A legal basement apartment takes twelve to sixteen weeks, plus the permit review.
An in-law suite takes nine to eleven weeks and a unit with its own entrance sixteen to twenty-two. Permit review for a new dwelling can take four to ten weeks, so we file drawings early and put the review time on your schedule.
Weeks before
Zoning, drawings, permit
Zoning confirmed, floor plan and fire plan drawn, permit filed. Kitchen and windows ordered on approval.
Weeks one to four
Egress and rough-in
Egress windows cut, walls framed, plumbing, wiring and ducts run for kitchen and bath, rough-in inspected.
Weeks five to ten
Fire and sound, then close
Fire-rated drywall on the ceiling, sound insulation, alarms linked, then drywall, tile and cabinets.
Final weeks
Finish and occupancy
Flooring, appliances and fixtures, final inspections, certificate of occupancy issued, walkthrough with you.
Remodeling concepts
Basement apartment conversion: conditions and possibilities.
AI-generated examples of existing conditions and remodeling possibilities. Each image is a separate concept, not a documented transformation of the same home.
What a legal unit is built from
Safety materials are named first, finishes second.
Inspectors look at what sits between the unit and your home: the ceiling, the door, the alarms and the exits. Your estimate names each product, so you can see the unit is built to pass.
Fire-rated drywall
USG Sheetrock Firecode X or similar five-eighths inch Type X board on the ceiling slows fire between the unit and the home above.
Fire-rated doors
A solid 20-minute rated door with a self-closing hinge separates the unit from the shared stair or the rest of the house.
Linked alarms
Hardwired Kidde or First Alert smoke and carbon monoxide alarms, linked so one sounding sets off every alarm in both homes.
Ductless heat and cooling
A Mitsubishi or Fujitsu mini-split gives the unit its own thermostat, so neither household argues over the temperature.
Sound insulation
Rockwool Safe'n'Sound between the joists and resilient channel under the ceiling cut footsteps and voices between floors.
Egress window wells
Bilco ScapeWel or galvanized wells with a ladder or steps, sized so an adult can climb out and a firefighter can climb in.
Written into every contract
Six promises you can hold us to.
The approved price is the final price. Change orders only with your written approval.
A credit for every working day of delay we cause. Weather and inspections excepted, in writing.
Dust barriers, floor protection and a clean-up before we leave. Your home stays livable.
A text or email every working day with photos and tomorrow's plan, or the day is free.
Workmanship warranty in writing, transferable to the next owner, backed by a fixed address.
A small deposit, then you pay only for work that is already completed, inspected and photographed.
Who is in your house
Three people build the apartment, and one of them handles the inspectors.
A basement unit takes months, so the faces matter. Everyone is background-checked and introduced by name, and the supervisor who deals with the building department is the same one who answers your texts.
Conversion supervisor
Handles zoning, permits, inspections and your updates.
Lead carpenter
Frames rooms, builds the fire-rated ceiling and hangs doors.
Master plumber
Runs the kitchen, bath, laundry and any ejector pump.
Illustrative project scopes
Basement apartment conversion: scope and budget examples.
Planning examples with illustrative budgets and durations. These are not completed customer jobs, invoices or promises about your project.
In-law suite for a mother
- Example budget
- $82,400
- Example duration
- 10 weeks
- Record type
- Illustrative scope
Legal one-bedroom unit
- Example budget
- $146,800
- Example duration
- 15 weeks
- Record type
- Illustrative scope
Unit with new side entrance
- Example budget
- $214,300
- Example duration
- 20 weeks
- Record type
- Illustrative scope
Your plans are not average
Who the unit is for changes what we build.
All three routes above follow the same safety rules. These are the situations we plan most often, and what each one does to the scope, the cost or the calendar.
A parent moving in
For a parent, we plan a step-free path from the driveway if the site allows, a low-threshold shower, lever handles, bright lighting and a door to the main house, so help is close while privacy stays intact on both sides.
Plan a basement suite for a parentA grown child saving to buy
Many families build a unit so a grown son or daughter can save for a down payment. We price a kitchenette or a full kitchen, sound insulation and separate heat, so both households live comfortably for a few years.
Price a unit for our grown childRent to help with the mortgage
If you plan to rent the unit while you live upstairs, it must be a legal apartment with a certificate of occupancy. We confirm your town allows it, design to the rules and give you the paperwork your insurer will ask for.
Price a legal rental unitA town with strict unit rules
Some towns cap unit size, require the owner to live on site or ask for an extra parking spot. We read the rules before drawing, design to them and answer the plan reviewer, so the permit is not denied late in the process.
Check my town's basement unit rulesAn older foundation
Stone or old block foundations need care when cutting for egress windows or a new door. An engineer looks at the wall first, and we price any reinforcement, waterproofing and drainage the new opening requires.
Price a unit in my older basementStep-free for a wheelchair
A basement unit can be accessible if the lot slopes to a walkout. We plan a level entrance, wide doors, a roll-in shower and a kitchen with open space under the sink, and price any grading the path needs.
Plan an accessible basement unitTwo households, one building
Footsteps, voices and a television carry through a basement ceiling. We add mineral wool, resilient channel and a solid door, and place the unit's bedroom under the quietest room upstairs where the layout allows.
Plan a quieter shared houseSuite now, apartment later
If a parent moves in now and a tenant may follow years later, we build the suite with the fire-rated ceiling, the egress and the kitchen rough-in already in place, so the later upgrade needs no demolition.
Plan a suite that can growWhat this service is
A basement apartment conversion, in terms the inspector uses.
Basement apartment conversion is the construction of a self-contained living unit in a basement, with sleeping space, a bathroom, a kitchen or kitchenette, egress windows, fire separation from the house above, linked alarms and its own heat, permitted as an in-law suite or a legal accessory dwelling. ProBuild Remodeling builds it as a licensed general contractor.
It covers zoning review, drawings, permits, egress windows, fire-rated ceilings and doors, kitchens, bathrooms, heating and cooling, sound control, and when needed a new exterior entrance through the foundation. It ends with final inspections and, for legal apartments, a certificate of occupancy. It does not include property management, tenant screening or rental listings.
It is for homeowners who live in the house and want a place for a parent, a grown child or a tenant who helps with the mortgage. It is not for investors converting a house they do not live in, or for a basement that only needs finishing as extra family space, which is basement finishing.
Terms on a basement unit estimate
- Accessory dwelling unit
- A second, smaller home on the same lot as a house, often called an ADU. Towns set their own rules for them.
- Certificate of occupancy
- The document a building department issues once a new dwelling passes inspection, allowing people to live in it.
- Fire separation
- Rated walls, ceilings and doors that slow a fire from spreading between the unit and the home above it.
- Type X drywall
- Five-eighths inch gypsum board with glass fibers that holds up longer in a fire than standard drywall.
- Egress
- A window or door large enough and low enough for a person to escape through in an emergency.
- Owner occupancy
- A zoning rule in some towns requiring the owner to live in either the house or the unit for it to be allowed.
- Underpinning
- Deepening a foundation to lower the basement floor and gain ceiling height. Costly, and needs an engineer.
- Interconnected alarms
- Smoke and CO alarms wired together so that when one detects a problem, all of them sound at once.
Basement apartment questions
Eight questions about basement apartments, before you commit.
How much does it cost to convert a basement into an apartment?
An in-law suite with a kitchenette costs $60,000 to $95,000. A legal apartment with a full kitchen, fire separation and its own heat costs $100,000 to $170,000. Adding a separate exterior entrance through the foundation brings it to $175,000 to $250,000 or more.
Is a basement apartment legal in my town?
It depends on local zoning. Many towns now allow accessory dwelling units, some with conditions like owner occupancy or size caps, and some still forbid them. We check your zoning before the first visit and design within it.
What makes a basement apartment legal?
Egress windows in sleeping rooms, enough ceiling height, a fire-rated separation from the house above, linked smoke and CO alarms, proper ventilation and a permit that ends in a certificate of occupancy. The exact list varies by town.
How tall does a basement ceiling need to be for an apartment?
Most codes ask for about 7 feet of clear height in living areas, with beams and ducts allowed to drop a little lower. If your basement is shorter, we reroute ducts first. Lowering the floor is possible but expensive.
Does a basement apartment need a separate entrance?
Not always. Many codes accept an entrance through the house for an in-law suite, as long as the unit has egress windows. A separate entrance adds privacy and helps with rental, and some towns require it for a legal unit.
How long does a basement apartment conversion take?
Nine to eleven weeks for an in-law suite, twelve to sixteen for a legal apartment and sixteen to twenty-two with a new entrance. Permit review for a new dwelling can add four to ten weeks before work starts.
Can a basement apartment have a full kitchen?
Yes, once it is permitted as a separate dwelling. In towns that ban second kitchens in single-family homes, an in-law suite with a kitchenette, a sink, a fridge and a microwave, is often allowed instead.
Will a basement unit raise my property taxes?
Often, because a permitted unit adds assessed value. The increase depends on your town's assessor. We cannot give tax advice, but we can give you the permit documents your assessor will ask for.
Basement apartments near you
Your remodeling address, within our service area.
Basement units depend on town zoning, so each is planned by a local team that reads your town's rules and builds under the license of your state. License numbers are on our licenses page.
- Maine
- New Hampshire
- Massachusetts
- Rhode Island
- Connecticut
- New York
- New Jersey
- Pennsylvania
- Delaware
- Maryland
- Virginia
- North Carolina
- South Carolina
- Georgia
- Florida
- Check your remodeling address
Free basement apartment estimate
Tell us your town and who will live there. We will tell you what is allowed.
Send the your answers. A conversion supervisor replies within 5 minutes during business hours, checks your zoning and books a visit to measure the basement.