Planning Your Accessory Dwelling Unit

Page Sections

Find out how to plan, design, and pay for your ADU.

Still have questions? Contact:
Housing

617-635-3880

send an email

12 Channel Street
9th Floor

Boston, MA 02210
United States

Planning Overview

Timeline showing a summary of the ADU process: highlighting the Planning Phase

The planning stage is one of the most important steps in the process to build an ADU.

During the planning stage, you will start to do the work to make your ADU idea come to life. You will need to make important decisions, such as how to finance the cost of your project and which building and design professionals you want to hire. The following sections contain information about paying for your ADU, designing your project, and hiring architects and contractors. These sections will help you as you work on clarifying the scope, schedule, and costs of your ADU project.

Before You Start: Know What You Can Build

If you don't already know what types of ADUs are allowed for your situation, we recommend you make sure you know what's possible before diving into planning your ADU. For more information about how to find out what you can build please see our page Researching Your ADU.

ADU Questions? We can help!

We'll answer your questions at any stage of the process. Email ADU@boston.gov

Paying for Your ADU

Budgeting for Your ADU

Determining how you will pay for your ADU project is one of the most important aspects of the planning stage. Generally, converting existing space -- such as a basement-- will cost less than building an ADU through new construction. As a rough benchmark, the total cost to build an internal ADU is generally between $75,000 - $100,000; the cost to build a detached ADU can run between $250,000 - $350,000. However, project costs can vary widely and will depend on the extent and scope of work of your individual project. Your architect and/or building team will be able to help you estimate the cost of your project.

Homeowners often borrow some or all of the total project cost, or use a combination of sources (such as cash, loans, and home equity) to finance their project. As you start your financing plan, remember to budget for costs that may arise before construction begins, such as the cost to hire an architect or builder or the cost to file a building permit application.

The following sections include information on different types of loans that could be used to help finance the cost of building your ADU. This information is meant as a starting place for your research into your own financing considerations.

Boston Home Center ADU Loan

The Boston Home Center offers gap funding of up to $50,000 to help income-eligible homeowners with the costs of constructing an ADU. The ADU Loan is a 0% interest, deferred loan with no monthly payments. Find out more here.

Cash-out Refinance

A cash-out refinance allows homeowners to replace their current mortgage with a new, larger mortgage and receive the difference in cash. Your new mortgage loan may have different terms than your original loan, such as a different loan period or interest rate. A cash-out refinance may be an option for homeowners who have built up equity on their home or who have seen their home's value increase over time.

Home Equity Loan

A home equity loan is a one-time loan that allows you to borrow against the appraised value of your home. Typically, you will receive your loan as a lump sum payment and pay back the loan amount, plus interest.

Home Equity Line of Credit (HELOC)

Similarly to a home equity loan, a home equity line of credit (HELOC) also allows homeowners to borrow against the value of their home. However, HELOCs allow a continuous (within a specified credit limit and borrowing period) access to funds that homeowners can tap into. Interest is only paid on the money that is used, but many HELOCs charge variable interest rates.

Construction Loan

Construction loans are specifically used to help pay for building or home renovation. These loans are usually short term (often 9-12 months). Sometimes, they can be folded into the overall mortgage loan after the initial construction loan period is up.

Boston's ADU Loan

Boston's 0%-interest loan for homeowners building ADUs.

ADU LOAN FACT SHEET

The ADU Loan Program offers gap funding of up to $50,000 to help income-eligible homeowners with the costs of constructing an ADU.

A zero percent (0%) interest, deferred loan of up to $50,000 for an ADU project. The loan only becomes due for repayment if the owner sells or transfers ownership of the property, or undertakes a cash-out refinance of the home.
There are no owner match requirements for homeowners with incomes below 120% of Area Median Income (AMI). Homeowners between 120 and 135% of AMI will need to match the City-funded loan 1:1 with their own funds or with a bank loan.
Homeowners are paired with a Boston Home Center Construction Specialist who monitors progress throughout the extent of construction.

Apply for the ADU Loan Program

ADU Loan FAQ

Who is eligible for the ADU Loan?

You must meet the following eligibility requirements in order to receive the ADU Loan.

City of Boston residents who own and occupy a 1-3 unit home;
Homeowners whose annual household income does not exceed 135% of AMI;
Homeowners must have less than $75,000 in financial assets, excluding the assets being used towards construction of the ADU, home equity, retirement funds, and college savings plans;
Homeowners may not have received home repair financial assistance from any City of Boston program within the past ten (10) years. This excludes de-leading funds.
Homeowners must be current with all City of Boston and home accounts, including property taxes and water bills, and mortgage and property insurances.

When should I apply for the loan?

You should apply for the ADU Loan once you have begun working with your architect and/or general contractor and have a solid understanding of the design and scope, including estimated cost, of your project.

What are the required submission documents?

You must first complete a loan application document. This can be done online; call our office at 617-635-4663 if you need further assistance.

Then, you must submit the following documentation to verify your eligibility. It is preferred that all documents are submitted at the same time in order to expedite the intake process. NOTE: we cannot process your application without your submission documents.

Copy of the Recorded Deed (also called a “Quitclaim Deed”, “Warranty Deed”, or “Certificate of Title”). A copy can be obtained at the Edward Brooke Courthouse - Registry of Deeds, 24 New Chardon Street, Boston, or go to www.suffolkdeeds.com.
If needed, an original Death Certificate for all deceased persons listed on the recorded deed (if not recorded with Suffolk Registry of Deeds). A Death Certificate can be obtained at the Registry of Births, Deaths, and Marriages, City Hall, Room 213, Boston, MA, 02201
Copy of current Homeowner’s Insurance Policy. If the home is located in a designated flood plain area, documentation of flood coverage is required.
Copy of the most recent signed Federal Tax Return including W-2 Forms and all Schedules. (IRS form 1040, 1040A, or 1040EZ) for all owners. If Self-Employed, provide a year-to-date Profit and Loss Statement signed by you and your accountant, and copies of the last two years of Federal Tax Returns.
Two current pay stubs for all household members 18 years old or older; and/or proof of income from all other sources such as Social Security Award Letter, Unemployment Compensation, Pension, etc.*
Current Mortgage Statement for all loans against property including any equity or rehab loans. Include a letter of explanation for use of equity loan.
Copy of most recent savings, checking and other account balance statements from all depository institutions (such as 401K’s, stocks, bonds, credit union, etc.) for all owners.
Two (2) estimates from licensed contractors for your home repair(s). Please include a copy of the following from your chosen contractor: Mass Home Improvement Contractor (HIC) Registration Certificate, Construction Supervisors License (CSL), Mass Lead Safe Renovators License or EPA Renovator Certificate, and Contractor Liability Insurance. Estimates Not required for Senior Home Repair Program.
Approved Building Permit from the Inspectional Services Department
Drawing/Plans Stamped by the Inspectional Services Department

* For all individuals over the age of 18. If person/s is/are not employed, copy of school transcript or explanation of circumstances and a No Income Affidavit (https://bit.ly/noincomeaffidavit) must be supplied.

You can submit documents via our online submission form.

If you do not have access to a Google account, please email your documents to homerepairsubmission@boston.gov or mail them to:

The Boston Home Center Attn: Homeowner Assistance Programs 26 Central Ave. Hyde Park, MA 02136

Once we receive this package, we will notify you about your application status.

What costs are eligible to be covered by the ADU Loan?

The ADU Loan may only be used for construction costs. It cannot be used to reimburse the homeowner for costs associated with designing or permitting your ADU. Typically, the loan is paid in installments directly to the contractor responsible for the construction work. Payments are made after inspections by the Boston Home Center's Construction Monitoring Unit, in order to determine that all work is going smoothly. We require that the homeowner pay their portion of the construction costs first, and then use the City's ADU Loan as gap financing to finish the project.

Designing Your ADU

Once you know what you can afford to build, your next step is to begin designing your ADU.

While the characteristics of your property or existing home, as well as zoning regulations, will inform what type of ADU you choose to build, your plan for how you want to use your new ADU will also shape its design. As you begin the design process, consider who will live in your ADU and what their needs will be. For example, you may opt to make specific design decisions if you know the ADU will be inhabited by an elderly relative who relies on a mobility assistance device, such as a wheelchair. There may be differences in the ADU design if you envision yourself living in the unit versus renting it to future tenants.

You can hire an architect, builder, or other design professional at any point while you prepare your design ideas. Some homeowners choose to hire a professional early on in the process to discuss their initial idea and assess the feasibility of building an ADU on their property. Other homeowners decide to hire a professional later to finalize architectural plans of the unit. Keep in mind that you will need to submit building plans stamped by a licensed architect as part of your building permit application with the Inspectional Services Department.

The City has developed various guides to help you clarify the design of your ADU.

Remember to always review these guides, as well as other relevant fire and building codes, with your architect or builder. The specific characteristics of your property will shape how these code requirements apply to your project.

ADU DESIGN CHECKLIST - INTERNAL UNITS ONLY

This document is meant to identify common building & fire code requirements that impact construction of internal ADUs.

GUIDANCE ON ADUs & FIRE CODE

This document is meant to explain visually and in plain language common building code and fire code requirements (not zoning code) that impact design and construction of attached and detached ADUs.

other code guidelines & resources

ADU WORKSHOP

The ADU Design Workshop is an opportunity for Boston homeowners who are interested in building an ADU in their home or on their property to get feedback from City staff before they submit a building permit application to the Inspectional Services Department.

The workshop is optional, but highly encouraged. It can be a helpful step in determining feasibility for building an ADU on your property or for preparing your final plans for your building permit application. At the meeting, you can get input on your ADU plan from city staff -- including staff from the Mayor's Office of Housing, the Planning Department, and the Inspectional Services Department -- with expertise in design and code requirements. They can help answer specific questions related to your project. You may also attend to listen to other project proposal or to learn more about the program.

Workshops are held virtually (via Zoom) on the first Thursday of each month, from 4-5:30 PM. Register at the link below.

UPCOMING ADU WORKSHOPS

Hiring Architects and Contractors

Finding and Working with Designers or Architects

The City does not keep a list of architects for contact. The following sites can be used as starting places to begin your search for an architect or designer.

Tips to keep in mind before you sign a contract or pay fees

Always do your research: read reviews online, ask for references and portfolios to ensure that they've worked on similar projects in the past
Shop around: get multiple quotes for the scope of work
Interview your architect: ask your potential architect questions about their process, design philosophy, estimated schedule, fee schedule, and responsibilities throughout the contract
Get all agreements in writing and be sure you receive a detailed contract: the contract should include a cost breakdown, anticipated project time frame, and schedule of payments.

Finding and Working with Contractors

Hiring a contractor is one of the most important steps in the process of designing and planning your ADU. The contractor you hire will be working with you for the entire extent of the project and overseeing your ADU's construction. Be sure to read the below tips, as well as these home improvement and contracting tips and these listed on the state's website, before you begin your search.

The City does not keep a list of contractors for contact. The following sites can be used as starting places to begin your search for a contractor.

Tips to keep in mind before you sign a contract or pay fees

Always do your research: read reviews online, ask for references and portfolios to ensure that they've worked on similar projects in the past. Check with the state's Office of Public Safety & Inspections and the Better Business Bureau to find out if any complaints have been filed against the contractor in the past.
Shop around: interview at least three contractors and request a written, detailed estimate from each one.
Ensure your contractor has valid state registration, and confirm the type of license they will need for the work required: Use this state website to look up your contractor's registration number. This fact sheet shows what type of licenses are required for specific work types.
Interview your architect: ask your potential architect questions about their process, design philosophy, estimated schedule, fee schedule, and responsibilities throughout the contract.
Get all agreements in writing and be sure you receive a detailed contract: the contract should include a cost breakdown, anticipated project time frame, and schedule of payments.