Planning Your Accessory Dwelling Unit
Find out how to plan, design, and pay for your ADU.
Planning Overview
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.
Paying 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, ADU project costs can start at roughly $275/sf. 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.
Want to learn more about building a realistic financing plan for your ADU?
View a recording of our recent online information session, in which we cover how to assess your own financial readiness, common options for financing, how to plan for expected costs, and how to sustain your ADU with smart planning for ongoing expenses. A copy of the presentation slides in English, Spanish, Vietnamese, Haitian Creole, and Cape Verdean Creole are available and the chat transcript is available as well.
Common Ways to Finance
The Boston Home Center offers staff support and financial assistance to income-eligible homeowners of 1-3 unit homes who are planning to build an Accessory Dwelling Unit (ADU) in their home or on their property. Income-eligible homeowners may apply to the ADU Financial Assistance Program to receive both a grant and a loan to help with costs to design, permit, and build their ADU. If eligible, homeowners may also apply for additional financing with one of our partner lenders. Find out more here.
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.
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.
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 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.
ADU Financial Assistance Program
The Boston Home Center offers staff support and financial assistance to income-eligible homeowners of 1-3 unit homes who are planning to build an ADU in their home or on their property. Income-eligible homeowners may apply to the ADU Financial Assistance Program to receive both a grant and a loan to help with costs to design, permit, and build their ADU. If eligible, homeowners may also apply for additional financing with one of our partner lenders.
The program is intended for financially prepared owner-occupants who have assembled an ADU design and building team and plan to soon file for a building permit. Applications to the ADU Financial Assistance Program will only be accepted if all required documents and participation prerequisites to join the program have been met.
TO QUALIFY:
- You must own and occupy a one, two, or three-unit home in the City of Boston and plan to build your ADU on that same property.
- Your annual household income must meet all income eligibility requirements
- You must have less than $100,000 in financial assets, excluding the assets being used towards construction of the ADU, home equity, retirement funds, and college savings plans
- You must be current on all City of Boston and housing-related payments, including property taxes, water, mortgage, and insurance
- You must have attended both the ADU Design Workshop and the ADU Budget Workshop within the past 3 months before applying.
- You must be working with a licensed architect to develop your ADU plans. Submission of draft or permitted plans is required as part of the application
- You cannot have received City home repair financial assistance within the past ten years, except for de-leading funds.
The ADU Financial Assistance Program is composed of different grant and loan options. Homeowners may choose to participate in all three, if they meet the appropriate eligibility requirements. In order to receive a loan from a partner lender, you must first apply for and receive funding from the Boston Home Center.
PROGRAM OPTIONS:
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.
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The Accessory Dwelling Unit (ADU) Guidebook provides you with practical guidance and inspiration for adding an ADU to your property, whether it is for additional living space, rental income, or housing for family members. We’ll walk you through what’s possible and what to consider in the design process.
ADU DESIGN CHECKLIST - INTERNAL UNITS ONLY
ADU Design Checklist: Diagrams
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These documents are meant to identify common building & fire code requirements that impact construction of internal ADUs.
- 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
- Massachusetts Comprehensive Fire & Safety Code (527 CMR 1.00)
- Massachusetts State Building Code (780 CMR)
ADU WORKSHOPS
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 ADU Budget Workshop provides a space for homeowners to consider the full scope of building an ADU in your property- from projecting an accurate cost estimate to identifying how to finance your ADU project.
Participation in both the Design and Budget workshops is required to enroll in the ADU Financial Assistance Program. However, attendance to either workshop is highly encouraged if you are interested in building an ADU on your property. It can be a helpful step in determining the feasibility of building an ADU on your property or helpful step in preparing your final plans for your building permit application.
At the meetings, you can get input on your ADU plans 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 proposals or to learn more about the program.
Workshops are held virtually (via Google Meet) on the first Wednesday and Thursday of each month, from 4-5:30 p.m. Register below.
UPCOMING ADU WORKSHOPS
Hiring Architects and Contractors
Hiring Architects and ContractorsThe 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.
- Boston Society of Architects ADU Directory
- Boston Chapter of the National Organization of Minority Architects
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.
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 contractor: ask your potential contractor 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.
