Care for
Family

A private home for aging parents or adult children.

Create
Rental Income

Additional long term housing, subject to local rules.

Add
Property Flexibility

Flexible space for today and tomorrow.

Flexible
Living

A home office, guest space or independent living.

Built for
Generations

Thoughtful design for multigenerational living.

WHAT IS AN ADU?

A Smaller Home. A Bigger Future.

An accessory dwelling unit (ADU) is a separate residential living space on the same property as a principal home. It includes its own sleeping, cooking and sanitary facilities with a separate entrance.
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Massachusetts law now makes it easier for many homeowners to build an ADU. Salt Spray Sheds focuses on custom, site-built structures, making detached ADUs, backyard cottages and in-law cottages a natural extension of the work we have been doing since 1994.

Could an ADU Work on Your Property?

Lot & Setbacks

Where can it legally be located?

Septic or Sewer

Capacity and Title 5 requirements matter.

Wetlands & Conservation

Protected areas can affect placement.

Historic Districts

Additional design or approval requirements.

Utilities & Access

Water, electric, heating, cooling and construction access need to be considered.

WHAT FITS IN AN ADU?

Sample ADU Layouts

Every property is different. These conceptual layouts show what is possible.

~450 square feet

studio layout

Living/Sleeping,
​Kitchen and Bath

~650 square feet

one bedroom

Living, Kitchen,
Bath, and Bedroom

~850 square feet

two bedrooms

Living, Kitchen,
Bath, and 2 Bedrooms

    Start exploring your adu

    You don't need to have everything figured out. 
    Tell us about your property and your ideas, and
    ​we'll help you figure out what's next.
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These are conceptual examples only. Final design, size and configuration will depend on your property, applicable requirements and project goals.
Frequently Asked Questions

Cape Cod ADU Questions

Can I build an ADU on my property in Massachusetts?

Massachusetts generally allows one qualifying protected use ADU by right where single family homes are permitted. The project must still comply with applicable requirements, including building code, setbacks, septic or sewer requirements, conservation regulations and other requirements that may apply to the property.

How large can an ADU be in Massachusetts?

A qualifying protected use ADU may generally be up to 900 square feet or one half of the gross floor area of the principal dwelling, whichever is smaller. The size that can actually be built will also depend on the property, applicable codes and site conditions.

Can an ADU be detached from my house?

Yes. Massachusetts recognizes detached protected use ADUs as well as attached and internal ADUs. A detached ADU can be a separate cottage style structure on the same property as the principal dwelling, provided the project meets applicable requirements.

Can I build an ADU if my property has a septic system?

Potentially. Title 5 and applicable local septic requirements still apply to ADU projects. Existing septic capacity, bedroom count and the condition of the system may need to be evaluated, and some properties may require a septic upgrade. Cape Cod homeowners should investigate wastewater requirements early in the planning process.

Do I need a special permit to build an ADU?

A single qualifying protected use ADU generally cannot be required to obtain a special permit or other discretionary zoning approval simply for the ADU use. A building permit is still required, and other applicable reviews and approvals may be necessary depending on the property and project.

Can I rent an ADU in Massachusetts?

Massachusetts protects the rental of qualifying ADUs and does not require the owner to occupy either the principal dwelling or the ADU. Cities and towns may, however, restrict or prohibit short term rental use, so homeowners should confirm the rules that apply in their municipality.

Can an ADU have more than one bedroom?

Yes. Massachusetts municipalities cannot impose their own bedroom limit on a protected use ADU beyond requirements established by applicable state codes. The number of bedrooms that works for a particular project will depend on the ADU size, layout, building requirements and, where applicable, wastewater capacity.

Does Salt Spray build ADUs on Martha's Vineyard and Nantucket?

Salt Spray Sheds builds custom structures throughout Cape Cod and has completed projects on Martha's Vineyard and Nantucket. Island projects require additional planning for transportation, materials, scheduling and local requirements, so we evaluate each project individually.

ADU requirements vary by property and municipality. Information on this page is intended as a general planning resource and is not a substitute for property specific guidance from your municipality or qualified professionals.
Cape Cod.
Martha's Vineyard.
Nantucket.
THREE UNIQUE PLACES.
ONE COMMITMENT.
Beautiful, functional structures built for the way you live.