If you have been weighing a renovation, thinking about how to bring a family member closer, or just trying to figure out the smartest way to get more from your Metrowest or Central Mass property before you sell, there is a development worth your attention. Massachusetts now offers free, professionally designed plans for accessory dwelling units, and recent changes to state law have made it dramatically easier to build one. For homeowners across Marlborough, Hudson, and the rest of MetroWest, this is one of those rare moments where state policy, market demand, and your own home equity line up. Here is what you need to know, and how to think about it if a sale is somewhere on your horizon.

What Is an ADU, and Why Is Everyone Talking About Them?

An accessory dwelling unit, or ADU, is a smaller, independent living space located on the same property as your main home. Sometimes it is a freestanding backyard cottage. Sometimes it is a converted garage, a finished basement with its own entrance, or an addition with a small kitchen and bathroom tucked above an attached garage. Whatever the form, an ADU has its own entrance, its own kitchen, and its own bathroom, which means someone can live there independently of the main household.

We have been fielding more questions about ADUs from MetroWest homeowners over the past year than almost any other topic, and it is not hard to see why. An aging parent who wants to stay close to family but keep their independence. An adult child saving for their own home who needs a soft landing spot. A homeowner who would like rental income to offset a mortgage. A growing family that needs more square footage without the cost and disruption of moving. An ADU can answer all of these needs on the same lot you already own.

The Massachusetts ADU Design Challenge: Free Plans, Real Designs

Here is the part that surprises most people. The Healey-Driscoll Administration ran a statewide ADU Design Challenge, inviting architects, builders, and designers from across Massachusetts to submit detached ADU plans. The goal was simple: remove one of the biggest early hurdles for homeowners, which is the cost and complexity of getting a professional design in hand before you can even talk to a contractor.

The result is a public library of free, downloadable ADU plans, ranging from compact studios under 500 square feet up to the full 900 square foot maximum allowed under state law. The designs cover a range of styles and priorities, including accessible, single-floor layouts that work well for aging in place, and options built around sustainable materials and efficient construction.

For Marlborough and Hudson homeowners, this matters in a very practical way. Instead of paying an architect thousands of dollars just to get to a starting point, you can browse the showcase, find a design that fits your lot and your goals, and bring that plan directly to a local contractor as a foundation for your project. It will not be a finished, permit-ready set of drawings specific to your property, but it gives you a real head start and a much clearer sense of cost and scope before you commit to anything.

Why Now: The Affordable Homes Act Changed the Rules

The timing of all this is not a coincidence. In August 2024, Governor Healey signed the Affordable Homes Act into law, and one of its most significant changes for homeowners involves ADUs directly. As of February 2025, ADUs up to 900 square feet, or half the size of your main home, whichever is smaller, are now permitted by right in single-family zoning districts across almost every city and town in Massachusetts.

What does by right actually mean for you as a Marlborough or Hudson homeowner? Before this law, adding a second living unit to your property often meant going in front of a local zoning board, applying for a special permit, and hoping for approval that was not guaranteed. That process could take months or years, and in many towns it simply was not an option. Now, if your plans meet the state's basic requirements, your town has to issue a building permit. No special hearing, no discretionary vote, no owner occupancy requirement standing in your way. You will still need a standard building permit, and you will still need to meet septic or sewer requirements and pass inspections, but the zoning roadblock that used to stop most homeowners before they started has been removed at the state level.

For a homeowner in Marlborough who has been quietly wondering whether their oversized backyard could ever hold an in-law suite, or whether their detached garage could become something more, this is the moment that question gets a much more encouraging answer.

What an ADU Could Mean for Your Home's Value and Appeal

This is where our perspective as your local real estate team comes in. We think about ADUs not just as a lifestyle upgrade, but as a strategic decision that can affect how your home shows, how it is priced, and who it appeals to when it eventually goes on the market.

First, there is the income angle. A legal, permitted ADU can generate rental income, which is something we increasingly see buyers ask about directly. In a MetroWest market where affordability is a constant conversation, a home that comes with built-in rental potential, or the proven ability to offset a mortgage payment, stands out.

Second, there is the multi-generational angle, which we see constantly in our work with families across Marlborough and Hudson. Buyers who are searching for a home that can accommodate an aging parent or a returning adult child are often willing to pay a premium for a property that already has, or could easily accommodate, a separate living space. A finished, code-compliant ADU can be the difference between a home that fits a buyer's complicated household and one that does not, even if the rest of the property checks every other box.

Third, there is the simple matter of usable square footage. An ADU adds living space to your property in a way that is far more flexible than a typical addition. It can be a home office today, a rental tomorrow, and a space for a parent the year after that. Buyers recognize that flexibility, even when they do not have an immediate use for it themselves.

All of that said, an ADU is a meaningful investment, and not every property or every situation will see the same return. The size of your lot, your town's specific implementation of the new rules, your septic capacity, and the overall condition and price point of your home all factor into whether an ADU is the right move before a sale, or simply a long-term enhancement for your own use. This is exactly the kind of decision where local expertise matters more than a generic online calculator.

Your Next Steps if You're Considering an ADU

If this has you thinking about your own property, here is how we would suggest approaching it.

Start by exploring the free designs in the state's ADU Design Challenge showcase. Even if nothing fits perfectly, it will give you a realistic sense of scale, layout, and style options, and a useful starting point for a conversation with a builder.

From there, talk to a local contractor who has experience with ADU projects in Marlborough, Hudson, or the surrounding MetroWest towns. Local knowledge matters here, because while the state has set a new baseline, individual towns can still have their own reasonable regulations around things like setbacks, parking, and septic capacity. A contractor who has already navigated your town's process will save you time and guesswork.

Before you move forward with permitting, it is also worth having a conversation with us. We are not contractors and we will not pretend to be, but we spend our days thinking about how improvements translate into value on properties just like yours across Marlborough and Hudson. If a sale is anywhere in your future, even a few years out, we can walk through how an ADU might affect your home's market position, who it might appeal to, and whether it makes sense to build now, build later, or focus your investment elsewhere.

Let's Talk About Your Property

Whether you are picturing a backyard cottage for a parent, a rental unit above the garage, or simply want to understand how an ADU might change your home's value before you list, we are happy to talk it through. Reach out and let's start with a conversation about what makes the most sense for your specific property and your goals.

📞 Call or text us at 508-868-4090, or 📅 schedule a free discovery meeting at calendly.com/kathleengoneau. We would love to help you think through your next chapter.

The Goneau Group │ Keller Williams North Central
Serving Marlborough, Hudson and MetroWest, MA
Equal Housing Opportunity