Massachusetts ADU Law Explained

The Massachusetts real estate world is ablaze with the new ADU law. What does it mean for Massachusetts real estate and how can homeowners and real estate investors alike benefit from this new law?

What is an ADU?

Also commonly referred to as “in-laws” or less commonly, “granny flats”, Accessory Dwelling Units, or “ADUs”, are independent living spaces on the same lot as a principal dwelling. In August 2024, the Affordable Homes Act was signed into law with the intent of making it easier to build more housing and thereby relieving pressure from the acute housing shortage in Massachusetts. 

What is an ADU?

Why is the Mass ADU Law Important?

Unequivocally, this law marks a significant shift in the regulatory ease of building ADUs.

Let’s say you are the owner of a single family home in Massachusetts in a single family zone, and you want to build an ADU on your property. 

Before the Mass ADU law, you would have had to abide by local zoning regulations. The zoning maps and ordinances across nearly all cities in Massachusetts are nothing short of monstrosities. Even with a background in land use, they can be impossible to make heads or tails of. I’ll try to explain:

We first have to see if the ADU is even an allowed use for the zone you are in. To do that, you’d go to the city’s zoning ordinance and find a use regulations table. If the use is allowed, then you’d check the dimensional regulations. 

Now, the permissibility, or lack thereof would have depended on a number of factors:

• Would the ADU be a detached structure or an attached structure?

• If attached, would the ADU have been on top of the principal dwelling, next to it, or in the basement?

• Since most housing in Massachusetts pre-dates zoning ordinances (in most cities, zoning wasn’t even a thing until the 60s or later), odds are your property is “non-conforming” as it is. If your property was completely conforming, you’d have to see if your ADU plans would make your house non-conforming. 

For example, let’s say you were going to build your ADU on top of the existing structure. You may now have a non-conformance for structure height. Maybe you were going to put your ADU on the rear of your house. Maybe that would result in a non-conformance for “rear yard setback”. 

If you had a pre-existing non-conformance, or are going to create a non-conformance with your ADU plans, odds are you’d almost certainly have to get a zoning variance. The zoning variance process, again, varies city by city, but in all likelihood, it looks something like this:

• Have an architect submit a set of drawings

• Get a rejection from your city’s planning/building department

• Have your architect or zoning attorney file for a zoning variance

• Get a date for a public hearing

• Flyer your neighborhood ahead of the hearing 

• Now this is the really fun part - have your neighbors join the hearing and listen to what they think about your plans!

Pre-ADU Law Regulatory Nightmare

I hope you’ve been nice to your neighbors, because if not, they are going to really let you have it here, and in a public forum nonetheless!

As you can see, zoning rules and regulations are incredibly complex. Worst of all, if you have to go this zoning variance route, there is no guarantee your variance is going to be approved. There is further no guarantee that even if it is approved that your neighbors won’t sue you for the variance, claiming they have been harmed by it. Not only will you be unable to build your ADU, but you will be out potentially tens of thousands of dollars in fees for your architect and zoning attorney.

And in fact, this are all of the reasons why this law was passed!

The new ADU law allows us to bypass nearly all of that.

Same Scenario Re-examined with Massachusetts ADU Law

With the new Massachusetts ADU law under that same scenario, we can bypass almost all of this. 

So what does this law say exactly? 

Disclaimer - I am not a zoning attorney, nor any attorney, nor am I an architect. This is for informational purposes only. Do your own due diligence.

With the Massachusetts ADU law, we can bypass a city’s zoning requirements and build an ADU between 350 and 900 square feet subject to certain conditions:

• The property is a single family 

• If the property is a single family, you can build an ADU up to the lesser of 900 square feet or one-half of the primary residence’s floor area

• The ADU can be attached to the primary residence, or detached from the primary residence. 

Implications of the Massachusetts ADU Law for Homeowners and Investors

As I’ve documented extensively in the years that I’ve been writing about the greater Boston real estate market, there is a severe inventory problem that has continued to put upward pressure on real estate prices even as mortgage interest rates have shot up.

This makes housing much more unaffordable for first time homebuyers and real estate investors alike. 

While it remains to be seen whether or not the ADU law can make a dent in the commonwealth’s housing crisis, It is certain that the ADU law creates vast wealth-building opportunities for first time homebuyers and real estate investors alike.

Whereas before the ADU law, you had to go through a complicated zoning and permitting process, we can now bypass a lot, but not all of that process.

People who own single family homes can now add an additional unit to their home. These units could be used for:

• Renting the unit to family members, such as aging parents, or children

• Renting the unit to non-family members, and therefore serving as a source of income

• Increasing the value of your home

For real estate investors, you can now add an additional unit to your property with less zoning/permitting risk. It will also make deals pencil out better. For example, maybe the fixer-upper single family on the market doesn’t pencil as a single family, but maybe it does when you add in the possibility of an additional unit. 

Beyond homeowners and investors, the ADU law is also good for the Massachusetts economy writ large. It creates more work for contractors, allows for more investment into its communities, and allows more people to live here. 

Opportunities Created for Homeowners by the Massachusetts ADU Law

Overall I’m a big fan, and whether you are a homeowner, prospective homeowner, and/or a real estate investor, you should be too!

If you are interested in discussing ADUs in more detail, including but not limited to getting connected with architects, contractors, and/or attorneys familiar with ADU laws, I’d love to hear from you!