Massachusetts Adopted a Strong ADU Law, but Local Regulations will Still Prevent Them

I grew up with an illegal ADU in my attic in Newton, MA that my mom used to house grad students from a nearby campus. The tenants were like members of our family; they literally walked through the center staircase in our house to access their cute, affordable, attic, studio apartment.

I was elated when Massachusetts recently passed the The Affordable Homes Act, which includes an ADU provision (Section 8 of Chapter 150 of the Acts of 2024), that on its surface, is a strong ADU law, making it the 7th US state to adopt strong ADU laws. These states include:

1. California
2. Oregon
3. Washington
4. Colorado
5. Montana
6. Arizona
7. Massachusetts

However, upon analyzing the law in the context of Massachusetts’ byzantine framework of local regulations, it’s hard to really see their ADU regulations as strong. This post contains a letter that I have submitting the Executive Office of Housing and Livable Communities, the office that the law charges with developing regulations that embody the law.

In the draft regulations, Executive Office of Housing and Livable Communities has done a disservice by deferring to local ordinances on their dimenional standards–specifically their setback and lot coverage standards. Given how onerous these standards are, this deference to the local zoning will undermine the statutory intent.

My hope is that this office will read my letter, and letters like it from fellow ADU advocates, and update their rules to contain clear and objective standards that will apply to all jurisdictions in MA.

More broadly, as other States look at ADU reforms, it is clear that being cognizant of the relative restrictiveness of local dimensional standards is critical to the success of a given ADU law. In the case of MA, jurisdictional dimensional standards are so oppressive, that it will be very difficult for average homeowners to build ADUs, in spite of the strong statewide legislation.

Other states like Oregon do not suffer under such oppressive jurisdictional dimensional standards, so preemptive statewide setback standards are less critical. But, in states like CA and MA, it is in everyone’s interest for the state to lay down the law with specific details on what is and is not a “reasonable standard” for ADU development.

Without further ado, here’s my open letter to the Massachusetts Executive Office of Housing and Livable Communities on their ADU Draft Regulations. (*Incidentally, feedback is due by 1/10/25)

Public Testimony

Introduction

The Executive Office of Housing and Livable Communities (EOHLC) is not complying with Massachusetts’ new housing law, the Affordable Homes Act with its draft ADU regulations. The Affordable Homes Act states that 

 “No zoning ordinance or by-law shall prohibit, unreasonably restrict or require a special permit or other discretionary zoning approval for the use of land or structures for a single accessory dwelling unit, or the rental thereof, in a single-family residential zoning district; provided, that the use of land or structures for such accessory dwelling unit under this paragraph may be subject to reasonable regulations, including, but not limited to, 310 CMR 15.000 et seq., if applicable, site plan review, regulations concerning dimensional setbacks and the bulk and height of structures…The executive office of housing and livable communities may issue guidelines or promulgate regulations to administer this paragraph.”

If a local ordinance such as setbacks, lot coverage, or heights, entirely prevent the ability to actually build the promised 900 sq detached ADU, the “Protected Use ADU”, do those local regulations still stand? Under these draft EOHLC regulations, the answer is yes. 

By deferring to local ordinances in its draft rules, EOHLC’s is effectively adopting these local standards as their own. These local standards aren’t sufficient for the Protected Use ADU. Thus, the office charged with protecting ADUs, is actually preventing them. 

The draft EOHLC regulations as they are currently written, pay deference to existing municipal prohibitions on ADUs in their dimensional standards. 

The result of this deference is that ADU law will be ineffective at enabling homeowners to actually build ADUs in MA, rendering the law largely meaningless in many cases.

Instead, the state must set preemptive standards for Protected Use ADUs. 

Legal Foundations

The The Affordable Homes Act itself was written to allow people to build ADUs in Massachusetts as stated clearly and boldly in the regulation title “Regulation of Protected Use ADUs in Single-Family Residential Zoning Districts”. 

The EOHLC draft regulations themselves state, “71.01: Statement of Purpose (1) St. 2024, c. 150, s. 8 (the Act) amended M.G.L. c. 40A, s. 3 to encourage the production of accessory dwelling units throughout the Commonwealth with the goal of increasing the production of housing to address statewide, local, and individual housing needs for households of all income levels and at all stages of life.”

The deference to municipal dimensional standards is not in alignment with the spirit or stated purpose of the law (Section 8 of Chapter 150 of the Acts of 2024). 

Dimensional Standards

In particular, in the draft rules, EOHLCs regulators default to underlying zoning standards. EOHLC staff  did not consider that ADUs have entirely different dimensional needs than single family homes and that most MA jurisdictions do not differentiate these, nor do they have a sophisticated codes that recognize these nuances. Local zoning codes in MA disregard ADU geometry altogether, and EOHLC is exhibiting a misunderstanding of market feasibility for the development of ADUs by deferring to these standards. 

In this letter, I will illustrate how local regulations in MA are guaranteed to stop homeowners from building ADUs, throttling the ADU potential in Massachusetts by approximately 50%. 

In particular, smaller lots in older streetcar suburbs of Boston (i.e. inside of Rte 128) are where most ADUs would normally be built in MA due to infill pressures and inflated underlying land values in the Boston metro area. But, small lots can’t build ADUs under existing local dimensional standards in MA.  

Let’s now examine in granular detail how the local dimensional regulations related to lot coverage and setbacks completely undermine the ADU law. 

Most Local Dimensional Regulations in MA prevent ADUs

There’s hundreds of local regulations to critically examine, but we’ll arbitrarily pick on Billerica, although it would be just as easy to pick on Belmont or Carlisle or countless others. 

We’ll select a property and try to fit a 900 sq ft ADU on it (which the state law theoretically allows homeowners to build), based on local dimensional standards. 

Dimensional Standards in Billerica

 See page 115 of Billerica’s dimensional regulations for residential properties. 

• Side yard- 15 ft. 
• Rear yard- 20 ft. 
• Lot coverage- 25%   

1) Starting with lot coverage, on a 5,000 sq ft lot, if there’s already a 1,000 sq ft home, it would be impossible to add a 900 sq ft detached ADU or anything approaching it (25% of 5,000=1,250 sq ft. 1,250 sq ft-1,000 sq ft leaves only 250 sq ft for anything else). 

2) Let’s look at an actual sample property in Billerica. 

This lot is 7,405 sq ft. 

25% (lot coverage) of 7,405 sq ft = 1,851.25 sq ft of buildable area. 

1,851.25 sq ft of buildable area, minus the existing building 1,376 sq ft= 475.25 (1,376 sq ft is based on the interior square footage assessment from the county tax assessor- https://billerica.patriotproperties.com/Summary.asp?AccountNumber=4460)

3) 475.25 sq ft is not sufficient for even a 1 BR ADU. 

Based on this one lot coverage standard alone, these homeowners couldn’t build a decent accessible ADU for someone to age in place, let alone a couple to age in place. 

4) Next, let’s examine how incredibly restrictive these setbacks are for ADUs.  It would be geometrically impossible to build an ADU on this lot, or literally any of the adjacent lots in this neighborhood for that matter, using Billerica’s local setback standards. Not a single one of these lots shown here could build ADUs with a side yard setback of 15 ft and a rear yard setback of 20 ft (see image below).

How Rear and Side Setbacks Hinder ADUs 

To illustrate how large rear and side yard setbacks hinder ADUs, we’ll now switch gears from text and use diagrams instead. 

For the reasons described above, we will use a standard urban lot. This lot is 5,000 sq ft. It is 50 ft wide and 100 ft deep. 

We’ll position the typical primary house built on that typical property 20ft from the front street lot line, to comply with typical front yard setback requirements. 

Here’s an aerial image of six standard 50 ft by 100 ft lots with typical homes.

This first diagram below shows a typical lot, mirroring the massing of the six lots above. It shows front yard setbacks, the primary dwelling, and a 6 ft fire separation between the primary dwelling and the potential buildable area in the back yard. Notwithstanding setbacks, about 35% of the property is left in which to place a detached ADU in the backyard… somewhere.  

In these diagrams, each background grid box equals 10 ft. The diagrammatic property is shown as being 10 boxes long, and 5 boxes wide. 

Now, let’s show the potential buildable area once 5ft setbacks have been applied. This buildable area is fairly constrained, but there’s sufficient room to fit a good-sized one-story ADU in any number of possible configurations within the buildable area confines. 

Next, let’s show the potential buildable area of that same property if 10 ft setbacks were applied. We’ve suddenly shrunk the potential size of the ADU from over 1,000 sq ft in the diagram above, to only 570 sq ft (19 ft x 30 ft). 

As a point of reference, 570 sq ft is just barely large enough to accommodate a reasonable 1BR ADU. 

Next, let’s show the potential buildable area if 15 ft setbacks were applied. We’ve now shrunk the potential size of the ADU from 570 sq ft to 280 sq ft. 

ADUs of this size make very little economic or practical sense to develop. I’ve visited over one thousand ADUs in the last 15 years, and only seen three ADUs this size. 

Next, let’s show the potential buildable area if 20 ft setbacks were applied. We’ve now shrunk the potential size of the ADU to a maximum buildable area of 90 sq ft. Given that that minimum size bathroom is ~35 sq ft, this would leave approximately 55 sq ft for the living space. A queen bed would take up 33 sq ft. The kitchen counter with a fridge, stove, and sink would take up more than 20 sq ft. 

There wouldn’t be any space left to actually stand up in an ADU of this size. 

Legislation that Defaults to Underlying Setbacks

In the absence of designating prescriptive setbacks that preempt local zoning, legislation allows jurisdictions to use their existing setback requirements for ADUs. 

Cities that have given thought to ADUs may have crafted conducive setback requirements for them. However, municipalities often default to the “underlying zoning” standard when regulating side and rear setbacks for ADU on a property. The underlying zoning standards were originally intended to define the buildable area for the primary dwelling. 

Since there is ample space even on small lots for developing primary dwellings, it was likely never a challenge to “respect the setbacks”. 

The problem is that EOHLC defers to “underlying zoning” requirements for rear and side yard setbacks, which carry over to detached ADUs. And, the underlying setback requirements in MA are very onerous. 

• Westford, Massachusetts –   30 ft rear yard setbacks, and 15 feet side yard setbacks 
• Weston, Massachusetts –     20-45 ft rear yard setbacks
• Stow, Massachusetts  –        40 ft rear and side yard setbacks

These types of setback requirements are unfortunately not the exception; they are the rule. 

Indeed, most cities have  similarly onerous setbacks unless it has specifically viewed this matter through the ADU developer prism of “reasonable” regulations. 

Setback standards are legacy standards for primary homes established by planning staff, long before they ever considered the requisite geometry of building a detached ADU.

Current planners may have never given thought to how their zoning code is institutionally hindering the development of ADUs because they “rarely see ADU applications”. 

Connecting the dots? 

If a state claims to want ADUs as a policy matter to create more housing choice, it must institute “reasonable” setback standards for detached ADUs. 

The State should instead set reasonable, clear and objective standards for ADUs, and cities should have to comply with those standards. 

These EOHLC draft rules are insufficient, and are not offering clear and objective, nor reasonable standards for homeowners to build ADUs. Rather, these draft rules are perpetuating classist (and racist) regulations. 

Ironically, this draft says that cities should provide “Design Standards” that are “Clear, measurable and objective provisions of Zoning, or regulations, which are made applicable to the exterior design of, and use of materials for an ADU.”

EOHLC is passing the buck entirely by not doing this actual work itself, as the law is clearly intended to do. It has taken a lazy path, and deferred to all existing underlying zoning in municipalities.

 To be sure, municipalities (ie. planning staff & elected officials & housing obstructionists) will appreciate this EOHLC draft, of course, because it prolongs and empowers jurisdictions to entirely stop people from building more housing as they have successfully done for decades in MA  

But, this was not the intent of the law. 

If local regulations were sufficient to foster ADUs, there wouldn’t have been a need for a state ADU law. 

Many of the lots inside of Rte. 128, where approximately 30% of the population of MA lives (and where the affordable housing crisis is acute), will not be able to build ADUs, as a result of these deferential EOHLC regulations. 

Inder these local rules, many homeowners will be stymied and frustrated by dealing with the confusing text and codes, the restrictive morass of local zoning codes, “death by 1,000 papercuts”, after spending thousands of dollars paying architects, and will throw up their hands in frustration and forget the idea of building an ADU.  

In a liberalized ADU market, 2/3rds to 3/4ths of new ADUs are built as detached ADUs; this is what the market tends to create for a variety of reasons. 

Given that most ADUs are developed in higher-cost urban areas–central city neighborhoods- the lots that host ADUs tend to be smaller, largely established prior to automobile domination. Conversely, residential properties established in the mid and latter part of the 20th century tend to be larger lots on the suburban and exurban fringe of metropolitan areas.  

Based on the cities where ADUs are actually being developed in greater quantities, it is fair to assess that more ADUs are built on smaller urban lots (5,000 – 7000 sq ft) than on larger suburban lots (7,000 – 20,000 sq ft).

When establishing statewide laws that will impact the cities where ADUs will actually be built, it is important that the zoning laws are written such that it will actually allow detached ADUs to be developed in these places. If an ADU  law & its regulations do not help achieve that outcome, then they have missed the mark.  

Creating Clear Standards for ADUs

With all of that explanation provided, the answers are actually simple. 

A “Reasonable” Setback Requirement for Detached ADUs is 5 ft

In practice, most rear yard and side yard setback standards tend to be set in 5 ft increments: 5 ft, 10 ft, 15 ft, 20 ft, etc. And, of those, 5 ft setbacks is the only increment that actually allows for the development of detached ADUs. So, I’m throwing out there that moving forward for the ADUs, the best practice for ADUs are 5 ft rear and side yard setbacks. 

Lot coverage standards for ADUs are unenforceable 

And as far as lot coverage goes, the State has clearly stated that it wishes homeowners to be able to build 900 sq ft detached ADUs. EOHLC has an obligation to protect the rights of homeowners to build these 900 sq ft detached ADUs on their property. 

Thus, the State must set preemptive dimensional regulations that stipulate that any lot coverage standards that prevent the construction of a 900 sq ft detached ADUs are unenforceable.