Is a Septic System Installed Before 1995 Automatically Non-Conforming for an ADU?

By Buz Artiano, BuildX | October 2026

Watch: MA ADUs, Title V & Why Septic Might Be the Wildcard w/ Kevin Grady | BuildX Podcast #01

Your septic system has been in the ground for thirty years and it's never backed up, never surfaced in the yard, and it passed the inspection when you bought the house. But then when you ask about adding an ADU, someone uses the term nonconforming. That word carries a cost with it. The worst case could mean a complete system replacement that has to be done before the foundation is put in.

My name is Buz Artiano, founder of BuildX. We have built dozens of ADUs across Massachusetts, with most of that work on the South Shore and through Plymouth County. We handle design, permitting, and construction in one place and that means septic becomes our problem before it becomes yours. That work starts with getting the Board of Health file, reading the existing system's approved design flow, and finding out what the town will accept under Title 5, the Massachusetts state code that deals with septic systems.

This question has an answer and it's not the answer most homeowners are hoping to get. We had a discussion with Kevin Grady of Grady Consulting, a civil engineer and land surveyor in Kingston who designs these systems for a living. What he told us about the state's position and the state's own documents match. What they leave room for is where your project is, and that is the part that's controlled by your town.

So Is Every Pre-1995 Septic System Automatically Non-Conforming?

Not by the date stamped on the permit. The test is if the septic system in your yard complies with the current code. But in reality, the date is the most accurate predictor, because MassDEP has answered this question in writing. In its published questions and answers on Title 5 compliance for accessory dwelling units, the Department says that any septic system not constructed in accordance with 310 CMR 15.000, the 1995 code, is non-conforming, and it gives systems built under the older 1978 code for an example.

The regulation defines the term itself. Under 310 CMR 15.002, a Nonconforming System is any system that's not in full compliance with the standards and requirements of 310 CMR 15.000 and hasn't got a variance or local upgrade approval for it. The regulation then says non-conforming systems include, but aren't limited to, these four things:

• Cesspools
• Privies
• Failed systems
• Systems with a design flow above 10,000 gallons per day

The phrase that decides your project is "but are not limited to". Homeowners read that four-item list, check and make sure they don't have a cesspool and then think they are clear. The list isn't complete. The important sentence is the first one, and it indicates you need full compliance with the current code. The Department's April 7, 2025 guidance document, which takes you through what happens to a system in each situation, is posted at mass.gov.

My System Passed Its Title 5 Inspection. Does That Make It Conforming?

No, and thinking those two things are the same test is the most expensive budgeting mistake we see for older properties. A Title 5 inspection checks your septic against a set of failure measures your system against a list of possible failures. If none of those apply then the system passes. This is just a test to see whether the thing is working.

Full compliance is a different and higher standard. MassDEP defines a system constructed in full compliance with Title 5 as one designed and constructed in accordance with every applicable provision of the current version of 310 CMR 15.000, and that includes a reserve area. The reserve area is land on your property that doesn't have any structures and meets setback requirements, where a replacement septic system could be put if the first one has to come out.

The Department has said that a system can pass a Title 5 inspection with no conditions even if the inspector sees circumstances that need to be followed up on with the Board of Health. That's because the inspection uses failure criteria instead of just looking for compliance. Your passing inspection report and your compliance report are two different things, and only one of them decides if you can add an ADU. MassDEP's questions and answers on this, revised September 11, 2025, are posted at mass.gov. Make sure you have the current version before you make a decision using it, because the Department has changed this once already and says it will continue to update it.

What the 1995 Title 5 Rewrite Changed About Older Systems

Kevin Grady's engineering account of the rewrite is short: Title 5 was rewritten in 1995, and the rewrite did away with systems that had a lot of depth. This is because of the soil. Soil treats the effluent before it gets to the groundwater, and forms a biomap that breaks down the effluent as it goes through. With a deep system the discharge is closer to the groundwater and so there's less surface to disperse across. Grady says the second reason is that oxygen is near the surface and oxygen lets bacteria thrive. A system that doesn't have it turns anaerobic.

The systems that didn't do well with the new regulations are the leaching pits. A leaching pit is a pit in the ground that's about six feet across and about three to 10 feet deep, and has two to four feet of stone around it. Effluent goes in and fills the pit, and then flows out into the surrounding soil. A leaching field does the same work, only it's spread out horizontally across a much larger area, closer to the surface.

Grady's own house got a permit around 1999 or 2000 with two leaching pits, which was later than the rewrite. He thinks that the reason his system passed is because the systems that were allowed before the Title 5 change were grandfathered in for a while but he has not researched it. At this point in time leaching pits are no longer permitted under Title 5. If your file shows that you have them, you're looking at a design the state deliberately took out of the code so the answer is now clear.

Could My Town's Own Standards Save My Older System?

In some towns, yes. This is the part of the answer that varies from town to town and it's the reason two people in different towns with exactly the same system will get different answers. Kingston is the example that's documented. Grady Consulting says that Kingston has long required a minimum leaching area of 800 square feet, which is larger than what the state minimum would be on many of those same lots. Grady's idea, which is just a probability not a certainty, is that the Kingston systems designed before 1995 comply with Title 5 anyway.

Grady confirmed that when a town puts in systems sized to a minimum leaching area instead of by bedroom count, the system is able to accept more flow than the house that's on it produces. Kingston decided on that standard so properties could. Grady's opinion is that this standard is proving its worth since the ADU law was passed. We have no adoption date for it, and no other Massachusetts town has been proven to us to have done the same thing, so as of now Kingston is a one-town example instead of a regional pattern.

Here's what we do on a real property with all this information, and why we do it before we deal with the design. We get the Board of Health file for the lot first, and what we're looking for isn't the pass stamp on the last inspection. We're reading the design plan, looking at the leaching area that's drawn on it, seeing if a reserve area was laid out, and what the approved design flow is. The leaching area is just one of many provisions, so an oversized field by itself doesn't answer the question. A file that has a complete engineered plan and a reserve area that's shown is something we can work with. A file with a hand drawn sketch of two pits and nothing else means we need to have a replacement conversation with the family in week one rather than in month four.

There's good news buried in the paperwork. Grady points out that Board of Health files have a lot more information than they used to, because every sale and every inspection since 1995 has been added to them. We all agree on where that is heading: genuinely old, never-touched systems are getting more rare in Massachusetts every year.

What Does a Non-Conforming Answer Do to My ADU Budget?

It takes the septic system from being an asset to something that needs to be replaced, and that's at the start of your budget not in the middle of your build. Grady discusses the entire subject with two outcomes. If your system is working and is up to the current requirements of Title 5, that's the best outcome available for you, because the current system can be added on to deal with added flow and the ADU can connect to it. If it's non-conforming or non-functioning, that is the worst situation and you have to start over.

We put the practical version of that to Grady on tape. There's an older house, a couple of old leaching pits, and a system that's been there a long time and was never upgraded. That means you can plan on a whole new septic system. Grady agreed, and added one thing worth remembering. You can ask for a variance, and the Board of Health is who hears it.

We don't give a dollar amount to a septic replacement during this part of a project, and we would advise you to be careful with any builder who does before the file is reviewed and you know what kind of soil you have. What we will tell a family early in the process is which column the system is in. That is the question that decides whether it's a go or a no-go decision. Because it's the one line item on the ADU budget that can change by the price of a small car depending on what kind of ground you have and what the town says.

Is a Full Replacement Always the Right Call?

We build ADUs so you'd expect us to tell you that the septic work is worth doing, and on most of our projects it is. But it isn't worth doing on all of them, and we'd rather say so early than watch a family find out late.

If the file comes back non-conforming, the lot is small, or the family budget can't afford a replacement system in addition to the building cost, then the property isn't ready for an ADU right now. That is a discussion that we want to have on week one, not four months into the process. Design-build with one company isn't always the right structure for every family. Some people want to have their own drawings, bid the work out, and manage all the work themselves, and that's another way to do it.

You can access your own Board of Health file. You don't need us or any other builder to do it. Then talk to more than one builder, and also to an independent civil engineer, before you make any decisions.

Where Your Older System Stands Before You Spend a Dollar on Design

Until the file says otherwise, keep a pre-1995 septic system in your ADU budget as a replacement item instead of an asset you already own. That one move protects your decision to move ahead or not, because septic is the one thing big enough to change the total. If the file and the town come back with good news, then it's a pleasant surprise and room in the budget. If they come back how the documents seemed to suggest, you're already planning for it.

The permit date is the question and the Board of Health holds the answer.