ADU Cost, Permits & Timeline: What Homeowners in Andover, MA Actually Pay
By Rick White, Bradford Construction Management
We get the same three questions from almost every Andover homeowner who calls us about an accessory dwelling unit. What does it cost? What permits are needed? How long does it take?
Fair questions, and most of the articles you will find online answer them with numbers from California. That does you no good in Essex County. So here is a straight answer, based on ADUs we have actually designed and built in Andover and around the North Shore.
What an ADU really costs in Andover
There is no single sticker price for an ADU, and anyone who gives you one over the phone is guessing. The cost comes down to a handful of things: how big the unit is, the finishes you choose, the site work your lot needs, and your utilities. Of all of those, the one that moves the number most is septic.
If your home is on a private septic system, an older or undersized system may need to be upgraded or replaced to handle the extra bedrooms. That work can run anywhere from a few thousand dollars to thirty or forty thousand, depending on your system and your soil. It is the single biggest reason two ADUs of the same size can cost very different amounts. That is why we look at your septic capacity before we ever talk about floor plans. We would rather tell you the hard part on day one than surprise you in month three.
We price our ADUs on a clear, itemized basis. You get a real number for the build, broken out so you can see what you are paying for at each stage, with base per-square-foot pricing you can review up front. Septic sits outside that base number because it genuinely varies from lot to lot, and we are not going to bury a guess inside your quote to make the total look tidy. You can see how we approach this on our design-build ADU services page.
For planning purposes, most detached ADUs in our area land in the mid-to-upper six figures once design, permitting, and the build are all in. Attached units and conversions of existing space usually come in lower because they share walls and systems with the main house. The honest answer is that your number depends on your lot, and we will give it to you in writing before you commit to anything.
The permits you need, and what changed in 2026
Here is the good news. As of February 2, 2025, Massachusetts allows one accessory dwelling unit by right in single-family zoning districts. By right means you no longer need a special permit or a public zoning hearing for a compliant ADU. For years that approval process was the part homeowners dreaded most, and the state took it off the table.
A few rules still apply, and they matter:
- Size. Your ADU can be up to 900 square feet, or half the gross floor area of your main home, whichever is smaller. Not 800. The number you want is 900.
- Building permit. You still pull a building permit, and the unit has to meet the state building, fire, and health codes like any home. At the end you receive a certificate of occupancy before anyone moves in.
- Parking. If your property sits within a half mile of an MBTA station or bus stop, the town cannot require extra parking. Outside that radius, Andover can ask for at most one space.
- Local site rules. The town can still apply reasonable rules like setbacks and height limits. Andover’s specific requirements are worth confirming with the building department before you design, since local bylaws get updated.
We handle the permitting as part of the design-build process. You are not the one standing in line at town hall or decoding a zoning bylaw. We have done this in Andover, so we know what the building department looks for.
How long an ADU takes to build
Plan on roughly eight to fourteen months from your first design conversation to move-in. It breaks down like this:
- Design: two to four months for the plan, the layout decisions, and revisions.
- Permitting: two to six months, though the by-right change has made this faster and far more predictable than it used to be.
- Construction: four to eight months on site, including inspections and final finishes.
The biggest thing you can do to keep it moving is start early. The ADU someone calls about in the fall is usually a spring start once the design and permitting are done. Get the septic check and the design underway now, and you are positioned to break ground when the weather opens up.
A real Andover ADU
To make this concrete, one of our recent Andover projects was a detached ADU with a ground-floor home office and a second-floor in-law suite, built for a family who wanted a parent close by with their own front door. We built it on an insulated concrete form foundation and shell, which makes a small space quieter and cheaper to heat and cool year round. The owners watched the whole thing come together through daily photos, so they always knew exactly what was happening on their property, even on the days they could not stop by.
That is the kind of build the new law makes possible, and it is the kind of work we document every single day.
Why Andover homeowners are building
Most of the families we work with are not chasing a trend. They have a real reason.
The most common one is keeping family close. An ADU lets you have an aging parent or an adult child nearby in their own space, close but not on top of each other. With home prices and rents where they are across Essex County, that is a powerful option that does not require anyone to move out of the area.
The second reason is income and value. A well-built ADU can bring in steady rent, and because the state now lets you build and rent one without living in either unit, the math works for more homeowners than it used to. It also tends to add lasting resale value to your property.
How we work
We run every ADU as a design-build job, which means one team handles your project from the first sketch to the final inspection. You are not hiring an architect, then a separate builder, then refereeing the gaps between them.
You get a clear, itemized price up front, so there is no surprise bill at the end. You get daily photo documentation, so you never have to wonder what happened on site or chase anyone down. And when the build is finished, we do not disappear. Through Bradford Home Services, we stay on for maintenance and support after the job is done. We have to stand behind our own work for as long as you live there, and we like it that way.
Frequently asked questions
Do you need a special permit to build an ADU in Andover? No. Since February 2, 2025, a compliant ADU is allowed by right in single-family zones, so no special permit or zoning hearing is required. You still pull a standard building permit, which we handle for you.
How big can an ADU be? Up to 900 square feet, or half the size of your main home, whichever is smaller.
How much does an ADU cost in Andover? It depends on size, finishes, site work, and especially septic. We price on a clear, itemized per-square-foot basis and give you a real number in writing before you commit. See our ADU services in Andover for more.
How long does it take? Most projects run eight to fourteen months from design to move-in, with permitting faster now under the by-right law.
Is extra parking required? Not if your home is within a half mile of an MBTA station or bus stop. Outside that, the town can require at most one space.
What about the septic system? On a private system, an older or undersized septic may need an upgrade to handle the added bedrooms. We check this first, because it is usually the largest single variable in the budget.
Thinking about an ADU in Andover?
If you are weighing an ADU, the best first step is a real conversation about your lot, your septic, and what you want the space to do. We will give you straight answers and a clear price, not a sales pitch. Learn more about our design-build ADU services or reach out through our contact page to start.
