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Custom ADU’s built Your Way—
With One Team from Concept to Completion
Every home tells a story—and yours should be written exactly the way you want it. Thanks to the new statewide ADU law, many MA homeowners can now build an ADU by right – no special permit.
We help you take advantage of it without getting crushed by septic and code problems. At Amex Construction, we combine design and construction. That means one team, one contract, and one clear process from the first sketch to the final walk-through. Whether you’re building a new ADU, converting a Barn, or a basement in-law suite, our design-build approach saves time, avoids miscommunication, and keeps your budget & Timeline under control.
Amex Construction helps Families expand, upgrade, and build with confidence.
Building an ADU in Massachusetts isn’t about picking from a catalog—it’s about creating a living space that fits Your Family and Property. From site prep and foundations to finishes and energy efficiency, Amex Construction builds ADU’s that are durable, beautiful, and uniquely yours.
At Amex we have a simple 4 step process to ADU’s
Step 1- Feasibility & Utility Review
Step 2- Preconstruction, Design & Permitting
Step 3- Site work & Construction
Step 4- Final Inspection & Move in
When we say we specialize in ADUs on septic, we mean we start in the dirt, not on Pinterest.
Upfront feasibility instead of guesswork
We review your existing Title 5 report, as‑built plans, and bedroom count, and bring in a septic engineer when needed. If the system has to be upgraded, we price and phase that with the ADU from the very beginning, instead of pretending it’s “separate” work and surprising you later
Engineering and permitting under one roof
We coordinate with your septic engineer, the Board of Health, and the building department so septic design, ADU plans, and permits all move together. You’re not stuck playing middleman between “the septic guys” and “the builder.”
Construction sequencing that actually works
We handle excavation, system replacement or upgrade, and the ADU build as one project. That keeps you out of the nightmare scenario where the ADU is finished, but you can’t legally occupy it because the septic sign‑off is stuck in limbo.
Bottom line: if your property is on septic, your ADU lives or dies on how well the dirt work is planned. That’s the part we’ve been doing for years; the ADU is just the structure that sits on top of it.
Why septic makes ADUs tricky – and why we’re built for it
In a lot of Southeastern Massachusetts, the real gatekeeper for an ADU isn’t the building inspector – it’s the septic system. If your home isn’t on town sewer, adding even a one‑bedroom ADU usually means proving your system can legally handle the extra flow under Title 5. If it can’t, you’re looking at an upgrade or full replacement before anyone signs off on the project.
Septic Considerations for ADU Projects:
Bedroom count and capacity
Title 5 septic design is based on bedroom count, not just square footage. Add a bedroom (or two) in an ADU and you can blow past your existing system’s design flow, which triggers an upgrade whether you planned for it or not. We figure that out at the feasibility stage instead of after you’ve fallen in love with a floor plan.
Nitrogen‑sensitive areas
On the South Shore and especially the Cape, more and more neighborhoods sit in nitrogen‑sensitive watersheds. New or expanded septic systems in those areas often need advanced nitrogen‑reducing technology and tighter standards. That’s more engineering, more review, and more cost if you don’t design for it from day one.
Local Boards of Health
Every ADU on septic ends up in front of a local Board of Health, and each town has its own expectations, forms, and “unwritten rules” about how ADUs and septic upgrades are reviewed. Boards across Massachusetts are issuing ADU septic guidance tied to Title 5 and the new statewide ADU law, so winging it is a fast way to stall your project.