What Exterior Details Show You Hired the Right ADU Builder?

By Buz Artiano, BuildX | September 2026

Watch: Plymouth ADU with 2-Car Garage Under! Full Tour of a Custom 900 sq ft Build BuildX

Every builder's website shows you the same finished ADU: clean siding, new grass, one photograph taken from the corner of the driveway in good light. After you look through four companies they all blur together, and you're supposed to select one from the photographs, just before you sign the largest construction contract of your life.

My name is Buz Artiano, and I am the founder of BuildX. We've built dozens of ADU projects across Massachusetts, mostly around the South Shore and Plymouth County areas. We are the only team you need: we do the design, permitting, and construction. So we see every phase of a project from the first site visit up until you move in. We evaluate septic constraints, zoning issues, utility connections and the requirements for a permit from the city. Massachusetts allows one accessory dwelling unit by right in single family zoning areas, although municipal building code, health code, and dimensional requirements still apply to every project. You can review the state requirements at mass.gov.

Here's our point of view on what actually makes the difference between one contractor or another. It's hardly ever something in the listing photo. It's the connections, the terminations, and the transitions: the places where one type of material meets another and someone needs to decide whether to do it fast or do it right. You can tell what those decisions were on a finished ADU if you know where to look.

Which Exterior Details Tell You Whether a Builder Did the Work Right?

All five of them. Where the heat pump is, how the refrigerant lines come into the wall, where the downspout water goes, whether the electric and cable service goes underground, and how the finish grade and stonework were left. You can check all five from outside of the ADU in less than ten minutes, without using a flashlight, a ladder, or any construction background at all.

These five aren't a random sample. They're the details that get left out first when the builder gets behind in the schedule or cut first when a schedule slips or one of the builder's costs goes up, and none of them can be seen in a photograph. A builder who did all five of these on a finished ADU made those decisions when the client was not standing there. That's the entire value of doing a walkaround. You aren't judging taste, you're seeing the decisions that were made when nobody was watching.

Here is what to look for on each one, and what each one tells you about the company that built it. Take this with you to any finished ADU, ours or anyone else's.

Where Should the Heat Pump Head Be Mounted on Your ADU?

The outdoor part of a ductless heat pump system, the metal box that moves heat in and out of the ADU, can be mounted two different ways. It can sit on a pedestal or a concrete pad on the ground, or it can hang from a bracket that's bolted to the foundation wall.

We suspend ours from the foundation because it keeps the space underneath the unit clear, and it keeps debris out.

The reason doesn't have anything to do with how it looks. That outdoor unit pulls air in through a coil, which sits low on the cabinet. If you put it on a pad, the leaves, mulch, grass clippings, and drifted snow all pile up against the intake. Every one of those is a service call, and some of them a service call in February using a snow shovel. By lifting the unit off the ground, the yard debris blows past it instead of collecting in it. It also means that years later, a technician working on that equipment can get a rake underneath it without pulling the unit off its mount.

When you are walking around, bend down and look under the outdoor unit. You want to see open air and a clean bracket line. A ground-mounted unit isn't a failure, and plenty of good contractors set them that way. But it's a choice that puts the maintenance on you.

What Should You See Where the HVAC Lines Enter the Wall?

Behind that outdoor unit, a bundle of refrigerant lines, a condensate drain, and a control wire go through the wall of the building. That opening is called the penetration, and it's the most important three inches on the outside of an ADU.

There are two ways to close it. Somebody can make an oversized hole, push the lines through, and then fill all the gaps with caulking. Or somebody can put in a fitted transition, which is a molded trim piece that's sized for the line that seals the opening and covers the cut edge of the siding.

We use the fitted transition, and we think it's the right way to do it. A hole that's packed with caulking is sealed the day the crew leaves but will open a few years later, because the caulking, the siding, and the line behind it all move differently during freezes and thaws. Water follows the gap that opens up. The wall cavity is where the framing is, and it's the one part of the building you can't inspect once the drywall is put up.

This is where we stand firm. On our projects, a caulked hole where the line set enters the wall means the wrong HVAC contractor did the job. Hear the difference, because it matters: that's our standard, not a building code requirement. Nobody will fail an inspection because of it, and you still own the wall.

Where Will Your Roof Water Go When It Leaves the Downspout?

If you walk around the outside of the ADU and look at the bottom of every downspout, there is one of two things happening. The downspout ends in an elbow over a splash block and the water goes out over the yard on its own. Or the downspout becomes a solid pipe that goes underground and then daylights downhill, which means the water comes out of the pipe into open ground at a lower elevation.

Every downspout on our Plymouth ADU is piped. We want controlled runoff, which means the water leaves the roof and goes somewhere we choose, rather than just wherever gravity takes it.

Roof water is the largest single volume of water your property has to handle, and it goes to the same four spots during every storm right at the base of the walls. If it's left to run across the surface, it flows to the low point next to the foundation, saturates the backfill, and then starts to damage the finish grade you just paid for. Piping it costs time and fittings on a day that the crew would rather pack up and be finished. It's one of the first things to get taken out of a bid and one of the last things a homeowner notices is missing. And that's exactly why it belongs on your list.

Buried Utilities Give You a Clean Yard and Protected Service

On the side elevation of the Plymouth ADU, the electric service and the cable wiring both run underground. There isn't an overhead drop going across the yard from a pole to a bracket on the corner of the building.

Underground service is a coordination job rather than a construction job. It has to be trenched and that needs to be scheduled with the utility company who has their own calendar. When a builder skips it, the reason is the sequence of things: it was too late to do the trenching, the crew left and the overhead line was the faster way to handle it.

What you get if you coordinate with the utility company, is a yard with nothing strung across it and a line that's out of reach of ice, wind and the tree limb that comes down in the bad weather. However, don't think that this has anything to do with how the unit is metered. Buried service and separate metering are two different questions, and the second one is a discussion with your builder directly.

Finish Grade and Stonework Tell You How the Job Ended

The last two weeks of a build are the ones a homeowner never pays attention to, and they are the ones that will affect the ADU for the next twenty years. At the rear of the Plymouth ADU there's a small rock wall that deals with the grade change. We built it from stone we found on the site, and the bottom stone was cut to fit that spot and no other.

Loam and seed is the other sign. On the day we filmed the walkthrough the lawn had about two weeks growth and was already filling in, because the finish grade was set and seeded on schedule rather than trying to work it in at the end. Above all of it is an architectural roof with a lifetime shingle, which means it's a shingle that's sold with a manufacturer warranty tied to ownership rather than a fixed term, and a maintenance-free exterior, meaning siding and trim will never need to be painted.

Three things to look at on the ground before you leave:

• Stone transitions that are tight, with no gaps packed full of loose soil
• Lawn that's established and knit together, not seed spread last Friday
• Grade that goes away from the building on every elevation

Where Does This Checklist Stop Being Enough?

You'd expect a builder to hand you a list of things his own crews do well. So here's where ours runs out.

Everything above is exterior and it tells you nothing about the wall assembly, the air sealing, the mechanical layout, or how a company will deal with you when a window package is six weeks late. A builder can put in a heat pump correctly and still be the wrong company for your project.

Some of these are our standards rather than requirements, and the HVAC fitting is the best example. A contractor who caulks that penetration hasn't broken any rule. He's just made a judgement about how long the detail lasts, and you're allowed to weigh that against price, schedule, and everything else on your list.

And a builder can do all five of these and still not be the right builder for you. If what you want is a fixed plan that has the lowest costs a crew can deliver, then a design-build is an expensive way to do it. And we'd rather say that now than later when signing contracts.

Ready to Run This Checklist on a Finished ADU?

The point of the walkaround is that it allows you to compare builders. If you do the same five checks on our work, then compare them with the next two companies you talk to, and you end up comparing how the construction is done instead of comparing sales pitches. That's a scorecard you built yourself, and it's the only kind worth trusting this late in the process.