WORCESTER | HOLDEN | SHREWSBURY | LEOMINSTER
Turn space you already own into space you can actually use. ARM Construction converts garages, basements, and attics into finished, code-compliant living space across Worcester County.
Most homes have space that is technically part of the house but is not doing anything for the people living in it. A two-car garage holding one car and a lot of storage. A basement with eight-foot walls and nothing in it but a furnace. An attic with a staircase that goes up to plywood. Converting that space is almost always cheaper per square foot than building new, because the foundation, the walls, and the roof already exist.
That is the appeal, and it is real. What homeowners tend to underestimate is that turning storage space into habitable space is a code question before it is a design question. Massachusetts has specific requirements for ceiling height, egress, insulation, moisture, and fire separation in living space, and existing garages, basements, and attics were built to satisfy none of them. Whether your conversion is straightforward or complicated depends almost entirely on how far the existing space is from those requirements, and that is what we look at first.
A garage conversion is the fastest route to a home office, a gym, a family room, an in-law suite, or a full accessory dwelling unit. The shell is there, the roof is there, and the utilities are usually close by. Done well, it looks like it was always part of the house rather than a garage door filled in with siding.
The part that catches people is underneath. Most garage slabs in Worcester County were poured about four inches thick, with no frost footings and no insulation below, because a slab holding a car does not need any of that. Habitable space in Massachusetts does. It needs an insulated, properly drained foundation set to frost depth, a floor system that is not cold to the touch in January, and framing and insulation that meet current energy code. Depending on what is there, that can mean underpinning the existing slab or pouring a new perimeter footing. We self-perform that work rather than subcontracting it, which is the difference between finding out about a foundation problem on day two and finding out about it in week six.
Fire separation is the other requirement worth knowing about. If any part of the garage remains a garage, code requires a rated separation between it and the living space, and that affects how the wall assembly gets built.
Three things decide whether a basement can become living space, and all three are worth checking before you get attached to a floor plan. Ceiling height comes first, because the Massachusetts code sets a minimum for habitable space and plenty of older basements in Princeton, Holden, and Worcester do not have it. Getting there means lowering the floor, which is a real excavation and underpinning job rather than a finishing detail.
Egress comes second. Any room used for sleeping needs a code-compliant way out that is not the stairs, which in practice means an egress window with a proper window well or a walkout door. Cutting an egress opening through a foundation wall is masonry and structural work, and it is one of the more common reasons a basement project needs a general contractor rather than a finish carpenter.
Moisture comes third and it is the one people try to skip. A basement that takes on water in the spring will ruin finished walls, flooring, and insulation, and no amount of waterproof paint fixes a drainage problem. We solve water at the source, through grading, gutters, and drainage, before anything gets framed. Finishing over a wet basement is money spent twice.
An attic conversion adds bedrooms or a home office without touching the footprint of the house, which makes it attractive on tight lots and in neighborhoods where setbacks limit what you can build. The constraints are structural. Most attic floors in older homes were framed as ceiling joists rather than floor joists, meaning they were sized to hold up drywall and insulation, not people and furniture. Reinforcing or sistering that framing is usually part of the job.
Headroom and access are the other two. Massachusetts code requires minimum ceiling height across a defined portion of the floor area, and a permanent staircase that meets code for rise, run, and headroom, which is often harder to fit than homeowners expect and sometimes has to come out of a room below. Insulation and ventilation matter here more than anywhere else in the house, since an attic converted without proper air sealing and ventilation becomes an oven in July and an ice dam factory in February.
A garage conversion built as a full accessory dwelling unit, with its own kitchen and bathroom, generally runs $95,000 to $175,000. A basement conversion built to the same standard runs $95,000 to $180,000. Converting either into a room rather than a full dwelling unit, such as an office, gym, or family room, costs considerably less, since you are not adding a kitchen, a bathroom, or a separate entrance.
The variables that move the number most are the ones you cannot see. Foundation work on a garage conversion can add $15,000 to $40,000 if the existing slab needs underpinning or a new frost-depth perimeter footing. Lowering a basement floor to gain ceiling height is a major excavation and underpinning project. Cutting an egress window through a foundation wall adds cost. Solving a water problem before finishing adds cost, and skipping it costs more later. This is why we look at the space before quoting rather than pricing by the square foot over the phone.
* Pricing estimates as of August 2026
If the plan is a separate living space rather than an extra room, Massachusetts law changed in your favor. Since February 2, 2025, one accessory dwelling unit is allowed by right on most single-family lots, with no special permit and no zoning hearing. Garage conversions, basement conversions, and attic conversions all qualify, and conversions are frequently the least expensive path to an ADU because the shell already exists.
The unit has to be self-contained, with its own entrance, kitchen, and bathroom, and can be up to 900 square feet or half the gross floor area of your main house, whichever is smaller. In the rural towns we serve, septic capacity under Title 5 is usually the deciding factor, since an ADU that adds bedrooms can push an existing system past its rated capacity. Our ADU and in-law suite page covers the law, the constraints, and the costs in detail.
We convert garages, basements, and attics in Worcester, Holden, Princeton, Sterling, West Boylston, and Boylston, along with Shrewsbury, Leominster, Westborough, Northborough, Southborough, and Grafton.
Where you are shapes which conversion makes sense. In Worcester and Leominster, where lots are tighter and adding onto the house often runs into setbacks, converting existing space is frequently the only practical way to gain square footage, and more properties are on town sewer, which takes the septic question off the table. In Princeton, Sterling, and Holden, lots are larger and an addition may be the better option, but older homes there also tend to have the lowest basement ceiling heights and the most moisture issues. In Shrewsbury, Grafton, and West Boylston, postwar housing stock means attached garages on slabs and full basements with reasonable height, which are often the most straightforward conversions in the county.
A conversion is deceptively structural. Underpinning a slab, cutting an egress opening through a foundation wall, reinforcing attic framing, and correcting drainage are all jobs that sit underneath the part anyone sees. They are also the jobs most likely to be subcontracted out, which is where schedules slip and problems get discovered late.
ARM Construction is run by Andrew Mercurio, a fourth-generation builder who started in masonry and grew the company into full general contracting. We self-perform the foundation, masonry, framing, and finish work. Andrew has held Massachusetts Construction Supervisor License #CS-093044 since 2011, and ARM Construction & Management Inc is a registered Massachusetts Home Improvement Contractor, registration #153199. We handle the permitting with your town and the inspection schedule, and you deal with one company from the first walkthrough to the final sign off.
For a complete overview of Additions and ADUs in Massachusetts, visit our Massachusetts Home Addition Guide.
What Our Customers Say
I can't say enough good things! I needed a small finish job done at the last minute, and Andrew made it happen quickly and without any stress. The craftsmanship was perfect and everything looks amazing. I'm extremely happy and would recommend him to anyone!
Andrew and his team are detail-oriented. They are skilled and helped me understand the process of renovating my kitchen. Fantastic communication & high quality service! I am so lucky to have them and recommend them to anyone! When they built my deck, it was so fast & efficient! Call Andrew, you won't regret it
Andrew replaced a garden window in my kitchen, and a sliding door. He did a meticulous job, and went above and beyond to accommodate some special requests that I had. His attention to detail and willingness to do whatever it took to make me happy didn't go unnoticed. Will definitely use him each and every time!
Here are the questions Worcester County homeowners ask us most about converting existing space. If yours is not here, call us at (774) 249-0221.
It depends on three things: ceiling height, egress, and moisture. The Massachusetts building code sets a minimum ceiling height for habitable space, and plenty of older basements in Worcester County do not have it without lowering the floor, which is a significant job. Any room used for sleeping needs a code-compliant means of egress, which usually means an egress window with a window well or a walkout door. And the space has to be dry, which means solving any water problem at the source rather than covering it. We check all three before design starts, because any one of them can change the project.
Sometimes, and it is worth being honest about. In Worcester County, where winters are real, a house with no covered parking is at a disadvantage on resale compared to one with a garage. If your property has a second garage, a detached garage, or enough driveway and outbuilding space that parking is not an issue, the conversion usually adds value. If it is your only garage and the driveway is short, think carefully. We would rather tell you that up front than after.
A garage conversion generally runs $95,000 to $175,000 when it is built as a full accessory dwelling unit with a kitchen and bathroom. Converting a garage into a room without a kitchen, such as an office, gym, or family room, costs considerably less. The number that surprises most homeowners is the foundation. Most garage slabs in this area were poured four inches thick with no frost footings and no insulation underneath, and habitable space in Massachusetts needs an insulated, properly drained foundation. Underpinning or a new perimeter footing can add $15,000 to $40,000 on its own.
Yes. Converting unfinished space into habitable space requires a building permit from your town, plus electrical, plumbing, and mechanical permits depending on the scope. Finishing a basement without a permit creates a problem you will meet again when you sell, since unpermitted living space typically cannot be counted as finished square footage and can hold up a closing. ARM Construction handles the permitting and the inspection schedule as part of the project.
Yes. Under the Massachusetts law that took effect February 2, 2025, garage conversions, basement conversions, and attic conversions all qualify as accessory dwelling units, and one ADU is allowed by right on most single-family lots. The unit has to be self-contained with its own entrance, kitchen, and bathroom, and can be up to 900 square feet or half the gross floor area of the main house, whichever is smaller. Conversions are often the least expensive route to an ADU because the shell already exists.
Massachusetts allows one ADU by right on most single-family lots. Here is what the law permits. ...more
Additions & ADUs
August 05, 2026•7 min read
ARM Construction & Management Inc
131 Houghton Road
Princeton, MA 01541
(774) 249-0221
Licensed and insured in Massachusetts. MA CSL #CS-093044 | MA HIC Reg. #153199
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