How Much Does a Home Addition Cost? The Short Answer
How much does a home addition cost? It depends most on whether you build out or up and how many rooms with plumbing it includes. Three reference points:
- National, by the square foot: according to Angi, ground-level additions run about $80 to $200 per square foot, and Angi puts second-story additions at about $100 to $300 per square foot nationally.
- New England, by project: the 2025 Cost vs. Value Report (New England) prices a midrange primary suite addition at $181,780 and an upscale one at $374,737.
- Our own work: three of our additions in Amesbury and Andover had budget bands of $650,000 to $700,000 (details below).
Norman Builders is a design-build company in Newton, NH, building additions for homeowners in the Merrimack Valley, the North Shore, the Seacoast and southern New Hampshire since 2007. To run numbers for a specific size, including 1,000 square feet, use our home addition cost calculator. This guide explains what moves the price.
Factors Influencing Home Addition Costs
Project Size and Scope
More square feet means more cost, but scope matters as much as size. A bedroom with a closet is a simpler build than a kitchen or bathroom of the same size, and adding a full level is a bigger job than a single room.
Labor and Permits
An addition brings in many trades: excavation and foundation, framing, roofing, siding, electrical, plumbing, HVAC, insulation, drywall, flooring and finish carpentry. Permits and inspections are set by your town, so ask your building department for its fee schedule early. One of our past clients, Dan M. of Andover, listed the trades on a large project of ours: "significant structural work, framing, roofing, plumbing, HVAC, sewer/excavation, tile, windows, and finish work."
Materials
The finish level sets a large part of the budget: windows, siding, roofing, flooring, cabinetry, counters, tile and fixtures. The Cost vs. Value figures above show how wide the spread can be: the upscale primary suite addition ($374,737) costs about twice the midrange one ($181,780), though the upscale project also has a bigger, higher-spec scope.
Geographic Location
National averages are only a starting point. In the Cost vs. Value data, a midrange primary suite costs $170,517 nationally and $181,780 in New England. Massachusetts and southern New Hampshire also bring local factors: in Massachusetts, the state septic code (Title 5) sizes systems by bedroom count, so adding a bedroom on septic can trigger a board of health review, and New Hampshire sizes septic systems by bedrooms too.
Building Direction
- Building out: needs lot space, setbacks that allow it, and a new foundation. Often a little cheaper per square foot.
- Building up: keeps the yard and footprint, but the roof comes off and the existing walls and foundation must carry the new level. Often a little more per square foot.
Site Preparation, Excavation, Demolition, and Cleanup
Ground-level additions start with excavation, footings or a slab, and removing whatever is in the way: a deck, a patio, part of an exterior wall. The job ends with grading and site restoration around the house, which was part of our Amesbury addition.
Architectural and Contractor Services
You will pay for design (plans, and a structural engineer when the structure changes) and for someone to run the job. In a design-build setup, one team handles both: we work with designers and architects on the plans, then an experienced project manager runs the schedule and budget and communicates with you regularly during the build.
Home Addition Cost Breakdown
Average Home Addition Costs
According to Angi, a room addition costs about $48,000 on average nationally, with most projects between $20,900 and $72,600. That covers a single room. Larger additions with bathrooms cost far more: the New England primary suite figures above run from $181,780 to $374,737.
Cost Per Square Foot
Angi's national figures are about $80 to $200 per square foot for building out and about $100 to $300 for a second story. Per-square-foot numbers are most useful for comparing options; a builder's estimate for your house is what you should budget from.
Room-Specific Costs
| Addition type | Cost | Source |
|---|---|---|
| Room addition (national average) | About $48,000; most $20,900 to $72,600 | Angi |
| Bathroom addition, midrange (New England) | $63,783 | 2025 Cost vs. Value |
| Bathroom addition, upscale (New England) | $116,146 | 2025 Cost vs. Value |
| Primary suite addition, midrange (New England) | $181,780 | 2025 Cost vs. Value |
| Primary suite addition, upscale (New England) | $374,737 | 2025 Cost vs. Value |
Additional Features
Price these separately, because they are often left out of early numbers: extending heating and cooling (or adding a separate system), electrical panel capacity, new windows and exterior doors, roofing tie-ins where the new roof meets the old, siding to match the house, and site restoration.
Types of Home Additions
The home additions we build include family room additions, second and third level additions, attached and detached garage additions, in-law additions and sunroom additions.
Room Addition
A single room at ground level, such as a bedroom, family room or office. Bedrooms need heat, power and a code-compliant egress window; adding a bathroom or kitchen brings plumbing and moves the cost up.
Home Extension
Smaller or specialized extensions: bump-outs that push one wall out a few feet, mudrooms, in-law suites for relatives, sunrooms, and garage additions for cars or storage.
Second-Story Addition
Adding a level keeps your footprint and yard, but it is the most structural option: the roof comes off, and an engineer needs to confirm the walls and foundation can carry the new floor. Angi puts second-story additions at about $100 to $300 per square foot nationally.
Attic Conversion
Finishing an attic adds a room without adding footprint, if the space can meet code. Under the 2021 International Residential Code (IRC), habitable rooms generally need at least 70 square feet, a ceiling height of at least 7 feet over most of the room, and sleeping rooms need an emergency escape opening. Massachusetts and New Hampshire base their residential codes on the IRC with state amendments, so confirm with your town. Insulation, ventilation and a code-compliant stair are usually the big costs.
Ways to Keep Addition Costs Down
- Watch the plumbing: every bathroom, kitchen or laundry adds trades. If the addition needs water, keeping it close to existing plumbing usually means shorter runs.
- Settle the design before construction: changes are cheapest on paper. Changing your mind once walls are framed costs labor twice.
- Choose the finish level on purpose: windows, cabinetry, tile and fixtures are among the biggest costs you control, so settle on a level before design starts.
- Compare detailed bids: ask each builder to price the same plans and list what is and is not included, so you compare like with like.
- Start with the space you need: a smaller first design with room to add features as the budget allows keeps the base price down.
What Our Projects Cost
Three of our additions, with the budget band printed on each project page:
- Two-bedroom addition and primary suite, Amesbury, MA (completed 2025, budget band $700,000): two new bedrooms, a primary suite with a vaulted, beamed ceiling and a primary bath with a walk-in tiled shower. We matched the rooflines, siding and window proportions so the new wing reads as part of the original house. The homeowners chose to add on rather than move as the family grew.
- Coastal kitchen and spa-inspired bath addition, Andover, MA (completed 2024, budget band $700,000): an open kitchen and living area with a large island, plus a primary bath with an oversized walk-in shower.
- Navy and white kitchen addition, Andover, MA (completed 2024, budget band $650,000): a kitchen built around a navy furniture-style island, a KitchenAid professional gas range with a pot filler, a beverage station, and glass doors to the outdoor living space.
Plans can also change scope once a homeowner sees the options. Debbie White of Hampstead, NH wrote: "We originally had planned a kitchen remodel but we ultimately decided to add an addition and expand the master bathroom and closet as well." And on schedule, Brad and Sara R. wrote that their Hampton Beach addition and renovation was planned to start in October 2010 and finish by February 2011, and "was finished on time."
Planning Your Addition With Norman Builders
Our design phase starts with defining the budget and an estimated project cost with as much detail as possible, before design work goes further. As a guide, our renovation process guide puts a home addition at 3 to 9 months. See finished work in our home addition projects, then request an estimate or call (978) 833-7337. We typically respond the same day or within 24 hours.
Frequently Asked Questions about Home Addition Costs
Is it cheaper to build up or out?
Per square foot, building out is usually somewhat cheaper, though the ranges overlap. According to Angi, ground-level additions run about $80 to $200 per square foot nationally and second-story additions about $100 to $300. Building up can still be the better choice when your lot has no room to grow, setbacks block an addition to the side or back, or you want to keep the yard. A second story needs the existing walls and foundation checked by an engineer, and the roof comes off during construction.
How much does it cost to build a 20x20 room?
A 20 x 20 room is 400 square feet. At Angi's national build-out range of $80 to $200 per square foot, a basic room comes to about $32,000 to $80,000; a bathroom, closet or higher finishes move it up. Our home addition cost calculator works through this and other sizes line by line.
What is the cheapest home addition?
A single ground-level room with no plumbing, or a small bump-out, is usually the least expensive way to add space, because it avoids the plumbing and venting a kitchen or bathroom brings. Finishing an attic that can meet code avoids a new foundation, though stairs, insulation and ventilation bring their own costs. According to Angi, a room addition costs about $48,000 on average nationally, with most between $20,900 and $72,600. For a bump-out that pushes one wall out a few feet, HomeGuide puts most projects at $5,000 to $35,000; see our guide to the cost to bump out a living room.
What is the most expensive part of a home addition?
The structure and any room with water. A ground-level addition needs excavation and a foundation; a second story means opening the roof and having an engineer confirm the house can carry the new level. Kitchens and bathrooms add plumbing, venting and more electrical work, which is why even a midrange bathroom addition costs $63,783 in New England, according to the 2025 Cost vs. Value Report.
