How much does a home addition cost in Maryland?

Three published figures, two of them from Baltimore

Angi's home addition page for Baltimore gives $80 to $200 per square foot building out and $300 to $500 building up. Its typical total runs $26,868 to $83,043, with an average of $54,719, and it says labor is about 40% to 60% of the total.

Its room addition page for Baltimore comes in at $85 to $210 per square foot, with an average total of $50,160.

The CostFlow AI Maryland calculator (2026) gives $90 to $280 per square foot and puts Maryland construction costs 12% above the national average. Its base number leaves out permits, demolition and site preparation. It lists permits at $500 to $3,500, architectural plans at $2,000 to $12,000 and structural engineering at $1,500 to $6,000 as separate items.

We didn't find anything that measures Montgomery, Prince George's or Charles County on its own.

Why a small addition looks expensive per foot

Some costs show up no matter how big the room is. CostFlow lists plans, engineering and the permit as their own lines. A 120 square foot bedroom needs a footing, a roof tie-in and an opening cut into the existing wall just as a 400 square foot family room does. Spread those over fewer feet and the per-foot number climbs.

Building up sits in a category of its own. In Angi's Baltimore figures, the range for going up starts above the top of the range for building out.

What we look at on a Maryland addition

Your county runs the permit, not the state. That's DPIE in Prince George's, the Department of Permitting Services in Montgomery, Planning and Growth Management in Charles, and the city in places like Rockville. Each office decides what the drawings have to show, and that decides how much design and engineering you pay for before anyone digs. There's more on permits for work in Maryland.

Next is the house you already have. If the electrical panel has no room for new circuits, or the heating can't reach one more room, a simple addition gets bigger. We want to find that on the first walk, when it's a line in the estimate, and not after framing, when it's a change order.

The room you're adding comes last. A bedroom with a closet is framing, insulation, drywall, trim and paint. A bathroom adds plumbing, venting and wet-area finishes, and CostFlow's own breakdown runs higher for a bathroom addition than for a home office.

How we price it

There's no addition price on this site because we don't have one on record we'd stand behind before seeing the house. We walk the lot and the wall the addition would join. You'll get a text confirming the date, the time and the address, and the written estimate follows by text within 24 to 48 hours, with the price and a link to approve it.

The estimate covers footing to paint on one scope, and we coordinate the permits and inspections. If opening the old wall changes the work, you hear about it and approve the change before we do it. We work within 30 miles of Washington, DC. See home additions.

Where these numbers come from

On October 25, 2026 we looked for published Maryland addition costs from sources outside the contracting trade, and these three pages are what turned up. They're market estimates, not our prices.

• Angi's Baltimore home addition page, labelled 2026 data, for the building-out and building-up ranges, the totals and the labor share.
• Angi's Baltimore room addition page, for the single-room range and average.
• CostFlow AI's Maryland room addition calculator (2026). It's an estimating tool, not a record of finished jobs, and it's where the exclusions and the separate design and permit lines come from.