An addition is the most expensive way to get more house — a new foundation, new framing, new roof, and the tricky work of tying all of it into a structure that has been settling for decades. It is also, often, cheaper than selling and buying in this market. Here is what it runs.

Cost per square foot, installed

• Bump-out (a few feet off an existing room, cantilevered or on a small foundation): $350–$650 / sq ft — small numbers, high per-foot cost because the fixed costs do not scale down.
• Single-room addition (family room, sunroom, bedroom on a crawlspace or full foundation): $300–$500 / sq ft.
• Primary-suite addition (bedroom + full bath + closet): $400–$600 / sq ft — the bathroom drives it up.
• Second-story addition (build up over an existing footprint): $350–$550 / sq ft, plus the cost of temporarily moving out and reinforcing what is below.
• Kitchen expansion (push the kitchen into new space): $500–$800 / sq ft with the new kitchen included.

So a 400 sq ft family-room addition is roughly $140,000–$200,000; a 250 sq ft primary suite around $110,000–$150,000.

What moves the number

Foundation type (frost-wall vs full basement vs slab), roof tie-in (a clean gable is cheap; matching a complex existing roofline is not), matching the exterior (siding and windows that no longer exist in that colour), site access for equipment, and what the addition connects to — cutting a new opening into a load-bearing exterior wall means a header and temporary shoring.

Permits, setbacks and the survey

Before design, we check your lot's setbacks and coverage limits against the town's zoning. In some Monadnock-region towns a modest addition is by-right; in others it needs a variance, which adds months. A quick zoning check at the start saves you designing something you cannot build.

Addition vs. finishing what you have

If the honest need is "a bedroom and a bath," compare the addition number to finishing the basement or a Thermasteel ADU in the yard — both can be half the cost. An addition wins when you need the space attached, on the main level, and connected to the existing rooms.