What's the cheapest type of home addition?

A bump-out — extending one wall by a few feet — is the cheapest per square foot because it can often skip a new foundation. Converting existing unfinished space (basement, attic, garage) is even cheaper, at $80–$200/sq ft.

Do I need an architect for a home addition?

For most additions over 100 sq ft or anything affecting structure, yes — both for code compliance and because the structural engineering is non-trivial. Many design-build firms (including BRAVA) include design in the project.

How long does a home addition take from start to finish?

Plan on 6–12 months total: 2–4 months for design and permits, 4–8 months for construction. Second-story additions and additions in historic districts can stretch longer.

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Cost GuidesJune 8, 202610 min read

Home Addition Cost per Square Foot — What to Expect in 2026

Single-story, second-story, and bump-out additions all price differently. Here's the per-square-foot math, by addition type, with the line items most homeowners miss.

Per-square-foot pricing by addition type

Single-story additions on a new foundation run $300–$500 per square foot in most US markets. Second-story additions cost more — $400–$700 per square foot — because they require temporary roof removal, structural reinforcement of the existing floor, and longer weather exposure.

Bump-outs (extending a single wall 4–12 feet to enlarge a kitchen, primary bedroom, or bath) are the most cost-efficient way to add space at $250–$400 per square foot, because they often skip a new foundation by cantilevering off the existing one.

What the per-square-foot number really includes

A complete addition price includes foundation or cantilever, framing, roofing and tying into the existing roof, exterior siding to match, windows and doors, insulation, electrical, plumbing if the room needs it, HVAC extension, drywall, flooring, paint, and trim. It does NOT typically include high-end finishes, cabinetry, or custom millwork — those get priced on top.

Tying into the existing house — matching siding, roofline, interior trim, floor height — is the silent budget killer. Older homes rarely have stock-matching materials still in production.

Permits, plans, and timeline

Additions almost always need architectural drawings, structural engineering, and permits — budget 8–16 weeks for design and approval before a shovel hits the ground. Construction itself runs 4–8 months depending on size and complexity.

Frequently Asked Questions

What's the cheapest type of home addition?: A bump-out — extending one wall by a few feet — is the cheapest per square foot because it can often skip a new foundation. Converting existing unfinished space (basement, attic, garage) is even cheaper, at $80–$200/sq ft.
Do I need an architect for a home addition?: For most additions over 100 sq ft or anything affecting structure, yes — both for code compliance and because the structural engineering is non-trivial. Many design-build firms (including BRAVA) include design in the project.
How long does a home addition take from start to finish?: Plan on 6–12 months total: 2–4 months for design and permits, 4–8 months for construction. Second-story additions and additions in historic districts can stretch longer.