Home Addition Cost Per Square Foot (2026): $150–$400

A home addition costs $150 to $400 per square foot in 2026, with most projects between $200 and $300. A small bump-out is at the low end; a second-story addition or one containing a kitchen or bathroom is at the high end.

Cost breakdown

• Bump-out (a few feet, cantilevered or small footing): $150-$250 per sq ft.
• Standard ground-floor room addition (new foundation, roof tie-in): $200-$320 per sq ft.
• Addition with a bathroom or kitchen: $300-$450 per sq ft.
• Second-story addition: $300-$500 per sq ft (structural reinforcement, temporary roof, whole-house disruption).
• Sunroom / three-season room: $100-$300 per sq ft depending on whether it's conditioned.
• Design, engineering, and permits: $3,000-$15,000+.

What actually drives the price

Addition type is the biggest driver: a bump-out reuses much of the existing structure, a full addition needs its own foundation and roof, and a second story needs the existing structure reinforced and the house opened up. Then: plumbing and electrical scope, foundation type and soil, roof tie-in complexity, matching existing siding and windows, finish level, and local permitting and impact fees.

Match the plan to the foundation question

The number hinges on what's under and over the new space. Photos of the area, the existing foundation and roofline, and the yard grade — plus whether the addition needs plumbing — let you give a per-square-foot range. Firm pricing needs plans, engineering, and a site visit.

What to ask for in addition photos

Ask for photos of the wall the addition will attach to, the roofline above it, the yard where it will sit (with the slope visible), the existing foundation where it meets the ground, and the electrical panel. Ask what the room is for, whether it needs plumbing, and roughly how big it should be. That's enough for a realistic per-square-foot budget range, and Fast Snap Pro turns it into an itemized starting estimate from your own rates while plans and engineering are still ahead. See also the bathroom remodel cost guide and kitchen remodel cost guide.

Example: a 300 sq ft family room addition

Line item	How it's priced	Example
Design, engineering and permits	Flat	$8,500
Foundation (crawlspace)	Flat	$14,000
Framing, roof tie-in, windows and siding	300 sq ft × $120	$36,000
Electrical and HVAC extension	Flat	$7,500
Insulation, drywall, flooring, trim, paint	300 sq ft × $45	$13,500
Total		$79,500 (about $265/sq ft)

Illustrative numbers only. Firm pricing needs plans and engineering.

Use a range like this as an early-stage budget so the homeowner can decide whether to move forward with design. Make sure the margin covers project management on a months-long job; the markup and margin calculator helps.

Frequently asked questions

How much does a home addition cost per square foot in 2026?

$150 to $400, most commonly $200 to $300. Additions with a kitchen or bathroom, and second-story additions, run higher.

Why is a second-story addition so expensive?

The existing structure has to be reinforced to carry the load, the roof comes off temporarily, and the whole house is disrupted — often $300 to $500 per square foot.

What's the cheapest type of addition?

A bump-out of a few feet, which can sometimes be cantilevered off the existing structure and avoid a full new foundation.

Can an addition be quoted from photos?

Only a rough per-square-foot range; a real quote needs architectural plans, structural engineering, and a site visit for foundation and grade.

Is it cheaper to build up or out?

Building out is usually cheaper per square foot if there's room on the lot. A second story avoids a new foundation but needs structural reinforcement, a temporary roof and more disruption.

How long does a home addition take?

Design and permits often take 1 to 3 months, and construction of a typical room addition 2 to 4 months.

Give faster ballpark numbers

Try Fast Snap Pro to turn customer photos into a starting price range built on your own rates, before you schedule the in-person walkthrough.