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What a home addition costs in New Jersey, worked out by size

Our North Jersey average for new finished floor space is $400 per square foot, labor and material included. At that rate a 12 × 12 ft room is about $57,600, a 20 × 20 ft addition about $160,000, and 1,500 sq ft about $600,000.

Kitchens and bathrooms inside the addition, a second story, and foundation or site conditions push the number up. Simple open rooms bring it down. The approvals come in a fixed order: for a one- or two-family home, zoning comes before plan review.

Published September 24, 2026 by AB Contracting & Design LLC, Belleville, NJ. N.J. HIC Reg. #13VH11431800.

Enclosed porch stripped to new framing and subfloor, with windows set
One of our jobs mid-build: new framing and subfloor, with the windows set.

Addition cost by size, at $400 per sq ft

Planning numbers at our average, labor and material. They are not quotes.

Home addition cost by size at $400 per square foot
SizeSquare feetAbout
12 × 12 ft room144$57,600
12 × 16 ft room192$76,800
12 × 24 ft addition288$115,200
16 × 22 ft addition352$140,800
20 × 20 ft addition400$160,000
20 × 25 ft addition500$200,000
800 sq ft800$320,000
1,000 sq ft1,000$400,000
1,200 sq ft1,200$480,000
1,500 sq ft1,500$600,000
2,000 sq ft2,000$800,000

Work out your size

Enter the length and width of the new space. The calculator multiplies it by our $400 average.

Length of the new space.

For a two-story addition, work out each floor and add them.

Your addition, at our average

Your addition, at our average
New finished floor space20 × 20 ft400 sq ft
At our North Jersey average400 sq ft × $400, labor and material$160,000
Planning numberabout $160,000

Kitchens and bathrooms inside the addition, a second story, and foundation or site conditions push the number up. Simple open rooms bring it down.

This is a planning number, not a quote. The full line-by-line cost comes once the plans are drawn.

What moves an addition above or below $400

  • A kitchen or bathroom inside it pushes the number up.
  • A second story pushes it up.
  • Foundation or site conditions push it up.
  • Simple open rooms bring it down.
  • Plans. We offer architectural drawings and also work with your architect. Additions start with a retainer when there are no approved plans yet.

See our additions, structural and roofing work

The approvals, in the order New Jersey requires them

From the state construction code, N.J.A.C. 5:23-2, and the Division of Consumer Affairs:

  1. Zoning approval. For an owner-occupied one- or two-family home, the building department won't start reviewing addition plans until zoning approval is in place (5:23-2.15). Your town's zoning rules decide where on the lot the addition can go.
  2. Sealed plans and the permit application. The plans carry the seal and signature of a New Jersey registered architect or licensed engineer. The construction official waives this only for a single-family homeowner who drew their own plans for their own detached house, with a sworn affidavit. Licensed plumbing, electrical and HVAC contractors seal and sign their parts of the application (5:23-2.15).
  3. Plan review, then the permit. No permit is issued until every required state, county and local approval is in place, and the addition can't be built without one (5:23-2.14 and 2.15).
  4. Inspections, then the final payment. Final inspections should be complete before you make the final payment to the contractor.

Plans filed after February 16, 2027 must meet New Jersey's 2024 codes, energy numbers included. What changed for additions on August 17, 2026

How other New Jersey builders' prices compare

Published figures for New Jersey additions, checked September 24, 2026:

  • Kenly Construction (September 2025 guide): $250–$400 per sq ft. A one-room bump-out at $80,000–$120,000 and a second story at $220,000–$400,000+.
  • Kubat Construction, South Jersey (July 2026): $200–$400 per sq ft.
  • KraftMaster Renovations: $125,000–$300,000+ for a one-story addition on a crawlspace, and $55,000–$75,000 to add a bathroom to it.
  • CostFlowAI's New Jersey calculator (reviewed February 2026): $104–$325 per sq ft for a room addition.
  • AB Contracting & Design: $400 per sq ft, our North Jersey average, labor and material.

Our average sits at the top of the per-square-foot ranges other New Jersey builders publish. It is an average for finished space with labor and material in it. The table above shows what it comes to at your size.

Sales tax and your contract

  • New construction is an exempt capital improvement in New Jersey (S&U-2).
  • With a completed Form ST-8, your contractor may not charge you sales tax on materials or labor.
  • Carpeting and other flooring installation is the taxable exception, at 6.625% (S&U-3).
  • A job over $500 needs a written contract with the contractor's registration number, dates, the work and the total price (Consumer Affairs).
  • The contractor gives you a copy of their liability insurance policy and the insurer's phone number.
  • You can cancel before midnight of the third business day after you get your copy of the contract.

Our registration number is #13VH11431800.

Addition cost questions

How much does a 20 × 20 addition cost in NJ?

About $160,000 at our North Jersey average: 400 sq ft × $400, labor and material. Kitchens, bathrooms, a second story or foundation work push it higher.

How much is a 12 × 12 addition to a house?

About $57,600: 144 sq ft × $400 at our average, labor and material.

How much is a 1,200 or 1,500 sq ft addition?

At our $400 average, 1,200 sq ft is about $480,000 and 1,500 sq ft about $600,000. Kitchens, bathrooms, a second story or site conditions push those higher.

Is it cheaper to build up or build out?

In our pricing, a second story pushes the number above the $400 average. Which costs less on your house depends on the foundation, your town's zoning and the plans. Your proposal shows the line-by-line cost once the plans are drawn.

Do I need an architect for an addition in New Jersey?

Almost always. Plans need the seal of a New Jersey registered architect or licensed engineer. The waiver covers only a single-family homeowner who drew their own plans for their own detached house. We offer architectural drawings and also work with your architect.

Is there sales tax on a home addition in NJ?

New construction is an exempt capital improvement. With a completed Form ST-8, your contractor may not charge you sales tax on materials or labor. Flooring installation is the exception the state lists as taxable, at 6.625%.

Sources

  1. N.J.A.C. 5:23-2, Uniform Construction Code, administration and enforcement, current through August 17, 2026: sections 2.14 and 2.15.
  2. NJ Division of Taxation, S&U-2, Sales Tax and Home Improvements.
  3. NJ Division of Taxation, S&U-3, Contractors and New Jersey Taxes, for the 6.625% rate.
  4. NJ Division of Consumer Affairs, Hiring Home Improvement Contractors.
  5. Builder figures from each linked page, checked September 24, 2026.

Want a number for your addition?

Call to talk the job through with Andrew, or send the details and Andrew will get back to you. An in-person estimate is $50, and it comes off your contract when you sign.

Call 908-331-0796Request an estimate