A midrange primary suite addition in the Middle Atlantic region costs about $195,129, according to the Remodeling 2025 Cost vs. Value Report (www.costvsvalue.com). Smaller additions cost less. Size, the foundation, the roof tie-in and whether the addition carries plumbing decide where yours lands.
What that figure covers
The Cost vs. Value report prices a defined job: a 24-by-16-foot primary bedroom suite over a crawlspace, with a walk-in closet, a soaking tub, a separate shower and a double vanity. A single-room bump-out without plumbing costs less. A two-story addition or one with a kitchen costs more.
For another yardstick, builders reported an average construction cost of about $162 per square foot for new single-family homes in 2024, according to the NAHB's Cost of Constructing a Home survey. Additions often cost more per square foot than new homes, because the new work has to tie into an existing house.
What drives addition costs
- Foundation. Slab, crawlspace or full basement.
- Stories. A second story over existing space needs the structure below checked, and often reinforced.
- Plumbing. A bathroom or kitchen in the addition adds rough-in and fixtures.
- Roof tie-in and siding match. Making new work look original takes time.
- Heating and cooling. The existing system may not carry the new space.
Zoning and permits in Mercer County
An addition needs a construction permit under N.J.A.C. 5:23-2.14 from the town's construction office; each town page on this site lists its office from the New Jersey DCA roster. It also has to meet the town's zoning setbacks and lot coverage. If it cannot, the owner can apply to the zoning board of adjustment for a variance under N.J.S.A. 40:55D-70, which adds time before any permit.
Resale
A midrange primary suite addition recoups about 27.1% of its cost at resale in the Middle Atlantic region, according to the Remodeling 2025 Cost vs. Value Report (www.costvsvalue.com). People add on because they need the space, not to turn a profit.
How MHG prices an addition
Every addition gets a free in-home estimate:
- A short phone call to hear what you want and set up a visit.
- A first meeting at your house to walk the space.
- A written preconstruction estimate.
- A second pass through the estimate together to settle scope and finishes.
- A deposit, then the final plan, budget and schedule before work starts.
- Week-by-week progress updates while the work is underway.
- A final walkthrough with you before the last payment.
More on home additions with MHG and New Jersey permits.
