How much does a 20x20 room addition cost in Northern Virginia?

In 2026, a finished, permitted 20x20 (400 sq ft) addition in Northern Virginia typically costs $80,000 to $140,000. A simple family room sits at the low end; adding a bathroom or kitchen pushes toward the top of the range and beyond.

What does it cost to pour a 20x20 slab?

Foundation work for a 20x20 addition — excavation, footings, and a poured slab or crawlspace — usually runs $8,000 to $16,000 in Northern Virginia, depending on soil, slope, and how the new foundation ties into the existing home.

Is 400 square feet enough for a primary suite?

Yes. A 20x20 footprint comfortably fits a primary bedroom, an en-suite bathroom, and a walk-in closet, though the bathroom adds meaningful cost compared with a plumbing-free family room of the same size.

Why is a 20x20 addition more expensive in NoVA than the national average?

Northern Virginia commands premium pricing because of high D.C.-area labor rates ($45–$70/hour for skilled carpenters), stricter local code and inspection requirements, and tighter, more complex lots in the inner suburbs.

Is a 20x20 addition cheaper per square foot than a smaller addition?

Yes — generally. Much of an addition's cost is fixed: design, permits, foundation tie-in, and mobilizing the crew happen regardless of size. A 400 sq ft footprint spreads those fixed costs further than a 200 sq ft one, bringing the per-square-foot rate down meaningfully.