The four main types of additions
A bump-out is a small extension of an existing room — usually 2 to 6 feet deep and under 100 square feet. Bump-outs are the cheapest type of addition because they often cantilever off existing framing, skip the new foundation, and share roof structure. Expect $180 to $280 per square foot for a basic bump-out.
A single-story addition — a new room attached to the ground floor with its own foundation and roof — is the most common type. This runs $220 to $400 per square foot for a standard bedroom or living space. Add complexity like multiple new rooms, vaulted ceilings, or site drainage work and the per-foot price climbs.
A second-story addition stacks new living space on top of existing first-floor rooms. This runs $300 to $550 per square foot because the existing structure usually needs foundation and framing reinforcement to carry the new load, and you’re stitching the new roof into the old one. Figure on $50,000 to $150,000 of structural and framing premium on top of the finished square footage.
Kitchen and bathroom additions are the most expensive per square foot — $400 to $700 — because they pack plumbing, electrical, HVAC, and expensive finishes into a small footprint. A 150-square-foot kitchen addition with mid-range finishes lands between $60,000 and $105,000.
What’s in the per-square-foot number
A mid-range $325 per-square-foot price includes: foundation, framing, roofing, siding, windows and exterior doors, drywall, basic electrical and HVAC extension, insulation, painting, and standard flooring. It does not typically include: landscape restoration, high-end finishes, custom cabinetry, tile beyond basic bath surrounds, or site work like grading and tree removal. Read every quote line-by-line — contractor scopes vary wildly.
Soft costs: architect, permits, engineering
Soft costs add 10 to 20 percent on top of construction. For a $200,000 addition, budget $20,000 to $40,000 in soft costs. Architect fees run 8 to 15 percent of construction cost for full service (design through construction administration) or a flat $3,000 to $12,000 for just a permit set. Structural engineering adds $1,500 to $5,000 and is required for most second-story additions. Permits scale with project value — $500 to $3,000 is typical. A zoning variance adds $1,000 to $5,000 and 60 to 180 days if setbacks or height are an issue.
Survey, soils report (if on a slope or fill), and landscape architect are smaller line items but still real — budget $500 to $3,000 combined.
Regional variation
Expect to pay 40 to 80 percent more in coastal California, Seattle, Boston, New York, and DC than in the Midwest or Southeast. Labor is the biggest driver — framing crews in the Bay Area charge three times what the same crew charges in Oklahoma. Material costs are closer to national, though specialty items ship expensively to the Mountain West and the Pacific Northwest. Climate also matters: additions in hurricane zones need impact-rated windows and extra tie-downs; additions in snow country need heavier roof framing and more insulation.
Design decisions that move the number
Ceiling height is the sneakiest cost driver. Going from 8-foot to 9-foot ceilings adds roughly $5 to $10 per square foot in framing, drywall, and HVAC. Vaulted or tray ceilings add $15 to $40. Window and door count matter: each window adds $600 to $1,800 installed; each exterior door $1,500 to $3,500. Roof pitch and complexity also matter — a simple gable is cheapest; dormers, hips, and valleys each add thousands.
Matching the existing house is another hidden cost. If your home has 40-year-old siding nobody makes anymore, budget for re-siding the visible wall (or all of it) so the addition doesn’t look bolted on. Roofing matches are easier — plan to redo the whole roof if it’s within 5 years of replacement anyway.
Timeline and financing
From first call to move-in, a typical addition takes 8 to 14 months: 2 to 4 months of design and permitting, 4 to 8 months of construction, 1 to 2 months of punch list and landscaping. Second-story and complex additions push 14 to 18 months. Most homeowners finance with a cash-out refinance, HELOC, or construction-to-permanent loan — appraisers value the addition at roughly 60 to 80 percent of cost for resale, so plan to stay in the house for at least 5 years to recoup.
DIY versus hiring a GC
Home additions are not DIY projects for most homeowners. Between structural engineering, permit drawings, scheduling 10 to 15 trades, managing inspections, and running the job for 6 months, you need either real construction experience or a general contractor. Acting as your own GC can save 10 to 20 percent but requires daily time investment and strong trade relationships. The pure DIY route — one owner swinging hammers — usually fails at the speed-of-framing and roof dry-in steps.
When to call a pro
Call an architect first for anything structural. Call a general contractor before the architect if your budget is tight — a GC can tell you what’s buildable for your number before you spend $10,000 on drawings. Get three bids on the finished drawing set. The middle bid is usually the right one; the low bid often hides scope gaps that become change orders.