A home addition in St. Petersburg costs $95 to $250 per square foot. A standard 15×20 room addition (300 square feet) lands between $48,000 and $65,000 with quality finishes, priced from 73 actual Tampa Bay addition projects. CraftLine Remodeling is a licensed and insured Florida design build contractor. We design the addition, handle City of St. Petersburg permits and engineering, and build it to final inspection.
What a Home Addition Costs in St. Petersburg (2026)
| Level | Cost per sq ft | 15×20 addition (300 sq ft) |
|---|---|---|
| Basic | $95 to $125 | $28,500 to $37,500 |
| Standard | $125 to $185 | $37,500 to $55,500 |
| Premium | $185 to $250 | $55,500 to $75,000+ |
Foundations matter here: slab on grade runs $4,500 to $7,500, stem wall and pile foundations for flood zones run $7,500 to $18,000. Full math with real examples in the room addition cost guide.
Cost by Addition Type
Square footage is only half the answer. What you put inside the walls moves the number more than the size does.
| Addition type | Typical cost | What drives it |
|---|---|---|
| Sunroom or flex room, 15×20 | $35,000 to $55,000 | No plumbing, simpler HVAC, lighter finishes |
| Bedroom or family room, 15×20 | $45,000 to $65,000 | Full insulation, flooring, closets, ducted HVAC |
| Primary suite with full bath, 15×20 | $65,000 to $95,000 | Bathroom rough in alone adds $8,500 or more |
| Second story addition | $75,000 to $125,000 | Structural reinforcement of the existing house, stairs, roof rework |
| Kitchen expansion | $48,000 to $68,000 | Cabinetry and appliances on top of the shell |
Wet rooms are the single biggest multiplier. A bathroom or kitchen inside the addition brings supply lines, drains with proper fall, venting, waterproofing, and an extra round of inspections. That is why a bedroom and a primary suite on the exact same 300 square feet can be $30,000 apart.
Addition or ADU? St. Pete Rewards Both
St. Petersburg is one of the friendliest cities in Florida for backyard units, and sometimes a detached ADU beats an attached addition: rental income, a private suite for family, and no shared wall. We built the guides on this exact decision: garage conversion vs detached ADU, the St. Pete ADU zoning map explained, and the ADU cost guide. In a consultation we will tell you straight which one your lot, your zoning, and your budget actually want.
The quick version: an attached addition is the cheapest way to add heated square footage, because it borrows the existing foundation edge, roofline, HVAC, and electrical service. A detached ADU costs more per square foot, since it needs its own everything, but it can produce rent and it does not consume the interior of your house during construction. If the goal is a bigger primary suite or a family room, build the addition. If the goal is income or a genuinely separate space for a parent or an adult kid, look hard at the ADU first.
Built for St. Pete Lots and Rules
Additions in St. Petersburg run into three local realities: smaller lot setbacks in the historic grid neighborhoods, flood zone elevation rules near the water, and matching 1920s to 1950s construction so the addition does not look bolted on. We design around all three first, then pull City of St. Petersburg permits and engineering, so inspections pass and the new space looks like it was always there.
Lot coverage is the constraint people hit first. The older platted neighborhoods in St. Pete were laid out on narrow lots, often 50 feet wide, and the zoning caps how much of that lot you can build on including the house, driveway, and any accessory structure. Plenty of homeowners come to us wanting to push out the back only to find the buildable envelope is smaller than they assumed. That is a design problem with real answers, going up instead of out, or reshaping the footprint, but it needs to be solved before anyone draws a floor plan.
The second is elevation. Much of the city sits in a special flood hazard area, which means the finished floor of new construction has to meet a required elevation, and a project valued at half or more of the structure value can trigger requirements for the whole house. We pull the flood zone and the property record before design so nobody discovers that at plan review. Second-story additions are the usual answer on the repeatedly flooded streets, and our Shore Acres and Venetian Isles remodeling page covers when that beats building out.
The third is character. A 1925 bungalow in Old Northeast and a 1955 block ranch in Shore Acres want completely different rooflines, window proportions, and exterior finishes. Matching an existing tile or metal roof and copying the original window rhythm costs a little more up front and is the difference between an addition that reads as part of the house and one that reads as an add on.
Permits and Schedule in the City of St. Petersburg
| Phase | Time | Notes |
|---|---|---|
| Design, survey, engineering | 3 to 5 weeks | Includes zoning and flood verification |
| City permit review | 4 to 6 weeks | Building plus electrical, mechanical, plumbing; fees typically $2,000 to $4,000 |
| Foundation and framing | 3 to 4 weeks | Slab or stem wall, walls, roof structure, strapping |
| Dry in and exterior | 2 to 3 weeks | Roofing, impact windows, stucco or siding |
| Rough in and inspections | 2 to 3 weeks | Electrical, mechanical, plumbing, insulation |
| Interior finish and punch | 3 to 4 weeks | Drywall, flooring, trim, paint, final inspection |
Because the addition goes up outside the existing wall, most families stay in the house the entire time. The disruptive stretch is short, usually a few days, when we open the connection between the old house and the new space.
What Homeowners Say
CraftLine Remodeling is a licensed and insured Florida contractor and a member of NARI Tampa Bay. 93 Google reviews, 5.0 rating. See finished work on our Tampa Bay before and after showcase.
Home Additions in St. Petersburg: Common Questions
How much does a home addition cost in St. Petersburg?
Expect $95 to $250 per square foot. A typical 300 square foot addition with quality finishes runs $48,000 to $65,000, and a primary suite with a full bathroom on the same footprint runs $65,000 to $95,000.
How long does an addition take?
Design and permitting with the City of St. Petersburg usually take 6 to 10 weeks, then 8 to 14 weeks of construction.
Should I build an addition or an ADU?
Depends on your lot and goals. Attached additions add living space cheapest per square foot. Detached ADUs add rental income and privacy. We will walk your property and tell you which one wins.
How much of my lot am I allowed to build on?
It depends on your zoning district and lot size, and the older St. Pete neighborhoods on narrow platted lots are the tightest. Setbacks, lot coverage, and impervious surface limits all apply, and any existing shed, deck, or driveway counts. We verify the buildable envelope before design so the plan we draw is a plan that can be permitted.
Do you handle flood zone requirements?
Yes. Elevation certificates, engineering, and the city review process are part of the project, not your problem. If you want a first read before the consultation, the ADU feasibility check pulls the FEMA flood zone and the ADU zoning for a Tampa Bay address in a few seconds.
Get Your Free In Home Estimate
Talk to a licensed contractor. No pressure, real numbers. Schedule your free consultation here or call (813) 522-4359. Also see St. Pete garage conversions and the free remodeling cost calculator.