2025 Cost Guide: How Much Does an ADU Cost in St. Petersburg?
"Accessory Dwelling Units" (ADUs) are the hottest topic in St. Petersburg real estate. Whether for aging parents ("Granny Flats") or as a lucrative Airbnb income stream, everyone wants one. But finding transparent pricing online is nearly impossible.
Contractors often hide behind "it depends." At Craftline Remodeling, we believe an educated client is our best client. Here is the honest breakdown of what it costs to build an ADU in Tampa Bay in 2025.
🚨 The "Price Per Square Foot" Myth
Stop asking for "price per square foot." Here is why: Building a small 400 sq ft unit is more expensive per foot than a 2,000 sq ft house. Why? Because you still have to pay for the "expensive" parts (Kitchen, Bath, HVAC, Electrical Panel) without the "cheap" square footage (empty bedrooms/hallways) to dilute the cost.
Expect specific project pricing starting at $250+ per sq ft for detached new construction.
Option 1: The Garage Conversion (Most Efficient)
Turning Existing Structures into Living Space
If you have a solid block garage, this is your fastest path to ROI. You are utilizing the existing shell and roof.
- Entry Level (Starting at $45k): Insulation, drywall, mini-split AC, basic LVP flooring, simply electrical. No plumbing (Studio/Office only).
- Full Suite (Starting at $70k): Cutting concrete for plumbing (adding a full bath + kitchenette), framing new impact windows/doors, upgrading electrical panel to 200amp.
Option 2: The Detached Cottage (New Construction)
Brand New 600 sq ft Guest House
Building from the ground up. This gives you total design freedom and higher resale value, but requires full site work.
- Site Work: Clearing land, pouring new slab foundation.
- Impact Rating: Miami-Dade rated windows/doors (Required by Florida Code).
- Utilities: Trenching new sewer/water lines from the main house.
- Finishes: Full sized kitchen, separate bedroom, washer/dryer hookups.
Where Does the Money Go? (The "Invisible" Costs)
Many homeowners budget for the building but forget the red tape. In St. Pete, "Soft Costs" can eat up 15% of your budget before we pour a single drop of concrete.
1. Permitting & Impact Fees ($5k - $12k)
The City of St. Petersburg charges fees to connect to their sewer/water systems. School board fees and park impact fees may also apply depending on the size of the unit.
2. Architectural & Engineering Plans ($3k - $6k)
You cannot draw these on a napkin. You need signed & sealed blueprints from a structural engineer to prove the building can withstand 140mph winds.
3. Site Prep & Utility Trenching ($4k - $10k)
Is your backyard accessible? If we can't fit a bobcat back there, hand-digging trenches for sewer lines increases labor costs significantly.
The ROI Reality Check
Is spending $160k on a backyard cottage worth it? Let's look at the numbers for a property in Historic Kenwood:
- Monthly Mortgage Cost (HELOC @ 7%): ~$1,100/mo
- Avg. Long Term Rent (1-Bed): $1,800/mo
- Avg. Airbnb Income (Occupancy 70%): $3,200/mo
Most of our clients see positive cash flow immediately, making the ADU "free" while it builds equity.
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