ADU Feasibility Study in Tampa Bay
Most homeowners who call us have already done two or three hours of online research on ADUs before the first conversation. They know what an ADU is. They think they know what it costs. What they almost never know is whether their specific lot is eligible, what size unit the zoning code actually allows on their parcel, and which three or four constraints will shape the design from day one.
A feasibility study answers those questions before anyone is asked to sign a construction contract. This page explains what a feasibility study is, what it checks, when you need a paid one, and when a free lot eligibility call is enough.
What a Feasibility Study Actually Checks
1. Zoning and overlay status: Base zoning district, whether ADUs are permitted by right or conditionally, overlay districts, Extended Family Residence rules (City of Tampa), pending code amendments.
2. Lot size, setbacks, and siting: Minimum lot size for your zone, front/side/rear setbacks, separation between primary and accessory structures, maximum allowable ADU square footage, height limits, architectural match requirements.
3. Infrastructure and utilities: Existing electrical service capacity (100-amp vs. 200-amp), sewer lateral age and condition, water service line size, natural gas availability, septic system capacity.
4. Flood, storm, and soil: FEMA flood zone designation, base flood elevation vs. existing grade, Coastal Storm Area designation, wind exposure category and ultimate design wind speed, soil bearing capacity.
5. Site constraints: Tree preservation ordinance impacts, easements, impervious coverage maximum and current coverage, stormwater retention requirements.
6. Market and intent: For family use — accessibility needs and §193.703 tax benefit eligibility. For rental — comparable rental rates, jurisdiction-specific rental rules, HOA covenants.
Four Ways a Tampa Bay Lot Can Disqualify Your ADU
1. Lot is in a zone that doesn't allow ADUs: In St. Petersburg, zones outside NS-1, NT-1, NT-2, NT-3, NT-4, and NSM do not permit ADUs. In the City of Tampa outside four overlay districts, only Extended Family Residences are allowed.
2. Lot is under minimum size for the zone: St. Petersburg's NS zone requires 10,000 sq ft unless the lot is on an alley or a corner. A standard 50 x 130 lot (6,500 sq ft) in an NS district mid-block with no alley cannot host an ADU under current code.
3. Coastal Storm Area or flood zone makes the project uneconomic: Lots in flood zones AE and VE require finished floor elevation above base flood elevation, adding $8,000–$25,000. Lots in Pinellas Coastal Storm Area cap ADU size at 750 sq ft.
4. Existing septic system cannot support added fixtures: On properties still on septic, the existing drain field often cannot handle a second kitchen and bathroom. Upgrade options can cost $15,000–$40,000. In some cases, the lot physically doesn't have room for an expanded drain field.
When to Stop at the Free Call vs. Pay for a Deeper Study
Free call is sufficient when: You are at least 6 months from building. You just want to confirm the lot is eligible and the rough cost is in range. You are still deciding between ADU types or deciding whether to move forward at all.
Paid feasibility study is worth it when: You are within 2–3 months of wanting to start design. You are buying a property specifically for its ADU potential. The lot has complicating factors (flood zone, septic, historic overlay, very small or irregular). You are comparing two or three lots. You are planning a rental-intent ADU and need a defensible rental rate projection before committing capital.
