Building permits, zoning and land rules in St. Mary Parish, Louisiana

At a glance

Building permit

Required for regulated construction; ask Planning & Zoning which work needs approval¹²

Zoning

Yes on unincorporated parish land³

Septic permit

Required from the Louisiana state health officer; the parish health unit's sanitarians run the local process⁶⁵

RV living

Private-land occupancy rule not confirmed; ask Planning & Zoning⁷

Tiny home

District standards may control size, placement and use⁸⁹

Owner-builder

Conditional contractor-licensing exemption; permits and safety codes still apply¹⁰

Private well

Licensed driller and state registration required; domestic wells follow post-installation notice rules¹¹

Who to call

Contact details are copied from each office’s official page and were checked against it on October 11, 2026.

Do you need a building permit in St. Mary Parish, Louisiana?

St. Mary Parish requires building permits for regulated construction, but we could not confirm the complete parish rule identifying covered projects and exemptions; ask Planning & Zoning about your proposed work.¹² Louisiana’s State Uniform Construction Code applies in St. Mary Parish, with mandatory residential-code enforcement for new construction, reconstruction, additions to homes previously built to that code and extensive alterations.¹² Extensive alterations cover work areas exceeding 50% of the dwelling-unit area.¹² Required building inspections must be conducted by a building-code enforcement officer or certified third-party provider, with the inspector on site except for roofing inspections.¹³

Who issues building permits in St. Mary Parish, Louisiana, and how do you reach them?

For unincorporated land, start with St. Mary Parish Planning & Zoning: (337) 828-4100 ext. 5280, permits@stmaryparishla.gov, Fifth Floor Courthouse, Franklin, LA 70538.¹⁴ Applications go through MGO Connect, but the full review, inspection, fee and approval procedure remains unconfirmed; request the project checklist before work begins.² Morgan City and Franklin issue their own building permits inside city limits.¹⁵¹⁶ Patterson has a municipal application process for covered exterior work in its historic district.¹⁷ Septic approval stays with the Louisiana Department of Health, Office of Public Health, including inside municipalities.⁴

How do septic permits work in St. Mary Parish, Louisiana?

Louisiana, rather than the parish government, regulates individual sewerage systems: no one may install, alter or operate one without first obtaining a permit from the state health officer.⁴⁶ State review includes the plans and considers whether connection to community sewer is feasible, along with soil, drainage, lot dimensions and health risks.⁶ Final approval requires compliance verification through an on-site state inspection, an installer certification or both, and the installer certification is due within 15 days after completion.¹⁸ The Louisiana Department of Health describes sanitarians in each parish health unit as the staff who inform, advise and operate the onsite sewage permitting system, and the local service for St. Mary Parish runs through the St. Mary Parish Health Unit in Morgan City; the parish government is not the septic permitting authority.⁵¹⁹ Ask the St. Mary Parish Health Unit for the application and site-evaluation steps.¹⁹ USDA soil data rates 0% of parish soils as free of severe limitations for a conventional drain field; that rating makes an early site evaluation essential but does not by itself prove that a parcel cannot support an approved system.²⁰

Can you live in an RV or tiny home on your land in St. Mary Parish?

We could not confirm whether unincorporated St. Mary Parish allows long-term RV occupancy, temporary private-land camping or tiny-home occupancy; ask Planning & Zoning about the proposed use.¹⁴ The parish has zoning on unincorporated land, and Louisiana's framework leaves dwelling size, setbacks and similar standards to local zoning districts.⁷⁸⁹ A tiny home therefore still needs a district and code review, while an RV question needs a direct parcel-specific answer from Planning & Zoning.¹⁴ Before buying, give Planning & Zoning the parcel number and describe whether the unit is temporary, connected to utilities or intended as a full-time dwelling.¹⁴

What are the steps to build a home in St. Mary Parish, Louisiana?

1. Ask St. Mary Parish Planning & Zoning to confirm jurisdiction, the mapped zoning district and the applicable dimensional standards.²¹¹⁴

1. Confirm sewer availability; if an individual system is needed, start state health review before fixing the house location.²²⁶

1. Submit the planning and zoning permit application through MGO Connect and ask for the current fee, plan and inspection checklist.²¹⁴

1. If supervising construction of your personal residence, ask Planning & Zoning for the required contractor-licensing exemption affidavit before permit issuance.¹⁰ The exemption generally allows 1 residence per year, measured from certificate-of-occupancy issuance, with exceptions for a change in legal marital status or an employment relocation exceeding 50 miles; health and life-safety codes still apply.¹⁰ A farmer building for agricultural purposes on owned or leased land may also have a contractor-licensing exemption, but it does not waive health or life-safety requirements.²³

1. Obtain a signed, numbered LaDOTD access permit before constructing a connection to a state highway.²⁴

1. Complete required building inspections and obtain final septic verification before occupancy.¹³¹⁸

What should you check before buying land in St. Mary Parish?

Check septic feasibility first: 0% of mapped parish soils rate as free of severe limitations for a conventional drain field, so an inexpensive parcel may need a costlier approved system.²⁰ Check flood status and elevation next; development in a regulatory floodway needs a no-rise certification before permitting under the statewide floodway standard, and ask Planning & Zoning to identify the local floodplain administrator and elevation requirements.²⁵¹⁴ Verify legal road access and determine whether a driveway meets a parish road or a state highway, because state-highway connections require LaDOTD approval.²⁴ If planning a well, Louisiana requires a licensed driller and state registration, with domestic wells following the applicable post-installation notification rule.¹¹ Finally, price insurance for the parcel: the typical annual premium is about $3,051, while the effective property-tax rate is about 0.4% and the median annual bill is about $515.²⁶²⁷²⁸

Watch-outs

• St. Mary Parish’s MGO Connect link does not establish which projects require building permits or provide the full fee, review and inspection procedure; request the checklist from Planning & Zoning.²
• A state septic permit is required before installing, altering or operating an individual sewerage system, and parish soils commonly pose severe conventional-drain-field limitations.⁶²⁰
• Private-land RV and tiny-home occupancy rules remain unconfirmed; ask Planning & Zoning for a written parcel-specific answer.¹⁴

Sources

1. St. Mary Parish Planning & Zoning Department (2026 county census)
2. Planning & Zoning Department - St. Mary Parish Government, quoted and re-checked
3. Unified Development Ordinance, quoted and re-checked
4. RS 40:5. General powers and jurisdiction, quoted and re-checked
5. Onsite Wastewater Program, quoted and re-checked
6. Louisiana Administrative Code Title 51, Part XIII, Public Health—Sanitary Code (Louisiana statewide rule), quoted and re-checked
7. Unified Development Ordinance (2026 county census)
8. RS 33:4721 — Regulation of size and use of buildings (Louisiana statewide rule), quoted and re-checked
9. RS 33:4721 — Regulation of size and use of buildings (Louisiana statewide rule), quoted and re-checked
10. Louisiana Revised Statutes § 37:2157 — Exemptions, quoted and re-checked
11. Louisiana Administrative Code, Title 43, Part VI, §701 (Louisiana statewide rule), quoted and re-checked
12. RS 40:1730.28 - Louisiana State Legislature, quoted and re-checked
13. R.S. 40:1730.23 — Enforcement of building codes by municipalities and parishes, quoted and re-checked
14. St. Mary Parish Planning & Zoning Department (stmaryparishla.gov)
15. Morgan City: Code of Ordinances, Chapter 22, Sec. 22-32 - Building permit required by owner and contractor (St. Mary Parish), quoted and re-checked
16. Franklin: Sec. 14-1. - Building permit—Required (St. Mary Parish), quoted and re-checked
17. Patterson: Code of Ordinances, Chapter 24, Sec. 24-8—Historic district permits and mobile homes (St. Mary Parish), quoted and re-checked
18. Louisiana Administrative Code Title 51, Part XIII, Public Health—Sanitary Code (Louisiana statewide rule), quoted and re-checked
19. St. Mary Parish Health Unit (ldh.la.gov)
20. Share of soils USDA rates "not limited" for a conventional septic drain field (SSURGO). A strict rating: the median county is about 6% and a tenth of counties are 0%, so a low figure means most lots need a site evaluation or an engineered system, not that septic is impossible. Cite it only with that caveat: Bolthole Index county data
21. Unified Development Ordinance, quoted and re-checked
22. Louisiana Administrative Code Title 51, Part XIII, Public Health—Sanitary Code (Louisiana statewide rule), quoted and re-checked
23. R.S. 37:2157 — Exemptions, quoted and re-checked
24. LaDOTD Access Connections Policy (Louisiana statewide rule), quoted and re-checked
25. State of Louisiana No Rise Certification Guidance (Louisiana statewide rule), quoted and re-checked
26. Typical home insurance premium: Bolthole Index county data
27. Effective property tax rate: Bolthole Index county data
28. Median property tax bill: Bolthole Index county data

Written October 11, 2026 from the rules quoted below, each taken from an official source and re-checked by an independent reviewer. This is research, not legal advice: rules change, so confirm with the office before you buy or build.