Do I need a permit for a water heater replacement?

Not if it's a straight like-for-like replacement: same size tank, same fuel type, same location. If you're upgrading the capacity, switching from gas to electric, moving it to a new location, or installing a tankless system, you need a permit. Gas and electric connections both require inspection. The building department considers this a mechanical permit. Plan 2-3 weeks for approval.

What's the frost depth for St. Louis, and why does it matter?

St. Louis has a 30-inch frost depth. This means any post, footing, foundation, or below-grade structure must extend deeper than the frost line to prevent heave damage in winter. Deck footings, shed foundations, fence posts, and garage slabs all need to account for this. Most St. Louis builders use 36-inch footings to stay safely below the line. If your structure is south of the city limits, frost depth can vary — always check with the building department.

Can I file my permit application online?

No. St. Louis does not offer online permit filing as of this writing. You must go to the Building Department at City Hall in person to submit your application. The department has a permit portal for checking application status and paying fees online, but the initial filing requires an in-person visit. Bring two copies of your plans, completed application forms, and proof of property ownership. Allow 30-45 minutes for intake.

How much does a permit cost in St. Louis?

Fees are calculated as a percentage of the project's estimated cost, plus any inspection fees. A deck permit is typically $150-$400 depending on size. A fence permit is usually $75-$150. Electrical permits are $75-$200. Mechanical permits (HVAC, water heater) run $100-$300. Plan-check fees are included in most residential permits, so there's no surprise surcharge. The building department will quote you on intake.

What happens if I skip the permit and build without one?

St. Louis code enforcement conducts routine neighborhood inspections and responds to complaints. If caught, you'll be ordered to stop work, remove the structure, or bring it into compliance. The building department can fine you, and you may face legal action if damage occurs or work is unsafe. Unpermitted work can also become a problem when you sell: the inspector during the home inspection will flag it, and your buyer's lender may require either a permit application or removal. Getting a permit up front is always cheaper than dealing with the fallout later.

I'm on a corner lot and want to build a fence. What do I need to know?

Corner-lot sight triangles are enforced strictly in St. Louis. Your fence must stay outside the sight triangle formed by the intersection of your lot's property lines and the right-of-way. Front-yard fences are limited to 3.5 feet in height within the sight triangle. A fence that violates the triangle will be rejected, and you'll be asked to remove it. Before you apply, measure the sight triangle from the city's right-of-way and verify your fence placement. The building department will provide a site plan template with property lines and the sight triangle marked.

How long does plan review take?

Routine residential permits (fences, small decks, electrical work) are usually approved in 1-2 weeks. Complex projects (additions, remodels, new structures) take 3-4 weeks. The building department works Monday through Friday and processes applications in order received. If your plans are incomplete or don't comply with code, you'll receive a note with deficiencies and have to resubmit — this extends the timeline by 1-2 weeks. Submitting detailed, code-compliant plans the first time speeds up approval.

Can I pull my own permit as an owner-builder?

Yes, Missouri allows owner-builders to pull permits for work on owner-occupied property. You are responsible for ensuring the work meets all code requirements and passes inspection. The building department does not grant exceptions or waivers for owner-performed work — it must pass the same inspections and comply with the same codes as contractor work. Electrical and plumbing work must still be done by a licensed professional, even if you pull the permit yourself. If inspection fails, you're responsible for all corrective work.

Complete Guide to Building Permits in St Louis, MO (2026)

Do I need a permit in St. Louis, Missouri?

St. Louis enforces the 2015 International Building Code with state amendments. The City of St. Louis Building Department handles all residential permits — they're strict about code compliance and plan review, but they move quickly once plans are approved. Most homeowners underestimate how many projects need a permit here. A shed, a fence, a water heater replacement, a deck, or even a significant bathroom remodel — nearly all of these trigger a permit requirement. The good news: St. Louis allows owner-builders to pull permits for owner-occupied work, though the building department inspects closely. The frost depth is 30 inches, which matters for deck footings, shed foundations, and fence posts — you'll see that requirement show up across multiple project types. The city also sits in an area with mixed soil conditions: loess in the upland areas, alluvium near the river, and karst terrain to the south, which can affect foundation work and excavation. Knowing whether your specific project needs a permit saves money, avoids fines, and ensures your work passes inspection the first time.

What's specific to St. Louis permits

St. Louis has a reputation for thorough plan review and high inspection standards. The building department expects clear, detailed plans — not sketches. If you submit hand-drawn or incomplete plans, expect a rejection and a restart. The upside: once your plans pass review, inspections are straightforward and appointments are usually available within a week. Many jurisdictions rubber-stamp routine work; St. Louis measures twice.

The 30-inch frost depth is the baseline for any below-grade work. Deck footings must extend below 30 inches — most St. Louis decks are built with 36-inch footings to account for winter frost heave. Sheds, garages, and foundation work all follow the same rule. If you're working south of the city limits, where karst terrain becomes more prevalent, expect extra scrutiny on excavation and foundation work; the building department may require a geotechnical report for cuts deeper than a few feet.

St. Louis requires permits for most structural changes, mechanical upgrades (HVAC, water heater, plumbing beyond repair), electrical work, and fence-building. Many homeowners assume a water heater swap doesn't need a permit — wrong. An HVAC replacement triggering a permit surprises many too. The rule is simple: if it's not a like-for-like replacement in the exact same location with the exact same capacity, it needs a permit.

The city does not currently offer online permit filing, though they do maintain a permit portal for status checks and fee payment. You'll need to visit the Building Department in person to file your initial application and pick up approved permits. Plan 30 to 45 minutes for intake. The department is at City Hall; hours are Monday through Friday, 8 AM to 5 PM. Confirm phone numbers and hours by searching 'St. Louis MO building permit phone' — office hours and staffing change seasonally.

Corner-lot sight triangles are enforced strictly. If your property is on a corner, fences and walls have setback restrictions. This trips up more homeowners than any other rule. Before you dig a fence post, measure your sight triangle from the city's right-of-way. The building department will reject a fence permit if the structure violates the triangle, and you'll be asked to remove the fence at your own expense.

Most common St. Louis permit projects

These projects account for the majority of St. Louis residential permits. Each has its own filing requirements, timelines, and inspection checkpoints. Click through to the project guide to see what you'll need to prepare and what to expect from the department.

Decks

Any deck over 200 square feet or any deck more than 30 inches high requires a full structural permit. The 30-inch frost depth means footings must extend below grade; most St. Louis decks are built on concrete footings 36 inches deep. Railings, stairs, and ledger-board attachment details are inspected closely.

Fences

Fences over 4 feet in rear yards and over 3.5 feet in front yards need a permit. Masonry walls over 3 feet always require a permit. Corner-lot sight triangles are a common reason for rejection — measure before you file. Pool barriers require a separate inspection.

Electrical work

Any circuit addition, panel upgrade, EV charger installation, or hardwired appliance (including HVAC and water heater) requires an electrical permit and inspection. Owner-builders can pull the permit, but a licensed electrician must do the work or the inspection will be denied.

Room additions

Room additions, bedroom conversions, and bathroom remodels with structural or plumbing changes all require a full permit. Cosmetic remodels (paint, flooring, fixtures) do not. The building department draws the line at structural changes, new walls, or electrical/plumbing upgrades beyond minor repairs.

Do I need a building permit in St Louis, MO?