You signed the lease. The landlord handed over keys to a space that's been empty for eight months, your rent commencement date is real, and you'd like to be open in ten weeks. Everything between here and there runs through the City of Naperville's permit desk.
Commercial tenants are usually surprised by two things. The first is that Naperville issues two different permits for moving into an existing space, and which one you need depends entirely on whether you're touching the building. The second is that the review clock doesn't start when you sign the lease — it starts when a complete, code-current drawing set lands in the City's portal, which is often weeks later than tenants assume.
Naperville Issues Two Commercial Permits — Know Which One You Need
Most municipalities lump this into one application. Naperville splits it, and the distinction matters because the two paths carry very different timelines.
A Tenant Build-Out Permit is issued for businesses that want to modify the interior or exterior of the building. That covers a new business taking a raw or dated space, a tenant change where the layout is being reworked, and an existing tenant remodeling in place. If you're moving walls, adding a demising partition, relocating plumbing, or reworking the electrical, this is your permit.
A Business Occupancy Permit is issued for a new business assuming a tenant space where no modification to the building is happening. It's also required when there's simply a change in business name or ownership — which catches a lot of people who buy an existing operation and assume nothing is owed to the City.
Worth knowing: minor cosmetic updates like painting and new carpeting do not require a permit on their own — though you may still owe a Business Occupancy Permit if you're a new business or the ownership changed.
The wrong assumption here is expensive in a specific way. Tenants who believe they're a "no permit needed" cosmetic refresh often discover mid-project that relocating a single outlet or adding a partition wall pushed them into build-out territory — and now they're applying with the crew already on site and the clock running on rent. That's the sequence we work to prevent on every tenant improvement project we take on.
Start With the Tuesday Morning Meeting
The City holds pre-application meetings for new businesses looking to occupy an existing commercial, retail, or industrial space. They run Tuesday mornings from 8:30 to 9:30 a.m. at the Naperville Municipal Center. Attendance isn't mandatory, but all businesses are encouraged to attend, and if you're new to this market it's the single highest-value hour you'll spend on the project.
Bring a completed Letter of Intent for Business Occupancies form. Questions about the meetings go to the TED Business Group at (630) 420-6100, Option 2.
What to actually ask while you're there:
- Is my use permitted in this zoning district as-of-right, or does it need relief?
- Does my scope trigger fire department or engineering review in addition to building?
- Is a change of use involved, and what does that pull in?
- What's the current expected review turnaround for a project my size?
- Which drawings does the City want sealed?
Ten minutes of answers here routinely saves two weeks of comment-and-resubmit later. Applications are filed through the City's online permitting portal, and the City has electronic submittal standards your drawing set has to conform to — worth confirming with your architect before the set goes out.
The Codes Changed on April 1, 2026
This is the detail most likely to generate plan review comments on a build-out set drawn from an older template.
Under Ordinance 26-010, passed by the City Council in February 2026, plans submitted on or after April 1, 2026 are reviewed against an updated code package: the 2024 International Building Code, 2024 International Existing Building Code, 2024 International Fire Code, 2024 International Mechanical Code, 2024 International Plumbing Code, 2024 International Fuel Gas Code, and 2024 International Property Maintenance Code, along with the 2023 National Electric Code and the 2018 Life Safety Code (NFPA 101). The current editions of the Illinois Accessibility Code, Illinois State Plumbing Code, and Illinois Energy Conservation Code apply on top of those.
For a tenant build-out, the two that bite hardest are the Existing Building Code and the accessibility requirements. The Existing Building Code governs how much of the rest of the space your alteration drags into compliance — a modest reconfiguration and a gut of the same suite land in very different places. Accessibility is the other: reworking a restroom, changing an entry, or reconfiguring circulation can trigger upgrades the tenant never budgeted for, and it's far cheaper to design them in than to receive them as a comment. If your space has an older restroom core or a stepped entry, get an ADA compliance read on it before you finalize the layout.
What Plan Review Actually Looks At
Depending on scope, a commercial submittal can pull building, zoning, engineering, and fire department review. On a typical office or retail build-out, expect scrutiny on:
- Occupancy classification and occupant load — this drives egress, restroom counts, and sprinkler requirements
- Egress — exit width, travel distance, door hardware, emergency and exit lighting
- Fire protection — sprinkler head relocation for the new ceiling grid and partitions, alarm device coverage, fire-rated assemblies at demising walls
- Accessibility — restrooms, door clearances, counter heights, routes through the suite
- Mechanical, electrical, plumbing — whether the existing rooftop unit and panel can serve the new layout at all
- Energy code — lighting power allowance, controls, envelope work where it applies
The scenario that quietly doubles a schedule is a change of use. Retail to restaurant, office to medical, warehouse to assembly — each one changes the occupancy classification, and with it the egress math, the restroom count, the ventilation, and often the sprinkler and fire alarm scope. Our Albatross Physical Therapy build-out in Naperville is a medical fit-out where clinical layout, equipment loads, and circulation all had to be resolved before drawings were worth submitting. The MRG commercial build-out, also in Naperville, carried a broadcast studio, boardroom, and full kitchen inside one office shell — three different sets of requirements in a single permit set.
Food Service Adds a Second, Separate Review
If you're opening a restaurant, café, bar, or anything else serving food in DuPage County, the City permit is only half of it. Food establishments go through a separate plan review with the DuPage County Health Department, which has its own submittal requirements and its own clock.
The plumbing schedule alone has to show the location and size of the hot water heater, fixtures, drains and floor sinks, waste water line connections, and the grease trap size and location. Grease interceptor sizing is set by the local sanitary district, with installation governed by the Illinois Plumbing Code — and the interceptor has to be genuinely accessible for maintenance, not tucked behind a three-compartment sink or other fixed equipment.
Run that review in parallel with the City submittal, not after it; tenants who sequence them lose a month for no reason. If you're planning a restaurant or hospitality build-out, the parallel path belongs in the schedule from day one.
How Long It Really Takes
The City is candid that review timeframes vary by complexity — its own guidance notes that a complex project such as a new single-family home may be reviewed within three to four weeks, while something simple like a fence or driveway may take less than a week. A commercial build-out set sits toward the complex end, and the honest variable isn't the first review. It's how many rounds of comments you generate. A clean set that anticipated the code package and the accessibility triggers can clear in one round; a set drawn without a pre-application conversation routinely takes two or three, and each round is dead time you're paying rent through.
On the construction side, inspections should be scheduled at least 72 hours in advance — the inspections line is (630) 420-6100, Option 1, and the department's hours are Monday through Friday, 9 a.m. to 4 p.m., closed 1 to 2 p.m. daily. That window sounds trivial until you're stacking rough-in inspections against a drywall crew that's already booked.
Our working rule for tenants: schedule backward from your rent commencement date, add the permit review, add the 72-hour inspection notices, add a comment round you hope you won't need — and if the number doesn't fit, negotiate the free-rent period before you sign, not after.
Budget: Where the TI Allowance Runs Out
Tenant improvement costs in this market vary by scope more than by square footage. A basic refresh — paint, carpet, lighting — might run $20–$35 per square foot. A full reconfiguration with new mechanical and custom finishes runs $60–$100+ per square foot.
The gap that catches tenants is between the landlord's allowance and the real number. An allowance is one of the most negotiable terms in a commercial lease — but it gets negotiated at letter-of-intent time, before anyone has priced the actual scope, which is exactly backwards. Getting a real estimate on the space before you finalize the lease is the only way to negotiate against a number instead of a hope.
The other budget risk is what's behind the walls: undersized electrical service, a rooftop unit at the end of its life, plumbing that isn't where the drawings say it is. We covered that category of surprise in our guide to the hidden costs of remodeling, and it applies at least as strongly to a twenty-year-old suite along the I-88 corridor as it does to a 1970s kitchen. If you're pricing an office build-out or a broader commercial interior renovation, a walkthrough before lease execution is cheap insurance.
Outside Naperville: DuPage, Will, and Kane
The two-permit structure described here is specific to Naperville. Every municipality in the western suburbs runs its own process, its own submittal standards, and its own review timeline — and they differ more than people expect across a fifteen-minute drive.
Aurora, Wheaton, Lisle, Downers Grove, Bolingbrook, Warrenville, and Woodridge each have their own commercial review track in DuPage County. Plainfield, Romeoville, and Joliet run through Will County jurisdictions. Geneva, Batavia, St. Charles, Oswego, and Montgomery sit in the Kane and Kendall County corridor — the City of Geneva Building Division can be reached at (630) 232-0032. Wherever your space is, call that municipality's building department before your architect starts drawing; that call is worth more than any general guide, including this one. For the residential side of the same question, our DuPage and Will County remodeling permit guide covers homeowner projects, and our Naperville service page lays out how we work in this market.
A Short Checklist Before You Sign
- Confirm your use is permitted in that zoning district — before the lease, not after
- Determine whether you need a Tenant Build-Out Permit, a Business Occupancy Permit, or both
- Attend a Tuesday pre-application meeting with a Letter of Intent form in hand
- Get a contractor's walkthrough and a real scope estimate before negotiating the TI allowance
- Check whether a change of use is involved — it changes everything downstream
- If food service is involved, start the DuPage County Health Department review in parallel
- Confirm the drawing set is being produced against the current code package
- Build permit review, comment rounds, and 72-hour inspection notice into the schedule
None of this is complicated. It's just sequential, and the sequence is unforgiving if you start it late. The tenants who open on time are almost always the ones who had the permit conversation before they had the keys.
Frequently Asked Questions
Do I need a permit if I'm only painting and putting in new carpet?
Not for the work itself — the City specifies that minor updates like painting and new carpeting do not require a permit. But if you're a new business assuming the space, or if there's been a change in business name or ownership, you still need a Business Occupancy Permit. And the moment the scope grows to include moving a wall, relocating plumbing, or reworking electrical, you're into Tenant Build-Out Permit territory.
What's the difference between a Tenant Build-Out Permit and a Business Occupancy Permit?
A Tenant Build-Out Permit is for businesses modifying the interior or exterior of the building — new tenants reworking a space, tenant changes, and existing tenants remodeling in place. A Business Occupancy Permit is for a new business taking over a tenant space without modifying the building, and is also required when the business name or ownership changes. Some projects need only one; some need both in sequence.
Does the April 2026 code update apply to my project?
If your plans were submitted on or after April 1, 2026, yes. Under Ordinance 26-010 the City reviews against the 2024 International Building, Existing Building, Fire, Mechanical, Plumbing, Fuel Gas and Property Maintenance codes, the 2023 National Electric Code, the 2018 Life Safety Code, and the current Illinois Accessibility, Plumbing and Energy codes. On tenant build-outs, the Existing Building Code and accessibility requirements generate the most comments — worth a conversation with your architect before the set is finalized.
Can we start demolition while the permit is still in review?
In some cases limited demo and site prep can proceed with landlord consent, but framing, electrical, and mechanical work cannot begin without permit approval. We start the permit process immediately after lease execution specifically to keep that gap as short as possible.
Do restaurants need anything beyond the City permit?
Yes. Food establishments in DuPage County go through a separate plan review with the DuPage County Health Department, with its own submittal requirements — including a plumbing schedule showing the hot water heater, fixtures, drains and floor sinks, waste line connections, and grease trap size and location. Grease interceptor sizing is determined by the local sanitary district under the Illinois Plumbing Code. Run it in parallel with the City review, not after.
Still have questions? Our remodeling FAQ page covers the broader set, or you can send us the details of your space and we'll tell you what the permit path looks like before you commit to a date.