Concord unpermitted improvements: the decision you make before closing
Concord unpermitted improvements on a duplex you’re buying create a fork in the road: legalize them now, or close with them as-is and sort it out later. The wrong call doesn’t just affect your inspection report—it changes what rent you can legally charge, what you can claim as base rent, and whether the city ever asks you to tear the work out. This is a local question, and the answer lives in Concord’s rent ordinance and building code, not in generic California advice.
Why this is harder than a standard inspection item
Most buyers treat unpermitted work as a repair credit conversation: get a quote, ask the seller to knock something off the price, move on. But on a Concord duplex, the unpermitted square footage or fixture sits inside a regulated rent structure. The ordinance ties allowable rent increases to the lawful base rent—and unpermitted improvements are generally not lawful. So the question isn’t just “does the deck meet code?” It’s “can I ever include that deck’s value in the rent I charge?”
People get this backwards in two ways. Some assume the city will never find out, so they close and keep the rent as-is. Others assume they can legalize everything later and raise the rent to match. Both are risky. Concord’s rental housing program has a process for verifying rent history and base rent, and unpermitted work can surface during a tenant petition or a city inspection. If the work was done without permits, the city can require you to bring it up to current code—or remove it. That cost lands on you, after closing, with a tenant already in place.
A genuine partial answer: what to check before you decide
Start with the city’s permit history for the property. Concord’s building division can tell you what was permitted and what wasn’t, usually for a small records fee. Pull the file for the duplex and compare it to what’s actually there: the extra bathroom, the converted garage, the finished basement, the second kitchen. Anything not in the file is unpermitted until proven otherwise.
Then check the rent ordinance’s treatment of improvements. Concord’s ordinance allows rent increases for certain capital improvements, but only if the work was done with permits and after the base rent was set. Unpermitted work done before you bought the property doesn’t qualify. That means you can’t add the value of that unpermitted ADU or extra bedroom to your rent roll—at least not until it’s legalized, and even then, the ordinance may treat the legalization date as the start of the improvement’s rent value, not the original construction date. This is the part that surprises buyers: legalizing the work doesn’t retroactively make it rent-worthy. You may be able to raise rent going forward, but you can’t recover the years of rent you think the seller was charging illegally.
For a duplex specifically, check whether the unit is subject to the ordinance at all. Concord’s ordinance has exemptions for owner-occupied duplexes, single-family homes, and certain other properties. If your duplex qualifies for an exemption, the rent calculation rules may not apply the same way—but the building code still does. Unpermitted work is still a code violation, and the city can still make you fix it. The exemption only changes the rent side, not the permit side. We covered the exemption details in Concord Duplex Owner-Occupied Exemption: Does It Apply? and the broader ordinance in Concord Rent Ordinance Due Diligence.
What legalizing actually involves—and what it costs you
Legalizing unpermitted work means pulling a permit now, for work that was done years ago. The city will inspect it against current code, not the code from when it was built. That’s the expensive part: a deck built in 2005 without permits may not meet today’s railing height or footing depth. A converted garage may need insulation, egress windows, or a separate electrical panel. You pay for the permit, the inspection, and whatever corrections the inspector requires. Sometimes the correction is minor; sometimes it’s a tear-out and rebuild.
You also need to consider the seller’s position. If you ask the seller to legalize before closing, you’re asking them to spend money and open their property to city inspection—something many sellers refuse. If you close with the work unpermitted, you inherit the liability and the timeline. The city won’t necessarily come looking, but if a tenant complains, or you apply for a different permit, or you try to refinance and the appraiser notes the unpermitted square footage, the issue surfaces. Then you’re fixing it on your schedule, with a tenant in place, possibly paying relocation costs if the work requires vacating the unit.
There’s a third path: close with the work unpermitted, but price it in. Get a contractor’s estimate for legalization, add a buffer for code corrections, and subtract that from your offer—or hold it in reserve. Then decide after closing whether to legalize immediately or wait. The risk with waiting is that the cost only goes up, and the rent ordinance doesn’t reward you for patience. The risk with doing it immediately is that you’re spending cash before the property cash-flows. Neither is wrong; it depends on your reserves and your tolerance for city involvement.
How the rent roll changes under the ordinance
Here’s the part most buyers miss: the rent you can charge after closing isn’t just the rent the seller was charging. Concord’s ordinance caps rent increases based on the lawful base rent, and unpermitted improvements don’t count toward that base. If the seller was charging rent that included the value of an unpermitted ADU, that rent may be unlawful. When you take over, you inherit that rent—but you also inherit the tenant’s right to petition for a rent reduction if the base rent was improperly calculated. That’s a real risk: a tenant who discovers the unpermitted work could file a petition, and the city could order you to reduce the rent and refund overcharges. The refund could go back years, depending on the ordinance’s lookback period. We walk through how to verify rent history before you set your numbers in Concord Rent History Verification Before Setting Base Rent.
If you do legalize the work, you may be able to apply for a rent increase based on the capital improvement—but only for the cost of legalization, not the original construction. And the increase is amortized over the ordinance’s schedule, which varies. The point is: legalizing doesn’t unlock the full market rent you imagined. It unlocks a lawful rent increase, which is often smaller than the gap between what the seller charged and what the unit would rent for on the open market. That gap is the cost of doing business in a rent-controlled city.
How we walk you through it
When a buyer brings us a Concord duplex with unpermitted improvements, we start with the permit file and the rent history—both pulled directly from the city. We map what’s unpermitted against what’s rent-relevant, and we build a simple decision tree: legalize now, legalize later, or price it in and close. We don’t guess. We check the current ordinance text for the specific unit type, because Concord’s rules differ for duplexes, single-family homes, and owner-occupied properties. We also look at the seller’s disclosure package: what did they admit to, and what did they omit? That changes the negotiation.
Then we run the numbers. What’s the cost to legalize, including a buffer for code corrections? What rent can you lawfully charge today, and what could you charge after legalization? How long until the legalization cost pays for itself in rent increases? If the numbers don’t work, we tell you. Sometimes the right move is to walk away, or to buy at a price that reflects the liability. Other times the unpermitted work is minor—a water heater or a small deck—and the fix is cheap and fast. The point is to decide before closing, not after, when your leverage is gone.
Our real estate services include this kind of pre-closing due diligence, and we can coordinate the permit history pull, the contractor estimates, and the rent ordinance analysis in one pass. If you’re already under contract, we can still help you renegotiate or plan the post-closing work. The earlier you bring us in, the more options you have.
What would you do with an unpermitted ADU?
If you found a Concord duplex with an unpermitted ADU that’s already rented, would you legalize it before closing, or close and deal with it later? What would tip your decision—the cost, the rent roll, or the risk of a tenant petition? Tell us in the comments, or reach out directly if you’re looking at a specific property.
About this article. This is general information and our own opinion, written from how we run operations for owners and businesses in Contra Costa County. It is not legal, tax, accounting, financial or other professional advice, it is not a recommendation to take or avoid any action, and it is not a substitute for advice about your own property, tenancy or business. CAO Investment Group is not a law firm, and reading this does not create an attorney-client or any other professional relationship. Local ordinances, fee schedules, forms, thresholds and deadlines change often and differ from city to city within Contra Costa County — anything here may be out of date by the time you read it, including as of the publication date shown above. Verify anything you plan to rely on against the current rules published by your own city or county, and speak to a qualified attorney, CPA or licensed professional about your specific situation before you act. We make no warranty that this information is current, complete or accurate, and we accept no liability for any action taken or not taken on the basis of it.
