Renting Out Your San Diego ADU: 2026 Rent Cap Rules

If you are building an ADU partly for the rental income, there is a set of rules that almost never comes up during design and permitting — and then lands in your lap the week you list the unit. California's statewide rent cap and just-cause eviction law, the Tenant Protection Act, sets limits on how much you can raise rent and when you can end a tenancy.

A new cap year started on August 1, 2026. Here is the number that applies in San Diego County, why a brand-new ADU usually sits outside these rules for years, and the one exemption that catches ADU owners off guard.

The 2026 number: 8.2% in the San Diego area

Under the Tenant Protection Act, annual rent increases on covered housing are capped at 5% plus the regional change in the cost of living, or 10%, whichever is lower. The cost-of-living piece comes from April Consumer Price Index data for your metro area, so the ceiling moves every year and differs by region.

For increases taking effect between August 1, 2026 and July 31, 2027, the maximum allowable increase in the San Diego area is 8.2%, according to the California Attorney General's rent cap resources.

Two other details in the statute matter as much as the percentage:

• The cap is measured against the lowest gross rent charged in the previous 12 months — not against a rate you briefly posted and then discounted.
• You may not raise rent on the same tenants more than twice in any 12-month period, and the two increases together still cannot exceed the cap.

Why a brand-new ADU usually sits outside these rules

Here is the part most homeowners are relieved to learn. California Civil Code section 1947.12 exempts housing that has been issued a certificate of occupancy within the previous 15 years from the rent cap. The just-cause eviction statute carries a matching 15-year exemption.

So if your detached ADU finals in 2026, it generally falls outside both the rent cap and the just-cause requirements until roughly 2041. That is not a loophole — it is the Legislature's deliberate choice to avoid discouraging new construction.

A few honest caveats, because this is where general guidance stops being useful:

• The exemption rolls off. Fifteen years is a long time, but it ends. Underwrite the unit as a long-term asset, not on the assumption that unlimited increases last forever.
• For a conversion — a garage or an interior space turned into a JADU — it is worth confirming with your jurisdiction exactly what document was issued and what date it carries. Whether the clock runs from the new unit's approval is a real question, not a formality.
• Some cities layer their own tenant-protection ordinances on top of state law, with their own definitions and their own exemptions.

The exemption that trips up ADU owners

There is a well-known carve-out in the rent cap statute for a two-unit structure where the owner lives in one unit as their principal residence. Plenty of homeowners hear "owner-occupied duplex" and assume a house-plus-ADU obviously qualifies.

It does not. Section 1947.12 spells out that the owner-occupied two-unit exemption applies only when neither unit is an accessory dwelling unit or a junior accessory dwelling unit. The Legislature wrote ADUs out of that specific exemption on purpose.

This is exactly why the 15-year new-construction exemption is the one that actually does the work for most ADU owners — and why it is worth knowing which exemption you are relying on, rather than assuming one applies because the unit sits in your own backyard.

State law is also only the floor. If you are in a jurisdiction with its own tenant-protection ordinance, check that ordinance too. The Attorney General's landlord-tenant resource page is a good, neutral starting point, and none of this is a substitute for a conversation with a real estate attorney about your specific property.

What to do before your first tenant moves in

None of this requires a law degree. It requires a little bookkeeping at the right moment.

Save the document that proves your date

Your certificate of occupancy or final inspection card is the single piece of paper that establishes your 15-year window. Scan it, date it, and file it with your closeout documents the week you receive it — not three years later when a tenant asks a question. If you are working through our process, this belongs in your project closeout package alongside warranties and as-builts.

Get the lease language right from day one

Several exemptions under the Tenant Protection Act are conditioned on giving the tenant written notice that the property is exempt, in language the statute specifies, included in the rental agreement. An exemption you qualify for but never disclosed properly is worth much less than one you documented at signing. Have a local attorney or a qualified property manager review your lease template once, before the first tenancy — it is inexpensive insurance.

Write down your baseline rent

Because the cap is measured against the lowest rent charged in the prior 12 months, keep a simple record of what was actually charged each month, including any concessions or discounted periods. When the exemption eventually expires, that history becomes your starting point.

Underwrite the rent, not just the build

The reason we raise this during planning rather than at handoff is that it changes how you should model the unit. An ADU that pencils only if rent climbs aggressively every year is a different investment than one that works at a steady, modest increase. If you are weighing loan options or a HELOC against projected rent, our notes on financing an ADU are worth reading alongside this — and looking through completed projects will give you a more grounded sense of what unit sizes actually rent for in North County.

As a construction management agency, our job is to make sure you are not surprised by anything, including the parts that arrive after the final inspection. The rules above are not obstacles. They are facts about the asset you are building, and they are much easier to plan around than to react to.

If you are thinking through an ADU in Carlsbad or anywhere in San Diego County and want a clear-eyed read on what your lot can support and what it would realistically cost, book a free site walk. We will look at the property together, talk through the numbers honestly, and you will leave with a plan whether or not you build with us.