If you’re buying a house in Nampa with a mother-in-law suite for your parents and you’re worried it won’t count as a legal ADU, this is what you do

If you’re buying a house in Nampa with a mother-in-law suite for your parents, that suite only counts as an ADU under Idaho’s new law if it has its own kitchen, bathroom and sleeping space. So step one is checking for a real kitchen. I’ll be honest, for years I called every basement bedroom with a mini fridge an “apartment.” Then the new statute politely corrected me, so let’s walk through what it actually says before you write an offer.

Does Idaho’s new ADU law apply in Nampa?

Yes, Idaho’s new ADU law applies in Nampa, because Senate Bill 1354 covers cities with more than 10,000 people. The U.S. Census Bureau counted 100,200 Nampa residents in 2020. Its estimate for July 2025 is 120,384, so Nampa clears the line on either count.

The law took effect July 1, 2026. However, cities have until February 1, 2027 to rewrite their own codes to match it. So we’re in an in-between stretch right now.

That’s why I’d call the City of Nampa before you count on anything. Nampa’s residential permits page already lists accessory dwelling units among the projects that need a permit. What I’d ask them is how they’re handling ADU applications until the new code is adopted.

Is a mother-in-law suite the same as an ADU under the new Idaho law?

A mother-in-law suite is only an ADU under the new Idaho law if it has its own cooking, sleeping and sanitation facilities. That’s the exact test in SB 1354. It defines an ADU as a self-contained living unit on the same lot as a single-family home.

So a bedroom and bathroom with a separate entrance is a nice setup. Still, without a kitchen, the statute doesn’t treat it as an ADU. So the protections in the law don’t attach to it.

This matters more than it sounds. The ADU protections stop a city from capping the size too small, requiring extra parking, or charging bigger fees. The same bill also keeps an HOA from enforcing a covenant that limits ADUs. A kitchenless suite gets none of that.

What do I do first when I find a Nampa house with a suite?

Check the suite for a real kitchen first, then verify permits, inspect it like a second house, and call your lender. None of it takes long in this order.

1. Check for a real kitchen. Look for cooking facilities, a bathroom and a place to sleep in the suite itself. Snap photos, because you’ll want them for step two.
2. Ask the seller for permits. If the seller says the suite was permitted, verify it with the City of Nampa. A kitchen added without a permit is a problem you’d be buying.
3. Put the suite in your inspection. Ask your inspector to treat it like a second little house. Then the stove circuit, plumbing and egress windows get a real look.
4. Call your lender early. If your parents will be on the loan, the rules change based on where they’ll live. Have that conversation before you write an offer.

What if I want to add a kitchen or build a detached ADU later?

If you want to add a kitchen or build a detached ADU later, SB 1354 gives you a lot of room. The floor it sets is one internal ADU or one detached ADU per lot. A city can choose to allow both, but it doesn’t have to.

As far as size goes, a city can’t cap an ADU below 1,000 square feet or 75% of the house. The law also bars an owner-occupancy requirement. Additionally, cities can’t require off-street or guest parking, although the law lists a few exceptions.

Fees are covered too. A city can’t charge higher impact or utility connection fees on an ADU than on a single-family home. Even so, “allowed by state law” and “approved by the city” are two different steps. I’d still get the city’s answer in writing before you pour a foundation.

Can I count my parents’ income to qualify for a bigger house in Idaho?

You can usually count your parents’ income to qualify for a bigger house in Idaho. The rules depend on whether they’ll live in the home. If they’re moving into the suite, they’re occupying borrowers, and a lender generally treats their income like yours (your lender makes the final call).

If they’re co-signing but living somewhere else, they’re non-occupant borrowers. Fannie Mae allows that income on a primary home. However, it caps the loan at 95% of the value through its automated system. On a manually underwritten loan, the cap is 90%.

There’s one more wrinkle on manual loans. Fannie Mae limits you to a 43% debt-to-income ratio using only the occupying borrower’s income. FHA is more generous with family. HUD’s FHA handbook allows up to 96.5% of the value on a one-unit home when the non-occupying co-borrower is a family member. Your lender will know which one fits.

How does a suite compare to a true ADU?

A suite and a true ADU can look the same on a tour, but the law treats them very differently. Here’s the side-by-side, based on the text of SB 1354.

	Suite with no kitchen	Internal ADU	Detached ADU
Counts as an ADU under SB 1354	No	Yes	Yes
Size protected to 1,000 sq ft or 75%	No	Yes	Yes
HOA can enforce a covenant limiting it	Check your CC&Rs	No	No
Can pair with a second ADU on the lot	n/a	Only if the city allows it	Only if the city allows it

The row I’d pay the most attention to is the HOA one. If a subdivision’s CC&Rs limit ADUs, the new law says the HOA can’t enforce that against a real ADU. The HOA can still set reasonable rules on design, size, height, setbacks and parking, though, and the law leaves short-term rentals of 30 days or less out of it. There’s no Idaho court ruling testing any of it yet, so I’d treat it as strong but new.

What does buying in Nampa look like right now?

Buying in Nampa right now means working in a market where asking prices have eased a little since spring. Realtor.com housing inventory data, via the Federal Reserve Bank of St. Louis, puts the median asking price in Canyon County at $500,000 in August 2026. That’s down from $514,470 in April.

Keep in mind that’s the asking price, so sale prices can land on either side of it. For context, the Census Bureau’s 2020 to 2024 survey puts the median value of owner-occupied homes in Nampa at $370,800.

Houses with a suite or detached unit don’t come up every week. When one does, knowing the law lets you move fast.

A home is shelter first, and that goes double when two generations are sharing it. If you want a hand checking a suite against the law, let me know.

Garrett with Living in Idaho at LPT Realty.

Updated September 2026