ADU fire sprinkler requirement in Howard County: what CB 3-2026 changed and what a detached unit needs.

Until this spring a Howard County homeowner could put an apartment inside the house and nowhere else. Council Bill 3-2026 changed that on April 8, 2026. A detached cottage behind a Clarksville colonial, an apartment over a new garage in Ellicott City, a converted barn in Glenwood, all of them are now a zoning question with a yes available. The call we get the week after the zoning yes is the sprinkler question, and in Howard County the answer is short. A detached ADU is a new house to the building code, and a new house in Maryland gets a 13D sprinkler system.

What Howard County allows now

CB 3-2026, filed as zoning regulation amendment ZRA-218, was signed February 6, 2026 and took effect April 8, 2026. It allows one ADU on a lot with a single family house in the residential districts, and the unit can be attached, detached or carved out of the existing house. The size cap is 75 percent of the main house’s footprint, the state number. Two bedrooms at most. The owner has to live in one of the two units. A permit is required for every one, which is the part that brings the building code and the sprinkler rule into the picture.

The county held a webinar on the bill and published the questions. Question 18 asked whether an ADU has to be sprinklered when the existing house is not. The county’s answer was that the building code regulates sprinklers and the bill does not change the building code. That is the right answer, and it is why the rest of this page is about the code, not the zoning.

Does a detached ADU need fire sprinklers in Howard County

Yes. The residential code Maryland adopts requires an automatic sprinkler system in every new one and two family dwelling, and state law, Public Safety Article section 12-504, bars a county from weakening that provision. Howard could not exempt a backyard cottage if it wanted to. A detached ADU is a new dwelling on its own foundation, so it gets a full NFPA 13D system, permitted and inspected the same way a new house in Maple Lawn does. Our statewide ADU guide lays out the three situations; this page is the Howard version of the first one.

The exception people hear about is real but narrow. The code does not require sprinklers for additions or alterations to an existing building that has none. A basement apartment in a 1988 house in Columbia, or a garage conversion that stays attached, is an alteration, and the house stays unsprinklered. Put the same apartment in a separate building and the exception is gone. If the house already has sprinklers, the new unit inside it gets heads too; our home additions guide covers the 50 percent addition test Howard applies to large attached work.

What a 13D system looks like on a small detached unit

A 600 to 1,000 square foot cottage carries six to ten heads, one riser with a control valve and a drain, and a short run of CPVC pipe in the ceiling. Bathrooms under 55 square feet, closets and a garage bay with nothing living above it can be left out under the standard. Every head is a listed residential head with a cover plate or a sidewall head where the ceiling is tight. The system has to run its two design heads for seven minutes on a one story unit under 2,000 square feet, which is the number that sizes the water supply, and the water supply is where a Howard ADU gets interesting.

Public water in the east, a well in the west

East of Route 29, Columbia, Elkridge, Ellicott City and the Route 1 corridor sit on public water. The ADU ties into the house service or gets its own tap, and the first thing we do is a flow test at the street, because a long run of three quarter inch pipe to the back of a deep lot can lose enough pressure to change the head layout. On most lots the house line carries it. On some the water meter has to grow, and that is a utility conversation we have before design, not after.

West of 29, Clarksville, Glenwood, Dayton, Glenelg and Woodbine are wells. The house pressure tank will not carry a sprinkler system, so the ADU gets its own stored water, a 300 gallon tank and a booster pump in conditioned space near where the well line comes in. That package is its own line on the quote, and it is the line that moves a western ADU out of the simple end of the range. Our well water guide covers tank sizing; the short version is that a photo of the pressure tank gauge and the pump tag tells us most of what we need.

The permit path through DILP

Zoning comes first. The ADU approval under CB 3-2026 is a zoning use, and nothing in the building permit moves until it is in hand. Then the building permit files with the Department of Inspections, Licenses and Permits in Ellicott City, and the sprinkler drawings and hydraulic calculations file with it under a Maryland State Fire Marshal fire protection license. Western lots add the tank and pump to the first plan set. Rough in happens with the framing inspection and includes a pressure test on the pipe. The final is an acceptance test with the inspector, and the certificate of occupancy for the ADU waits on it. Our Howard permit guide walks the six steps in order.

What it costs

A small detached ADU is priced like new construction, and the fixed pieces of the system, the riser, the valve, the permit and two inspections, are a bigger share of the bill on 800 square feet than on 3,000. Expect the top of our published new construction range per sprinklered square foot. A western well lot adds the tank and pump package. Both numbers are on our cost page, and our Howard County cost article shows how the two halves of the county differ. We quote each ADU from the plans, and the quote holds.

When to call us

The day the plan set exists and before the water line is sized. A builder who lays out the ADU without the sprinkler supply ends up moving the tank after the slab is poured or upsizing a line that was already trenched. Send the zoning approval, the plans and, on a well, the gauge and pump tag photos. We tell you which supply you are on, flow test if it is public, and send a number before you commit to a builder. If the unit is a garage with an apartment above it, read our detached garage guide first; the bay below can stay dry while the apartment above gets heads.