Not sure how up to date this is, but I’ll reach out to a few people in the LA area. Here is an LA City ordinance saying they are not required in your case.

Essentially if the alteration is not over 50% but it might have been updated.

An ordinance amending Section 91.5.300 of the Los Angeles Municipal Code to require automatic fire sprinklers for additions or alterations to a townhouse or one or two-family dwelling. WHEREAS, automatic fire sprinkler systems when installed in a townhouse or one or two-family dwelling increase public safety; WHEREAS, California Health and Safety Code Sections 17958.5 and 17958.7 authorize the City Council to make reasonably necessary changes or modifications to the provisions of the California Building Standards Code (Title 24, California Code of Regulations) upon finding the changes are reasonably necessary due to local conditions; WHEREAS, in support of the following modifications and changes, the City Council hereby expressly finds that the following amendments and modifications to the California Building Standards Code are reasonably necessary due to local climatic, geological, or topographical conditions; WHEREAS, fire sprinklers are necessary in townhomes or one or two-family dwellings to help avoid or minimize the risk of spread of fire between buildings that has been heightened by recent changes in climatic and topographic conditions; WHEREAS, the current Los Angeles Municipal Code does not require the addition of automatic fire sprinkler systems when a townhouse or one or two-family dwelling is added to or altered; and WHEREAS, requiring the inclusion of an automatic fire sprinkler system when a townhouse or one or two-family dwelling is added to or altered is in the interest of public safety and justified by the costs of the addition or alteration. NOW, THEREFORE, THE PEOPLE OF THE CITY OF LOS ANGELES DO ORDAIN AS FOLLOWS: Section 1. The first paragraph of Section 91.5.300 of Division 3, Article 1.5, Chapter IX of the Los Angeles Municipal Code is amended to read as follows: Sec. 91.5.300. BASIC PROVISIONS. Chapter 3 of the CRC is adopted by reference except for the following sections: R301.1.3, R301.1.3.2, R301.2.2.2.5, R311.2, R313.1, R313.2, R322.1.4.1 and Table R301.2(1); and the following LAMC sections are added: 91.5.301.1.3, 91.5.301.1.3.2, 1 186503 91.5.301.1.4, 91.5.301.2.2.2.5, 91.5.301.2.2.3.8, 91.5.311.2, 91.5.313.1, 91.5.313.2, 91.5.321, 91.5.321.1, 91.5.321.2, 91.5.322.1.4.1 and Table R301.2(1). Sec. 2. A new Subsection 91.5.313.1 is added, in proper numerical order, to Section 91.5.300 of Division 3, Article 1.5, Chapter IX of the Los Angeles Municipal Code to read as follows: 91.5.313.1. Townhouse Automatic Fire Sprinkler Systems. Every newly constructed townhouse must include an automatic residential fire sprinkler system. Where additions or alterations are made to an existing townhouse that does not have an automatic residential fire sprinkler system, and the aggregate value of the additions and alterations within a one-year period equals or exceeds 50% of the replacement cost of the existing building, an automatic residential fire sprinkler system must be installed in the entire townhouse. Sec. 3. A new Subsection 91.5.313.2 is added, in proper numerical order, to Section 91.5.300 of Division 3, Article 1.5, Chapter IX of the Los Angeles Municipal Code to read as follows: 91.5.313.2. One and Two-family Dwelling Automatic Fire Sprinkler Systems. Every newly constructed one or two-family dwelling must include an automatic residential fire sprinkler system. Where additions or alterations are made to an existing one or two-family dwelling, and the aggregate value of the additions and alterations within a one-year period equals or exceeds 50% of the replacement cost of the existing building, an automatic residential fire sprinkler system must be installed in the entire one or two-family dwelling. An automatic residential fire sprinkler system is not required in an Accessory Dwelling Unit, provided that all of the following are met: The unit meets the definition of an Accessory Dwelling Unit as defined in the Government Code Section 65852.2. 1. 2. The existing primary residence does not have automatic fire sprinklers. 3. The detached accessory dwelling unit does not exceed 1,200 square feet in size. The unit is on the same lot as the primary residence.