Charles County, MD Building Safety: Fire Sprinkler Requirements (2026)

1 to apply the same NFPA 13D design-and-installation standard to one- and two-family dwellings. 2 exception governing additions and alterations to existing buildings that were never sprinklered: no automatic sprinkler retrofit is required unless the addition increases the existing square footage by more than 50%, or the alteration touches more than 70% of the existing square footage. The code counts an entire room as 'added or altered' once more than half of its total linear framing length is new, removed, or replaced, and totals every added or altered room's square footage toward those 50%/70% thresholds.

Cross the threshold, and the whole structure is reviewed and inspected as if it were new construction, with an automatic fire suppression system retrofitted throughout, not just in the new portion.