Code of Massachusetts Regulations
780 CMR - STATE BOARD OF BUILDING REGULATIONS AND STANDARDS
Chapter 7 - Fire and Smoke Protection Features
Section 705 - EXTERIOR WALLS
Subsection 705.3 - Buildings on the same lot
For the purposes of determining the required wall and opening protection and roof-covering requirements, buildings on the same lot shall be assumed to have an imaginary line between them.
Where a new building is to be erected on the same lot as an existing building, the location of the assumed imaginary line with relation to the existing building shall be such that the exterior wall and opening protection of the existing building meet the criteria as set forth in Sections 705.5 and 705.8.
Exception: Two or more buildings on the same lot shall either be regulated as separate buildings or shall be considered as portions of one building if the aggregate area of such buildings is within the limits specified in Chapter 5 for a single building. Where the buildings contain different occupancy groups or are of different types of construction, the area shall be that allowed for the most restrictive occupancy or construction.