Habitable Areas for Dwelling Units

As micro units and efficiency dwelling units become more prominent in architectural design, specific code requirements related to room size and minimum dimensions have become increasingly important. In Massachusetts, a few of these requirements come from 780 CMR, Massachusetts State Building Code, and 105 CMR 410.00 State Sanitation Code, which are used to establish the minimum required habitable area for dwelling units.

When sizing individual dwelling units, the following key code requirements must be used together to ensure that all necessary provisions are met:

Massachusetts State Building Code

  • All habitable spaces, other than a kitchen, must not be less than 7 feet in any plan dimension, §1208.1.
  • Every dwelling unit must have at least one room that is at least 120 square feet in net floor area. Furthermore, other habitable rooms are required to be at least 70 square feet in net floor area, §1208.1.

State Sanitation Code

  • Every dwelling unit shall contain at least 150 square feet of floor area for its first occupant, and at least 100 square feet for each additional occupant, which is calculated on the basis of total habitable room area (note that this applies to total area of the dwelling unit);
  • In a dwelling unit, every room occupied for sleeping by one occupant shall contain at least 70 square feet of floor area, and every room occupied by more than one occupant shall contain at least 50 square feet of floor space for each occupant (i.e. 70 square feet total for one occupant, 100 square feet total for two occupants);
  • In a rooming unit (i.e. dormitory), every room occupied for sleeping by one occupant shall contain at least 80 square feet of floor area, and every room occupied by more than one occupant shall contain at least 60 square feet of floor space for each occupant (i.e. 80 square feet total for one occupant, 120 square feet total for two occupants).

If you are considering a development that includes micro units or have any additional questions on this topic, send us an email at info@crcfire.com.