The Massachusetts State Building Code (780 CMR 9th Edition) provides two main design methodologies for public parking garages, either “open” or “enclosed”. Developers and design teams can capitalize on several advantages when designing parking garages as an “open parking structure” versus an “enclosed parking structure”, with the most prevalent being the cost savings associated with the omission of mechanical ventilation & sprinkler systems. These advantages, along with several other notable ones, are further detailed below:
- Sprinkler System Omission: In general, where open parking garages are constructed as standalone structures or separated from other portions of mixed-used development by a firewall (i.e. Texas Wrap Configuration), sprinkler protection of the parking garage is not required when meeting the openness criteria in 780 CMR Section 406.5.2 and Mass General Law Section 26G.
- Height and Area Increases: Significant increases in the allowable height and area are permitted for single-use open parking garages. This in turn allows for less restrictive construction types and reduction in the required fire-resistance rating of building elements.
- Fire Separation Distance: Open parking garages having a fire separation distance of 10 feet or more are permitted to have unlimited unprotected openings, regardless of its construction type (780 CMR Table 602 Note C).
- Exit Stair Openness: Stairways serving open parking garages are not required to be enclosed in fire-resistance rated shaft construction (780 CMR 406.5.9, 1019.3(6)). Even though stairways are not required to be enclosed, the exit access travel distance from each tier is permitted to terminate at the closet riser of the stair (780 CMR 1017.3(1)).
- Mechanical System Omission: Mechanical exhaust or supply duct systems serving only open parking garages are not required to be enclosed in fire-resistance rated construction (780 CMR 712.1.10.3).
To utilize the above advantages, there are certain fire protection and life safety considerations that architects, owners, and developers should be aware of when designing open parking garages in accordance with 780 CMR Section 406.5:
- Single use: In order to apply the height and area increases for open parking garages (in lieu of the normal height and area limits in IBC chapter 5), the structure must be used exclusively for the parking or storage of private motor vehicles. No other uses in the building are permitted with the exception to offices, waiting rooms, and toilet facilities having a combined area of 1,000 sf at the grade level tier.
- Omission of Automatic Sprinkler System: Below are critical design features to note where sprinkler systems are omitted from the open parking garage:
- Mass General Law Section 26G requires non-sprinklered open parking garages to have a net free area of at least 25% of the total perimeter wall area of each tier, a 5% increase from the base provisions in the IBC.
- Stairways serving as a required accessible means of egress must have a minimum 48” minimum clear width between handrails (780 CMR 1009.3).
- Fire department vehicle access roads must be designed to extend within 150 feet of all portions of the exterior wall on the first story. This distance is increased to 250 feet for fully sprinklered buildings (527 CMR 18.2.3.2.2).
- Decorative Screens: The net free area of openings must be utilized for the purposes of achieving natural ventilation. As decorative screens have become desirable and popular for covering openings of parking garages, the resulting impact to the garage’s natural ventilation openings must be considered, to ensure that the new effective free area remains above the required percentage.
There are certainly several cost benefits of designing public parking garages as “open” versus “enclosed”, however, it is critical for developers and design teams to consider all building and fire protection design features associated with the advantages of open parking garages in order to maintain compliance with 780 CMR and Mass General Law.
If you have questions on open parking garage features, please reach out to our office at info@crcfire.com to find out how we can assist.