Table 601 - Type roof construction and fire rating

[Yikes]

Existing building in California with steel frame, and record drawings say Type 1A; it's a gov't-owned rec center with gymnasium. Roof beams are less than 20' above finish floor. Existing beams have spray-on fireproofing thickness that is currently equivalent to 1 hour. There is no fireproofing on the metal roof deck. Current table 601 says "roof construction and associated secondary members" require 1 1/2 hours fireproofing. I don't know what code required at time of original permit; all I know is that it was legally permitted, inspected and occupied.

Owner is proposing adding some rooftop HVAC units that require some new/additional secondary structural members for support; these will attach to other existing secondary or primary structural members. The new members themselves will be fireproofed to 90 minutes, but are now trying to determine if and where any additional fireproofing is required elsewhere on the existing building.

Questions:
1. In table 601, does the phrase "roof construction" also include the metal roof deck itself, or do they only mean the beams, purlins, etc. that support the decking?

2. Does the Calif. Existing Building Code allow us to just spray the new beam supports for the HVAC for 90 minutes, and leave the rest of the previously permitted structure, deck and fireproofing as-is, even though the existing is less than the 90-minute fireproofing rating required by current code?

 

[RLGA]

Are you sure it says "IA"? When was it built?

 

[Yikes]

The original was built in 1975, and the record drawings are missing the cover sheet that describes the building type. There is no C of O available from 1975.
There was an alteration done in 2016 by one of LA's mega-architecture/engineering firms whose expertise I would normally respect, and those alteration record drawings are calling it type 1A.

 

[RLGA]

This may have been built under the UBC originally (at least California's version of the UBC, and most likely the 1973 edition), and probably was classified as Type II (Noncombustible), which required 1-hour roofs. However, if the decking is above 25 feet, then protection of the roof (other than structural frame members) is not required but must be noncombustible. If the roof construction is between 18 and 25 feet, then the entire roof would have been required to have a ceiling of not less than 1-hour construction.

Either a ceiling was installed but removed later on, or they obtained some kind of waiver.

Starting in the 1985 UBC, this type of building would have allowed unprotected noncombustible roof construction if the building was sprinklered and the exposed area under 25 feet does not exceed more than 35% of the building's floor area.