From your third paragraph I understand that as long as each individual conference room, break room, etc are less than 750 s.f. or 50 occupants, they are classify as B occupancy even though they all may be more than 10% of the floor area thus their occupant load would be calculated with 100 sf/occupant. Is this correct?
Not exactly. The function of the spaces are still what they are and the occupant load must still be determined by Table 1004.1.2. However, for occupancy group classification, which is different than "Function of Space" per Table 1004.1.2, it can be Group B or whatever occupancy group the space is located.
Now, with that said, some jurisdictions may allow the determination of a story's occupant load be based on the application of an occupant load factor for the entire gross floor area.
For example, let's assume an open office building includes a 675 sq. ft. conference room. The conference room has an occupant load of 45 based on 15sf/occupant (i.e. "assembly, unconcentrated") per Table 1004.1.2. The floor area of the entire open office story is 10,000 sq. ft.Subtracting the area for the conference room, the story has 9,325 sq. ft. of office area, which, at 100sf/occupant, is 93 occupants. Thus, technically, the occupant load of the story is 138 (i.e. 93 + 45 = 138). However, if the conference room is used solely by the occupants of the building, some jurisdictions will allow the occupant load of the story for story means of of egress be based on the gross floor (i.e. 10,000 sq. ft. / 100sf/occupant = 100 occupants). In either case, the occupant load of the conference room should be shown in the code data on the drawings to indicate that that the conference room is not a Group A-3 occupancy.
In this particular tenant improvement project, I have a space with offices, restrooms, conference room, break room server and warehouse. The 10% considered to determine the qualified accessory spaces, does it include all these spaces or just the office areas?
The 10% limitation applies to all occupancies considered accessory. If some occupancies are considered using the separated or nonseparated occupancy methods, then they are not considered accessory occupancies.
For example, if the 10,000 sq. ft. building has a 2,000 sq. ft. warehouse that is separated from the remaining 8,000 sq. ft. per Table 508.4, then the warehouse is not an accessory occupancy. So, if you have a 1,000 sq. ft. conference room, which is a group A-3 (occupant load exceeds 50 and is over 750 sq. ft.), it can be considered an accessory occupancy, because it does not exceed 10% of the story's floor area in which it is located (10% of 10,000 sq. ft. = 1,000 sq. ft.).
I hope this helps.