The Two-Hour Wall That Was Supposed to Make Two Buildings
An owner of a single-story, 58,000 sq ft, fully sprinklered Type IIB building - half wholesale furniture storage (S-1) and half showroom (M) - wants to add 14,000 sq ft of showroom. The architect proposes a 2-hour fire wall between the new showroom and the warehouse so that each side can be treated as a separate building for allowable area. As detailed, the wall is 2-hour gypsum board on steel studs that stops at the underside of open-web steel joists running continuously across the building over an unprotected metal roof deck; the joists bear on the wall's top track. The wall contains two 20-minute labeled double doors with magnetic holders released by the fire alarm. There is no fireblocking at the wall line and no draftstopping in the concealed ceiling space.
1. Will this wall create two separate buildings for allowable-area purposes?
Read the worked answer
No. As detailed, the wall is not a fire wall.
A fire wall must satisfy all of the following, and this detail fails several:
- Structural stability independent of the construction on either side. Members on one side cannot rely on the wall for support, and the wall cannot rely on the framing for lateral stability. Open-web joists bearing on the wall's top track is a direct conflict.
- Vertical continuity. The wall must extend from the foundation through the roof, projecting above the roof surface by the distance the code requires (30 in. is the usual figure) unless the roof construction within the specified distance is protected to the required rating. Stopping at the underside of unprotected joists and deck leaves the assembly with no protection over the wall line.
- Continuity through concealed spaces. The wall must be continuous through concealed spaces, and fireblocking is required where the wall line meets the concealed space. None is provided.
- Protection of penetrations and openings. Joists running continuously across the wall are unprotected structural elements bridging the separation. Penetrations must be protected, and the opening protectives must be rated for the wall.
Result: there is one building. The area of the combined structure must be checked against the allowable area for the occupancies present, and the 14,000 sq ft addition cannot be justified by the wall as drawn.
2. Evaluate the door assemblies in the proposed wall.
Read the worked answer
The doors are under-protected and the hold-opens need review.
- Rating. Opening protective ratings are keyed to the rating of the wall they serve. A 20-minute door assembly corresponds to a 1-hour partition, not a 2-hour fire wall. A fire wall of this rating requires a higher-rated labeled assembly, installed in a listed frame with the labeled hardware.
- Operation. Fire door assemblies must be self-closing and latching. Magnetic holders are acceptable only where they release upon activation of the fire alarm or smoke detection serving the area, and upon loss of power. They may not be wedged, propped or otherwise held open by field-installed means.
- Field conditions. The doors must be installed with the correct clearances, with no field modifications to the label, and with the undercut and gasketing per the listing. A missing or painted-over label is a failure.
- Consequence. If the applicant converts the wall to a fire barrier between occupancies instead of a fire wall, the door rating changes with the barrier rating, but the barrier still does not create two buildings for area purposes. That distinction, not the door rating, is what dooms the design as proposed.
3. If the wall cannot create two buildings, how does the area analysis proceed and what options does the owner have?
Read the worked answer
One building, one area analysis - then a menu of real options.
- Combined check. With no compliant separation, the building area is the sum of both sides. Where occupancies are not separated, the height and area must satisfy the most restrictive occupancy in the mix at the proposed construction type, and each occupancy is evaluated at its tabulated allowance. Sprinkler and frontage increases are applied as the tables permit, not as the applicant wishes.
- Compliant fire wall. Rebuild the separation to meet the fire wall provisions in full - independent structural stability, projection above the roof or protected roof within the required distance, continuity through concealed spaces, protected penetrations and appropriately rated opening protectives - and document it as two buildings. This is expensive but legitimate.
- Fire barrier plus separated occupancy. A fire barrier of the rating required between the occupancies permits the separated mixed-occupancy analysis, in which each occupancy's area is checked separately. A fire barrier is not a fire wall and does not split the building for height and area of the structure as a whole, so the barrier option only works if the area math actually closes.
- Reduce or redistribute program. Cut the added showroom area, convert some warehouse area to showroom, or upgrade the construction type.
Also required regardless of path: fireblocking at the wall line and at penetrations of concealed spaces, and draftstopping in the concealed ceiling space where its area exceeds the permitted limits. These are commonly missed on plans that focus only on the big wall.