Fire wall - Structural stability

[AntPayne]

Situation: Occupancy E (High School), construction type II-B.

Using a firewall to separate building into 2 separate buildings (IBC 2012 503.1)

See attached image - our desired location for the firewall separation results in one of the "buildings" overlapping the other on upper floors.

IBC 2012 - 706.2 Structural stability.

Fire walls shall have sufficient structural stability under fire conditions to allow collapse of construction on either side without collapse of the wall for the duration of time indicated by the required fire-resistance rating or shall be constructed as double fire walls in accordance with NFPA 221.

Our understanding is that if the structure has the same fire protection rating as the firewall - 2hrs - that this would be acceptable, as the structure and firewall will not collapse before the 2hr limit required.

I'd appreciate any feedback on the application of the code to this situation.

Thanks.

 

[cda]

Welcome from north tx

............

 

[cda]

That is a new one,

If it were so it would be an exception

From 09 commentary

706.2 Structural stability. Fire walls shall have sufficient structural stability under fire conditions to allow collapse of construction on either side without collapse of the wall for the duration of time indicated by the required fire-resistance rating.

Since the collapse of one building from fire conditions should not cause the collapse of an adjacent building, a fire wall is required to be capable of withstanding the collapse of the construction on either side of the wall. An exception to the provision is found in Exception 5 to Section 706.6. In this situation, the issue of structural stability would still apply if the fire was in the buildings located above the horizontal separation required in Section 509.2, Item 1. However, it would clearly be impossible for the buildings above the separation or for that matter the fire wall to be able to withstand the collapse of the building beneath it. Since the building below is of Type IA construction and the separation has a 3-hour fire-resistance rating, this should not be a problem. See 706.6, Exception 5, regarding fire walls in this situation.

There are various methods of designing and constructing fire walls for structural stability during a fire. Among the systems used are cantilevered or freestanding walls, laterally supported and tied walls, and double wall construction. For masonry walls, the NCMA TEK Bulletin 5-8B contains helpful information. For an example with a masonry fire wall, see Figure 706.2(1). The Gypsum Association Fire Resistance Design Manual contains construction details for area separation walls (party wall/fire walls) which have been accepted as fire walls. For an example of a gypsum board fire wall, see Figure 706.2 (2).

The collapse of structural members at some distance from the wall can generally be ignored, but the structural members that are supported by the wall or that are attached directly to the wall for lateral support do require special attention.

 

[cda]

Is the building sprinkled??

Total sq ft for entire old and new building ?

 

[AntPayne]

CDA,

Yes building is sprinklered.

Total square footage for level 1 is 70848. We're splitting the building in 3 with 2 firewalls Area A -49257, Area B 12046, Area C - 9555. Total allowable per floor is 51,330 using sprinklers and frontage.

The other firewall (between A and C) is straightforward, this one (between A and B) is the problem. We could potentially go with type IIA construction and remove this firewall but would prefer type IIB to reduce cost.

 

[AntPayne]

CDA,

Looking at your response it appears IBC 2012 510.2 would apply:

510.2 Horizontal building separation allowance.

A building shall be considered as separate and distinct buildings for the purpose of determining area limitations, continuity of fire walls, limitation of number of stories and type of construction where all of the following conditions are met:

1. The buildings are separated with a horizontal assembly having a fire-resistance rating of not less than 3 hours.

2. The building below the horizontal assembly is not greater than one story above grade plane.

3. The building below the horizontal assembly is of Type IA construction.

4. Shaft, stairway, ramp and escalator enclosures through the horizontal assembly shall have not less than a 2-hour fire-resistance rating with opening protectives in accordance with Section 716.5.

Based on this, my understanding is that:

1. the separation would need to be 3hrs, rather than the 2 hrs I had indicated

2. building B (below the separation) would need to be type IA construction

 

[cda]

It looks like there is a vertical wall??

Not into height and area calcs

Guess you are over?

 

[Builder Bob]

I would state that the continuity of the firewall is incorrect in the diagram attached for a true fire wall....

706.6 Vertical continuity.

Fire walls shall extend from the foundation to a termination point at least 30 inches (762 mm) above both adjacent roofs.

Exceptions:

1. Stepped buildings in accordance with Section 706.6.1.2. Two-hour fire-resistance-rated walls shall be permitted to terminate at the underside of the roof sheathing, deck or slab, provided:2.1. The lower roof assembly within 4 feet (1220 mm) of the wall has not less than a 1-hour fire-resistance rating and the entire length and span of supporting elements for the rated roof assembly has a fire-resistance rating of not less than 1 hour.2.2. Openings in the roof shall not be located within 4 feet (1220 mm) of the fire wall.2.3. Each building shall be provided with not less than a Class B roof covering.3. Walls shall be permitted to terminate at the underside of noncombustible roof sheathing, deck or slabs where both buildings are provided with not less than a Class B roof covering. Openings in the roof shall not be located within 4 feet (1220 mm) of the fire wall.4. In buildings of Type III, IV and V construction, walls shall be permitted to terminate at the underside of combustible roof sheathing or decks, provided:4.1. There are no openings in the roof within 4 feet (1220 mm) of the fire wall,4.2. The roof is covered with a minimum Class B roof covering, and4.3. The roof sheathing or deck is constructed of fire-retardant-treated wood for a distance of 4 feet (1220 mm) on both sides of the wall or the roof is protected with 5/8-inch (15.9 mm) Type X gypsum board directly beneath the underside of the roof sheathing or deck, supported by a minimum of 2-inch (51 mm) nominal ledgers attached to the sides of the roof framing members for a minimum distance of 4 feet (1220 mm) on both sides of the fire wall.5. In buildings designed in accordance with Section 510.2, fire walls located above the 3-hour horizontal assembly required by Section 510.2, Item 1 shall be permitted to extend from the top of this horizontal assembly.6. Buildings with sloped roofs in accordance with Section 706.6.2.