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Supporting Construction of a 2-Hour Horizontal Assembly - 2009 IBC

B

braskan

Member
Joined
Dec 16, 2014
Messages
5
Location
Colorado Springs
When exterior bearing walls are used as part of the supporting construction of a 2-hour assembly (I-1 above/I-2 below), are the 2-hour exterior walls still allowed to be rated from exposure from the inside only per 705.5 if the fire sep. distance is greater than 10 feet?

OR, does the charging language of 712.4 that states: "The supporting construction shall be protected to afford the required fire-resistance rating of the horizontal assembly supported." control? Meaning, if the horizontal assembly is required to be protected from both sides, then that last sentence of 712.4 would also require the exterior wall to be protected from both sides. Comment away!
 
It doesn't meet any of the exceptions?

712.4 Continuity. Assemblies shall be continuous without openings, penetrations or joints except as permitted by this section and Sections 708.2, 713.4, 714 and 1022.1. Skylights and other penetrations through a fire-resistance-rated roof deck or slab are permitted to be unprotected, provided that the structural integrity of the fire-resistance-rated roof assembly is maintained. Unprotected skylights shall not be permitted in roof assemblies required to be fire-resistance rated in accordance with Section 705.8.6. The supporting construction shall be protected to afford the required fire-resistance rating of the horizontal assembly supported.

Exception: In buildings of Type IIB, IIIB or VB construction, the construction supporting the horizontal assembly is not required to be fire-resistance-rated at the following:

1. Horizontal assemblies at the separations of incidental uses as specified by Table 508.2.5, provided the required fire-resistance rating does not exceed 1 hour.

2. Horizontal assemblies at the separations of dwelling units and sleeping units as required by Section 420.3.

3. Horizontal assemblies at smoke barriers constructed in accordance with Section 710.
 
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IMO, ...Table 602 [ `09 IBC ] allows it to be rated from the interior side only,

if the exterior wall has a separation distance of more than 10 ft.

From the `09 IBC, Section 705.5 - Fire-resistance rating: "Exterior walls

shall be fire-resistance rated in accordance with Tables 601 and 602 and

this section.........The required fire-resistance rating of exterior walls with

a fire separation distance of greater than 10 feet (3048 mm) shall be rated

for exposure to fire from the inside............The required fire-resistance

rating of exterior walls with a fire separation distance of less than or equal

to 10 feet (3048 mm) shall be rated for exposure to fire from both sides."

Section 712.4 - Continuity: "Assemblies shall be continuous

without openings, penetrations or joints except as permitted by

this section and Sections 708.2, 713.4, 714 and 1022.1......Skylights

and other penetrations through a fire-resistance-rated roof deck or

slab are permitted to be unprotected, provided that the structural

integrity of the fire-resistance-rated roof assembly is maintained.

Unprotected skylights shall not be permitted in roof assemblies

required to be fire-resistance rated in accordance with Section

705.8.6..........The supporting construction shall be protected to

afford the required fire-resistance rating of the horizontal assembly

supported."

Exception: In buildings of Type IIB, IIIB or VB construction, the

construction supporting the horizontal assembly is not required to be

fire-resistance-rated at the following:

1. Horizontal assemblies at the separations of incidental uses as

specified by Table 508.2.5, provided the required fire-resistance

rating does not exceed 1 hour.

2. Horizontal assemblies at the separations of dwelling units and

sleeping units as required by Section 420.3.

3. Horizontal assemblies at smoke barriers constructed in accordance

with Section 710

Again, ...IMO, ...I believe that Table 602 provides guidance on a

specific [ rather than a general ] type of fire protection........."The

supporting type construction shall be protected" mentioned in

Section 712.4, ...is specifically allowed to be on the interior side

only, if there is a separation distance of more than 10 ft.

+ ~ ~ ~ +
 
Builder Bob said:
Follow the steps in chapter 1, specific rules supersede general rules.... IN this case, the statement is supporting construction is a general statement, the fire protection rating requirements id a specific rule that applies to fire separation distance.
Click to expand...
Our jurisdiction has adopted the 2011 Regional Building Code (www.pprbd.org), and Chapter 1 of the IBC is expressly deleted as part of the Commercial Building Code (RBC302.3), thus the above statement does not apply. In lieu of IBC Chapter 1, the RBC has it's own Chapter 1 for Administration. Section RBC101.4 talks about Differing Requirements and states: "Where, in any specific case, different section of this Code, or other codes, ordinances, or resolutions of the Jurisdiction or other governmental body specifying different requirements, the more restrictive shall govern."
 
Back to my gut....you are separating the occupancies from each other, not the outside world...fire "downstairs" is contained by horizontal assembly and exterior walls rated on inside, mission accomplished...but again, not sure if I can get there specifically in code...
 
= \ = \ =



braskan,

In what Chapter would you go to to find out how to

rate the exterior walls, ...based upon your type of

construction ?

= / = / =
 
north star said:
= \ = \ =

braskan,

In what Chapter would you go to to find out how to

rate the exterior walls, ...based upon your type of

construction ?

= / = / =
Click to expand...
Chapter 6, tables 601 & 602, provided type of construction and/or fire sep. distance are the only items requiring rated construction.
 
What type of construction are you talking about?

A structural steel frame type of construction supporting the horizontal assembly would not require the whole wall to have a 2-hour rating. Only the primary frame would need to be protected.

PRIMARY STRUCTURAL FRAME. The primary structural frame shall include all of the following structural members:

1. The columns;

2. Structural members having direct connections to the columns, including girders, beams, trusses and spandrels;

3. Members of the floor construction and roof construction having direct connections to the columns; and

4. Bracing members that are essential to the vertical stability of the primary structural frame under gravity loading shall be considered part of the primary structural frame whether or not the bracing member carries gravity loads.

If it is a bearing wall system then only the interior needs to provide the protection as long as the fire separation distances are met.

705.5 Fire-resistance ratings.

Exterior walls shall be fire-resistance rated in accordance with Tables 601 and 602 and this section. The required fire-resistance rating of exterior walls with a fire separation distance of greater than 10 feet (3048 mm) shall be rated for exposure to fire from the inside. The required fire-resistance rating of exterior walls with a fire separation distance of less than or equal to 10 feet (3048 mm) shall be rated for exposure to fire from both sides.
 
Thank you all for your input. The official interpretation from ICC that was received at the end of last week was that even for supporting construction requirements, exterior walls need only be rated from the inside, provided the fire separation distance requirements are met - See below.



RE: 09 IBC 712.4 and 705.5

Background: The exterior walls of a VA building are also the supporting construction for a 2-hour horizontal assembly acting as an occupancy separation between I-2 and I-1 occupancies. The design professional is providing an assembly showing protection from one side for these walls, stating it is allowed per 705.5.

Q1: Does 705.5 mean that when the wall is rated due to Table 601 or Table 602, either requirement would allow the protection from one side only?

A1: Yes. Section 705.5 first states that exterior walls shall be rated in accordance with Tables 601 and 602. Then it states that a rated exterior wall with a fire separation distance greater than 10 feet shall be rated for exposure from the inside, which includes walls rated per Table 601 or Table 602.

Q2: Does the one sided provision apply when the 2-hour rating is also being driven by 712.4 for supporting construction, and not chapter 6?

A2: Yes. Section 705.5 states that the required fire-resistance ratings of exterior walls that have a fire separation distance greater than 10 feet shall be from the inside. This would include a fire resistance rating required for an exterior load bearing wall that is rated because it supports an horizontal assembly.

 
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