2012 705.2.3 allowable exception

[Francis Vineyard]

VB sprinklered office building, 30 ft. FSD to the interior lot line.

Am I interpreting this correct that since R-3 VB doesn't get the 10 ft. exception in accordance with section 705.8.1 (Table 602) then the office building combustible deck needs to have at least a FSD of 20 ft. before protection is required (1406.3)?

705.2.3 Combustible projections.

Combustible projections extending to within 5 feet (1524 mm) of the line used to determine the fire separation distance, or located where openings are not permitted, or where protection of some openings is required shall be of at least 1-hour fire-resistance-rated construction, Type IV construction, fire-retardant-treated wood or as required by :Next('./icod_ibc_2012_14_par084.htm')'>Section 1406.3.

Exception: Type VB construction shall be allowed for combustible projections in Group R-3 and U occupancies with a fire separation distance greater than or equal to 5 feet (1524 mm).

705.8.1 Allowable area of openings.

The maximum area of unprotected and protected openings permitted in an exterior wall in any story of a building shall not exceed the percentages specified in Table 705.8.

Exceptions:

1. In other than Group H occupancies, unlimited unprotected openings are permitted in the first story above grade plane either:

1.1. Where the wall faces a street and has a fire separation distance of more than 15 feet (4572 mm); or

1.2. Where the wall faces an unoccupied space. The unoccupied space shall be on the same lot or dedicated for public use, shall not be less than 30 feet (9144 mm) in width and shall have access from a street by a posted fire lane in accordance with the International Fire Code.

2. Buildings whose exterior bearing walls, exterior nonbearing walls and exterior primary structural frame are not required to be fire-resistance rated shall be permitted to have unlimited unprotected openings.

 

[RLGA]

FV, I'm having a hard time trying to figure out what your question is.

VB with a 30-foot FSD does not require a fire rating per Table 602. Therefore, Exception 2 to 705.8.1 applies and unlimited unprotected openings are permitted. I don't know how the section on projections plays into this. With a FSD of 30 feet, do you have a projection that extends to within 5 feet of the lot line?

 

[Francis Vineyard]

Ron thanks for response to help me clarify.

1) The 5 ft. is less restrictive than Table 602

2) The 705.8.1 exception for IIB and VB is less restrictive than Table 705.8

3) 705.2.3 is saying though an exterior wall is beyond the FSD, projections are required to be FRTW into the area that would require openings to be protetced.

4) Section 1406.3 provides a sprinkler exception though type VB not required to be rated (Table 601) it applies because of 705.2.3 FRTW in the FDS

705.2.3 Combustible projections.

Combustible projections extending to within 5 feet (1524 mm) of the line used to determine the fire separation distance,

or located where openings are not permitted, or where protection of some openings is required

shall be of at least 1-hour fire-resistance-rated construction, Type IV construction,

fire-retardant-treated wood or as required by Section 1406.3.

 

[RLGA]

FV:

1) Table 602 applies to walls and not projections; therefore, Table 60 doesn't factor in the equation when looking at projections.

2) Yes, because Exception 2 states that buildings that are not required to have fire-resistive construction for exterior walls and structural frame based on Table 601 or FSD based on Table 602 are permitted unlimited unprotected openings (no need to put a protected opening in a nonprotected wall).

3) FRTW is only one option. It can be a 1-hour tested assembly, Type IV construction, or in accordance with 1406.3. There are three conditions that require protection: 1) within 5 feet of the lot line, 2) within an distance where openings are prohibited (i.e. 3 feet); and 3) within a distance that requires protection of some openings (i.e. 3 to 5 feet per Table 705.8. I don't know why they bothered with the latter 2, since the first one seems to be the default.

4) 1406.3 does not require balconies and other projections of Type VB construction to be rated because Table 601 does not require floor construction to be rated. Thus, the exceptions would not come into play. If it were Type VA construction, then a sprinkler system extended to the balconies/projections would negate the requirement to have the balconies/projections rated as for floor construction. However, the aggregate length of the balcony/projection is limited to 50% of the building's perimeter, regardless if it is fire-resistive protected or not. If a sprinkler system is extended to these areas, then there is no limit on the length per Exception 4.

Based on your situation, the only issue that affects your building is probably the length of a projection or balcony.

 

[Francis Vineyard]

Ron, my ability to clarify is weak, so here's another attempt;

1 & 2)) I believe Table 602 is reference by 705.8.1 exception 2 to permit a reduction of the FSD for unlimited openings in type IIB and VB construction where the wall is not required to be rated.

3) My confusion to this section for R-3 and U of VB construction is the code adds another exception to allow unprotected projections were limited and protected openings are required.

4) Right; I believe the first paragraph of 1406.3 is misleading when 705.2.3 reference this to infer this section only apply to VA, instead that if it is VA then it should be constructed accordingly; for VB (exception 3) is a reminder that NFPA 13 can be used where combustible projections may not be "approved" material in accordance with 705.2.2 (as opposed to "any materials permitted by this code"; 602.5).

Another question is the intent of section of 705.2 only for roof and floor projections that may retain heat; the 1406 commentary seems to imply that decks at grade should be treated as projections to be protected.

Is the code definition of fire area considering decks as "horizontal assemblies of a building"?

Commentary: "Balconies, porches, decks and supplemental exterior stairways that are not attached to or supported by the building are separate structures and are to be built accordingly. Although the structural support may be independent, such structures could serve to assist vertical fire spread depending on the construction of the exterior wall and the presence of lack of opening protectives."

Where am I confused in VB construction about projections such as a deck to be protected or non-combustible that extends into the FSD from a wall that is beyond the FSD?

 

[RLGA]

FV (I hope you don't mind me using that):

1) & 2) Section 705.8.1 does not reference Table 602, or 601, directly. However, it does infer them by mentioning "required" fire-resistance ratings for exterior bearing walls, exterior nonbearing walls, and structural frame. Yes, it does not establish a minimum distance, but relies really on Table 602 (i.e. Table 601 may not require fire-resistive construction, but based on FSD, Table 602 might still require it; thus making this exception irrelevant). Since Table 602 requires some level of fire-resistive construction for a FSD of less than 10 feet, then all walls within that distance are subject to the requirements of Section 705.8.1.

3) A building of Type VB construction located more than 5 feet from the lot line (i.e. line used to determine FSD) may have unprotected projections for Group R-3 and Group U, if they extend to within 5 feet or less of the lot line. The meaning of "where protection of some openings is required" in Section 705.2.3 is confusing at best--you have to start from the lot line and not from the building. At "3 to less than 5" feet, protection of some openings is required as Section 705.2.3 states; thus, the three conditions stipulated in Section 705.2.3 essentially boil down to anything less than 5 feet. So, for Type VB construction with Groups R-3 or U and having a FSD greater than 5 feet, some openings (10%) are permitted to be unprotected and the exception to Section 705..2.3 allows unprotected projections beyond that 5-foot barrier.

4) I think we are in agreement here. The reference to 1406.3 does extend what could be called an exception to VB construction by pointing to floor construction in Table 601. However, the length requirement is still applicable.

On another point, we, as professionals either in our jobs or on this forum, try to tell people that construction types cannot be mixed on a building unless a fire wall is used to separate the buildings of differing construction types. Then, the IBC uses language like "Balconies and similar projections on buildings of Type III, IV and V construction shall be permitted to be of Type V construction..." (Exception 3, Section 1406.3). Taken literally, it means that a Type III and IV building may have portions that are classified as Type V without the fire wall separation. We all know this isn't what it is supposed to mean, but when it is said like that, it gives people with marginal knowledge of the building code the idea they can mix construction types. This isn't the only location where this occurs.

Just sounding off. If I had the time and money, maybe I would try to get some of these and other oddities changed in the code.

 

[Francis Vineyard]

FV (I hope you don't mind me using that)

Ron,

I much prefer FV than some of the other misspellings.

A search of this site and others have had this same discussion with similar clarity.

Thanks for sounding off.

 

[Francis Vineyard]

I found an explanation that followed my application where the vb building is beyond the FSD but the projection encroaches (granted don't know if the Oregon code is the same as IBC): Appeals/City of Portland, Oregon

1406.3 says projections for all types of construction in the FSD shall be FRTW or . . . followed by exceptions; permitted to be combustible if sprinklered.

Appreciate the help from this forum.

 

[RLGA]

1406.3 says projections for all types of construction in the FSD shall be FRTW or . . . followed by exceptions; permitted to be combustible if sprinklered.

I don't interpret Section 1406.3 that way at all.

The way I interpret the section is if the projection is of FRTW, regardless of construction type, then the rest of the section, other than the length limitation, is moot.

However, if not constructed of FRTW, then it must be fire-resistance rated per Table 601 or be of Type IV construction (another case of allowing the "mixing" of construction types). For Type VB, just because floors aren't required to be fire-resistance rated per Table 601 doesn't mean you have to go back to the first part of the section that requires FRTW.

In a convoluted way, this section is making an exception for construction types that require fire-resistance rated floors. What it's saying, to me, is "You either rate the system per Table 601, or we'll allow you to use FRTW."