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Asymmetrical Exterior Wall Construction Type IIIB

T

texasbo

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Jan 4, 2010
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Bearing wall, Type IIIB. Table 601 requires 2 hour. Separation is over 30'.

704.5, 2006 IBC allows fire resistive construction on inside only.

I would like to know if the group requires a specific assembly number for an asymmetrical fire resistive wall, or if you would allow (as I would), a typical 2 hour listed symmetrical assembly, but with the rated materials only on the inside.

Thanks
 
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Doesn't Table 602 reduce the fire resistance rating requirements to " 0 ", for separation distances

greater than 30', ..in all occupancy groups ( from the 2006 IBC ) ?

.
 
The fire resistance of a wall assembly is substantially borne by the membrane on the fire-exposed side. This is clarified in 2006 IBC Section 721; though the associated calculations are only applicable for up to 1-hour fire-resistance-rated construction, the approach as presented in IBC 721.6.2.3 should still be valid:

721.6.2.3 Exterior walls. For a wall having more than 5 feet of horizontal separation, the wall is assigned a rating dependent on the interior membrane and the framing... The membrane on the outside of the nonfire-exposed side of exterior walls having more than 5 feet of horizontal separation may consist of sheathing, sheathing paper, and siding...
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Therefore, if a symmetrical 2-hour tested assembly were presented as the basis for the design, the membrane prescribed by the tested assembly should only be required on the interior face, with exterior treatment such as described in 721.6.2.3.

If the referenced assembly were based on a double-stud wall, it would seem that the installation should be completed as prescribed per the assembly up to the interior face of the exterior membrane against the outer framing.

If the referenced 2-hour assembly were asymmetrical, a Fire Protection Engineer could be engaged to assist in identifying how this code provision may be satisfied.
 
Papio Bldg Dept said:
I will assume you are talking about IIIB construction as indicated in your title, and not the post.
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Yes, did you have an opinion relative to the question?
 
AegisFPE said:
The fire resistance of a wall assembly is substantially borne by the membrane on the fire-exposed side. This is clarified in 2006 IBC Section 721; though the associated calculations are only applicable for up to 1-hour fire-resistance-rated construction, the approach as presented in IBC 721.6.2.3 should still be valid:Therefore, if a symmetrical 2-hour tested assembly were presented as the basis for the design, the prescribed membrane should only be required on the interior face.

If the referenced assembly were based on a double-stud wall, it would seem that the installation should be completed as prescribed per the assembly up to the interior face of the exterior membrane against the outer framing.

If the referenced 2-hour assembly were asymmetrical, a Fire Protection Engineer could be engaged to assist in identifying how this code provision may be satisfied.
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Excellent; thanks Aegis. That was my opinion as well.
 
texasbo said:
Yes, did you have an opinion relative to the question?
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sorry, i got called away. Table 601 says 2 hrs, with footnote 'g' noting element shall not be less than designated by Table 602. 602.3 notes that Type III construction consists of exterior walls of non-combustible construction allowing interior elements to be of any material permitted by code.

I would say 2hr construction, but I am not sure why you would design a IIIB building when you already have a 30' fsd. Don't see too many III & IVs around here.

I am also in agreement with AegisFPE.
 
globe trekker said:
Texasbo,I misinterpreted Table 601! My apologies sir!

.
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No apology necessary; the code needs to clarify which table takes precedence in different conditions; it is definitely not clear as written, in my opinion. In fact, I was being sneaky when I put "over 30'" in the original post instead of "over 5'", because I thought there might be comments about 601 vs 602.
 
Papio Bldg Dept said:
I would say 2hr construction, but I am not sure why you would design a IIIB building when you already have a 30' fsd. Don't see too many III & IVs around here.
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No, I don't see too many either. This time it's all about maintaining historic integrity. It's an adaptive reuse of an old grain mill. They are actually using metal studs (although maybe FRTW) in the assembly.
 
texasbo said:
No, I don't see too many either. This time it's all about maintaining historic integrity. It's an adaptive reuse of an old grain mill. They are actually using metal studs (although maybe FRTW) in the assembly.
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A little OT, but would it being an old grain mill throw it into Chapter 34/IEBC, thus allowing you to use the archaic materials tables? Sounds like it has the potential to be neat project. What will the new occupancy/use be?
 
Papio Bldg Dept said:
I would say 2hr construction, but I am not sure why you would design a IIIB building when you already have a 30' fsd. Don't see too many III & IVs around here.I am also in agreement with AegisFPE.
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IIIB because of occupancy, area, building height, or insurance requirements.
 
Papio Bldg Dept said:
A little OT, but would it being an old grain mill throw it into Chapter 34/IEBC, thus allowing you to use the archaic materials tables? Sounds like it has the potential to be neat project. What will the new occupancy/use be?
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You're absolutely right, but much of it, including the portion in question, is new, and must match the existing construction. This is one of the more complex projects I've done, and I've done multi-million square foot malls, corporate headquarters, resort hotels, etc. This project includes historic designation, existing construction, new construction, mixed occupancies, multiple construction types separated by fire walls, fire walls terminating at exterior shed roof projections, occupied concrete grain storage silos, occupied steel silos, 4 floors in some places, occupied basements, multiple assembly occupancies, retail, office, roof structures, you name it!
 
brudgers said:
IIIB because of occupancy, area, building height, or insurance requirements.
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Definitely occupancy, area and building height. I don't know about insurance.
 
texasbo said:
Definitely occupancy, area and building height. I don't know about insurance.
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Construction type affects rates - for large scale development relatively small differences in rates can mean real money.
 
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