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help with firewall

B

BSSTG

Gold Member
Joined
Nov 30, 2009
Messages
729
Location
Seadrift, Tx.
Greetings,

2012 IBC type II construction

Can someone tell me what they mean in 2.1 "lower roof assembly"? Are they referring to the supporting structure? I don't see any guidance in the commentary. Does this in anyway eliminate the need for fireproofing on one side or the other of the firewall on the underside of the roof deck if you have an uneven roof?

This is an exception we may want to use to eliminate the need for a parapet for a firewall on an addition to an existing church to eliminate the requirement for sprinkling.

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:

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.

BSSTG
 
each item must be met

And seems clear in the commentary also

You might have trouble meeting all on the existing side!!
 
The 'lower roof assembly' simply refers to one side of the fire wall having a roof at a lower elevation than the other side - anchor stores in strip malls tend to have higher roofs for example. The supporting structure for a fire wall IS the fire wall.
 
How about using exception #1?

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.

706.6.1 Stepped buildings.

Where a fire wall serves as an exterior wall for a building and separates buildings having different roof levels, such wall shall terminate at a point not less than 30 inches (762 mm) above the lower roof level, provided the exterior wall for a height of 15 feet (4572 mm) above the lower roof is not less than 1-hour fire-resistance-rated construction from both sides with openings protected by fire assemblies having a fire protection rating of not less than 3/4 hour.
 
Ok Let's rephrase the question.

If there are 2 roofs intersected by a firewall, and each roof has a different level or pitch, does only the lower roof structure have to meet the requirement of 4' out being 1 hour rated?

What we have is an existing type II bldg. Owner wants to add on another section which will be a flat roof. Existing bldg. has a pitched roof. Can we meet these requirements without jacking with the existing roof? The new roof can be made lower than the existing building roof. We need to get away from the parapet requirement for roof drainage.

MT I was looking at that ex too. It seems to me in looking at it that way would indicate that we could intersect the new bldg. section at a lower level even though it might only be a few inches and not have to be concerned with the older section of roof as long as it's a class b roof covering and the new fire wall meets up with the upper level roof structure.

I'm tempted to ask ICC for an interpretation. Of course they put their disclaimer on there and say it's up to the AHJ. Gotta love it.

Thanksabunch

BS
 
MT In looking at that exception again I don't think that will work. We will not have a minimum of 30" in between the 2 roof levels. Not enough to work with there.

BS
 
BSSTG said:
Ok Let's rephrase the question.If there are 2 roofs intersected by a firewall, and each roof has a different level or pitch, does only the lower roof structure have to meet the requirement of 4' out being 1 hour rated?

What we have is an existing type II bldg. Owner wants to add on another section which will be a flat roof. Existing bldg. has a pitched roof. Can we meet these requirements without jacking with the existing roof? The new roof can be made lower than the existing building roof. We need to get away from the parapet requirement for roof drainage.

MT I was looking at that ex too. It seems to me in looking at it that way would indicate that we could intersect the new bldg. section at a lower level even though it might only be a few inches and not have to be concerned with the older section of roof as long as it's a class b roof covering and the new fire wall meets up with the upper level roof structure.

I'm tempted to ask ICC for an interpretation. Of course they put their disclaimer on there and say it's up to the AHJ. Gotta love it.

Thanksabunch

BS
Click to expand...
appears the answer is yes

look at example Figure 706.6.1(3) FIRE WALLS—EXTENSION EXCEPTION ,,, if you can meet all the other requirements

lo
 
Thanks guys,

I tend to agree. I do have an issue with the way 706.6.1 is written however. It states "where a fire wall serves as an exterior wall". In looking up the definition of "exterior wall", the definition would indicate that the exterior wall cannot be a fire wall. I see it as a conflict myself. That said, I'm with you on the intent of the section 706.6.1. That will solve the problem and it makes sense too. A sidebar to all of this code stuff is that it seems to me sometimes common sense is out the window.

BS
 
How about the problem of

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.

Are they going to be able to meet this on both sides?
 
Yes....you are protecting the "higher building" from the lower building. If it burn through the highest roof, only the birds, planes, and sky might be affected...
 
cda said:
How about the problem of 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.

Are they going to be able to meet this on both sides?
Click to expand...
I think so, if it's designed correctly. It is a unique concept that I have not seen before. It will be interesting drawings.......You know my boss thinks I'm nuts for enjoying messing with this stuff. Maybe he's right.

BS
 
Upon rereading, how are you going to handle roof venting in existing building? That new firewall would have to go to the upper roof deck.....
 
BSSTG said:
Thanks guys,I tend to agree. I do have an issue with the way 706.6.1 is written however. It states "where a fire wall serves as an exterior wall". In looking up the definition of "exterior wall", the definition would indicate that the exterior wall cannot be a fire wall. I see it as a conflict myself. That said, I'm with you on the intent of the section 706.6.1. That will solve the problem and it makes sense too. A sidebar to all of this code stuff is that it seems to me sometimes common sense is out the window.

BS
Click to expand...
Where the firewall is not a lot line but separates buildings on the same lot.



 
steveray said:
A firewall is ALWAYS an "exterior" wall as it creates separate buildings....and therefore you lose open perimeter and so on...
Click to expand...
Not according to the definition

EXTERIOR WALL. A wall, bearing or nonbearing, that is used as an enclosing wall for a building, other than a fire wall, and that has a slope of 60 degrees (1.05 rad) or greater with the horizontal plane.

FIRE WALL. A fire-resistance-rated wall having protected openings, which restricts the spread of fire and extends continuously from the foundation to or through the roof, with sufficient structural stability under fire conditions to allow collapse of construction on either side without collapse of the wall.

Fire walls are also used to create separate fire areas within a building

FIRE AREA. The aggregate floor area enclosed and bounded by fire walls, fire barriers, exterior walls or horizontal assemblies of a building.......
 
cda said:
Sprinkle itCheaper and better insurance , plus trade offs
Click to expand...
We have tried and tried to talk these folks into it. Their issue is not so much the pricing of the sprinkler system as it is the cost of getting an ample water supply. A fire line to this building would be extremely costly. Yea my boss says they've done a few cost comparisons over the years and found that in all of the instances he was involved with the cost of the sprinkler system would pay for itself in about 10 years or so. I've never messed with it myself and don't know.

BSSTG
 
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