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Unprotected openings?
- Thread starter Sifu
- Start date
2021 IBC
706.5 Horizontal Continuity
Fire walls shall be continuous from exterior wall to exterior wall and shall extend not less than 18 inches (457 mm) beyond the exterior surface of exterior walls.Exceptions:
- Fire walls shall be permitted to terminate at the interior surface of combustible exterior sheathing or siding provided that the exterior wall has a fire-resistance rating of not less than 1 hour for a horizontal distance of not less than 4 feet (1220 mm) on both sides of the fire wall. Openings within such exterior walls shall be protected by opening protectives having a fire protection rating of not less than 3/4 hour.
- Fire walls shall be permitted to terminate at the interior surface of noncombustible exterior sheathing, exterior siding or other noncombustible exterior finishes provided that the sheathing, siding or other exterior noncombustible finish extends a horizontal distance of not less than 4 feet (1220 mm) on both sides of the fire wall.
- Fire walls shall be permitted to terminate at the interior surface of noncombustible exterior sheathing where the building on each side of the fire wall is protected by an automatic sprinkler system installed in accordance with Section 903.3.1.1 or 903.3.1.2.
706.5.1 Exterior Walls
Where the fire wall intersects exterior walls, the fire-resistance rating and opening protection of the exterior walls shall comply with one of the following:- The exterior walls on both sides of the fire wall shall have a 1-hour fire-resistance rating with 3/4-hour protection where opening protection is required by Section 705.8. The fire-resistance rating of the exterior wall shall extend not less than 4 feet (1220 mm) on each side of the intersection of the fire wall to exterior wall. Exterior wall intersections at fire walls that form an angle equal to or greater than 180 degrees (3.14 rad) do not need exterior wall protection.
- Buildings or spaces on both sides of the intersecting fire wall shall assume to have an imaginary lot line at the fire wall and extending beyond the exterior of the fire wall. The location of the assumed line in relation to the exterior walls and the fire wall shall be such that the exterior wall and opening protection meet the requirements set forth in Sections 705.5 and 705.8. Such protection is not required for exterior walls terminating at fire walls that form an angle equal to or greater than 180 degrees (3.14 rad).
From my above posting of the applicable code sections, there are a couple of options depending on some additional information that is needed.
What construction type is used, and do the exterior walls use combustible exterior sheathing?
Why are the exterior walls 2-hr rated? Generally, this is the most intriguing element to me - having 2-hr rated walls, I can't imagine why the exterior window openings are not rated irrespective of the horizontal continuity of the fire wall assembly.
What construction type is used, and do the exterior walls use combustible exterior sheathing?
Why are the exterior walls 2-hr rated? Generally, this is the most intriguing element to me - having 2-hr rated walls, I can't imagine why the exterior window openings are not rated irrespective of the horizontal continuity of the fire wall assembly.
steveray
SAWHORSE
IIIB?
Perhaps...although fairly uncommon for an apartment building I would say.
steveray
SAWHORSE
We get some old mill building conversions....
steveray
SAWHORSE
Short answer...yes....if you meet the requirements...With the extension you will meet the 180 exception and then it is just the termination...Just trying to stop it from burning "around the corner/ end" of the FW...
Sifu
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The exterior walls are 2-hr for type IIIA construction. The openings do not require protection unless required by some other section of code (like 705).
It is the language of 706.5.1 that confuses me, specifically the 180° language. From everything outside of the code that I have read the windows do not need protection, but just taking the code language into account I'm not as sure.
Ok, so the 2-hr walls take care of the Type III-A construction. Assuming sufficient FSD, likely no requirement for protected openings from 705.8.
Next part to consider is 706.5. Given the residential use, I presume that you have an automatic sprinkler system, either 13 or 13R? Thus, Exception #3 to 706.5 is likely the design basis.
Final part to consider is 706.5.1. Design basis here is likely condition #2. Per the image presented, it appears that this works.
So in summary, I think you are correct in assessing that the windows are permitted to be unprotected.
Sifu
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FSD not an issue, NFPA 13 system, FRTW sheathing and framing for exterior walls. My confusion stems from the illustrations provided by the commentary, but I'm not sure they apply if the fire wall extends out to the end. I'm thinking not now. I read it over and over and still think it could be clearer.
FRTW is not non-combustible. It has limited ability to ignite, but is not non-combustible.
IMHO, you need to follow Exception #1 to 706.5 and have 3/4-hr opening protectives.
The FRTW sheathing works fine for Type III-A per 602.3, but as you read that section, take note that even therein it differentiates FRTW from noncombustible.
602.3 Type III
Type III construction is that type of construction in which the exterior walls are of noncombustible materials and the interior building elements are of any material permitted by this code. Fire-retardant-treated wood framing and sheathing complying with Section 2303.2 shall be permitted within exterior wall assemblies of a 2-hour rating or less.
Sifu
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I read it. And I questioned (myself) as to 706.5, but my conclusion has been that it is considered as a substitute for non-combustible in type III construction. Is it not? Am I reading it as a blanket substitution when it should not be in the context of 706.5.? If I am, I think a lot of other people are too.
I would only take it in the context of 602.3 or where permitted by Section 603.
Absolutely should not be applied in the context of 706.5.
steveray
SAWHORSE
This section has always been foolish to me, but CT is right....The Ch 6 and Ch 7 requirements are separate and distinct...
the 180 thing is about the fire burning around the firewall, in other words it burns out of the building on one side, it won't want to make a 180 and burn back in...It may take a hard left and burn into a 90 degree or 179 degree wall, but not a 180..If the walls are "in plane" the heat is likely to go anywhere but there......Better?
the 180 thing is about the fire burning around the firewall, in other words it burns out of the building on one side, it won't want to make a 180 and burn back in...It may take a hard left and burn into a 90 degree or 179 degree wall, but not a 180..If the walls are "in plane" the heat is likely to go anywhere but there......Better?
Sifu
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MAN, I just can't see this. Forget that my belief about FRTW might be wrong.....
What does 706.5 apply to? 706.5.1?
I had some surgery recently, and MAY not be operating at 100% mental capacity, but I swear this language has never made sense to me. Maybe my high quality illustrations will help you help me.
What does 706.5 apply to? 706.5.1?
I had some surgery recently, and MAY not be operating at 100% mental capacity, but I swear this language has never made sense to me. Maybe my high quality illustrations will help you help me.
The fire wall ends at the first corner it hits on the exterior. The wall that continues in the plane of the fire wall is an exterior wall that faces the imaginary lot line.
After the fire wall hits that first corner there is no structure on the exterior side to brace the row of studs on the exterior side of the shaft liner. To build exterior studs outside the shaft liner you’d have to tie them to the interior row of studs. The outer row of studs could not remain standing without the inner row of studs.
After the fire wall hits that first corner there is no structure on the exterior side to brace the row of studs on the exterior side of the shaft liner. To build exterior studs outside the shaft liner you’d have to tie them to the interior row of studs. The outer row of studs could not remain standing without the inner row of studs.