Wall assembly rating

[Allied]

I am looking for materials for a top of wall CMU that has a 3 hour fire rating.
Can a 2 hour rated material with mineral wool be used on both sides of the wall, would that provide a 4 hour rating?

 

[steveray]

Are you talking about a joint? Why 3 and 4 hour?

 

[RLGA]

UL has no head-of-wall joints that are rated for three hours.

Is this for a fire wall or a fire barrier? For fire walls, the IBC does not allow 3-hour fire walls to terminate at the underside of a deck. For fire barriers, you will just have to grout solidly for the full depth with mortar to maintain the rating. If the joint needs to be a movement joint, then you will need an engineering judgment that the B.O. will accept, which is very unlikely.

 

[steveray]

3 and 4 do.....Silent on rating...

For fire walls, the IBC does not allow 3-hour fire walls to terminate at the underside of a deck.

3.Walls shall be permitted to terminate at the underside of noncombustible roof sheathing, deck or slabs where both buildings are provided with not less than a Class B roof covering. Openings in the roof shall not be located within 4 feet (1220 mm) of the fire wall.
4.In buildings of Types III, IV and V construction, walls shall be permitted to terminate at the underside of combustible roof sheathing or decks, provided that all of the following requirements are met:

1. 4.1.Roof openings are not less than 4 feet (1220 mm) from the fire wall.
2. 4.2.The roof is covered with a minimum Class B roof covering.
3. 4.3.The roof sheathing or deck is constructed of fire-retardant-treated wood for a distance of 4 feet (1220 mm) on both sides of the wall or the roof is protected with 5/8-inch (15.9 mm) Type X gypsum boarddirectly beneath the underside of the roof sheathing or deck, supported by not less than 2-inch (51 mm) nominal ledgers attached to the sides of the roof framing members for a distance of not less than 4 feet (1220 mm) on both sides of the fire wall.

1. 3.Walls shall be permitted to terminate at the underside of noncombustible roof sheathing, deck or slabs where both buildings are provided with not less than a Class B roof covering. Openings in the roof shall not be located within 4 feet (1220 mm) of the fire wall.
2. 4.In buildings of Types III, IV and V construction, walls shall be permitted to terminate at the underside of combustible roof sheathing or decks, provided that all of the following requirements are met:
   
   1. 4.1.Roof openings are not less than 4 feet (1220 mm) from the fire wall.
   2. 4.2.The roof is covered with a minimum Class B roof covering.
   3. 4.3.The roof sheathing or deck is constructed of fire-retardant-treated wood for a distance of 4 feet (1220 mm) on both sides of the wall or the roof is protected with 5/8-inch (15.9 mm) Type X gypsum boarddirectly beneath the underside of the roof sheathing or deck, supported by not less than 2-inch (51 mm) nominal ledgers attached to the sides of the roof framing members for a distance of not less than 4 feet (1220 mm) on both sides of the fire wall.

 

[Yankee Chronicler]

I am looking for materials for a top of wall CMU that has a 3 hour fire rating.
Can a 2 hour rated material with mineral wool be used on both sides of the wall, would that provide a 4 hour rating?

There have been some good answers, but I think you need to express the question better. A "wall assembly" is a wall. "CMU" is the acronym for Concrete Masonry Unit. The way the question is phrased, it seems you have a wall of some undisclosed material that you want to put a 3-hour rated Concrete Masonry Unit on top of -- for undisclosed reasons.

As the other responders appear to have guessed, my guess is that what you are really asking about is a rated joint seal assembly for the intersection of a 3-hour concrete masonry wall against the underside of a floor or roof of undisclosed materials. I respectfully submit that if you don't understand the terminology that applies to the elements you are joining, you cannot hope to arrive at a solution that conforms to the code.

You need to open the IBC and study section 715, "Joints and Voids." IBC 715.1:

715.1 General. The provisions of this section shall govern the
materials and methods of construction used to protect joints
and voids in or between horizontal and vertical assemblies

It seems we are all guessing this is what you are asking about. If so, then we can proceed to IBC 715.3:

715.3 Fire-resistance-rated assembly intersections. Joints
installed in or between fire-resistance-rated walls, floor or
floor/ceiling assemblies and roofs or roof/ceiling assemblies
shall be protected by an approved fire-resistant joint system
designed to resist the passage of fire for a time period not less
than the required fire-resistance rating of the wall, floor or
roof in or between which the system is installed.

What this tells us is that you need a joint seal system (or "assembly") that has been tested and listed by some recognized accrediting agency such as U.L., Warnock-Hersey, or similar. You can't just throw a bunch of stuff at the joint and call it good. The ICC Commentary for section 715.3 goes on to say:

In order to maintain the efficacy of the fire-resistance rated
assembly, these openings must be protected by
a fire-resistance-rated joint system with a rating equal
to the assembly in the same plane. Where two assemblies
intersect, the fire rating of the joint must be the
same as the fire rating of the assembly (or assemblies)
of the same plane as the assembly where the joint
occurs. This section is not intended to regulate joints
installed in assemblies that are provided to control
shrinkage cracking, such as a saw-cut control joint in
concrete. This section contains 10 locations where a
fire-resistant joint system is not required to be installed
to protect the joint. These generally are locations
where a separation or protected opening is not
required or where the joint occurs within an area that is
bounded by other means of protection.

 

[RLGA]

@steveray, yes, you are correct--in my haste, I didn't read down far enough.

 

[steveray]

We all do it from time to time….when it’s for free….my answers get much more accurate when there is money involved…

I had to look it up to make sure I hadn’t screwed up in the past…on that one…

 

[Allied]

3 and 4 do.....Silent on rating...



3.Walls shall be permitted to terminate at the underside of noncombustible roof sheathing, deck or slabs where both buildings are provided with not less than a Class B roof covering. Openings in the roof shall not be located within 4 feet (1220 mm) of the fire wall.
4.In buildings of Types III, IV and V construction, walls shall be permitted to terminate at the underside of combustible roof sheathing or decks, provided that all of the following requirements are met:

1. 4.1.Roof openings are not less than 4 feet (1220 mm) from the fire wall.
2. 4.2.The roof is covered with a minimum Class B roof covering.
3. 4.3.The roof sheathing or deck is constructed of fire-retardant-treated wood for a distance of 4 feet (1220 mm) on both sides of the wall or the roof is protected with 5/8-inch (15.9 mm) Type X gypsum boarddirectly beneath the underside of the roof sheathing or deck, supported by not less than 2-inch (51 mm) nominal ledgers attached to the sides of the roof framing members for a distance of not less than 4 feet (1220 mm) on both sides of the fire wall.
4. 3.Walls shall be permitted to terminate at the underside of noncombustible roof sheathing, deck or slabs where both buildings are provided with not less than a Class B roof covering. Openings in the roof shall not be located within 4 feet (1220 mm) of the fire wall.
5. 4.In buildings of Types III, IV and V construction, walls shall be permitted to terminate at the underside of combustible roof sheathing or decks, provided that all of the following requirements are met:
   1. 4.1.Roof openings are not less than 4 feet (1220 mm) from the fire wall.
   2. 4.2.The roof is covered with a minimum Class B roof covering.
   3. 4.3.The roof sheathing or deck is constructed of fire-retardant-treated wood for a distance of 4 feet (1220 mm) on both sides of the wall or the roof is protected with 5/8-inch (15.9 mm) Type X gypsum boarddirectly beneath the underside of the roof sheathing or deck, supported by not less than 2-inch (51 mm) nominal ledgers attached to the sides of the roof framing members for a distance of not less than 4 feet (1220 mm) on both sides of the fire wall.

I am talking about a caulking joint at the head of a CMU walk. They are wanting a 3 hour rated caulk. My questions was if I use a 2 hour rated caulk on each side with mineral wool in between will that result in 3 hour rating , technically a 4 hour??? The joint is 3/8"-1.5".

 

[Yankee Chronicler]

I am talking about a caulking joint at the head of a CMU walk. They are wanting a 3 hour rated caulk. My questions was if I use a 2 hour rated caulk on each side with mineral wool in between will that result in 3 hour rating , technically a 4 hour??? The joint is 3/8"-1.5".

There is no "3 hour rated caulk," and that's not what the code calls for. The code calls for a rated "joint seal system." What you describe may work -- but it can only be accepted if some testing agancy has tested it and listed it.

Something such as this: https://www.rockwool.com/uk/product...ts/firepro--softseal-linear-joint-seal-en-gb/