New 2-hour fire wall construction at existing building?

[PatrickGSR94]

2-hour fire wall (structurall independent) adjacent to an existing building: I'm guessing CMU or other masonry or concrete design is probably the only viable solution?

We have a church facility that has been added on several times over the years. It's a mixture of A-3 and E, with a small area of B. 2-story building, fully sprinklered, with voice evac. Using Mixed Use Nonseparated, with A-3 as most restrictive, we're allowed 35,625 SF (Type II-B multistory with full open space all around the building). Current building gross floor area is 30,567. So we could add up to 5,058 SF per floor to remain Mixed Use Nonseparated. As a side note, I did run the numbers with the weighted averages for Mixed Use Separated, and there's no help there.

So if they need more than 5,000 SF, it seems that a fire wall is the only option, to create separate buildings. A structurally independent fire wall along the outside face of (not not actually attached to) the existing building. I don't know of any other way to achieve this other than CMU block or other masonry or concrete construction. We discussed the double-stud shaft wall liner with burn clips wall design for area separation walls, but as far as I know that's only for wood construction, and also can't really be properly constructed from only one side, against existing construction.

Code calls for a 3-hour fire wall for A and E uses, which can be reduced to 2-hour for fully sprinkled buildings. So 2-hour CMU with all its associated reinforcing and footings, and 90-minute doors in that wall for access through it.

Am I missing anything important?

 

[steveray]

You lose the "open space" with the firewall and 2 buildings...well, part of it anyway...

 

[classicT]

That's how I've seen it done. (2-hr masonry wall)

 

[PatrickGSR94]

You lose the "open space" with the firewall and 2 buildings...well, part of it anyway...

so you're saying that depending on the length of where the buildings adjoin, it could kick the existing building into non-compliance, since it changes the open space increase percentage?

Although, it's only going to affect a 9% of the existing building perimeter, so the existing building should still be OK. With 66% increase instead of 75, the existing building is allowed to be 34,770, and it's currently at 30,567.

 

[mtlogcabin]

Do you have enough open space to use the unlimited are requirements?

507.6 Group A-3 buildings of Type II construction.
The area of a Group A-3 building not more than one story above grade plane, used as a place of religious worship, community hall, dance hall, exhibition hall, gymnasium, lecture hall, indoor swimming pool or tennis court of Type II construction, shall not be limited provided all of the following criteria are met:

1. The building shall not have a stage other than a platform.

2. The building shall be equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1.

3. The building shall be surrounded and adjoined by public ways or yards not less than 60 feet (18 288 mm) in width.

 

[steveray]

so you're saying that depending on the length of where the buildings adjoin, it could kick the existing building into non-compliance, since it changes the open space increase percentage?

Although, it's only going to affect a 9% of the existing building perimeter, so the existing building should still be OK. With 66% increase instead of 75, the existing building is allowed to be 34,770, and it's currently at 30,567.

I don't think it is a straight 9%, but yes, you need to do the calcs and make sure the existing building works...

 

[steveray]

Do you have enough open space to use the unlimited are requirements?

507.6 Group A-3 buildings of Type II construction.
The area of a Group A-3 building not more than one story above grade plane, used as a place of religious worship, community hall, dance hall, exhibition hall, gymnasium, lecture hall, indoor swimming pool or tennis court of Type II construction, shall not be limited provided all of the following criteria are met:

1. The building shall not have a stage other than a platform.

2. The building shall be equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1.

3. The building shall be surrounded and adjoined by public ways or yards not less than 60 feet (18 288 mm) in width.

I think he said 2 story...

 

[MADrkTEK]

2-hour fire wall (structurall independent) adjacent to an existing building: I'm guessing CMU or other masonry or concrete design is probably the only viable solution?

We have a church facility that has been added on several times over the years. It's a mixture of A-3 and E, with a small area of B. 2-story building, fully sprinklered, with voice evac. Using Mixed Use Nonseparated, with A-3 as most restrictive, we're allowed 35,625 SF (Type II-B multistory with full open space all around the building). Current building gross floor area is 30,567. So we could add up to 5,058 SF per floor to remain Mixed Use Nonseparated. As a side note, I did run the numbers with the weighted averages for Mixed Use Separated, and there's no help there.

So if they need more than 5,000 SF, it seems that a fire wall is the only option, to create separate buildings. A structurally independent fire wall along the outside face of (not not actually attached to) the existing building. I don't know of any other way to achieve this other than CMU block or other masonry or concrete construction. We discussed the double-stud shaft wall liner with burn clips wall design for area separation walls, but as far as I know that's only for wood construction, and also can't really be properly constructed from only one side, against existing construction.

Code calls for a 3-hour fire wall for A and E uses, which can be reduced to 2-hour for fully sprinkled buildings. So 2-hour CMU with all its associated reinforcing and footings, and 90-minute doors in that wall for access through it.

Am I missing anything important?

There are alternative approaches that may be feasible depending on your circumstance.

in consideration that you need to build a fire wall immediately adjacent to the existing structure, you could build the fire wall with rated IMP (insulated metal panels) as a way to erect the wall without needing to access the one side for finishing or fastening. The IMP panels can be laterally supported to both sides (to each building) by using break-away clips (FERO Break away is an example): the clips are designed to release their connection with the adjacent structure should it burn and collapse. If that happens, the clip on the opposing side would remain intact still laterally supporting the IMP. If that side is burning too, then there’s really nothing left for the fire wall to protect…

Another solution I used was a condition where the existing building wall was masonry and already inherently had the fire-resistance rating needed. We just needed to reclassify it, seal penetrations and modify the existing lateral connections it had to the existing building so it could achieve structural independence. Fortunately this condition was a gable wall not otherwise used for primary structure. We used a similar product to replace the existing rigid lateral bracing along the top of the wall. And when the addition was built, we did the same; used break-away clips for the redundant bracing needed for the wall.

if you have a condition where you have some structure bearing on the wall you need to be structurally stable as a fire wall, options may be considered that rely on fireproofing existing primary structure that is connected to your wall. Intumescent coatings are being used widely anymore and they offer a clean and simple solution to coating existing structure to achieve rating requirements (There are caveats though I won’t get into them). The concept I am leading you to is that the fire wall (in your case) is required to stand for 2 hours. If you have something connected to it that cannot be modified to break away while leaving the fire wall standing, then you need to protect that connecting member and find a way to keep it from failing for two hours.

Finally, in consideration of how you describe this project, see if this design approach is feasible:
if you still have 5,000 sf of space you can add to the existing building, then see if there are any spaces , rooms, other functions you could design into that initial 1,000 - 5,000 sf so that you have the ability to plan and build an entirely new fire wall away from the existing structure so you are free to use wall assemblies that require access to both faces of the wall when building. It will open up easier and cleaner ways to achieve the structural independence as well.

good luck!

 

[Atarcht]

There are alternative approaches that may be feasible depending on your circumstance.

in consideration that you need to build a fire wall immediately adjacent to the existing structure, you could build the fire wall with rated IMP (insulated metal panels) as a way to erect the wall without needing to access the one side for finishing or fastening. The IMP panels can be laterally supported to both sides (to each building) by using break-away clips (FERO Break away is an example): the clips are designed to release their connection with the adjacent structure should it burn and collapse. If that happens, the clip on the opposing side would remain intact still laterally supporting the IMP. If that side is burning too, then there’s really nothing left for the fire wall to protect…

Another solution I used was a condition where the existing building wall was masonry and already inherently had the fire-resistance rating needed. We just needed to reclassify it, seal penetrations and modify the existing lateral connections it had to the existing building so it could achieve structural independence. Fortunately this condition was a gable wall not otherwise used for primary structure. We used a similar product to replace the existing rigid lateral bracing along the top of the wall. And when the addition was built, we did the same; used break-away clips for the redundant bracing needed for the wall.

if you have a condition where you have some structure bearing on the wall you need to be structurally stable as a fire wall, options may be considered that rely on fireproofing existing primary structure that is connected to your wall. Intumescent coatings are being used widely anymore and they offer a clean and simple solution to coating existing structure to achieve rating requirements (There are caveats though I won’t get into them). The concept I am leading you to is that the fire wall (in your case) is required to stand for 2 hours. If you have something connected to it that cannot be modified to break away while leaving the fire wall standing, then you need to protect that connecting member and find a way to keep it from failing for two hours.

Finally, in consideration of how you describe this project, see if this design approach is feasible:
if you still have 5,000 sf of space you can add to the existing building, then see if there are any spaces , rooms, other functions you could design into that initial 1,000 - 5,000 sf so that you have the ability to plan and build an entirely new fire wall away from the existing structure so you are free to use wall assemblies that require access to both faces of the wall when building. It will open up easier and cleaner ways to achieve the structural independence as well.

good luck!

MADrkTEK, thank-you for your input - the IMP concept you mention is a new one to me, but seems really advantageous. Are you able to share a bit more of the detailing and how this was done?

 

[MADrkTEK]

MADrkTEK, thank-you for your input - the IMP concept you mention is a new one to me, but seems really advantageous. Are you able to share a bit more of the detailing and how this was done?

information on the system can be found here: https://metlspan.com/products/wall/fire-rated/