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Being told I need two fire dampers to serve a single fire wall. The fire wall is made of a "double wall", essentially two masonry walls next to each other with a very small (less than 2-inch) air gap in-between. The engineer on the project is stating that this "double wall" requires a fire damper in each.
I've never come across this as a requirement before. Do I need two fire dampers? Posted anonymously for discussion. Discuss This | Submit Your Question | Subscribe
10 Comments
10/4/2019 10:28:29 am
A double fire wall is an assembly of two rated wall, so each wall is required to maintain its rating in the event that the other wall collapses. Therefore, each would have to have its own fire damper. This is also true if there is a door through the wall, each wall would have to have an appropriately-rated door.
efi sher
10/4/2019 11:45:27 am
Why to use double fire wall if you can construct a single fire wall with the required fire rating.The rating of the wall is for the whole element no matter the side.
Cyril McIvor
10/4/2019 11:49:15 am
A double skin masonry wall is very common and only requires a single fire damper constructed to suit the width of the two skins including the gap between. It would be impossible to install two fire dampers as it is not possible to installed the required angles for each damper for each skin. The installation of fire dampers requires the damper to have retaining angles on both sides of the wall. 10/4/2019 12:46:31 pm
CYRIL MCIVOR, please define "double skin wall". If you have two 2-hour walls together to make a three hour wall, but only one fire damper, how do you maintain the 2-hour rating of the unprotected opening when the wall with the damper collapses?
Paul Pinigis
10/4/2019 01:53:51 pm
From NFPA 221, 2018:
Cyril McIvor
10/4/2019 02:00:23 pm
The sole reason to construct a wall with two skins is to achieve the nominated fire rating level. If a check of a masonry wall construction manual is made it will be seen that this wall is most likely only rated for 2 hours as a combined system (similar to dry wall construction) with brick ties between the two skins of masonry. Otherwise why build to separate wall systems so close together.
Paul Pinigis
10/4/2019 03:10:14 pm
CYRIL MCIVOR, I don't think that you understand the requirements for firewalls. Please read NFPA 221 before suggesting that anyone else go back to kindergarten.
Efi SHER
10/5/2019 12:23:45 am
Why use double wall for 3 hours
Matt Duggan
11/3/2020 07:12:29 pm
I am reading this thread from the perspective of the person needing the double fire wall with a door in each fire wall. Doors would have to swing opposite directions to meet this requirement, I think, which means a double fire wall could not be used in an egress condition where doors both have to open in the direction of travel to the exit. Sounds like I need a tied or cantilevered fire wall instead of a double fire wall for my situation. I need a codes illustrated book for this
Moderator
11/10/2020 06:25:48 am
Matt - your question makes for a great discussion. I've posted it as a daily question today, here: Leave a Reply. |
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