NCARB Pratice test
Taking the practice test and have a question about this answer. After looking at UL to double check, all assemblies with wood stud walls require two layers of gyp on the exterior. How is this correct? I understand how this is structurally independent but not getting the layers of gyp.
So the party wall is going to be in between 2 apartments. They want 2-hr rated, and structurally independents walls, one for each apartment.
Type A is the only choice that has a structurally independent 2-hr rated wall.
Type B is one wall, so if the studs start to burn, it's going to effect 2 apartments.
Type C isn't 2-hr rated.
Hope this helps!
Rebekka O'Melia, Registered Architect, NCARB, B. Arch, M. Ed, Step UP, Step UP ARE 5.0 Courses
How could wall type A have a 2-hour fire-resistant rating. Looking up this wall type through the USG: Fire-Resistant Assemblies catalog this wall type meets a 45-min. fire resistant assembly at best: one layer 1/2" Sheetrock Firecode C Core gypsum panels each side of 2X4 wood stud framing as opposed to a wall assembly with 2-layers 5/8" Type X each side. If given this question I would have been left perplexed despite given my experience and knowledge with fire rated construction assemblies that a 2X stud wall with two layers of 5/8" Type X gyp. board each side meets the 2-hour assembly requirement that I would have been torn between wall Type A and wall Type B but because of the additional requirement that each wall must be structurally independent for each unit hence the double wall that I would have reluctantly chosen Wall Type A and have crossed my fingers that that was the correct answer. Although the explanation given lacks and does nothing for us as well it is still up to NCARB to be much more specific and not lacking in their explanations to help us.
For Option A, they are showing not 2 separate walls, but rather 1. The wall system is built like this (simplified for clarity):
1 Layer GWB + Wood 2x4 + 1 Layer GWB + Air + 1 Layer GWB + Wood 2x4 + 1 Layer GWB
In comparison to wall B, they both have 4 total layers of GWB, whereas Wall C only has 2 total layers GWB.The amount of GWB layers probably relates to the fire ratings.
It may seem counterintuitive to build a wall this way, as opposed to something closer to a traditional singular wall, but its a very common way to provide fire protection, as well as sound isolation / improvement. If you would like to research the many types of walls that have been fire-tested and rated, check out the UL prospector page. https://iq.ulprospector.com/en/_?tt=1041
I hope this helps to clarify.
Please sign in to leave a comment.