Gypsum Area Separation Wall for Townhouse Separation
Posted: Tue Mar 17, 2020 6:08 pm
Hello Jerry,
I am working on a townhouse project under the NJ IRC, 2018. It's three stories, not sprinklered, type VA (protected wood framing) construction.
I have a question regarding the common walls (R302.2.2), which in the case of my design are also bearing walls. I believe the following requirements apply at these walls:
1) 2 hour rated separation (R302.2.2, item 2)
2) Minimum 1 hour fire resistance for bearing walls (IBC type VA definition)
The solution I've found for a wood-framed common wall in this application is a Gypsum area separation wall assembly, which consists of two wood stud walls, each with GWB on their outside face, separated by a gap within which is a continuous shaftwall of 2" Gypsum held in place by H channels and aluminum clips which melt away in the event of a fire from one side.
For example see: http://www.usg.com/content/dam/USG_Mark ... -SA925.pdf
2 hour UL rating: https://www.marinoware.com/wp-content/u ... d-U347.pdf. The UL document describes the assembly as comprising the "Separation WAll" (the 2" gypsum shaftwall in the middle) and the "Protected Walls" (the stud walls on either side).
Does the assembly satisfy both requirements (1) for a 2-hour separation and (2) for a minimum 1 hour fire resistance for bearing walls?
It seems that the two hour rating achieved by the 2" shaftwall (the "Separation Wall") in the assembly is really protecting one side of the wall from the other side (i.e. each "protected wall" from a fire on the other side). That is, if there's a fire at Townhouse A and it collapses, the 2" shaftwall remains in place an protects adjacent townhouse B. Am I correct that the 2 hour rating does not provide fire resistance at the bearing walls (protected wall) on either side of the shaftwall for fire coming from their respective sides, and therefore does not provide the required 1 hour fire resistance rating for a bearing wall in type VA construction? For example, if there's a fire in Townhouse A, does the assembly provide protection to the bearing wall supporting Townhouse A?
Even if the 2-hour rating in U347 does not technically cover the 1 hour fire resistance rating requirement for the bearing walls in type VA construction, would a code official still accept the assembly as complying with the 1 hr requirement since the "protected walls" have GWB on one side, and are essentially a 1-hour chase wall (U341) with a shaftwall in the middle?
I greatly appreciate any thoughts you have on this. Also, if there's a better way to achieve a wood-framed common or double wall in type VA townhouses, please advise. I'm trying to avoid costly CMU if possible, and also to avoid sprinklers.
Many thanks
Behrang
I am working on a townhouse project under the NJ IRC, 2018. It's three stories, not sprinklered, type VA (protected wood framing) construction.
I have a question regarding the common walls (R302.2.2), which in the case of my design are also bearing walls. I believe the following requirements apply at these walls:
1) 2 hour rated separation (R302.2.2, item 2)
2) Minimum 1 hour fire resistance for bearing walls (IBC type VA definition)
The solution I've found for a wood-framed common wall in this application is a Gypsum area separation wall assembly, which consists of two wood stud walls, each with GWB on their outside face, separated by a gap within which is a continuous shaftwall of 2" Gypsum held in place by H channels and aluminum clips which melt away in the event of a fire from one side.
For example see: http://www.usg.com/content/dam/USG_Mark ... -SA925.pdf
2 hour UL rating: https://www.marinoware.com/wp-content/u ... d-U347.pdf. The UL document describes the assembly as comprising the "Separation WAll" (the 2" gypsum shaftwall in the middle) and the "Protected Walls" (the stud walls on either side).
Does the assembly satisfy both requirements (1) for a 2-hour separation and (2) for a minimum 1 hour fire resistance for bearing walls?
It seems that the two hour rating achieved by the 2" shaftwall (the "Separation Wall") in the assembly is really protecting one side of the wall from the other side (i.e. each "protected wall" from a fire on the other side). That is, if there's a fire at Townhouse A and it collapses, the 2" shaftwall remains in place an protects adjacent townhouse B. Am I correct that the 2 hour rating does not provide fire resistance at the bearing walls (protected wall) on either side of the shaftwall for fire coming from their respective sides, and therefore does not provide the required 1 hour fire resistance rating for a bearing wall in type VA construction? For example, if there's a fire in Townhouse A, does the assembly provide protection to the bearing wall supporting Townhouse A?
Even if the 2-hour rating in U347 does not technically cover the 1 hour fire resistance rating requirement for the bearing walls in type VA construction, would a code official still accept the assembly as complying with the 1 hr requirement since the "protected walls" have GWB on one side, and are essentially a 1-hour chase wall (U341) with a shaftwall in the middle?
I greatly appreciate any thoughts you have on this. Also, if there's a better way to achieve a wood-framed common or double wall in type VA townhouses, please advise. I'm trying to avoid costly CMU if possible, and also to avoid sprinklers.
Many thanks
Behrang