Gypsum Area Separation Wall for Townhouse Separation

[bbehin]

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

[Jerry Peck - Codeman]

First, a question: Is there a property line between the townhouse units, or is the townhouse building actually (and effectively) like an apartment building in which there is "one" building which contains "more than one unit"?

If the townhouse building is separated by a property line, each townhouse is in fact "its own building".

If the townhouse building is "one building", the NEC requirements for that "one building" are different than if each townhouse was "its own building".

Back to your question with another question: Is the separation wall between townhouses, which is also considered to be a load bearing "exterior wall" like other exterior walls, or is that wall non-load bearing?

Your linked to document states, at the top of page 5: (bold and underlining are mine) "USG area separation wall systems are lightweight, non-load-bearing gypsum panel partition assemblies used to provide fire-resistive protection for common walls in townhouse construction."

Keep in mind that when using a proprietary design that all materials must ... must ... be consistent with that proprietary design - from the top of page 6: (bold and underlining are mine) "USG area separation wall systems have been comprehensively tested for fire resistance ratings only when all of the system components are used together. Substitutions of any of the components are not recommended and are not supported by USG."

The Testing Results, on page 7, does not clearly state that it meets the ASTM E119 test (similarly, for STC, it also only states "STC ratings up to 60 are available." ... not that it has an STC rating of 60.

Another question: Are there any electrical, plumbing, ductwork, etc (MEPs) in that wall?

Your local AHJ would need to make the final call, but what I read results in 'more questions than answers'.

[bbehin]

Hello Jerry,

Thank you for the response.

The townhouse units are all on the same lot. It is one building which contains multiple units, separated by "common walls" as defined in IRC R302.2.2

The common walls are load bearing walls.

I believe the quote on page 5 refers to just the shaft wall (3.5" thick as stated in the text, or 3/4" gap + 1" gyp + 1" gyp + 3/4" gap) and not the full assembly which includes the potentially load bearing stud walls on either side. If you go to the UL listing for the system (https://www.marinoware.com/wp-content/u ... d-U347.pdf), you'll see that the "protected" walls - i.e. the stud walls on either side of the shaftwall which are being protected by the shaftwall from fire on the other side, can be bearing or non-bearing.

This brochure by National Gypsum provides a clearer explanation on page 2 of how the various components of the system interact: https://designcenter.nationalgypsum.com ... onwall.pdf

My central question is this:

type VA construction requires the bearing wall to be 1-hour protected. I assume this includes protection from a fire occurring inside the townhouse which the wall is supporting. I am asking if the U347 2 hour rating applies only to fire separation between townhouses (protecting the wall from a fire at the adjacent townhouse). Can the stud wall within the assembly be assumed to have 1 hour protection against a fire occurring within the townhouse on its own side of the common wall?

There is no ductwork in the wall. We plan to have electrical as allowed by R302.2.2, but it would not penetrate the 2" shaftwall. Plumbing is a question. R302.2.2 forbids it, but page two of the National Gypsum brochure (https://designcenter.nationalgypsum.com ... onwall.pdf) states that the load bearing walls can have MEP in them.

I can design the project without plumbing in the wall if need be. The real question is whether I can use the wall in a type VA construction (with 1 hour protection requirement) to begin with.

Apologies if this is getting complicated and thank you again for taking a look at it.

Best Regards
Behrang

[Jerry Peck - Codeman]

The answer seems to be in the wording of the code.

The code addresses two types of walls:
- two separate 1 hour rated walls
- one common 2 hour rated wall

And with your reference being to a "common wall", that puts another aspect into what the code requires.

That design is trying to make that "common wall" into "two separate walls" - and is trying to fit between the two stated requirements, which then requires engineering and local AHJ approval.

[bbehin]

Thank you Jerry. I'll dig further with the local AHJ.

-Behrang

[Jerry Peck - Codeman]

Behrang,

Let's parse the words of the New Jersey Edition of the IRC (available here: https://codes.iccsafe.org/content/NJRC2 ... g-planning ):

(bold and underlining are mine)

R302.2 Townhouses. Walls separating townhouse units shall be constructed in accordance with Section R302.2.1 or R302.2.2.
- R302.2.1 Double walls. Each townhouse shall be separated by two 1-hour fire-resistance-rated wall assemblies tested in accordance with ASTM E119, UL 263, or Section 703 of the International Building Code.
- R302.2.2 Common walls. Common walls separating townhouses shall be assigned a fire-resistance rating in accordance with Item 1 or 2. The common wall (blah, blah, blah ... the rest is not being typed as it does not apply to the question at hand)
- - 1. Where a fire sprinkler system in accordance with Section P2904 is provided, (blah, blah, blah ... does not apply as no fire sprinkler system is being provided)
- - 2. Where a fire sprinkler system in accordance with Section P2904 is not provided, the common wall shall be not less than a 2-hour fire-resistance-rated wall assembly tested in accordance with ASTM E119, UL 263 or Section 703.3 of the International Building Code.

That Item 2 in Section 302.2.2 is what I am referring to.
- R302.2.2, Item 2, "Common walls"
- - Item 2. Where a fire sprinkler system ... is not provided, the common wall shall be not less than a 2-hour fire-resistance-rated wall assembly ...

I looked at your last reference again ( https://designcenter.nationalgypsum.com ... onwall.pdf ) and it states: (bold and underlining are mine)
- Technical Data
- - The Area Separation Wall System has a non-bearing wall rating of 2 hours and is listed in the UL Fire Resistance Directory as Design No. U347 and in the GA-600 Fire Resistance Manual as file numbers ASW 0800, ASW 0981 and ASW 0998.
- - The Area Separation Wall System has been evaluated for code compliance in UL Evaluation Report UL ER R3501-01.
- - The Area Separation Wall System may be built up to a maximum of 66 ft. (20.1 m) high.
- - Do not use the Area Separation Wall System where exposure to constant dampness and/or water may occur.
- - Although steel framing and Gold Bond® brand eXP® Gypsum Panels can withstand temporary exposure to moisture during construction, protect the finished wall as soon as possible.
- - Protect insulation in the Area Separation Wall from getting wet.
- - Do not install until the building is enclosed.
- - Properly store materials supplied to the jobsite, support off the ground, and protect from inclement weather.

The first item in the list above is key as I read it. The "Area Separation Wall System" is addressing the entire system as I read it, not just that inner layer between the two stud walls. This reading is supported by the use of "Area Separation Wall System" as an all encompassing term in the second, third, and fourth items in the list above.

That link references "UL Fire Resistance Directory as Design No. U347", which is here: https://www.marinoware.com/wp-content/u ... d-U347.pdf

The UL document states the following: (bold and underlining are mine)
- Nonbearing Wall Rating — 2 Hr (See Items 4, 4A and 4B) (Separation Wall, See Items 1,2 and 3)
- Bearing Wall Rating 2 Hr. (Protected Wall, See Items 4 and 4A)
- Nonbearing Wall Rating 2-Hr (Protected Wall, See Item 4, 4A and 4B)
- Finish Rating — 120 Min (See Item 4)
- STC Ratings — 61, 69, 70 (See Items 7 - 7B)

The second item in the list above seems to contradict what this ( https://designcenter.nationalgypsum.com ... onwall.pdf ) National Gypsum document states.

Thus my 'local AHJ approval".

It comes down to the wording in the various documents and the code ... and the way the local AHJ read them.

Added this regarding the term "protected wall" by UL: https://www.ul.com/news/qa-area-separation-wall-design

[bbehin]

Thank you Jerry. Yes, it's an apparent ambiguity which I hope to address with the local official.

Best Regards
Behrang