Putty Pads Required? Noncommunicating Stud Space

Putty Pads Required? Noncommunicating Stud Space

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luckylerado

luckylerado

Senior Member
Location
Lake of the Ozarks
Given a 2x6 metal stud wall on 16" Centers

Are the stud cavities considered to be noncommunicating?

IBC 714.3.2 Exception 1

"...Such boxes on
opposite sides of the wall or partition shall be
separated by one of the following:

1.1. By a horizontal distance of not less than
24 inches (610 mm) where the wall or
partition is constructed with individual
noncommunicating stud cavities..."
 
"1.1. By a horizontal distance of not less than
24 inches (610 mm) where the wall or
partition is constructed with individual
noncommunicating stud cavities..."

If you have 24" horizontal or more between boxes, then it doesnt matter if the stud cavities are linked (communicating) or not. I'd consider cavities linked only if they are staggered stud, where the entire wall is open between studs, and there are no true "bays". Cavities between wooden studs would be "communicating" if holes were bored horizontally (for electrical cable) and not firestopped, and horizontal firestop between studs is not required. Openings in steel studs (which they all have), all would have to have putty pad wrapped boxes if 24" or less, or 100"sq opening (more than 7 4sq boxes) in a wall. iirc, the insulation type can also have a role in firestop requirements; wool bats allow more 'play' in what you can do.

I'd check 3M's website, they have excellent information re: fire stop requirements.

eta: Upon re-reading my post, it's ambiguous. I do not think metal studs are communicating, regardless of factory holes or field KOs, unless they were staggered stud.

Here's the rule on the insulation (same section as OP mentioned):

1.2. By a horizontal distance of not less than the depth of the wall cavity where the wall cavity is filled with cellulose loose-fill, rockwool or slag mineral wool insulation

and the 100sq in/100ft2 rule:

1. Membrane penetrations of maximum 2-hour fire-resistance-rated walls and partitions by steel electrical boxes that do not exceed 16 square inches (0.0103 m2) in area, provided the aggregate area of the openings through the membrane does not exceed 100 square inches (0.0645 m2) in any 100 square feet (9.29 m2) of wall area. The annular space between the wall membrane and the box shall not exceed 1/8 inch (3.1 mm). Such boxes on opposite sides of the wall or partition shall be separated by one of the following:
 
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JFletcher said:
...I'd consider cavities linked only if they are staggered stud...I do not think metal studs are communicating, regardless of factory holes or field KOs, unless they were staggered stud.
Click to expand...

This has been my position also but I am having trouble proving it in black and white. I have an AHJ type interpreting it to mean that without fire wool or fire-blocking there is no acceptable distance in a rated wall section that boxes can penetrate both sides of the wall and not require putty pads due to the use of metal studs. I have pointed to this section many times in the past to defend not using putty pads but the term "non-communicating" had never been an issue.
 
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Thanks for clarifying the question.
From an archived thread:

From the UL White Book:

6. Metallic Electrical Outlet Boxes
Listed single and double gang metallic outlet and switch boxes with
metallic or nonmetallic cover plates may be used in bearing and nonbearing
wood stud and steel stud walls with ratings not exceeding 2 h. These
walls should have gypsum wallboard facings similar to those shown in
Design Nos. U301, U411 and U425. The metallic outlet or switch boxes
should be securely fastened to the studs and the opening in the wallboard
facing should be cut so that the clearance between the box and the wallboard
does not exceed 1/8 in. The surface area of individual metallic outlet
or switch boxes should not exceed 16 sq in. The aggregate surface area
of the boxes should not exceed 100 sq in. per 100 sq ft of wall surface. The
aggregate surface area of the boxes may be exceeded when Wall Opening
Protective Materials (CLIV) are installed according to the requirements of
their Classification.
Metallic boxes located on opposite sides of walls or partitions should be
separated by a minimum horizontal distance of 24 in. This minimum
separation distance between metallic boxes may be reduced when Wall
Opening Protective Materials (CLIV) are installed according to the requirements
of their Classification.
Metallic boxes should not be installed on opposite side of walls or partitions
of staggered stud construction unless Wall Opening Protective Materials
are installed with the metallic boxes in accordance with Classification
requirements for the protective materials.


http://forums.mikeholt.com/showthread.php?t=143046
 
Here's something in print
Metallic boxes located on opposite sides of walls or partitionsare intended to be separated by a minimum horizontal distanceof 24 in. This minimum separation distance between boxes maybe reduced when Wall Opening Protective Materials (QCSN)(commonly known as putty pads) are installed according to therequirements of their Classification.

from
http://www.ul.com/wp-content/uploads/2014/04/Ul_outletboxes.pdf
 
JFletcher said:
Here's the page I was looking for:

http://www.fireretardantsinc.com/putty/pdf/3m_putty_pads.pdf

Note on page 2, "No Putty Pad Required":

UL rated U300 or U400
series wall or partition
assembly with minimum
3-1/2 in. (9.2 cm) wide studs
or minimum 3-1/2 in.
(8.8 cm) wide steel studs in
conjunction with listed steel
cover plates.
Click to expand...

No offense intended, but that's a 20 year old publication and published by a manufacturer. I think a current UL publication trumps that.
 
mgookin said:
No offense intended, but that's a 20 year old publication and published by a manufacturer. I think a current UL publication trumps that.
Click to expand...

true. I've seen more recent things from 3M, remember getting failed for an inspection when I had it identical to a photo on 3M's site, so bottom line (and what every site pretty much says) 'AHJ has final say'.
 
mgookin said:
Metallic boxes should not be installed on opposite side of walls or partitionsof staggered stud construction unless Wall Opening Protective Materials
are installed with the metallic boxes in accordance with Classification
requirements for the protective materials.
Click to expand...

Bingo. Thank you for the reference.

Based on this I am going to argue that "staggered stud construction" is synonymous with "communicating stud cavity" and that standard steel stud framing does meet the definition of non communicating.

You may have saved me like 6 bucks and it feels good knowing that I have not been doing it wrong :lol:
 
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