Devices installed in a Residential Common use wall

[stuartdmc]

We are bidding a large multifamily apartment complex and my question is, are we required to
Fire/sound wrap all boxes that are installed in a common wall? My definition of a Common Wall is ;
a wall (1 of 2 hour fire wall)that is shared or between two units, a unit wall that is adjacent to the corridor wall.

Any help would be appreciated.
Thanks.
Stu.

 

[480sparky]

It's not an NEC issue.... it will fall under the local building and fire codes. Contact your AHJ for the real scoop.

 

[RICK NAPIER]

NEC 300.21 requires you to maintain the fire rating of the penetrations you make. You would need to check the building plans to identify if these are fire rated walls. It sounds that this is likely.

 

[stuartdmc]

NEC 300.21 requires you to maintain the fire rating of the penetrations you make. You would need to check the building plans to identify if these are fire rated walls. It sounds that this is likely.

We're proposing to use the residential "plastic" boxes that are rated for 1-2 hour, why isn't that adequate? By wrapping the already rated box seems redundant.

 

[RICK NAPIER]

If your using the IBC in your area this would apply.

713.3.2 Membrane penetrations. Membrane penetrations shall comply with Section 713.3.1. Where walls or partitions are required to have a fire-resistance rating, recessed fixtures shall be installed such that the required fire-resistance will not be reduced.

Exceptions: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:

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;
1.2. 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;
1.3. By solid fireblocking in accordance with Section 717.2.1;
1.4. By protecting both outlet boxes with listed putty pads; or
1.5. By other listed materials and methods.

2. Membrane penetrations by listed electrical boxes of any material, provided such boxes have been tested for use in fire-resistance-rated assemblies and are installed in accordance with the instructions included in the listing. The annular space between the wall membrane and the box shall not exceed ¹/₈ inch (3.1 mm) unless listed otherwise. Such boxes on opposite sides of the wall or partition shall be separated by one of the following:

2.1. By the horizontal distance specified in the listing of the electrical boxes;
2.2. By solid fireblocking in accordance with Section 717.2.1;
2.3. By protecting both boxes with listed putty pads; or
2.4. By other listed materials and methods.

3. Membrane penetrations by electrical boxes of any size or type, which have been listed as part of a wall opening protective material system for use in fire-resistance-rated assemblies and are installed in accordance with the instructions included in the listing.

 

[Dennis Alwon]

Make sure the outlets in adjoining units are not in the same stud space.

 

[RICK NAPIER]

Make sure the outlets in adjoining units are not in the same stud space.

That is covered in part 2 of the long response above.

 

[dana1028]

We are bidding a large multifamily apartment complex and my question is, are we required to
Fire/sound wrap all boxes that are installed in a common wall? My definition of a Common Wall is ;
a wall (1 of 2 hour fire wall)that is shared or between two units, a unit wall that is adjacent to the corridor wall.

Any help would be appreciated.
Thanks.
Stu.

Typically those projects spell out the exact type of fire protection needed [to include the type and mfr. of fireproofing material]; sometimes they spell out the type & mfr. of boxes as well.

Every similar project I have inspected has had very detailed 'penetration' specifications for all the trades.

 

[bobserrano]

As far as the fire resistance goes all the responses are very helpfull. In addition to fire resistance I think that the reason for wrapping all boxes in the common walls is to limit sound transmission. Just about every new multi-family developement I have inspected in the last few years has had detailed requirements to limit sound transmission at common walls. A few have had to pass sound tranmission testing (testing by a third party) as provision of completion.

 

[steve66]

Make sure the outlets in adjoining units are not in the same stud space.

I always thought that was sufficient too, and I'm sure it is for residential with wood studs.

But would that also apply to a commercial installation with metal studs??

Looking at the reference posted:

"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;
"

I wouldn't think metal studs would be "noncommunicating".

Steve

 

[construct]

But would that also apply to a commercial installation with metal studs??

My take has always been yes because the code does not distinguish between the two types of material. In the Building Code, convetional light-frame construction includes wood and metal studs. The code only refers to "stud cavities". However, your question does make a good point. Metal studs are manufactured with openings to accomodate piping and wiring methods for mechanical, electrical, and plumbing.............so that would allow one stud cavity to communicate with another. I don't know that I have ever seen this addressed.:?

 

[renosteinke]

Having participated in the NRTL full-scale fire tests that directly led to the codes cited, I think I can shed some light on the topic.

First off, there is a wealth of data that supports the view that metal studs are identical, in terms of fire wall rating performance, to wood studs. Don't get all worried about the pre-punches- especially when the stud bays are filled with insulation.

Secondly, when it comes to the fire rating, only one thing really matters: gypsum thickness. It doesn't really matter which side of the wall has the gypsum.

So the question becomes, what if there's a small hole in the gypsum, on one face of the wall? Well, the tests told us that size does matter, and the cut-off seemed to be somewhere between the 4-square box and the 4-11. Personally, I read the test results as saying you don't need the putty pads for a 4-square ... but code writers decided to be conservative, and want the pads, starting with the 4-s box.

The next issue was having a hole on both faces of the wall. The tests showed this to be a bad thing, even for holes as small as 1/2" diameter. Hence the need to seal penetrations. Opposing boxes in the same stud bay are pretty much the same as putting a hole through the wall, whether the boxes are offset or not. Think 'duct' or 'chimney.' So, don't put a hole on both sides of the cavity. Code writers, again to be conservative -and to cover walls with 24"OC studs- simply wrote that the holes have to be at least 24" apart .... to guarantee that they would be in different bays.

I'm not saying I agree with the rules, but that's where they come from.

Also, recognize that there are many wall assemblies that have two separate rows of studs, one for each face. This is usually done for sound control. One problem with these designs is that there are no 'isolated' stud bays, the entire area between the wall faces is one big cavity. That's what the 'communicating' is all about.

 

[steve66]

So which boxes require the pads?

I think I've seen it stated that plastic boxes are "listed", and don't require the pads.

But metal boxes require the pads? It that all sizes, or just 2 gang and above. (I'm not quite following all the box types: Is a 4-11 box one of the 4-11/16" boxes? What's a 4-s - a 4 square??)

 

[cadpoint]

My take has always been yes because the code does not distinguish between the two types of material. In the Building Code, convetional light-frame construction includes wood and metal studs. The code only refers to "stud cavities". However, your question does make a good point. Metal studs are manufactured with openings to accomodate piping and wiring methods for mechanical, electrical, and plumbing.............so that would allow one stud cavity to communicate with another. I don't know that I have ever seen this addressed.:?

What people forget is that in this case it's the "Total Assembly" of the type of construction that gets graded to some rating with-in the building code's.

Insulation plays a major part of the assembly. Fire rating starts on the outside of the assembly, but is measured by the total assembly when rated.

I've worked with spec'd jobs that let only that bay of stud spacing be installed in vertical only; or if laterial - all horizonital holes are closed as they run through metal studs. I've pasted both the inside and outside of Metal boxes, but not both.

The metal stud industry has never stated anything about how there product is destroyed as services are run through the wall, maybe other to imply that their material respects of strength, and aspects of usage are to be maintained.

 

[renosteinke]

The building code says that non-rated boxes that are 16 square inches or larger need the pads. That would include the usual 4-S/4-square/1600/2-gang box. I suppose they may have chosen to go by box size, rather than opening size, to avoid disputes based upon the specific mud ring selected, or the neatness of the hole in the wall.

The testing indicated there was no need until you got to the larger 4-11, or 4-11/16" square box. The code was written to include the smaller box 'just to be sure.'

 

[roger]

Just use these.

Click Here for more info.

Roger