1/4 inch Set Back

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Re: 1/4 inch Set Back

The explanation in the handbook states: "The terms surface and with a surface of make it clear that the requirements of this section apply only to the construction of the surface of the wall or ceiling, not to the structure or subsurface of the wall or ceiling. Therefore, a wall constructed of wood but sheathed with an outer layer of gypsum board is permitted to contain boxes set back or recessed not more than 1/ 4 in. Using an opposite example, a wall constructed of metal studs but finished with wood panels requires that contained outlet boxes be mounted flush with the combustible finish."
 
Re: 1/4 inch Set Back

sheetrock = non-combustible

Pierre
I'm curious as to why you would ask. I would of figured this would be elementary for someone of your skill.
 
Re: 1/4 inch Set Back

A receptacle installed in the kitchen cabinet for a microwave or hood fan.

At rough-in the electrician installs the box just as he did the others. Sheet rock is hung and box is flush. Cabinet is installed and now the box is recessed. Cabinet is made form wood which will burn.

This is one thing that every code official should look at in every house and charge a inspection fee for the return trip. One of the top ten violations in this area.
 
Re: 1/4 inch Set Back

Originally posted by jwelectric:
A receptacle installed in the kitchen cabinet for a microwave or hood fan.

At rough-in the electrician installs the box just as he did the others. Sheet rock is hung and box is flush. Cabinet is installed and now the box is recessed. Cabinet is made form wood which will burn.

This is one thing that every code official should look at in every house and charge a inspection fee for the return trip. One of the top ten violations in this area.
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Arlington makes a nice "sleeve" to remedy this situation. We keep them in the trucks. Also used when backsplash is tiled.
To answer thread, sheetrock is considered noncombustible.
 
Re: 1/4 inch Set Back

John
Is the product that the surface of sheetrock is made of noncombustible?

I understand that gypsum itself is noncombustible.

Why am I asking these types of questions? I am in the process of building my own PPTs for a few different types of presentations. I believe when they are finished that the final product will be exceptional in content and pictures, to help all in our industry have a better understanding of the code and theory behind the code.

You guys have only yourselfs to blame for my anal approach- or hardliner approach as has been mentioned of my style :D
Detail, Detail, Detail!

[ November 30, 2005, 12:14 PM: Message edited by: pierre ]
 
Re: 1/4 inch Set Back

i've see the paper burn in fires, non-combustible usually requires a specific flame spread rating. do not have stats available, but would assume that normal sheetrock does not satisfy non-flammable as there is fire rock specifically for this.

any installation requiring fire retardation requires fire rock. garage wall hybrid ratings (garage wall ratings with 1/2" sheetrock are not "ratings" but local accepted practice) are not derived from the rating of the sheetrock unless fire rock.
 
Re: 1/4 inch Set Back

In areas where the finish will be over the sheetrock we always install adjustable boxes. They can be cranked out to fit flush with the wood or in the case of a backsplash, with the tile etc.
 
Re: 1/4 inch Set Back

Originally posted by pierre:
What is the "surface" of sheetrock made out of?
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Ok I get it. I didn't mean to offend. It's made out of paper which is combustible. Aside from the fact that "we've always done it that way", I have no technical explanation to give you. Even wallpaper on sheetrock, I would consider non-combustible.

Once we start with plwood veneer, cabinet backs, and yes even carpet on the walls; then we have a combustible surface. Break out the cheater rings, arc-shields, switch ring extenders, etc.
 
Re: 1/4 inch Set Back

Sweet! We're going five pages arguing the burn properties of sheetrock. I'm in. :D

Non Combustible.
 
Re: 1/4 inch Set Back

Originally posted by electricmanscott:
Sweet! We're going five pages arguing the burn properties of sheetrock. I'm in. :D
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and a 6 cent plastic part eliminates the need for the whole discussion.
 
Re: 1/4 inch Set Back

Fire Rock still has the same paper on it, The difference is the Fire Rock has glass fibers in it to give it strength when the fire burns away the paper. There is reference material that does explain that gypsum board is a non-combustible surface. I'll try to find it.

One way it was explain to me is ever try to burn a piece of paper laying flat on a concrete floor? It wont burn because the concrete will remove the heat faster then the fire can heat up the paper. this is the same for the paper on gypsum board
 
Re: 1/4 inch Set Back

Ok, I'm in to. If gypsum wallboard is so noncombustable then why is it necessary for sometimes several layers of it on fire rated walls?. I alway's wanted to know that.
 
Re: 1/4 inch Set Back

NFPA 1 Fire Prevention Code
2-1.105 Noncombustible Material. A material that, in the form in which it is used and under the conditions anticipated, will not ignite, burn, support combustion, or release flammable vapors when subjected to fire or heat. Materials that are reported as passing ASTM E136, Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750?C, shall be considered noncombustible materials. (102:2-2)


2-1.33 Combustible. A material that, in the form in which it is used and under the conditions anticipated, will ignite and burn; a material that does not meet the definition of noncombustible or limited-combustible. (101:3.3.29)
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Hope this doesn't take all the fun out of this thread! :D
 
Re: 1/4 inch Set Back

So, the paper on sheet rock is combustable, but the gypsum is not...okay.

After reading Dave's post, I have come to this conclusion.
Sheet rock is combustable until the paper burns away, then it is not combustable anymore ;)
 
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