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cart0181 10-25-2008 08:25 PM

Combustible ----> Non-Combustible Wall
I need to "convert" a standard plaster/lath wall into one that is completely non-combustible. I'm pretty sure the wall is load-bearing. How can I accomplish this? Thanks.

DangerMouse 10-25-2008 08:45 PM

ok, i'll bite.... why?


Sammy 10-25-2008 08:48 PM


Termite 10-26-2008 12:53 AM

Yeah, I'm going to have to ask why as well. Is the intent of the noncombustible wall to separate two adjoining residential spaces (duplex, etc) or separate occupancies of another sort (house from a business)?

I'm well versed in firewalls and fire separation assemblies but need to know exactly what you're doing. The question is just way too vague.

bjbatlanta 10-26-2008 11:16 AM

KC, is plaster considered combustible or does it not have a fire rating?? Just for my own edification....

DangerMouse 10-26-2008 11:27 AM

i didn't think plaster burned neither. i wondered the same thing.


nap 10-26-2008 12:08 PM


Originally Posted by bjbatlanta (Post 176964)
KC, is plaster considered combustible or does it not have a fire rating?? Just for my own edification....

there is a difference between a wall being fire rated and totally non-combustable. A fire wall is not neccessarily completely non-combustable. It is merely rated to restrict fire travel for a specified period of time.

OP needs to clarify what he needs and why.

bjbatlanta 10-26-2008 12:27 PM

Very true, nap. Even the face paper on the drywall and the tape on the joints is "combustible". And cart1081 did specify "completely non-combustible". Sammy may be on the right brick??

DangerMouse 10-26-2008 12:33 PM

yeah, he could just put up steel barn siding.... that's pretty well firePROOF... need more input


Termite 10-26-2008 04:28 PM

I wouldn't think that plaster has any combustible properties to it...
But you don't see much plaster in rated walls in these parts either. A fire protection engineer could certainly specify plaster when determining a wall assembly's fire rating, although I've never seen it done, and am unaware of any UL or GA fire rated assemblies that incorporate it.

NAP is correct, noncombustibility is not usually an issue in residential (type 5) construction, the assembly of wall board, insulation, and framing in a certain way lends itself to resisting passage of fire and protection of structural elements.

Sheetrock is fire resistant, but the paper face is in fact combustible. Sheetrock's ability to withstand heat and fire comes only from the moisture content of the gypsum core. When the moisture is cooked out of it, the panel fails.

bjbatlanta 10-26-2008 06:35 PM

Thanks KC. It was my own curiosity that sparked the question. Common sense says plaster would be a "fire resistive" substance. Since it is not commonly seen/used, I was interested to see if you were aware if it had any "rating". Didn't mean to get the thread off track. Understand that it's probably not a "cut and dried" answer, and here the key word was "non-combustible" not fire rated. Looking forward to more info from cart0181 to see how this plays out. The fire marshal always holds the "trump" card when it comes to getting a C.O., so it's nice to have as much knowledge of ratings/codes as possible to keep up.

Termite 10-26-2008 09:32 PM

I'd say that plaster would definately be noncombustible. Remember that materials themselves don't really have a "rating". In order to get a rating you've got to combine materials. What I mean is that sheetrock or plaster alone are pretty worthless in a fire without other means of support (studs, joists, etc), creating an assembly.

There is a big misconception out there that sheetrock has an hourly rating...Like 5/8" type X gypsum is 1 hour. Not true. To get the one hour rating, the rock has to be fastened a certain way with certain screws or nails to certain framing members at a certain spacing. Fire is laid to the assembly for an hour, and then the assembly is hit with a firehose stream. Even if the assembly survives the fire, it may fail due to the hose stream portion of the test. Every UL and GA assembly you see have passed that test.

DangerMouse 10-27-2008 07:36 AM

well, this guy could be a 'fire artist' that uses a flame-thrower to do his art, for all we know! until he comes back to tell us why, all we can do is speculate! but it's interesting anyways....


cart0181 10-27-2008 05:13 PM

Wow! Okay, I've definitely found the right forum here! Thanks everyone so far for your responses. I apologize for not checking back on this sooner. I didn't expect such a great response.

The application I'm talking about here is for a wood-burning stove. Unfortunately, I haven't been able to identify the manufacturer of the stove because I got it "as is" and I believe it is very old, maybe even antique. If I knew the manufacturer, I could follow their guidelines if they had it UL listed, but that option seems out at this point. That being said, I can follow the "Standard" clearances set forth by the NFPA section 211. These codes require a clearance of 3 feet in all directions from ANY combustible material (yes, the lath boards qualify, as do the wood studs they're mounted to) unless you use some sort of "clearance reduction system," which reduces the clearance to 1 foot. The clearance reduction system is basically a non-combustible wallboard such as Durock spaced out 1 inch from the combustible wall using non-combustible spacers of some sort. That would be no problem, but unfortunately, 1 foot isn't quite close enough for me.

So the problem remains. How can I get closer than 1 foot? It seems to me the only way to do it is to eliminate all wood from this wall by re-building it entirely with non-combustibles. As I already said, I do want the wall where it is and I believe it to be load bearing. Unless someone else here can think of another sneaky way to do it?

I'll post some pics also to make it more clear what's going on.

cart0181 10-27-2008 05:27 PM

Here's the pictures, just click the thumbnail for a larger size.

The stove is positioned exactly 1 foot from the combustible walls in the pictures. Unfortunately, it's not where I want it to be. I need it a little closer so it will be out of the walking path. There will also be a pad which must extend 18" from the front loading door which would put it half way into the hallway. Totally unacceptable!

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