# Are plaster walls considered combustible



## ckdeuce (Feb 15, 2008)

Are plaster walls (not-drywall) considered as a combustible material?  Can I run a 2" clearance pipe closer to plaster?


----------



## fecrousejr (Feb 15, 2008)

ckdeuce said:
			
		

> Are plaster walls (not-drywall) considered as a combustible material?  Can I run a 2" clearance pipe closer to plaster?



Combustibility of a wall assembly depends on more than wall surface finish.  If the plaster is on a wood frame wall, then it is considered to be a combustible wall.  Varyious plaster types and thicknesses will provide certain definable fire resistance ratings, but will not render a wood stud wall as "non-combustible".  Feel free to check out the UL web site for the specifics of flamespread / smokespread / fire resistance.


----------



## jbrown56 (Feb 15, 2008)

Hi, Plaster itself is non combustable. If you have thin coat or veneer plaster, there is only 1/2" blueboard behind attached to studs. If you have a home built in the 50's and 60's ou will have 1/2' brownboard, 1/2" of base coat and 1/4" finish plaster. If your home is older than that you will have horsehair plaster on wood laths attached to studs. I would be concerned about the combustables behind the plaster. I would consult the mfg. specs. and give it some extra space.

Jim


----------



## jbrown56 (Feb 15, 2008)

Hi, Plaster itself is non combustable. If you have thin coat or veneer plaster, there is only 1/2" blueboard behind attached to studs. If you have a home built in the 50's and 60's ou will have 1/2' brownboard, 1/2" of base coat and 1/4" finish plaster. If your home is older than that you will have horsehair plaster on wood laths attached to studs. I would be concerned about the combustables behind the plaster. I would consult the mfg. specs. and give it some extra space.

Jim


----------



## fecrousejr (Feb 15, 2008)

Jbrown - 

For that matter, the IBC (and UL) consider gypsum board (drywall) to be non-combustible.  The distance to combustible construction should take into account the structure of the wall.  As a certified code official, if I saw any UL listed vent or flue being used in a situation that even brought the distance and definition into question, I would advise the owner that, despite the semantics, he may be putting his property insurance at risk.  Ultimately, it only becomes an issue AFTER something fails, and then it's a matter of who has the best lawyer.  Try to find a way to stick to the clearances specified on the UL approval of the item in question.


----------



## begreen (Feb 15, 2008)

Not a code expert here, but it would seem that UL is more concerned with gypsum board as a fire barrier, rating it for the time it stops the spread of fire. A wood stove application is very different. The paper on gypsum board is combustible as are the wood studs behind them. With a wood stove the greater concern is pyrolysis which happens to the wood behind the drywall or plaster as it is heated over a long period of time. It's combustion point is lowered and eventually can it catch fire at much lower temps.


----------



## fastrac (Feb 15, 2008)

We try and simplify things and use 2 terms 

Protected wall 

and 

Non protected wall

the majority of our intallations are installed as non protected walls and we follow those clearance, If you cant see whats in the wall (almost always impossible) then it would be a mistake to assume whats behind it. 

Most of the clearance we follow are not because we are afraid of a ember or spark setting a home on fire, its more meant for the costant heat soak of a hearth product lowering the combustion tempiture of whats hidden inside a wall and setting the home on fire.


----------



## savageactor7 (Feb 15, 2008)

I'm not an authority but decided to bury my my sheetrock when it wouldn't burn on a very an out door fire. However sheetrock is usually nailed to combustibles like 2x4's or over lath like you would find in older houses...

...it's what the sheetrock covers up that you have to worry about.


----------



## d.n.f. (Feb 15, 2008)

By doubling up the sheet rock boards you can double your fire barrier burn through times.  I used to know the numbers but a 45 minute regular sheet of drywall will give you 90 if doubled up.

What the killer is in most homes are the holes caused by pipes (and the pipes themselves), hvac, and electrical.  Poor sealing of these penetrations become passageways for smoke, heat, and flame.  A hot steel pipe that penetrates through a non combustible wall can also ignite stuff on the other side or interior wooden 2 x 4s.


----------



## begreen (Feb 15, 2008)

Yep, add this opening between floors and maybe add a fan to it. Now you're talking nice fast fire spread.


----------



## struggle (Feb 15, 2008)

If it i snot itself the paint on the surface will certainly be and will spread a fire to things that can burn.


----------



## stoveguy13 (Feb 15, 2008)

It is a combustibale wall need to keep proper clearances.


----------



## fecrousejr (Feb 16, 2008)

Read the UL requirements on the vent / chimney pipe you are planning to use.  The wording is very specific.  It has to be to meet the UL test criteria.  The wording USUALLY refers to "combustible construction", not "combustible surface".  Any wood frame wall is considered, under ALL building codes, to be "combustible construction", except for a VERY few exclusions where the wood has been "fire retardant treated".  Follow the requirements for distance from combustible construction.  Otherwise, WHEN you have a fire, your homeowner's insurance won't have to pay.


----------



## ckdeuce (Feb 16, 2008)

What about (non paper backed) fiberglass insulation?


----------

