Is Drywall Combustible?
An interesting question. Can you attach drywall directly in contact with a masonry chimney?
Two Views
|
Drywall in not Combustible According to USG in an article pointed out by Jeff Lockhart
Date: Wed, 23 Oct 2002
Jim,
I just came across something which I've never seen
mentioned in any article dealing with fireplace &
chimney clearances. I've wanted to wrap my (interior)
chimney & the sides of the firebox in sheetrock, as
I've seen in many pictures, but both the old & new
codes wouldn't permit it. But this data sheet from USG
lists sheetrock as a limited-combustible, and states
that it would be allowed. Here's the article:
Regards,
USG Data Sheet
In the National Fire Protection Association's NFPA
101 Code for Safety to Life from Fire in Buildings and
Structures, a noncombustible material is defined as a
material that, "in the form in which it is used and
under the conditions anticipated, will not aid
combustion or add appreciable heat to an ambient
fire." Materials are tested for noncombustibility in
ASTM E 136 Standard Test Method for Behavior of
Materials in a Vertical Tube Furnace at 750 deg. C. The
test exposes small samples of the material to a stream
of air heated to 750 deg. C, (1382 deg. F). The material is
deemed noncombustible if:
2) There is no flaming after 30 seconds.
3) Once the sample loses 50% of its weight, there is no
flaming and sample temperatures never exceed 750 deg. C,
(1382 deg. F). ASTM E 136 is an extremely strict test and
under its criterion, few building materials qualify as
noncombustible. Two USG Interiors products which do
are CERAMIC HERITAGE and most THERMAFIBER insulation
products.
This last requirement can be confusing because the
three national model building codes, (ICBO's Uniform
Building Code, SBCCI's Standard Building Code and
BOCA's National Building Code), all allow composite
materials that meet the NFPA's definition of
limited-combustible, to be classified as
noncombustible.
|
Drywall is Combustible According to the State of New Jersey as pointed out by Michael Thomas 2/26/07 Jim, Thought you might find this Bulletin (below) of interest:
Michael Thomas
BULLETIN NO. 90-3 It has recently come to the attention of the Department of Community Affairs that gypsum wallboard is something being mistakenly considered a noncombustible material when applying the clearance-to-combustibles requirements of the Mechanical Subcode. The definition of "noncombustible" in the Mechanical Subcode differs from the definition in the Building Subcode. The Building Subcode's Section 703.4.2, Composite Materials, states that a material having a structural base of noncombustible material (meeting ASTM E136), with a combustible surface not more than 0.125 inch thick, and having a flame-spread rating not greater than 50 (when tested in accordance with ASTM E84) is acceptable as a noncombustible material. Because the Building Subcode allows such "composite" materials, gypsum wallboard can be considered noncombustible as defined by the Building Subcode. The Mechanical Subcode does not contain such a provision for composite materials. Noncombustible materials in the context of the Mechanical Subcode are those materials which pass ASTM E136. Gypsum board, because of its combustible facing, will not pass ASTM E136. (The only exception to this applies to Type I commercial kitchen hoods at Section 507.9 of the Mechanical Subcode.) The difference in standards is due to the different purposes of the two subcodes. The Building Subcode is concerned with the performance of a material under the conditions during a fire, while the Mechanical Subcode is concerned with performance during exposure to a constant high-heat source. Therefore remember, under the Mechanical Subcode, gypsum wallboard is classified as a combustible material.
|
|
Michael, That is interesting. Thank you. In my opinion the State of New Jersey Department of Community Affairs Division of Codes and Standards got it right and their view is at odds with USG. How has USG reacted? I notice the data sheet on their website that Lockhart pointed out for me is no longer on line. I think I will just post both the USG and New Jersey views. This is a small issue as it relates to masonry fireplaces. I'm disappointed that drywall can't just be glued to masonry chimneys but there are other materials and larger clearance to combustibles code issues. Thanks again.
Best,
3/4/15 I've not heard any resolution to this issue. Frankly I think the State of New Jersey got it right but, wow, that ASTM E 136 Standard tests the material at 750 deg. C, (1382 deg. F). That's really hot. The general standard built into the code is that combustibles such as wood framing cannot exceed 90 deg. F above ambient. That's about 160 deg. F or about 1,200 deg. F less that the ASTM noncombustibility test. While the New Jersey is correct about the Mechanical Subcode being concerned with performance during exposure to a constant high-heat source, I wonder at what temperature the "limited-combustible" draywall beginis to catch fire or sacrefice itself. Is it around 1,382 deg. F? What happens to drywal at 200 or 300 deg. F? The outside of a masnry chimney will never get that hot. I don't like framed out chases. Exposing the masonry walls and eliminating the air spaces helps dissapate the heat and is safer. Very conservatively, if you can't glue drywall straight on the maosnry at least you could use masonry backer-board whcih, without the paper backing, does seem to be "Non-Combustible" per ASTM E 136. Jim Buckley
|
Back to Technical Discussion
Buckley Rumford Fireplaces
Copyright 1995 - 2015 Jim Buckley
All rights reserved.
webmaster