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Inside of 12' tall parapet - Roof of Wall?

R

redbird11

SAWHORSE
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Apr 10, 2018
Messages
45
Location
Over the rainbow
2018 IBC
IB construction. Following non-combustible requirements for the walls in all exterior face of wall locations. Confused about the inside face of the parapet. Is it a wall or a roof?
 
I would think the height of the parapet is part of the answer. If its just a foot, then i would call it “roof” because the roof membrane probably turns up and terminates on that vertical surface. I have seen roofs with 3-4 ft parapets, that would become a “wall” to me.
 
Parapets are part of the exterior wall per Chapter 7. Look at the definition of an exterior wall—60 degrees or more from the horizontal is a wall. Even if the roofing membrane turns up the inside face of the parapet all the way up to the coping, regardless of height, it is still part of the wall.
 
Maybe but you are not suppose to be on the roof for other than maintenance and besides, flat roofs collect: leaves, snow and rain that can block unmaintained drains.
 
Thank you for all the replies! Okay, so I have now found 705.11.11 Parapet Construction.

"Parapets shall have the same fire-resistance rating as that required for the supporting wall, and on any side adjacent to a roof surface, shall have non-combustible faces for the uppermost 18 inches, including counterflashing and coping materials."

Then the commentary seems to say the opposite of "uppermost".

Commentary - "Parapet wall construction shall be of combustible or noncombustible material depending on the exterior wall requirements of the type of construction and shall be of fire-resistance-rated construction as required for the exterior wall. The interior wall covering facing the roof, including the flashing, shall be noncombustible to a height of 18 inches above the roof.

So which approach is correct?
 
The code language shall always prevail over the commentary. I believe that the intent is to have the uppermost 18-inches as non-combustible to prevent flame spread from traveling up the face of the wall and to the other side. Use of non-combustible materials at top-of-wall would prevent active flame spread.

That said, if the building is Type I-B construction, then Table 601 will require (see exceptions) that the roof be of 1-hr construction.

Additionally, per IBC Table 1505.1, Type I-B construction shall have a minimum roof covering classification of Class 'B'.
 
Another aspect to consider is that if the building is Type I-B, then the use of combustible cladding on the exterior of the building should be very limited.

1405.1.1 Types I, II, III and IV construction
On buildings of Types I, II, III and IV construction, exterior wall coverings shall be permitted to be constructed of combustible materials, complying with the following limitations:
  1. Combustible exterior wall coverings shall not exceed 10 percent of an exterior wall surface area where the fire separation distance is 5 feet (1524 mm) or less.
  2. Combustible exterior wall coverings shall be limited to 40 feet (12 192 mm) in height above grade plane.
  3. Combustible exterior wall coverings constructed of fire-retardant-treated wood complying with Section 2303.2 for exterior installation shall not be limited in wall surface area where the fire separation distance is 5 feet (1524 mm) or less and shall be permitted up to 60 feet (18 288 mm) in height above grade plane regardless of the fire separation distance.
  4. Wood veneers shall comply with Section 1404.5.
The above section will generally rule out combustible exterior cladding where fire separation is 5-ft or less, except for small architectural features.
 
I guess the problem there is there is no membrane roofing that I am aware of that is non-combustible.....Not sure that even Class A is...ASTM E136?
 
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