Parapet wall and roof venting

[mtlogcabin]

Trying to vent a flat and the question came up.

1. If the one-hour parapet exceeds the 30 inch minimum can the roof be vented to the inside as long as the vents are 30 inches above the roof deck?

2. If the one-hour parapet exceeds the 30 inch minimum can the roof be vented to the inside as long as the vents are 30 inches above the roof deck and a fire damper is installed?

2009 IBC

705.11.1 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 noncombustible faces for the uppermost 18 inches (457 mm), including counterflashing and coping materials. The height of the parapet shall not be less than 30 inches (762 mm) above the point where the roof surface and the wall intersect. Where the roof slopes toward a parapet at a slope greater than two units vertical in 12 units horizontal (16.7-percent slope), the parapet shall extend to the same height as any portion of the roof within a fire separation distance where protection of wall openings is required, but in no case shall the height be less than 30 inches (762 mm).

 

[peach]

See if 1203.2 applies ....

 

[texasbo]

1. In my opinion, yes

2. In my opinion, not necessary

And I assume that the parapet is above an exterior wall that has a fire separation distance that requires a rating and opening protection? If not, there are no requirements.

The section would be more clear if it said parapets had to have the same fire rating AND OPENING PROTECTION as the exterior wall.

 

[RJJ]

I would raise the question is the venting material equal to or 1 hr. I would also like to see how the venting is to be accomplished. I agree in part with Texasbo.

 

[brudgers]

If it is less than 30" it's not a parapet....

 

[mtlogcabin]

This is a 25 ft wide VA B occupancy building constructed between 2 existing buildings on a downtown city lot. A 30 inch one-hour rated parapet is required. He can't use exception 4.3 of 705.11 because it only leaves 5 ft for his mechanical equipment penetrations (RTU) which will not fit. My thought is to rate the parapet and install another vent wall up the inside of the rated parapet. Due to the roof design it can only be vented from the 2 sides requiring the rated parapets.

This project is not in my jurisdiction so I am trying to offer the designer different options that the AHJ will accept under alternate methods.

 

[mark handler]

Maybe I don't understand what you are proposing but, I'm going to step into the muck and say no.

You are providing a path for the fire to bypass the 30" parapet, defeating the purpose of the parapet.

The UBC use to require the top 18" minimum to be of noncombustible facing.

If anything you need to provide the vents LOW and a 30" parapet above the vent.