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Bathroom exhaust duct in an exterior 1 hour wall

R

Robert

Registered User
Joined
Jan 29, 2016
Messages
341
Location
Pinole, CA
Hello. Plan checker is asking to conform to CBC 717 for ducts penetrating fire rated assemblies. The wall is an exterior 1 hour wall (based on distance from property line), unsprinklered B occupancy. Section 717.5.6 states that the ducts need to have fire dampers in exterior rated walls. Are there exceptions for a bathroom exhaust fan? I see exceptions for fire partitions (717.5.4) but is an exterior rated wall considered a fire partition? Thanks.
 
IBC Table 708.5 allows 10% of unprotected openings in a non-sprinkled building if the wall is 5 feet or more from the property line
 
So here is my thought... the requirement that you appear to be indicating comes from CBC Table 602; the building is most likely within 5 to 10-ft of the property line, therefore the exterior wall is required to have a 1-hr rating. From here, move over to Ch 7 and Section 717 for 'Ducts and Air Transfer Openings'; this in turn creates a loop b/w 717.5.6 and 705.10 that does not specifically address when protection of a duct or air transfer opening is required.

CBC Code Sections noted above

602.1 General
Buildings and structures erected or to be erected, altered or extended in height or area shall be classified in one of the five construction types defined in Sections 602.2 through 602.5. The building elements shall have a fire-resistance rating not less than that specified in Table 601 and exterior walls shall have a fire-resistance rating not less than that specified in Table 602. Where required to have a fire-resistance rating by Table 601, building elements shall comply with the applicable provisions of Section 703.2. The protection of openings, ducts and air transfer openings in building elements shall not be required unless required by other provisions of this code.

Exception: Noncombustible structural members supporting solar photovoltaic panels are not required to meet the fire resistance rating for the following:
  1. Photovoltaic panel supported by a structure and having no use underneath. Signs may be provided, as determined by the enforcing agency prohibiting any use underneath including storage.
  2. Solar photovoltaic (PV) panels supported by noncombustible framing that have sufficient uniformly distributed and unobstructed openings throughout the top of the array (horizontal plane) to allow heat and gases to escape, as determined by the enforcing agency.
  3. Solar photovoltaic panels supported by a structure over parking stalls where the panels constitute the roof and all the following conditions are met (see Figure 5-1):
3.1. The area within the perimeter of the solar photovoltaic array has maximum rectangular dimension of 40 feet by 150 feet.
3.2. The distance between solar photovoltaic array structures is a minimum of 10 feet clear.
3.3. The driveway aisle separating solar photovoltaic array structures has a minimum width of 25 feet clear.
3.4. Solar photovoltaic array structure is used only for parking purposes with no storage.
3.5. Completely open on all sides (other than necessary structural supports) with no interior partitions.
​
717.5.6 Exterior walls
Ducts and air transfer openings in fire-resistance-rated exterior walls required to have protected openings in accordance with Section 705.10 shall be protected with listed fire dampers installed in accordance with their listing.

705.10 Ducts and air transfer openings
Penetrations by air ducts and air transfer openings in fire-resistance-rated exterior walls required to have protected openings shall comply with Section 717.
Exception: Foundation vents installed in accordance with this code are permitted.
​
 
Much appreciate the replies. To answer some questions: The exterior wall is LESS than 5' from property line (but greater than 3') so unfortunately the 10% allowance of unprotected openings cannot apply. ADAguy, all CA workplaces are required to be smoke free (a few exceptions that don't apply here). So I am still stuck with a fire damper for a 4" diameter bath fan? Does that exist? I suppose I can run it up the exterior wall 2 stories and vent through roof, though it would still be penetrating the interior wall membrane voiding the 1 hour requirement.
 
Robert, if you are less than 5' from PL, then I think you are correct: your only options are to (a) provide fire damper or (b) run it up to the roof.
When I have encountered this situation in the past, I've run it up to the roof via an interior bathroom wall that is at least 5' away from PL, instead of the exterior wall.
 
Yikes said:
Robert, if you are less than 5' from PL, then I think you are correct: your only options are to (a) provide fire damper or (b) run it up to the roof.
When I have encountered this situation in the past, I've run it up to the roof via an interior bathroom wall that is at least 5' away from PL, instead of the exterior wall.
Click to expand...

Thank you Yikes, that's the solution.
 
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