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Shafts

October 2nd, 2009

I recently made a visit to a new, 3 story retail development. The purpose was to inspect two 2-hr fire-resistance rated duct shafts.  The shafts were continuous from the rooftop HVAC unit to the first floor, with openings onto all floors. Two previous inspections had failed for improper support of the shaft wall and improper framing for the fire/smoke dampers.

The building was reviewed as 2B construction and therefore the floors and columns required no rating. As the shaft walls (typical core board/metal stud construction) were built on the concrete floor, it didn’t meet the requirements for support.

Shaft walls must meet the requirements of a fire barrier and Section 706.5 of The 2006 International Building Code states “The supporting construction for fire barrier walls shall be protected to afford the required fire-resistance rating of the fire barrier supported…”  This means the horizontal and vertical steel which supports the concrete floor adjacent to the shaft must maintain the 2-hr rating. In this case, the columns and beams responsible for supporting the shaft wall were protected with spray on fireproofing.

elevation

Framing requirements for the fire/smoke dampers are specified by the damper manufacturer.  These may include doubling vertical framing members for larger dampers, specific methods for corner returns on the horizontal members and minimum and maximum clearances between the framing and the damper.

The installation of these shafts exceeded the minimum code requirements in two ways.  First, the shafts connected less than four stories.  IBC 2006 section 707.4 only requires a 1-hr rating.  Second, the shafts were not required at all.  Section 716.6.3 Nonfire-resistance-rated floor assemblies (remember Type 2B construction=no floor rating) only requires a fire damper installed at the floor line when connecting not more than three stories.

Now the design professional, building owner or building insurer might have required this higher level of protection (remember the Code is only a minimum requirement). The cost of shaft wall construction, additional protection of structural steel and fire/smoke dampers (including the electronics for the activation of the smoke dampers) should have been considered.

PLAN VIEW

PLAN VIEW

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Elevator Lobbies

May 11th, 2009


On a recent visit of a renovation of a high rise building, I noticed smoke dampers installed in transfer openings in a wall which formed a required elevator lobby.  As the construction documents were approved under 2006 Michigan Building Code, an elevator lobby is required at each floor where an elevator connects 3 or more  stories.  Previously, International Building Code and Michigan Building Code required these lobbies only when the elevator opened into a rated corridor.

elevator-shaft

Existing 2-hr masonry walls formed 3 sides of the lobby and approximately 6 ft of metal stud wall made up the remaining wall which I was inspecting.  2 HVAC penetrations were made in this wall one was ducted and the other was the transfer grille.

IBC/MBC 2006 require the walls that make up this elevator lobby to meet the requirements of fire partitions.  There is an exception, when the building has an NFPA 13 or 13R fire suppression system, that allows these walls to be smoke partitions.  The design professional chose to take this exception.  Let’s review the requirements for both.

fire-smoke-chart

As you can see, the fire partition will require a 20 min door, a fire damper and some firestopping, but by using the exception and denoting the wall as a smoke partition a smoke damper will be required for the transfer grill.  Smoke dampers are a more costly item, not only for materials but for labor charges because of its motorization and activation requirements.  The cost of the smoke damper would greatly outweigh the costs of upgrading to a fire door and joint/penetration firestopping.

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