How tall can a LGMF building be?

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What is the absolute tallest light-gage metal building allowed by IBC?

Standalone LGMF Building

LGMF buildings can be considered either Type I or Type II buildings as they are non-combustible construction.  From there, it is simply a matter of the required fire rating for each classification.

IBC Table 504.4 limits Type II buildings to 5-stories or Type IB buildings to 12 stories.  Refer to diagram above.

The tallest standalone LGMF building would be 12 stories and be limited to 180 ft (easily accomplished in 12 stories).

LGMF building on podium

Similar to a wood framed podium, IBC Section 510.2 allows the use of podium construction to build a LGMF building above a Type IA podium structure.

In this case, the limiting factor in the maximum height allowed for a Type IB building of 180ft.  This means we can put as many podium levels under the 12-story LGMF as we can fit to stay below the 180ft height limit.  See diagram above.  This typically means around 4-6 stories additional depending of floor-floor heights and the selected structural system.

Can a LGMF building be built on a podium?

Absolutely!

  • LGMF structural systems are heavier than wood framed structures, so expect more substantial transfer podiums.
  • Podium is required to be non-combustible Type IA construction with a 3-hour fire rating.
    • Composite steel
      • Steel beams with a slab-on-deck
    • Post-tensioned concrete
      • Typically a flat slab
    • Conventional concrete
      • Typically a flat slab (but thicker than post-tensioned)

Major benefits?

  • Provides an intermediate price point between wood framing and Type IA framing, steel and concrete
  • May be required for certain use/occupancies.  For instance, the I-2 use/occupancy may require non-combustible construction even at 2-4 story building.
  • Typically comes with lower insurance costs when compared to wood framed construction, due to the non-combustible nature.
  • Can help in meeting FM global requirements where wood framing cannot.

Things to consider?

        1. Grade can be your friend – the max building height is measured from average grade, so if you have a sloping site, average grade can be above the ground floor elevation.
        2. Use post-tensioned concrete for the podium levels.  PT provides the thinnest structural system to help maximize ceiling height.
        3. There are a variety of LGMF structural systems.  Some have shallower structural assemblies than others, but this typically has a tradeoff in terms of limited span lengths or weight of structure.
          1. Joist based systems – Ecospan, Hambro, etc
          2. Slab based systems – Epicore MSR, New Millenium Versa-dek, etc
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