How ICFs Provide Airtight and Fire-Resistant Common Walls for Multi-Family Buildings

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Fire-resistant multifamily construction requires fire (common) walls to compartmentalize the units. Builders often use double stud multi-layer fire-rated gypsum boards for the firewalls; unfortunately, while these provide fire-resistance, they often leak air. Fortunately, Fox Blocks insulated concrete forms (ICFs) are a superior solution for a firewall system. Fast and straightforward to install, Fox Blocks furnishes both fire-resistance and air tightness for the firewalls of a multi-family building.

The Rise in Multi-family Construction in the United States

Since 2011, multi-family starts, completions, and permits have steadily increased - in fact, the number of buildings with five or more units nearly doubled between 2019 and 2020.

In particular, empty nesters and young people like multi-family housing because it offers a more affordable and safe living situation than a single home. Living in multi-family housing also eliminates numerous household and yard chores, which increases their free time and saves money.

Why Multi-Family Buildings Require Firewalls

According to the International Building Code [IBC], the design of a multi-family building must prevent the spread of fire and smoke from unit to unit. The design must also ensure that if the wall collapses, as the result of a fire, the adjacent units will remain structurally intact.

Builders can achieve both of these goals by including fire barrier compartmentalizing in the building’s design, which involves dividing the building or its units into sections that prevent the spread of fire and smoke from unit to unit. In essence, the goal is to contain the fire to its point of origin until first responders can get there.

Compartmentalize with Firewalls

Firewalls provide an effective way to compartmentalize a multi-family building.

A firewall in a low rise multi-family building extends continuously from the foundation to the underside of the fire-protected roof sheathing - or it may extend through the roof to a parapet closure. Typically, firewalls obtain a three to four-hour fire-resistance rating and are often thicker than standard walls.

Air Sealing Problems with Fire-Rated Gypsum Board

The International Energy Conservation Code (IECC) requires a 3 or 5 ACH50 (depending on the climate zone) air leakage measurement for all units within multi-family buildings. The Leadership in Energy & Environmental Design (LEED) certification program, ASHRAE Standard 189, and ASHRAE 62.2 also provide comparable compartmentalization requirements.

Unfortunately, builders find it difficult to air seal fire-rated gypsum boards to these standards. First, it can be challenging to identify all the locations that need sealing, and second, builders must use the appropriate sealing materials for specific areas.

Why it is Difficult to Properly Air Seal Gypsum Board Firewalls

  • Gypsum board fire-rated walls contain two separate wood-framed walls, insulated and covered with multiple layers of gypsum board with a fire or air gap between them. According to the DOE, firewall assemblies tested and certified by UL are not designed or tested for airtightness. Air leakage through these assemblies may exceed the air leakage limits mandated by the International Residential Code (IRC) and the International Energy Conservation Code (IECC).
  • Firewalls extend from the foundation to the underside of the sheathing and secure tightly against the exterior wall. However, thoroughly stopping the airflow requires an application of a sealant material across the inevitable gaps between the rigid framing materials. Firewalls not sealed at the perimeter location will allow airflow from the exterior
  • Gap-sealing products used in the perimeter of these walls must meet applicable fire rating and testing standards.

Fire-Resistant and Air-Tight Firewalls with Fox Block ICFs

They are a superior solution to firewalls in multi-family buildings compared to double stud multi-layer fire-rated gypsum boards. Quick and easy to install, Fox Blocks ensures excellent airtightness and fire-resistance. Fox Blocks have an ASTM E119 fire-resistance rating of 2-hours for the 4-inch blocks and 4-hours for the 6-inch blocks.

There are several other advantages when used for conventional wall construction:

  • They provide the structure to handle the floor system.
  • They are easier and faster to build then double wood stud or masonry fire wall.
  • They provide excellent airtightness between units.
  • The wall system lessens the transfer of sound between the interior walls of a multi-family residential building. Fox Blocks have a Sound Transmission Class rating of STC 45-50+.
  • They contribute towards a healthy indoor environment.
    • Fox Blocks control moisture accumulation in the wall system because the blocks provide a solid continuous monolithic concrete wall with a perm rating of below 1.0. Moisture can lead to unhealthy mold.
    • They do not contain unhealthy VOCs.

Please contact Fox Blocks or visit our website for more information on installing airtight firewalls in multi-family buildings.