Material Roundup: Fire Resistant Construction

fire resistant wood
Large wildfires can easily sweep through populated areas, but purposeful material choices can strengthen structures and give ample time to leave in the event of a fire.

Fighting fire with construction materials

Designing and building in the face of natural disasters is nothing new, but as fires become more prevalent in many regions of the United States, material engineers and construction professionals are getting more innovative. Large wildfires can easily sweep through populated areas, but purposeful material choices can strengthen structures and give ample time to leave in the event of a fire. Fire resistant construction materials also offer protection from other types of fires, including electrical, kitchen, car, and lightning related fire.

Construction materials used to prevent fire fall under the classification of passive fire resistance, with rating codes determined by the International Building Code. Here is our roundup of fire resistant construction materials—some centuries old and some using brand new technology.

Fire Rated Brick Assemblies

Brick on its own is naturally resistant to fire, able to withstand high temperatures without melting or combusting, but different masonry applications have various fire ratings. For exterior cladding, brick is an excellent choice, with typical 3 5/8” brick veneer offering a 1-2 hour fire rating.

Brick, like other noncombustible building materials, can meet assembly requirements for construction types 1 and 2, which indicates that the material will not burn well or add fuel to an existing fire.

New Innovations in Concrete

Concrete is another class 1 material, good for fire separation and structural products in fire-prone areas. On its own, concrete masonry and solid concrete have high fire resistance periods; but added aggregates, such as limestone, sand, silicone, and hemp, are solving for lower carbon emissions and even higher fire ratings. Using concrete on the exterior of a building, as well as between floors, can help keep fire from spreading to interior framing and more combustible materials. For any penetrations in the concrete slab, fire stopping products  such as various types of foam insulation can be used to close any gaps.

Insulated Concrete Forms (ICF) are also rising in popularity, and although poured concrete is higher in cost, the solid concrete walls create a nearly fireproof structure, limiting any damage to cosmetic levels and retaining the tensile strength required for safety.

Tested Assemblies and Coatings

For any type of structural steel, a spray-applied fire-resistive materials (SFRM), or spray-on fireproofing, will be necessary to meet fire rating codes for construction type 1 and type 2. Spray-on fireproof coatings can also be used on wood and gypsum board, but contractors must be sure to research whether the coating’s fire rating is for a specific application (wet vs. dry) and thickness.

Pre-tested assemblies can help to mitigate any concern for fire-resistance and are commonly understood across architecture, engineering, and construction professionals. A structural UL tested assembly for a 1-hour wall includes specifications for type X gypsum board, fiberglass insulation, and staggered steel studs that are spaced 16” apart.

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Fire Resistant Wood

It seems counterintuitive that wood could be fireproof. But using the correct treatment, for structural wood as well as plywood, can slow the spread of fire. By using treated lumber rather than raw wood, your project can see not only a safer result, but also lower insurance rates and the ability to meet higher building codes. The treatment is commonly made from chemicals such as ammonium phosphate, sulphate, and zinc chloride.

Treated lumber can be used for:

  • Exterior framing
  • Roof trusses
  • Decks and patios
  • Interior walls
  • Door and window casings

Type X Drywall and Wool Insulation

While 1/2” drywall is the norm, upgrading to a 5/8” type X gypsum board can highly increase the fire resistance of your construction project. Standard drywall only holds a 30-minute fire rating, but type X drywall is filled with glass fiber that gives it an additional layer of protection, especially in fire prone areas like garages and electrical equipment.

Fiberglass insulation can be part of a fire-rated assembly, but is not fire-rated on its own. If your client is requesting fire-rated insulation, consider mineral wool, which has been known to resist fire when exposed to temperatures greater than 1000°C/1832°F. Mineral wool insulation is also specified for projects that require acoustic dampening or sound control.

Pressurized Staircase Systems

For taller buildings, especially over ten stories, the fire rating of any stairwell is crucial. One method of preventing fire and smoke from traveling between floors is mechanical pressurization of the stairwell. By placing a specialized fan and pressure sensor at the top of the stair tower, it creates an environment that keeps smoke from filling stairwells, allowing people to exit the building and keeps the air clear for fire fighting crews.

Fire Safety

Of course, with any building, the basics of fire safety apply. Fire extinguishers for the kitchen and garage should be available and current, fire ladders should be available for second floor bedroom windows, and smoke detectors strategically placed not only on the ceilings, but also within HVAC ductwork to provide early smoke alarms.

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