Fireboard on the outside looks like any other drywall. It's different though, because it's more fire-resistant to slow down the spread of a fire from one room in your house, to other rooms. But it won't stop a fire's spread. You should think of it as a heat and smoke retardant, not a fire barrier.
What Makes Fireboard Different?
Fireboard is a fire retardant gypsum wallboard. It's main ingredient is the same gypsum sandwiched between sheets of paper, like other types of drywall. What enables fireboard, also known as type X drywall, to resist fire longer:
- Glass fibers that act as reinforcement to stop the board from disintegrating as quickly as other drywall.
- Thicker 5/8″ sheets versus 1/2″ inch thick drywall, the most common thickness used in residential homes. When the joints between multiple pieces of drywall are covered, it will also resist the passage of smoke.
Some of the literature suggests that fire rated gypsum wallboard includes other non-combustible materials but a thorough search didn't yield any information. If you want to learn more, here are some of the documents reviewed:
- Georgia Pacific's Toughrock Technical Guide for Gypsum Board offers 35 pages with all the information you could ever want on gypsum wallboard. Want more? Here's a fascinating video showing how gypsum wallboard is manufactured.
- American Gypsum's FireBlock Type X Gypsum Wallboard data sheet. Under fire resistance ratings, they stated “Fire rated assemblies are specified from tests performed by independent laboratories. These designs are made up of specific materials in a precise configuration. When choosing construction details to meet certain fire resistance requirements, care must be taken to insure that each component of the selected assembly is the one specified in the test and are assembled in accordance with the requirements of the design.”
Where Should You Use Fireboard
Fireboard is rarely used throughout residential homes because of the cost. According to This Old House, “… Type X drywall is slightly more expensive, about $0.75 more per sheet”. Labor costs may also be higher for the thicker/heavier 5/8″ sheets which are slightly harder to work with.
Building codes typically require the wall between the house and an attached two car garage to be fire-rated. A 24 ft wide garage with a 12 ft ceiling would need 8 sheets of drywall, so the added cost isn't a burden. Now consider how many sheets of drywall even one room, say 12 by 12 feet needs. When you multiply this number by 8 rooms plus hallways, you begin to appreciate why builders use your standard 1/2″ gypsum wallboard.
- Walls: 12 ft by 8 ft ceiling = 3 sheets per wall x 4 walls.
- Ceiling: 12 ft by 12 ft = 4.5 sheets of drywall.
- Total: 12 sheets (walls) plus 4.5 sheets (ceiling) = 17 sheets (4 by 8 ft sheets).
Other buildings/rooms that require fireboard include those surrounding HVAC systems and/or shared walls. While not common in existing housing, builders are constructing many new homes with these walls, configured as attached townhouses (photo above) and/or multi-family housing.
Planning a drywall project? Here's a drywall calculator you might find helpful.