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options for fireproofing underside of stairs

Trevor_Lambert | Posted in General Questions on

Do the underside of stair treads need some kind of fire barrier? 

If so, what are options besides drywall or cementitious board?

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Replies

  1. Expert Member
    BILL WICHERS | | #1

    Usually 5/8" drywall is used when fire rated assemblies are built. I don't know of any specific assemblies for stairs, but if you use 5/8" drywall, you should get similar performance to what you'd get using that drywall on a wall. A wall with 5/8" drywall on each side is a 1 hour wall assembly (assuming you build to one of the specified assemblies, but a 1 hour wall is pretty much a regular studwall using 5/8" type X drywall on both sides but no other unique differences). I would count a layer of 5/8" drywall as 30 minutes of resistance if this isn't something that needs a specific rating (which would require a listed assembly to be used).

    Bill

  2. Malcolm_Taylor | | #2

    Trevor,

    If the stairs are not part of a rated assembly - that is a required fire separation between two occupancies - then all they need is fire-blocking at the floor above to stop flame spread. The stairs themselves usually act as that.

  3. jberks | | #3

    ⅝" type X or C drywall is generally the requirement for a fire seperation, including under stairs when a fire seperation is required. (At least in my neck of the woods).

    You asked for other options where I assume it's to satisfy a code, so this is pretty much the only option based on prescriptive building codes.

    But if you're asking for personal performance, you can add mineral wool/rockwool under the stairs, a double later 5/8" drywall (both layers seams mudded) intumescent paint, and have no openings in the ceiling under the stairs (like downlights).

    You'll get pretty robust fire resistant performance with that.

    Jamie

    1. Malcolm_Taylor | | #4

      I guess another way of phrasing it is that if a horizontal fire separation is required, the underside of a stair needs to be treated in the same way the other flat or sloped ceilings are.

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