NFPA285 and interior Gyp Bd.

[JTHOMP6395]

Many of our projects are tall enough and use the "right" combination of materials to require NFPA 285 compliance. NFPA 285 test assemblies typically are built with gyp board fitting tightly to the slab above within the test chamber. Many projects in the real world don't have a nice clean flat slab condition that allows board to be installed tight to the underside. Most of our projects are steel frame construction, with a spandrel beam parallel to the exterior wall and a few inches in from the light gauge metal framing, making fastening of the gyp board above the bottom flange of the beam and installation of a second gyp bd cover over a deflection track nearly or completely impossible. That means a gap of undetermined size in the interior gypsum board type X finish...which could be seen as compromising the tested assembly. I'm polling what the general practices other firms use to deal with this:

1. Extend the gyp board as high as it can be fastened (i.e. bottom of beam) and don't worry about the rest since the test deals with flame propagation up the outside of the wall
2. Extend the gyp board as high as it can be fastened, and fill (in some manner) the stud cavities above or out to the beam with mineral wool insulation or some type of firestopping spray (assuming this is NOT balloon framing)
3. Extend the gyp board full height, and fasten as high as you can, leaving the spandrel condition next to the beam unfastened and untaped/unmudded
4. Construct a soffit around the spandrel beams with type X gyp board to provide continuity to the underside of deck on the interior side of the beam, with or without firestopping of penetrations.
5. Move all steel framing farther away from the outside wall to provide sufficient space to get in there and get it done, thereby adding additional steel cost for outriggers and slab edge support.
6. Use all noncombustible materials in the exterior wall assembly to negate NFPA285 requirements.
7. Build everything with CMU.

A survey of our own drawings and those in our market done by others suggests that generally, the gap at the top of wall is ignored. Thoughts as to the compliance of that?

 

[cda]

Welcome,

First question is supposed to be an easy one. Like 2+2=

So question not in my field, give it a few days for answers



1* Scope.
1.1.1* This standard provides a test method for determining the fire propagation characteristics of exterior wall assemblies and panels used as components of curtain wall assemblies that are constructed using combustible materials or that incorporate combustible components.

 

[TheCommish]

I think there is a difference between the NFPA 285 test which is for the wall assembly and the need to provide fire protection/rating/stop between floors.

 

[steveray]

Interior or exterior gyp? You are talking 1403.5 IBC?

 

[JTHOMP6395]

For further disclosure, most of our projects (and the focus of my question) relates to CFMF and gypsum sheathing walls. We often use foam insulation, with fluid applied air/vapor barrier on the exterior of the sheathing. We try to target type II-B construction on our projects, with most floors not rated as horizontal assemblies. My question was directed only toward the interior gypsum finish, and whether firms "accept" a gap at the top of stud framing where the gyp can't be fastened - not as a question of providing or maintaining a rating at the floor, but as a "requirement" to meet the description of the NFPA-285 tested wall assembly (since it is an ASSEMBLY test) that in the tested condition has gyp bd tight to the underside of slab above.

 

[steveray]

I can't imagine that the interior covering matters much to exterior flame propagation, but "as tested" it is....

1403.5 Vertical and lateral flame propagation. Exterior
walls on buildings of Type I, II, III or IV construction that are
greater than 40 feet (12 192 mm) in height above grade plane
and contain a combustible water-resistive barrier shall be
tested in accordance with and comply with the acceptance
criteria of NFPA 285. For the purposes of this section, fenestration
products and flashing of fenestration products shall
not be considered part of the water-resistive barrier.

 

[JTHOMP6395]

SO, not much consensus yet. The "tested in accordance with....NFPA 285" I take to mean that an architect COULD be called on the carpet by an AHJ if the interior gyp board did not extend full height, as is common based on the wall assembly tests. Does anyone else have any comment on how they approach it?