Exposed joists in a 1/2hr rated corridor.

[Ryan Schultz]

So we have a Type VB w/ R-2 occupancy.

I would like to have exposed floor joists in the corridors.

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First off, per TABLE 1020.1 CORRIDOR FIRE-RESISTANCE RATING it looks like the corridors need to be 0.5hr rated. Is this a correct reading?

Dumb question, i assume this applies to the floors as well, correct?

Assuming that it does, does anyone know a UL rated assembly that achieves the 0.5hr rating with exposed wood joists?

Per the heavy exception and TABLE 602.4 WOOD MEMBER SIZE EQUIVALENCIES, could we use 3 1/2 x 5 1/2" LVL for the joists, and achieve our rating?

Happy 4th!

 

[Ryan Schultz]

Forget to mention, is fully sprinklered.

 

[cda]

Not sure how you get a rated corridor with exposed wood.

Built the rated corridor to code,,

Than add the fake or fire retardant wood decoration??

 

[cda]

“”I would like to have exposed floor joists in the corridors. “””

Are these part of the ceiling floor assembly for the story above???

 

[cda]

Yes 1/2 hour rating required

 

[RLGA]

You probably could, but the floor, too, must be constructed to heavy-timber requirements per Section 602.4.6.

 

[Ryan Schultz]

ugg. 1/2 is so minimal, common sense wise, you'd think you could achieve this rating with heavy timber joists and a gyp bd. covered sheathing.

Beyond the prescriptive application of ul ratings, is there a way to approach this via a 'calculated' approach i wonder?

 

[RLGA]

For floor and roof assemblies, fire resistance is determined from the exposed underside of the assembly—not from the top side. Therefore, you have to have something protect the joists. For a 1/2-hour rating, you probably could wrap all the exposed surfaces, including joists, with 5/8-inch gypsum board per Table 722.6.2(1) and not include the joists in the calculation as the airspace between joists would have contributed to the performance of the assembly if the gypsum board was continuous across the bottom of the joists.

 

[Ryan Schultz]

But if the joist's themselves are heavy timber (with an integral 1hr rating themselves) it would seem you wouldn't need to 'wrap' them.

 

[tmurray]

ugg. 1/2 is so minimal, common sense wise, you'd think you could achieve this rating with heavy timber joists and a gyp bd. covered sheathing.

Beyond the prescriptive application of ul ratings, is there a way to approach this via a 'calculated' approach i wonder?

We see it some here. They use char ratings on the wood as an insulator...there was a bunch of research done by the National Research Council here in Canada about it.

The structural engineer needs to be involved so they can tell the building official that the loss of the wood won't compromise the structure of the building (i.e., the joist might be rated for an hour based on the char, but will fail due to the loss of structural strength).

This is treated as an alternative solution to the prescriptive requirements though.

 

[RLGA]

But if the joist's themselves are heavy timber (with an integral 1hr rating themselves) it would seem you wouldn't need to 'wrap' them.

I thought you were going back to using regular joists. You might be able to get approval by using glue-laminated joists of the size mentioned and applying 5/8-inch gypsum board to the underside of the deck in between joists. However, that will be something that the building official will have to approve and not us here on the forum.

 

[Ryan Schultz]

However, that will be something that the building official will have to approve and not us here on the forum

Gotcha.. Will give it a try and report back!

 

[Ryan Schultz]

Per TABLE 722.6.2(1) TIME ASSIGNED TO WALLBOARD MEMBRANES, it looks like we can go with (2) layers of 19/32-inch wood structural panel bonded with exterior glue as well, to achieve that 30 minute.

That is, assuming exposed heavy timber will work for the AHJ.

 

[cda]

Any chapter 8 problems?

 

[ADAguy]

What happened to the waiver of rating if the building is fully sprinklered?

 

[cda]

The half hour is required

Even with sprinklers

 

[Chrisjoneill]

If you have the height build a rated floor ceiling and put decorative beams underneath

 

[Ryan Schultz]

For those curious, with the help of XC engineering, on p24-34 are the calcs to determine the fire rating of exposed wood joists and plywood.

Sheet A800, has the following detail.

Revit files here.

All open source.

Cheers.

about OpeningDesign: http://openingdesign.com/about/

 

[Ryan Schultz]

For floor and roof assemblies, fire resistance is determined from the exposed underside of the assembly—not from the top side.

@RLGA , can you tell me where this concept is called out specifically in the code? Would like to educate myself.

Thanks, Ryan