If its a bearing wall and its required to have a rating than the supporting assembly is usually required to be rated too. Happens a lot in wood framed construction .

I think it may be because the building is platformed framed and the ceiling / floor is supporting the second story exterior wall.

I really don't know. This has been a challenging project, including multiple major re-designs based on a flaky client, and lots of questions to the permitting office because it's within 2' of the property line which is a new thing for me. It took two weeks to get my last question answered and the builder has paused work, waiting for a permit, so I'm trying to get everything right.

In case it's not clear, the concept is a floor exposed from below, and several feet above grade, so from a practical viewpoint it's similar to a projection. But by the letter of both the IRC and IBC I can't find a place that says it's required.

Platform framing answers my question. Any way to have the required FRR on the exterior of wall passing in front of the floor assemblies? Give it it's own structure and you don't have to worry about the floors.

I would extend the exterior wall system (5/8" type X plus 1/2" OSB) down over the floor framing. The interior side of the exterior wall is required to have a rating as well, but a fire would not start within the floor assembly so it seems like that might work.

I added a drawing below.

Or do you mean extend the wall system down to grade? That's possible but causes other problems.

WG, in my area, we're only required to FRR the side exposed to fire when dealing with EBF issues along the property line and or setbacks so we get to choose what is easiest. 2x layer 5/8 on inside is cheaper and easier as long as you detail the jambs. Laying a sub floor of FRR sheathing would likely work for me but it's not something I've done before. I'd just cast it in concrete. That exposed floor is going to be cold without a toasty warm basement underneath.

We are 14" from the property line so we need to protect both sides of the wall. The builder is my PGH book co-author and neither of us ever do normal assemblies so thick jambs are no problem, if they were allowed on this wall, but they're not.

We both often do R-40 floors over open air and have had no complaints. Our heating degree days are around 7,000 and the design temp is around 5F; you're likely a little colder there. 

Because we're so close to the property line, with a non-friendly neighbor, any excavation is going to cause problems. We were hoping that helical piers would work below grade.

Yes, it's the left side of this section-in-progress:

The image didn't post. I'll post it as a comment below.

SFR. Wood-framed on wood posts on helical metal piles or possibly concrete piers.

Why would UL L570 not work?

It looks like it would. As I said, this is new stuff for me, and the only resources I've been using are the codes and GA-600, the gypsum association handbook.

Try UL Product iQ. You have to create an account however it's free and you can search through assemblies.

https://iq2.ulprospector.com/s...

GA book is still referencing other tests such as UL, which has a lot more information that GA does not show. Most jurisdictions will not accept GA listing and just the actual tests and it's information. I use GA just to flip through and find something that would work then actually list the test number.

L570 might be overcomplicating it. That is pretty common for commercial applications as it's intended to meet both fire AND IIC sound requirements. You should be able to find something simpler than this in the prescriptive fire requirements portion of your local code. Perhaps TABLE 721.1 - 21-1.1?

I had looked through those and just did again. They all appear to be intended for roofs/ceilings, not floors over open air. 722.6.1 allows you to add up the components yourself so that's what I'm planning on now, with fingers crossed that the plan reviewer accepts it.

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They are for floor and roof systems; this is a floor? Where do conclude it can’t be used for an open air condition? (not sure applying gyp in that space would be a good time though)

Pier is concrete or wood? If concrete, I don't see a problem.

My plan was wood posts on concrete footings, but I could do concrete piers up to the floor system.

In my opinion, the pier and floor would need to be rated as it's supporting the wall.

Yes, I don't see how you can omit rating the pier, floor itself as that is also in the setback, then the wall and overhangs as well. If the floor is not required to be rated, then I would rate the pier, introduce a beam (rate it) then the wall that is being supported by the beam.

I don't think it's about the floor being in the setback. In the IBC any construction supporting a rated wall or floor must be rated. The pier and floor appear to be supporting the wall. 

I'm not sure if this is different in the IRC.

I understand that, but why is the wall rated? As he mentioned above it is because of some setback issue. If the rating is supposed to protect from one side or the other, I don't see how an exposed floor as proposed would not be treated the same way as a wall.

To add, you can design this so the wall is not supported by the floor itself, but by a beam that is rated. Does that mean we don't have to rate the floor as it's not supporting secondary rated members? If the floor is supporting the rated wall it needs to be rated as you said, but if it wasn't supporting the wall I think it needs to be rated as well, just like the wall. 

I would agree that even if the floor wasn't supporting the wall it should still be rated. 

I don't know if in the IRC this would be required. I do think in the IBC it would be. At the very least I think my AHJ would want some type if non-combustible sheathing on the underside of the floor.

heavy timber is rated 1 hr. 6x6 posts would comply.

OA, as far as I can tell, for components that support a floor that is required to be rated, the IRC requires that support to be rated, but it doesn't say anything about what supports walls.

Poop, that's a great idea--run a rated beam under the wall and hang the floor joists from that. Not ideal from a thermal point of view but I might find a solution for that.

I can't find anywhere in the IRC or IBC where this situation is specifically addressed.

That's interesting WG.