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Rooftop Deck: A Story Under IRC?

radioatlas

radioatlas

Registered User
Joined
Sep 27, 2018
Messages
25
Location
North Carolina
Is a rooftop deck considered a story by the IRC? Example, we have an enclosed stair that opens onto a roof deck with three floors of living below. If yes, then are we are kicked out of the IRC into the IBC. Jurisdiction is North Carolina. Thanks to all in advance!
 
2018 IRC definition of "Story" - That portion of a building included between the upper surface of a floor and the upper surface of the floor or roof next above.

If you don't have a floor or roof above the deck, then it is not a story.

I would argue that it is an Exterior Deck per R507, using materials and conditions not prescribed in this section, which throws you back to R301.1. If you design the roof to be able to support an exterior deck with 40 psf live load with a complete and direct load path to the foundation per R301.1, then I think you can stay in the IRC.

If you do have a roof above the deck... I think you may have a story... you should talk to your building official and see what they think.
 
This question is coming up more and more and more lately, so you aren't alone. Beniah provided good informaiton about the definition of a story. Often the issue becomes the access from the interior and having a closed in (roof) landing at the top of the stairs and a door to access the roof. Denver is trying to figure this out in their 2021 amendments right now as rooftop decks on narrow and tall townhouses is popular in the market. I expect to see proposals next year for the 2024 IRC to better address this.

One thing to keep in mind is that the ASCE 7 and the IBC require a greater design live load for "decks" than for the interior area they serve (1.5 times). There is an increased density of occupants anticipated on decks. So when it comes to considering the roof top deck for egress and life safety purposes, remember that we expect MORE people on that highest floor at one time than any other floors.

Fun stuff.
 
Thanks to both. Yes, the question is centered on the stair access having a 'roof.' Is there any chance this access stair situation can be classified as a mezzanine?
 
2018 IRC - Mezzanine : An intermediate level or levels between the floor and ceiling of any story.

I don't think you can call it a mezzanine unless you have a floor or ceiling above it to create a "story" - and we want to avoid having a "story" to stay in the IRC.

I'm not an expert in the IBC, but aren't there exceptions in the IBC for structures on roofs that would not have to be considered a story? The presence of such an exception in the IBC means nothing in the IRC world, but perhaps if you could locate one of these examples in the IBC and cite it when you talk to the building official, they might be willing to work with you on their interpretation.

Being nice to the B.O. works wonders...
 
It might depend on whether the building official considers an enclosed stairway as an additional story. You also need to check whether your zoning code includes the stair in the building height, especially if the building is elevated out of a flood plain.
 
Already in the comments of this thread the other big oversight is being revealed. "Story" and "story above grade plane". Pretty important part of this conversation. A mezzanine is not a story. It's a level within a story. A habitable attic can be a story but not be a story above grade plane. I can build a 5 "story" house with 6 "floors" but still be 3 stories above grade plane and under the IRC. I might not be able to use prescriptive structural designs, but that's not connected to the story above grade plane limitations in the IRC.

If you can design your 4th "story" landing to fit the provisions for a habitable attic that is not a "story above grade plane" then you can do it. There is nothing saying you can't have a door from a habitable attic that accesses the lower "story" roof.
 
[RB] HEIGHT, STORY. The vertical distance from top to top of two successive tiers of beams or finished floor surfaces; and, for the topmost story, from the top of the floor finish to the top of the ceiling joists or, where there is not a ceiling, to the top of the roof rafters.

and that is the top of the 3rd story and will provide access to your roof
 
Similar situation here. Multiple dwellings were built with a roof deck, and the stairs terminated in a room on the deck with a roof. Three full stories AGP with a roof deck and stair "room". This was all prior to my arrival. They were permitted under the IRC, though not through any critical analysis, just allowed without question. So of course, folks are now wanting to add on to the little room, like a bathroom, a closet, a kitchen, etc. Just in case you might ask...I don't remember exactly what the outcome was of the one I was involved with...it was removed from my work load after I started down this path. I can see allowing them as an IRC dwelling, even with the little stair access room, but in doing so you are kicking the can down the road if it's not done through some sort of formal process to limit future additions. IMHO, these could have been permitted with an alternate request or code modification that came with stipulations.

The big difference for us is that as an IRC dwelling we have no fire suppression, but in the IBC we do.
 
If the landing had a floor level above it and below it, yes.

If it is at floor level, no. It has to be between floor levels per definition.

If it has no floor/ceiling above it, no.
 
radioatlas said:
Is a rooftop deck considered a story by the IRC? Example, we have an enclosed stair that opens onto a roof deck with three floors of living below. If yes, then are we are kicked out of the IRC into the IBC. Jurisdiction is North Carolina. Thanks to all in advance!
Click to expand...
Just did a project like this in Houston, TX 2021. Three story single-family enclosed stair to roof deck. The city allowed this under IRC as long as the landing area was no bigger than 70 SF (or basically not another occupied room).
 
I know of a similar situation as the one I posted about in another nearby AHJ (by similar I mean exactly). The CBO contacted me discuss it and he informed that either a staff opinion or an interpretation (not sure which) was written that permitted these landing rooms as unoccupiable space. I have not located that document so I can only repeat what I was told. Next time I see the CBO I will ask him if he has it. I would think this falls apart the minute someone tries to "inhabit" the space as anything other than a transitional space. This sounds like the same conclusions Houston came up for LaNouba.
 
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