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Habitable Attic Area Calculation

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wtravisl

Registered User
Joined
Dec 2, 2021
Messages
23
Location
Texas, US
Hi all -
I read through several previous posts on this topic and didn't see exactly what I was looking for, as this portion of IRC was thoroughly updated for 2021.

I'm looking for clarity or correction, specifically pertaining to the provisions for a habitable attic NOT constituting a story (the 326.3 Exceptions).
I'm designing a habitable attic above a 2 story residence, and due to local zoning code, it's imperative that the residence be considered 2 stories based on IRC's criteria.

The terminology in question is found in Exception 1 & 1.1:
"The aggregate area of the habitable attic is either of the following: Not greater than one-third of the floor area of the story below."

Of those three bolded terms, the only one is directly defined by Chapter 2: "habitable attic": A finished or unfinished habitable space within an attic.
And "habitable space": A space in a building for living, sleeping, eating or cooking. Bathrooms, toilet rooms, closets, halls, storage or utility spaces and similar areas are not considered habitable spaces.

Based on this, I believe that when I sum the 'aggregate area' of my 'habitable attic', I'm only totaling up 'habitable spaces'. I will omit stairs, halls, baths, closets, etc.
And it is that 'habitable space' total that needs to be less than 1/3 of the 'floor area' of the story below, to avoid being counted as a story. (along with meeting the rest of the exceptions listed)

First, I welcome any feedback on that reading. I want to make sure I'm not missing something & being overly aggressive with that interpretation.

Second, "floor area" isn't a defined term, and I'd like to know whether or not to include an inset balcony on the 2nd floor in that floor area total. By 'inset' I mean a corner of the rectangular house plan is carved away, and the balcony is 'tucked-in' under the roof above, rather than projecting out.

IBC would count this as part of its "building area" definition (not surrounded by walls, but included within the horizontal projection of the roof above).
But I haven't been able to find specific guidance on this in IRC.

Many thanks -
 
e hilton said:
So unless the space is used only for one of those 6 uses, then it is habitable space. And doesn’t that make it a story?
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According to 326.3, A habitable attic shall be considered a story, unless it meets a series of exceptions listed in that section.
The habitable attic I'm designing will not constitute a story.
 
Seems like the real test of your potential "2nd story" is
Did you have to alter the original roof with dormers or some modification or is the accessible window in the gable end.
 
Not sure if it will help, but ... under Canadian Codes there are codes for the minimum height of various spaces. In similar situations, I have calculated the amount of an attic space that meets the minimum height, and use that to calculate the "habitable" floor area.
 
When you caculate the floor area of the second floor that will be used in the formula which determines the allowed area of the proposed attic remodel will you include the area of stairs, closets and bathrooms found on the second floor?

And by the way, I only have a 2019 Residential code so what you are up against with the 2021 Residential code is a mystery to me.
 
My take, I would argue floor area is the entire floor below as the code didn't state habitable area below.

Its reasonable to suggest that a "floor" encompases the entirety of all floors for the story below regardless of it being habitable.

Im unsure of the inset balcony but it sounds like it should be considered.

Thankfully, i don't have a code book nearby, generally have 2 entire days a week away from any, and Im unsure of the codes language for minimum wall height (attic knee wall) so can't speak with any certainty towards that as being part of habitable, area but would assume that the habitable attic area calculation should not count areas without the required wall height, bathrooms, halls etc...
 
Genduct said:
Seems like the real test of your potential "2nd story" is
Did you have to alter the original roof with dormers or some modification or is the accessible window in the gable end
Click to expand...
Why? Where in IRC does it speak to "roof modifications" as evidence of a story?
 
Inspector Gift said:
Is your reason to avoid having a 3rd story due to sprinkler requirements?
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Good question - no. Actually this concern stems from the local jurisdiction's land development codes, which include 'tiered' height/story setbacks from property lines. I.e., within a certain distance from a neighboring property, we are only allowed 30'H and 2 stories.
 
ICE said:
When you caculate the floor area of the second floor that will be used in the formula which determines the allowed area of the proposed attic remodel will you include the area of stairs, closets and bathrooms found on the second floor?

And by the way, I only have a 2019 Residential code so what you are up against with the 2021 Residential code is a mystery to me.
Click to expand...
This is a great question. I agree that it seems odd to be switching back and forth to different definitions of "area" in the same calculation. But my argument is that this is how IRC chose to define this calculation. Generally, they decided that if you've got a 'reasonable amount' of occupied livable space tucked under the roof, it doesn't need to count as a story.

And I mentioned this in another response - I'm not haggling over this definition to avoid sprinklers. We are 13D/P2904 sprinklering these units. This has to do with our local jurisdiction's land development code. We have 'tiered' setbacks along some property lines, and are limited to 30'H and 2 stories within a certain distance. This is purely about aesthetics and massing.
 
Enrgxprt said:
My take, I would argue floor area is the entire floor below as the code didn't state habitable area below.

Its reasonable to suggest that a "floor" encompases the entirety of all floors for the story below regardless of it being habitable.

Im unsure of the inset balcony but it sounds like it should be considered.

Thankfully, i don't have a code book nearby, generally have 2 entire days a week away from any, and Im unsure of the codes language for minimum wall height (attic knee wall) so can't speak with any certainty towards that as being part of habitable, area but would assume that the habitable attic area calculation should not count areas without the required wall height, bathrooms, halls etc...
Click to expand...
Thank you. I agree with your definition of 'floor area' here; like IBC 'gross floor area'.
 
Your logic should win.

The aggregate area is the total area considered to be 'habitable attic' which includes within definition 'habitable space'. 'Habitable space' defines the area which is not calculated for the space.

The 'story' and 'attic' requirements for safety are different with attic/habitable attic being more restrictive. Interpretation that aggregate includes the additional areas omitted by definition (and creating a story) can simply be countered with the code/safety items now not required as a story. If that does not work just cut the area back to ½ since sprinklered...
 
This sounds more like a zoning code than a building code issue.

I don't think you have to count any area with a ceiling height less than 5 ft. as habitable apace, even if is is part of a habitable room.
 
wtravisl said:
Why? Where in IRC does it speak to "roof modifications" as evidence of a story?
Click to expand...
What I had in mind are questions like,
Was the space originally unheated, non habitable, storage ?
built for what level of live floor load?
Often the "conversion of non habitable space adds to the assessment for property tax purposes in addition to the safety aspects of the Code like an accessible window or stairway width
Altering the roof line might also affect the mean height and trigger some other requirements in the local or generic code source.

So my remark was a general, what else is considered with the expansion of living space. Somewhat like any addition. It is a little grey area but therefore needs even a closer look as to size of joist etc, Don't you agree?

PS In Philly, we call most of our Legacy row home basements CELLERS to distinguish that the space is for incidential storage, hvac and usually the washer dryer
But is NOT a Habitable Basement. especially now that we have the Emergency Exit window wells for below grade spaces
That reference is in our Zoning / Use Code
 
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