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Reveiw of the 2009 IRC--What is a room?

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Robert Ellenberg

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I recently started a full reading of the 2009 IRC. In the past I have found that even though I know the code fairly well there will be things that will "bite" me because I missed them. So the last thing I do before falling asleep several nights a week is to read word for word the sections I don't know as well that might apply to what I would do and make notes on things I might miss. So each time I come up upon something I think is not clear, I will post it here as a question and revise the thread each time I have a new question to pose.

Under light and ventilation, "R303.1 Habitable rooms. All habitable rooms shall have an aggregate glazing area of not less than 8 percent of the floor area of such rooms. Natural ventilation shall be through windows, doors, louvers or other approved openings to the outdoor air. Such openings shall be provided with ready access or shall otherwise be readily controllable by the building occupants. The minimum openable area to the outdoors shall be 4 percent of the floor area being ventilated."

What is a "room" is it a habitable area (which is defined in the code) that is closed off from other areas by a door? We usually refer to a kitchen as a room and sometimes as a kitchen dining room but the kitchen frequentely will not have a window or any natural ventilation.

I know the exceptions with adjoining "rooms" and common walls ect. but here is my question: The code doesn't define a room so what is a room?
 
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I tend to believe that the boundaries of a room are shown on the plans. Some rooms have "missing" walls or "additional" doors. In any case the design professional is in the best position to determine the boundaries.

In your light and ventilation example it seems reasonable that since the windows are a percentage of the floor area one can ignore room boundaries and simply use total (openable) window area/total floor area.
 
A room is a space with at least 70 square feet of area that has the required head room.
 
2009 IRC from I-Quest

R304.2 Other rooms.

Other habitable rooms shall have a floor area of not less than 70 square feet (6.5 m2).

Exception: Kitchens.
 
My first printing edition includes Section R304 (unchanged from 2006).
 
I don't think the question of "what is a room" is any clearer but let's move on to my next question which relates to what I see as conflicts of how sunrooms or porches are defined.

In the definition section (which is referenced in the below sections), it defines a Sunroom, "SUNROOM. A one-story structure attached to a dwelling with a glazing area in excess of 40 percent of the gross area of the structure's exterior walls and roof."

Then go to 303.1 where it describes the required ventilation for Habitable rooms (note it doesn't say Habitable Spaces) and see one of the exceptions, "3. Use of sunroom additions and patio covers, as defined in Section R202, shall be permitted for natural ventilation if in excess of 40 percent of the exterior sunroom walls are open, or are enclosed only by insect screening."

Then this follows a few sections later,

“R303.7.1 Sunroom additions. Required glazed openings shall be permitted to open into sunroom additions or patio covers that abut a street, yard or court if in excess of 40 percent of the exterior sunroom walls are open, or are enclosed only by insect screening, and the ceiling height of the sunroom is not less than 7 feet (2134 mm).”

To me a Sunroom is correctly defined. It is a room with 40% or more of glazing and usually has some of it that will open though that is not a requirement of the definition.

But the sections describing ventilation of habitable rooms require it to be an open porch or a screened porch even though they are calling it a Sunroom. As I read this, if a sunroom is outside of a room that requires a glazed opening (which is where most sunrooms are located), the sunroom cannot be a fully glazed room, even if that glazing can be opened. I would have thought the intent would have been that the sunroom has to have opening glazing if outside a habitable room but that's not what it says.

What do you think it says and since it applies to Sunroom additions, does that mean it doesn’t apply if you build the sunroom initially when you build the house so that it is not an addition?
 
Review of the 2009 IRC--Headroom in a stairwell

“R311.7.2 Headroom. The minimum headroom in all parts of the stairway shall not be less than 6 feet 8 inches (2032 mm) measured vertically from the sloped line adjoining the tread nosing or from the floor surface of the landing or platform on that portion of the stairway.

Exception: Where the nosings of treads at the side of a flight extend under the edge of a floor opening through which the stair passes, the floor opening shall be allowed to project horizontally into the required headroom a maximum of 43/4 inches (121 mm). “

I simply don’t know what this means—can someone explain?
 
I think it means that the stair edge can extend directly under the ceiling of the lower floor up to 4 3/4". Picture a 44" wide stair projecting through a 36" wide opening, centered in the opening. In this example, 4" of each end of the stairway is allowed to project directly under the ceiling of the lower floor.
 
Jobsaver said:
I think it means that the stair edge can extend directly under the ceiling of the lower floor up to 4 3/4". Picture a 44" wide stair projecting through a 36" wide opening, centered in the opening. In this example, 4" of each end of the stairway is allowed to project directly under the ceiling of the lower floor.
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That's what I "see" when I read this
 
That's what I initially thought but I couldn't figure out (and still can't) how that would affect the headroom in the stair run and that is what is is an exception to.
 
As lame as this sounds, I think they are trying to avoid people bumping their heads on stair openings or a ceiling for stairs "too wide" for a given opening. Walking up a wide stair, not realizing you are not centered or clear? Also, to help ensure the handrail can be used while progressing through the opening.

I grew up in a house that had a stairwell to an attic/workshop. There was a brick flue that protruded into the space. I ran into that flue plenty, especially when carrying something up or down, paying a little more attention to the feet, and wall clearances, than the brick flue clearance.
 
I thought they had to clarify that section because some gung-ho inspector person wouldn't allow the railing width (and related tread width) to be "under" the ceiling of the floor below.
 
Robert, what exactly is your concern? Is it natural light and ventilation or headroom?
 
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