Story Height & cathedral ceilings

[SDS]

2021 IRC, SDC D <135mph

Does story height limit or impact the peak height of a cathedral ceiling/roof?

As an example, is it possible to have a 24' span 12/12 rafter-framed cathedral ceiling, on a 10' tall wall, using a ridge beam, with a non-bearing exterior gable end-wall closing it off...something where the vault's peak is taller than story height, with a non-bearing end-wall

Or is something like that not allowed due to the 11'-7" story height restricting the height of the ceiling?

 

[Paul Sweet]

You would probably have to have a full-height column supporting each end of the ridge beam, unless there are rooms each side of the cathedral ceiling space to provide lateral support for the 10' walls.. There's a good chance the columns would have to be LVL or glulam, and possibly wider than the wall, so their buckling stress isn't exceeded.

 

[Yankee Chronicler]

2021 IRC, SDC D <135mph

Does story height limit or impact the peak height of a cathedral ceiling/roof?

As an example, is it possible to have a 24' span 12/12 rafter-framed cathedral ceiling, on a 10' tall wall, using a ridge beam, with a non-bearing exterior gable end-wall closing it off...something where the vault's peak is taller than story height, with a non-bearing end-wall

Or is something like that not allowed due to the 11'-7" story height restricting the height of the ceiling?

I don't see how whether or not the end wall is load-bearing makes any difference to the question.

2021 IRC:



I can see two conflicting arguments. If the height of a building is measured to the mid-point of the highest roof, why wouldn't the same apply to your cathedral ceilinged story? But the definition of "story" makes no mention of mid-point, or average height. The story height, by definition, is measured to the top, which would be the peak. By this analysis, your story is 22 feet high.

Unfortunately, even the IRC Commentary fails to take into account cathedral ceilings. I think if I were reviewing the plans, I would extrapolate from the definition of building height and use the mid-point of the sloped ceilings. Unfortunately for you, that would still result in a story height oif 16 feet, which is more than 11'-7".

 

[steveray]

T602.3(5)....2x6 might get you 20'

 

[Yankee Chronicler]

T602.3(5)....2x6 might get you 20'

View attachment 14522

How does that get around the definition of story height?

 

[steveray]

How does that get around the definition of story height?

It gets him 20' studs on the gable...And the ridge gets engineered, so no problem...

R802.3​

A ridge board used to connect opposing rafters shall be not less than 1 inch (25 mm) nominal thickness and not less in depth than the cut end of the rafter. Where ceiling joist or rafter ties do not provide continuous ties across the structure as required by Section R802.5.2, the ridge shall be supported by a wall or ridge beam designed in accordance with accepted engineering practice and supported on each end by a wall or column.

 

[SDS]

It gets him 20' studs on the gable...And the ridge gets engineered, so no problem...

R802.3​

A ridge board used to connect opposing rafters shall be not less than 1 inch (25 mm) nominal thickness and not less in depth than the cut end of the rafter. Where ceiling joist or rafter ties do not provide continuous ties across the structure as required by Section R802.5.2, the ridge shall be supported by a wall or ridge beam designed in accordance with accepted engineering practice and supported on each end by a wall or column.

This is getting closer to the question I am trying to ask...

Is a non-bearing gable end-wall's allowable height (or any non-bearing wall) restricted by story height?

The issue of no longer being allowed to prescriptively design a ridge beam (???) is an entirely separate thread. Personally I think there is a typo in the new verbiage

the ridge shall be supported by a wall or ridge beam OR SHALL BE designed in accordance with accepted engineering practice and supported on each end by a wall or column.

...but I digress...

The cathedral ceiling example in my OP is just the most common design situation the question of story height arises as they're typically enclosed by an exterior wall and it is usually non-bearing.

So there is this....

R301.3​

The wind and seismic provisions of this code shall apply to buildings with story heights not exceeding the following:

1. 1.For wood wall framing, the story height shall not exceed 11 feet 7 inches (3531 mm) and the laterally unsupported bearing wall stud height permitted by Table R602.3(5).

...and this down at the bottom...

Individual walls or wall studs shall be permitted to exceed these limits as permitted by Chapter 6 provisions, provided that story heights are not exceeded.

Item #1 seems to state that story height applies to only bearing walls, however the bottom note seem to suggest it applies to all walls as it doesn't differentiate between bearing/non-bearing, effectively limiting all wall height to story height

Am I wrong here or are non-bearing walls excluded from this story height verbiage?

By default a cathedral ceiling is most commonly going to exceed story height, requiring enclosing end-walls that are taller than story height, bearing or otherwise.

In my experience, gable walls and such have always been considered non-bearing unless they aren't, and their height has only been limited by allowable stud height, not story height...

 

[jfmann77]

Two primary issues must be carefully considered for design of gable endwall with sloped ("cathedral") ceiling, such that there is no attic floor to provide lateral bracing for wall framing;
(1) Design capacity to resist lateral wind force.
(2) Design capacity for support of ridge beam.

The following issues must be considered;
(1) Design capacity of full-height wall studs, if used. Deflection typically governs design of such studs, which may have to be doubled.
(2) For full-height wall studs (if used); Design capacity of connections at each end of wall studs. "Standard" prescriptive nailed connections often do not have adequate design shear capacity, even using Load Duration Factor of 1.6 for wind.
(3) For alternate wall framing, using horizontal beam instead of full-height wall studs; Design capacity of horizontal beam and design capacity of connections at each end of beam.
(4) For column to support ridge beam; (1) Design capacity of column must consider lateral-buckling, as for any column, and (2) Column must be designed to resist.....at same time........ vertical force, from ridge beam, and lateral wind force, acting as beam-element.
(5) As for any ridge beam..........connection to support must have adequate design capacity to resist wind uplift force due to wind uplift pressure on tributary roof surface areas. Design wind uplift force from end of ridge beam must then be distributed.......via "continuous load path" down to other elements that have adequate design capacity to provide resistance.

 

[SDS]

I don't see how whether or not the end wall is load-bearing makes any difference to the question.

2021 IRC:

View attachment 14520

I can see two conflicting arguments. If the height of a building is measured to the mid-point of the highest roof, why wouldn't the same apply to your cathedral ceilinged story? But the definition of "story" makes no mention of mid-point, or average height. The story height, by definition, is measured to the top, which would be the peak. By this analysis, your story is 22 feet high.

Unfortunately, even the IRC Commentary fails to take into account cathedral ceilings. I think if I were reviewing the plans, I would extrapolate from the definition of building height and use the mid-point of the sloped ceilings. Unfortunately for you, that would still result in a story height oif 16 feet, which is more than 11'-7".

The confusion here (for me), in a cathedral ceiling case, is that part that says "to the top of the rafters".

Top of rafter is considered the top edge of the framing member, not where that member's end is located, measured vertically. In a cathedral ceiling situation the top edge of the member is rising so where do you measure to for story height?

Is it the peak? Midpoint as you're saying?

Now add in prescriptive wall bracing which is limited to 10' height (SDC-D)...how do you provide wall bracing on a wall enclosing a cathedral ceiling taller than 10'?

Are prescriptively designed vaulted ceilings limited by either story height (11'-7") or by wall bracing (10') when they are abutted by exterior walls? This is my question.

Either case seems to effectively exclude cathedral ceilings from prescriptive design where that ceiling is taller than either 10' or 11'-7, depending on which case you're going by.

 

[Yankee Chronicler]

A story is a story. IRC 2021 definitions:

[RB] 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.

[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

Taken together, the entirety of the space under/within a cathedral ceiling is a story. To further complicate things, the height of a building with a sloped roof is

[RB] HEIGHT, BUILDING. The vertical distance from
grade plane to the average height of the highest roof surface.

It's grammatically and logically difficult to justify saying that the height of a story is greater than the height of the building in which the story is located. I would go with applying the building height criterion, and measure the story height to the mid-point of the sloped roof-ceiling assembly. If that exceeds the prescriptive height for design, the wall will have to be designed by a licensed architect or a licensed structural engineer.

 

[steveray]

T602.3(5) gives you gable studs...up to 20'....24"OC

 

[jfmann77]

A story is a story. IRC 2021 definitions:





Taken together, the entirety of the space under/within a cathedral ceiling is a story. To further complicate things, the height of a building with a sloped roof is



It's grammatically and logically difficult to justify saying that the height of a story is greater than the height of the building in which the story is located. I would go with applying the building height criterion, and measure the story height to the mid-point of the sloped roof-ceiling assembly. If that exceeds the prescriptive height for design, the wall will have to be designed by a licensed architect or a licensed structural engineer.

Key requirement is that wall framing have adequate design capacity to resist code-specified design loads. That very basic requirement........which is stated in R301 as well as in IBC........takes precedence over any prescriptive provisions including those based on "story height".
For gable endwall, each wall stud must have adequate design capacity........including; (1) Stud with greatest length, (2) Connections at each end of each stud and (3) Elements that must provide lateral bracing for each end of each stud.

Often overlooked is design capacity of long wall studs to resist lateral wind pressure acting outward........which is basic requirement. For outward lateral wind pressure, inside edge of wall stud (in bending) is in compression. If there is no interior wall sheathing..........as very often occurs for gable endwall.......there is no lateral bracing for compression edge, such that lateral buckling may greatly reduce allowable bending stress.

 

[Yankee Chronicler]

Whether or not a stud or a series of studs in a wall are structurally stable has nothing to do with the definition of a story.

 

[jfmann77]

Whether or not a stud or a series of studs in a wall are structurally stable has nothing to do with the definition of a story.

Though original post asked whether limits for story-height should govern height of gable endwall...........essential issue that post raises is;..... What design factors govern height of gable endwall.
Relative to building code.........not Zoning Code which may limit overall height of building...........most important design factor for gable endwall is design capacity for structural design forces (loads).
As reported after several major hurricanes...........failure of gable endwall due to wind is one of primary reasons for major damage to wood-framed houses.
Review of many building plans for wood-framed residential construction shows that design of gable endwall is very often "overlooked".

 

[bill1952]

"[RB] 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."

At what point on the often sloped roof next above do you measure to?

 

[Yankee Chronicler]

"[RB] 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."

At what point on the often sloped roof next above do you measure to?

See post #10 for my opinion.

 

[SDS]

T602.3(5) gives you gable studs...up to 20'....24"OC

View attachment 14988

Now put a vaulted ceiling on the inside of the wall with its peak something above 10' and brace that wall with a prescriptive braced wall panel that is limited in height to 10' stud height.

Can it be done?

A story is a story. IRC 2021 definitions:





Taken together, the entirety of the space under/within a cathedral ceiling is a story. To further complicate things, the height of a building with a sloped roof is



It's grammatically and logically difficult to justify saying that the height of a story is greater than the height of the building in which the story is located. I would go with applying the building height criterion, and measure the story height to the mid-point of the sloped roof-ceiling assembly. If that exceeds the prescriptive height for design, the wall will have to be designed by a licensed architect or a licensed structural engineer.

This is the answer I think applies...I just cannot find anything in the IRC that states it plainly like you have YC.