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Eave height

Mr. Inspector

Mr. Inspector

SAWHORSE
Joined
Nov 28, 2009
Messages
4,364
Location
Poconos/eastern PA
All the definitions I can find say a eave is a overhang:

In construction, eaves are the edges of a roof that extend past a building's walls, creating an overhang that protects the building from the elements. Eaves can serve both practical and aesthetic purposes.

2018 IRC requires frost footing if the eave is more than 10' high. If there are no eaves is there no height limit?
 
Is the "frost footing" required because there is more exposure to frost? What I mean is, when there is an eave, it provides some protection eliminating the need for the extra footing?

I'm asking because this has never come up in my climate....
 
The 2018 IRC does not define "eave."

I would define "eave" as a horizontal roof edge. Eaves may or may not overhang.

Google likes the Oxford Languages definition, which it claims is "the part of a roof that meets or overhangs the walls of a building." Again, no need to overhang.

Cheers, Wayne
 
Mr. Inspector said:
2018 IRC requires frost footing if the eave is more than 10' high. If there are no eaves is there no height limit?
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This section only applies to free-standing accessory structures under 600 square feet, correct? Section R403.1.4, exception 1?

wwhitney said:
The 2018 IRC does not define "eave."

I would define "eave" as a horizontal roof edge. Eaves may or may not overhang.

Google likes the Oxford Languages definition, which it claims is "the part of a roof that meets or overhangs the walls of a building." Again, no need to overhang.

Cheers, Wayne
Click to expand...
I like this approach.
 
wwhitney said:
The 2018 IRC does not define "eave."
Click to expand...
I agree however it is not a "grey area" ;) There are specific code sections that refer to the eave or the rake of a roof. Therefore, a definition is not needed.

The eave is the lowest portion of the roof

[RB] MEAN ROOF HEIGHT. The average of the roof eave height and the height to the highest point on the roof surface, except that eave height shall be used for roof angle of less than or equal to 10 degrees (0.18 rad).

R804.3.2.1.1 Eave overhang.
Eave overhangs shall not exceed 24 inches (610 mm) measured horizontally.

R804.3.2.1.2 Rake overhangs.
Rake overhangs shall not exceed 12 inches (305 mm) measured horizontally. Outlookers at gable endwalls shall be installed in accordance with Figure R804.3.2.1.2.

R905.2.8.5 Drip edge.
A drip edge shall be provided at eaves and rake edges of shingle roofs. Adjacent segments of drip edge shall be overlapped not less than 2 inches (51 mm). Drip edges shall extend not less than 1/4 inch (6.4 mm) below the roof sheathing and extend up back onto the roof deck not less than 2 inches (51 mm). Drip edges shall be mechanically fastened to the roof deck at not more than 12 inches (305 mm) o.c. with fasteners as specified in Section R905.2.5. Underlayment shall be installed over the drip edge along eaves and under the drip edge along rake edges.
 
mtlogcabin said:
The eave is the lowest portion of the roof
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Locally, not globally; different eaves in different locations of the same roof may be at different heights.

Also, even that is not 100% unambiguous. If the roof edge has a slight slope, it's probably still an eave, but with enough slope, it becomes a rake. Where the transition occurs is not clear to me.

Furthermore, if the roof overhang varies along the length of a wall, the roof/wall intersection could be a level line, while the roof edge has a significant slope, like 2:12. Is that roof edge an eave (which would be true with a constant overhang) or a rake (since it is sloped)?

mtlogcabin said:
Therefore, a definition is not needed.
Click to expand...
I disagree. The IRC can omit the definition if it is confident that the usual dictionary definition will make the meaning clear. But in the section you quoted, if the word "eave" were replaced with "foo", and neither the dictionary nor the IRC had a definition of "foo," while we might be able to divine the meaning of foo, it wouldn't be unambiguous and would certainly generate arguments.

Cheers, Wayne
 
This is a free-standing garage less than 600 sq ft.

mtlogcabin said:
I agree however it is not a "grey area" ;) There are specific code sections that refer to the eave or the rake of a roof. Therefore, a definition is not needed.

The eave is the lowest portion of the roof

[RB] MEAN ROOF HEIGHT. The average of the roof eave height and the height to the highest point on the roof surface, except that eave height shall be used for roof angle of less than or equal to 10 degrees (0.18 rad).

R804.3.2.1.1 Eave overhang.
Eave overhangs shall not exceed 24 inches (610 mm) measured horizontally.

R804.3.2.1.2 Rake overhangs.
Rake overhangs shall not exceed 12 inches (305 mm) measured horizontally. Outlookers at gable endwalls shall be installed in accordance with Figure R804.3.2.1.2.

R905.2.8.5 Drip edge.
A drip edge shall be provided at eaves and rake edges of shingle roofs. Adjacent segments of drip edge shall be overlapped not less than 2 inches (51 mm). Drip edges shall extend not less than 1/4 inch (6.4 mm) below the roof sheathing and extend up back onto the roof deck not less than 2 inches (51 mm). Drip edges shall be mechanically fastened to the roof deck at not more than 12 inches (305 mm) o.c. with fasteners as specified in Section R905.2.5. Underlayment shall be installed over the drip edge along eaves and under the drip edge along rake edges.
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This is just confusing me more. This definition and sections are not in my 2018 IRC. And now I am getting a lot of different definitions for eave. None of these things are telling me where exactly to measure to. The other inspectors I work with also are telling me different things. I do have this which seems to suggest that I measure up to the edge and top of the roof overhang no matter how low it is which could be very low for a 12/12 roof slope or an A frame structure, and I have seen small, cantilevered roofs with a drip edge below the main roof usually over an over door:

R905.2.8.5 Drip edge. A drip edge shall be provided at
eaves and rake edges of shingle roofs. Adjacent segments
of drip edge shall be overlapped not less than 2 inches (51
mm). Drip edges shall extend not less than 1/4 inch (6.4
mm) below the roof sheathing and extend up back onto
the roof deck not less than 2 inches (51 mm). Drip edges
shall be mechanically fastened to the roof deck at not
more than 12 inches (305 mm) o.c. with fasteners as specified
in Section R905.2.5. Underlayment shall be
installed over the drip edge along eaves and under the
drip edge along rake edges.


I also have this in the 2018 IRC that does not help because it is not calling it an eave:

R802.7.1.1 Cantilevered portions of rafters. Notches
on cantilevered portions of rafters are permitted provided
the dimension of the remaining portion of the rafter
is not less than 31/2 inches (89 mm) and the length of
the cantilever does not exceed 24 inches (610 mm) in
accordance with Figure R802.7.1.1.

My boss found a definition that said where the walls and roof meet which would mean on the gable end too.

Here is a copy of the exception that I am talking about in section R403.1.4.1. Notice it also does not say where to measure from (floor, footing, sill plate, highest or lowest grade point?):

1. Protection of free-standing accessory structures
with an area of 600 square feet (56 m2) or
less, of light-frame construction, with an eave
height of 10 feet (3048 mm) or less shall not be
required.

I need exact points, from where to where?
 
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The intention of this section is the theory that allowing a structure to heave with the frost could be ok as long as the building will not go far enough out of plumb that the structure would be damaged by it's own weight if the frost heaves higher on one side than the other.

They limit it to 600 square feet so that you won't have too drastic a difference between the frost heave and subsequent settling on one wall than the opposite, because the ground is more likely to be the same composition and temperature the closer together the walls are.

They limit the height to 10' to the eave because the taller you get, the more pronounced the lean would be and the more weight would be off kilter.

I recommend that you don't over-think this. I would measure to the top of the top plate, as that would be the "eave height" in 99% of all scenarios. If they don't like it, they can find someone else to approve it.

Especially since having a garage door unavoidably compromises the wall bracing to some extent, I would err on the side of being conservative.
 
From the point the bottom plate touches foundation. That is your effective wall height for resisting lateral loads. The foundation height above grade is irrelevant in my opinion.
 
Mirriam-Webster

eave
noun

1: the lower border of a roof that overhangs the wall —usually used in plural
2: a projecting edge (as of a hill) —usually used in plural
 
mtlogcabin said:
R905.2.8.5 Drip edge.
A drip edge shall be provided at eaves and rake edges of shingle roofs. Adjacent segments of drip edge shall be overlapped not less than 2 inches (51 mm). Drip edges shall extend not less than 1/4 inch (6.4 mm) below the roof sheathing and extend up back onto the roof deck not less than 2 inches (51 mm). Drip edges shall be mechanically fastened to the roof deck at not more than 12 inches (305 mm) o.c. with fasteners as specified in Section R905.2.5. Underlayment shall be installed over the drip edge along eaves and under the drip edge along rake edges.
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How did this ever get in the code?? Ridiculous. There are many ways to flash roof edges and provide a drip line offset that don't fit this definition.

OK, back to the topic
 
There is a definition for eave height in the ASCE 7 -16 edition

EAVE HEIGHT, ft : The distance from the ground surface adjacent to the building to the roof eave line at a particular wall. If the height of the eave varies along the wall, the average height shall be used.

This correlates with wwhitney's post. Anything that extends past this definition is an overhang (eave or rake).
 
I called the ICC for the definition of an eave. The person I asked was stumped. Referred me to others. Still waiting for to hear back.

How can this be a gray area if ICC cannot answer a simple question?
 
mtlogcabin said:
I agree however it is not a "grey area" ;) There are specific code sections that refer to the eave or the rake of a roof. Therefore, a definition is not needed.

The eave is the lowest portion of the roof

[RB] MEAN ROOF HEIGHT. The average of the roof eave height and the height to the highest point on the roof surface, except that eave height shall be used for roof angle of less than or equal to 10 degrees (0.18 rad).

R804.3.2.1.1 Eave overhang.
Eave overhangs shall not exceed 24 inches (610 mm) measured horizontally.

R804.3.2.1.2 Rake overhangs.
Rake overhangs shall not exceed 12 inches (305 mm) measured horizontally. Outlookers at gable endwalls shall be installed in accordance with Figure R804.3.2.1.2.

R905.2.8.5 Drip edge.
A drip edge shall be provided at eaves and rake edges of shingle roofs. Adjacent segments of drip edge shall be overlapped not less than 2 inches (51 mm). Drip edges shall extend not less than 1/4 inch (6.4 mm) below the roof sheathing and extend up back onto the roof deck not less than 2 inches (51 mm). Drip edges shall be mechanically fastened to the roof deck at not more than 12 inches (305 mm) o.c. with fasteners as specified in Section R905.2.5. Underlayment shall be installed over the drip edge along eaves and under the drip edge along rake edges.
Click to expand...

None of these actually say where or what an eave is or what part of the eave to measure to where.

Talked to another person form the ICC for an interpretation and again they were stumped.

I ask the BCO of the township and he wasn't sure too. Finally, he decided that I should measure from the average level of the grade to the bottom of the lowest part of the overhang on the walls that support the rafters or if no overhang to the top of the top plate of the same walls.
 
I finally got an interpretation from the ICC:

We are concerned about the wall where the load from the roof rests. As a generic exception, this frost protection section limits the size of the building and the wall height to limit total load on the foundation. So the eave limit is the height of the wall, really the top plate at the eave. If the roof is a gable roof (typical), then the maximum wall height will be taller on the gable ends. So we look at the wall height at the eaves. The IRC in general has a limit of 10-ft wall heights. Even though the language used is ‘eave’, we are really concerned about the top plate maximum height.

Also, the IRC assumes that eaves extend only 2 ft horizontally beyond the wall, unless supported by posts/columns.
 
Good to know they agree with all the engineers that use ASCE 7 for design purposes.
It is also critical when using the wind and cladding tables that are based on "mean roof height" to determine what applies.
Any roof extension over 2 foot in length those tables would not be applicable.

[RB] MEAN ROOF HEIGHT. The average of the roof eave height and the height to the highest point on the roof surface, except that eave height shall be used for roof angle of less than or equal to 10 degrees (0.18 rad).
 
mtlogcabin said:
[RB] MEAN ROOF HEIGHT. The average of the roof eave height and the height to the highest point on the roof surface, except that eave height shall be used for roof angle of less than or equal to 10 degrees (0.18 rad).
Click to expand...
Do you measure from the top or the bottom of the eave (overhang)?

I got his email later from the ICC after I said I still don't know where to measure from to the eave.

Measure from top of concrete or masonry foundation to top of top plate of wall.
I agree – this exception has been siting in the code without being updated to current language. We need someone to submit a code change. Would you like to shepard a code change? Changes for the IRC are due at the beginning of January.

I also got a phone call from someone else from the ICC to measure from the grade. They did not say the lowest or highest point of the grade.
 
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