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storage shed less than 120 SF

E

ELLEN09US

Member
Joined
Oct 31, 2014
Messages
140
Location
LOS ANGELES
Hi All,

Per CBC 105.2 work exempt from permit
1. One-story detached accessory structures used as tool and storage sheds, playhouses and similar uses, provided that the floor area is not greater than 120 square feet (11 m2).

Is this gross or net floor area?
Also, what's the limit of number of structures? can someone build 3-4 structures under 120 sf?

Thank you!
 
The limit of the number of structures will likely be limited by other factors outside of building code. The exemption from requiring permits does not exempt the structure from other building code requirements or zoning and land use codes. For example you will still need to follow setback and use requirements that are outlined by your jurisdiction. Some jurisdictions have limits on the number of buildings (of any kind) per parcel. Also you have to be aware of things like storm water mitigation laws. I think in general you can't cover a lot with more than 50% impervious surfaces (i.e. roof) without some special improvements. Best thing to do is to research your local codes and/or talk to a city/county planner.
 
Look to Chapter 2 Definitions for floor area. Go by gross floor area unless otherwise indicated. Why? Virtually all building officials and building departments and local jurisdictions are going to lean to the particular definition that will provide for the least you can do without a permit because the goal is ultimately to require as much (within reason) to be under the permit review. This provision of structures under 120 sq.ft. goes back to the Uniform Building Code. Now, if we go back to 1994 Uniform Building Codes (which is a few code editions before the first I-Codes), the particular language is as follows:

"1. One-story detached accessory buildings used as tool and storage sheds, playhouses and similar uses, provided the projected roof area does not exceed 120 square feet ( 11.15 m2)."

Chapter 2 of 1994 Uniform Building Codes: "FLOOR AREA is the area included within the surrounding exterior walls of a building or portion thereof, exclusive of vent shafts and courts. The floor area of a building, or portion thereof, not provided with surrounding exterior walls shall be the usable area under the horizontal projection of the roof or floor above."

So roof projected area is the key. So, if you take a plan view of the structure, the 120 sq.ft. is counted to the end of the rafter or vergeboard and not necessarily to the gutters. Therefore, 120 sq.ft. takes into account roof overhang. So, the roof can be 120 inches x 144 inches. Some building officials counted the gutter.... some didn't. This mean, you had to be careful to not build the walls all the way out to 10 ft. x 12 ft. because if you did and your shed had a roof projection of even just a gutter (6"), the nitpicky stickler of a building official may flag that shed as work not done under permit where a permit is required and be a pain in the butt.

Since it wasn't just UBC that incorporated same or similar provisions by this time, the regional building codes in different parts of the U.S. had a slight variation on the word form.

The current IBC building codes have updated the text and use the floor area definition. Now, remember the UBC floor area. They didn't have separate gross floor area and net floor area. It was just floor area.

Code text history and understanding the lineage of the codes from the UBC era and the changes through into the IBC code era and the editions since then is important. So it is still useful to have copies of the UBC in digital form across various code editions.

As you read the Gross Floor Area's definition in Chapter 2 of IBC, it is the closest and most applicable definition that would be used here. Net Floor area is for interior measuring. If you recall the UBC language for the 120 sqft. was operating from the projected roof area. It would be an exterior measurement. The gross floor area definition even refers to usable areas under the roof projection.

Since UBC, the changes in the IBC resulted in a slight change in measuring. Sometimes measuring the roof was more dangerous so they generally went with exterior wall measurements and include the area of a porch. Therefore, if you in fact have a usable area under the roof (meaning the roof almost certainly needed to project like 4 to 5 feet or more but then it would have a usable area.

So, it would be the GROSS FLOOR AREA. Net Floor Area would not be used as they are measured on the interior side which the building department may or may not have access to at a given time. In addition, using net floor area may inadvertently result in a person building a storage shed structure that is over 150 sq.ft. by putting in corridors, mechanical room, closet, etc. and kind of defeating the 120 s.ft. area limit which would be a significant departure from the UBC era.
 
RickAstoria said:
Look to Chapter 2 Definitions for floor area. Go by gross floor area unless otherwise indicated. Why? Virtually all building officials and building departments and local jurisdictions are going to lean to the particular definition that will provide for the least you can do without a permit because the goal is ultimately to require as much (within reason) to be under the permit review. This provision of structures under 120 sq.ft. goes back to the Uniform Building Code. Now, if we go back to 1994 Uniform Building Codes (which is a few code editions before the first I-Codes), the particular language is as follows:

"1. One-story detached accessory buildings used as tool and storage sheds, playhouses and similar uses, provided the projected roof area does not exceed 120 square feet ( 11.15 m2)."

Chapter 2 of 1994 Uniform Building Codes: "FLOOR AREA is the area included within the surrounding exterior walls of a building or portion thereof, exclusive of vent shafts and courts. The floor area of a building, or portion thereof, not provided with surrounding exterior walls shall be the usable area under the horizontal projection of the roof or floor above."

So roof projected area is the key. So, if you take a plan view of the structure, the 120 sq.ft. is counted to the end of the rafter or vergeboard and not necessarily to the gutters. Therefore, 120 sq.ft. takes into account roof overhang. So, the roof can be 120 inches x 144 inches. Some building officials counted the gutter.... some didn't. This mean, you had to be careful to not build the walls all the way out to 10 ft. x 12 ft. because if you did and your shed had a roof projection of even just a gutter (6"), the nitpicky stickler of a building official may flag that shed as work not done under permit where a permit is required and be a pain in the butt.

Since it wasn't just UBC that incorporated same or similar provisions by this time, the regional building codes in different parts of the U.S. had a slight variation on the word form.

The current IBC building codes have updated the text and use the floor area definition. Now, remember the UBC floor area. They didn't have separate gross floor area and net floor area. It was just floor area.

Code text history and understanding the lineage of the codes from the UBC era and the changes through into the IBC code era and the editions since then is important. So it is still useful to have copies of the UBC in digital form across various code editions.

As you read the Gross Floor Area's definition in Chapter 2 of IBC, it is the closest and most applicable definition that would be used here. Net Floor area is for interior measuring. If you recall the UBC language for the 120 sqft. was operating from the projected roof area. It would be an exterior measurement. The gross floor area definition even refers to usable areas under the roof projection.

Since UBC, the changes in the IBC resulted in a slight change in measuring. Sometimes measuring the roof was more dangerous so they generally went with exterior wall measurements and include the area of a porch. Therefore, if you in fact have a usable area under the roof (meaning the roof almost certainly needed to project like 4 to 5 feet or more but then it would have a usable area.

So, it would be the GROSS FLOOR AREA. Net Floor Area would not be used as they are measured on the interior side which the building department may or may not have access to at a given time. In addition, using net floor area may inadvertently result in a person building a storage shed structure that is over 150 sq.ft. by putting in corridors, mechanical room, closet, etc. and kind of defeating the 120 s.ft. area limit which would be a significant departure from the UBC era.
Click to expand...

To correct myself, the gross floor area would be an interior measurement but also may including measuring usable areas not surrounded by exterior walls under the horizontal projection of the roof.

Gross Floor Area would result in a number much closer to that of the UBC and includes all floor area within the exterior walls and usable areas surrounding exterior walls under the roof. Imagine a small gazebo with a small storage shelf structure to store lawn rakes and stuff.
 
Note: This 120 sq.ft. limit or even the 200 sq.ft. limit for certain things exempt from building permits under IRC does not apply to zoning permit and other reviews of your local city or county/parish. What is exempt under one area of local law is not necessarily exempt from permits under another.

In addition, just because a permit is not required does not mean the building codes does not apply.
 
Rick there is one other definition in the IBC that you did not comment on that might help muddy the waters some more and that is

[BG] AREA, BUILDING. The area included within surrounding exterior walls, or exterior walls and fire walls, exclusive of vent shafts and courts. Areas of the building not provided with surrounding walls shall be included in the building area if such areas are included within the horizontal projection of the roof or floor above.

Gross and net floor areas are usually referred to when calculating occupant loads for different occupancy types.
I think the intent of the ICC codes is to not include the horizontal projections when using the exemption from a permit for certain structures of less than 120 sq ft in the IBC or 200 sq ft in the IRC.
 
The IBC jumped back and forth between 120 sq ft and 200 sq ft for the exemption so we stayed with the 200 sq ft exemption with regards to the IBC
Ricks very thought out explanation starting with the UBC is a great example of how the codes are applied from AHJ to AHJ over the years. The IRC uses the term "floor area" throughout the code and the majority of the time it appears to be referring to the actual floor area excluding walls within a building or room. However there is no definition in the IRC for floor area or even building area. This is where 104.1 should be used and applied by the building official to clarify the AHJ's position and ensure it is consistency throughout the years.

[A] 104.1 General.
The building official is hereby authorized and directed to enforce the provisions of this code. The building official shall have the authority to render interpretations of this code and to adopt policies and procedures in order to clarify the application of its provisions. Such interpretations, policies and procedures shall be in compliance with the intent and purpose of this code. Such policies and procedures shall not have the effect of waiving requirements specifically provided for in this code.
 
mtlogcabin said:
Rick there is one other definition in the IBC that you did not comment on that might help muddy the waters some more and that is

[BG] AREA, BUILDING. The area included within surrounding exterior walls, or exterior walls and fire walls, exclusive of vent shafts and courts. Areas of the building not provided with surrounding walls shall be included in the building area if such areas are included within the horizontal projection of the roof or floor above.

Gross and net floor areas are usually referred to when calculating occupant loads for different occupancy types.
I think the intent of the ICC codes is to not include the horizontal projections when using the exemption from a permit for certain structures of less than 120 sq ft in the IBC or 200 sq ft in the IRC.
Click to expand...

The particular section: "Section 105.2 1. One-story detached accessory structures used as tool and storage sheds, playhouses and similar uses, provided that the floor area is not greater than 120 square feet (11 m2)."

That is why I didn't use "building area". Honestly, "Building Area" would fit into the original UBC. However, codes do have to be enforced by the words and definitions and when "floor area" is used and there is a definition for "floor area" in Chapter 2 of the building codes then must be used. Actually, there's two of them now.... gross floor area and net floor area.

Honestly, amendments over the years, complicated the mess a little more but "building area" is not used in the text of Section 105.2.1, which I would reason would actually fit into the older UBC era. This provision was a carry over from UBC. If you have a copy of the 1994 UBC, you would note that there is NO definition for 'building area' but a definition for 'area' which says 'see Floor Area'. That meant to use floor area as the definition. Therefore "building area" as a definition in the building code is a more recent adoption.

Also, the definition of Floor Area is UBC days is a little different then how it had been amended in I-codes over the past 20 or so years.

I used precedents of prior code versions when IBC was known as UBC, NBC, etc. UBC was used in the west coast states like California and therefore would have been the historic practice and definitions. UBC goes back to 1927 or about.... so it's "intent" was when it was adopted originally and with consideration of subsequent amendments. When did the old.... ICBO, BOCA, or whatever they were, intended is kind of muddy because who do we talk to from who knows when to give insight of the actual intent back in those days. How well was the records kept about the intent and "floor discussion" when they were voting to adopt it into the model codes all those years ago. This provision in 105.2.1 didn't come into existence in the I-codes days but from the prior editions of codes before the I-codes. This is why I went back to a little before IBC model code came into existence. I know the OP's code reference is from California building codes and that it's amended but this section isn't specifically a deviation from the model code in this particular case. In the UBC days, they didn't have "building area" which I think may make sense to use but to use it, the particular text from Section 105.2.1 would need to change the text "Floor Area" to "building area".

Here's the text from 1994 Uniform Building Code:
"1. One-story detached accessory buildings used as tool and storage sheds, playhouses and similar uses, provided the projected roof area does not exceed 120 square feet ( 11.15 m2)."

In this case, there isn't a definition for "roof area" but a definition for "area" which says "see Floor Area" and then you go to that definition which says:

"FLOOR AREA is the area included within the surrounding exterior walls of a building or portion thereof, exclusive of vent shafts and courts. The floor area of a building, or portion thereof, not provided with surrounding exterior walls shall be the usable area under the horizontal projection of the roof or floor above."

The definition would fit the "building area" definition very closely which I would agree with you and that "building area" is actually a closer match to the Uniform Building Code's original intent for this definition and in the next cycle of the IBC, we should amend the text for this particular exemption to change "floor area" to "building area". I would agree with you and I would not fault a building official using the definition for "building area" because its actual definition is what was used for Floor Area in the Uniform Building Codes days... almost verbatim. I would concur with you to use that definition but to clean up code language, they should amend the text to use the words "building area" (with the specialize bold or italicization to indicate to refer to the code definition). This would actually restore it closer to original intent in the UBC that got muddied up in the I-codes years through the numerous amendments.
 
RickAstoria said:
The particular section: "Section 105.2 1. One-story detached accessory structures used as tool and storage sheds, playhouses and similar uses, provided that the floor area is not greater than 120 square feet (11 m2)."

That is why I didn't use "building area". Honestly, "Building Area" would fit into the original UBC. However, codes do have to be enforced by the words and definitions and when "floor area" is used and there is a definition for "floor area" in Chapter 2 of the building codes then must be used. Actually, there's two of them now.... gross floor area and net floor area.

Honestly, amendments over the years, complicated the mess a little more but "building area" is not used in the text of Section 105.2.1, which I would reason would actually fit into the older UBC era. This provision was a carry over from UBC. If you have a copy of the 1994 UBC, you would note that there is NO definition for 'building area' but a definition for 'area' which says 'see Floor Area'. That meant to use floor area as the definition. Therefore "building area" as a definition in the building code is a more recent adoption.

Also, the definition of Floor Area is UBC days is a little different then how it had been amended in I-codes over the past 20 or so years.

I used precedents of prior code versions when IBC was known as UBC, NBC, etc. UBC was used in the west coast states like California and therefore would have been the historic practice and definitions. UBC goes back to 1927 or about.... so it's "intent" was when it was adopted originally and with consideration of subsequent amendments. When did the old.... ICBO, BOCA, or whatever they were, intended is kind of muddy because who do we talk to from who knows when to give insight of the actual intent back in those days. How well was the records kept about the intent and "floor discussion" when they were voting to adopt it into the model codes all those years ago. This provision in 105.2.1 didn't come into existence in the I-codes days but from the prior editions of codes before the I-codes. This is why I went back to a little before IBC model code came into existence. I know the OP's code reference is from California building codes and that it's amended but this section isn't specifically a deviation from the model code in this particular case. In the UBC days, they didn't have "building area" which I think may make sense to use but to use it, the particular text from Section 105.2.1 would need to change the text "Floor Area" to "building area".

Here's the text from 1994 Uniform Building Code:
"1. One-story detached accessory buildings used as tool and storage sheds, playhouses and similar uses, provided the projected roof area does not exceed 120 square feet ( 11.15 m2)."

In this case, there isn't a definition for "roof area" but a definition for "area" which says "see Floor Area" and then you go to that definition which says:

"FLOOR AREA is the area included within the surrounding exterior walls of a building or portion thereof, exclusive of vent shafts and courts. The floor area of a building, or portion thereof, not provided with surrounding exterior walls shall be the usable area under the horizontal projection of the roof or floor above."

The definition would fit the "building area" definition very closely which I would agree with you and that "building area" is actually a closer match to the Uniform Building Code's original intent for this definition and in the next cycle of the IBC, we should amend the text for this particular exemption to change "floor area" to "building area". I would agree with you and I would not fault a building official using the definition for "building area" because its actual definition is what was used for Floor Area in the Uniform Building Codes days... almost verbatim. I would concur with you to use that definition but to clean up code language, they should amend the text to use the words "building area" (with the specialize bold or italicization to indicate to refer to the code definition). This would actually restore it closer to original intent in the UBC that got muddied up in the I-codes years through the numerous amendments.
Click to expand...

In short, I agree with you that "Building Area" definition is more correct to intent because it's definition IS the definition used for Floor Area in the Uniform Building Codes and 105.2.1 provisions was carried over from the UBC into the I-codes about 20 years ago. This would actually be the definition that should be used and 105.2.1 should be amended to refer to the building area definition. This would be more consistent with building enforcement practices over the past 90+ years.
 
What Bill said above. It has been removed from our IRC and is not exempt from the permit and inspectional processes.
 
If a shed is proposed with an interior floor area of 200ft² (120ft² if IBC) I walk away. I am not sweating the thickness of the walls. Just what I do....right or wrong.
 
I found this at LA County code:

One-story detached accessory buildings used as tool and storage sheds, shade structures, pump houses, and similar uses, provided the gross floor area does not exceed 120 square feet (11.15 m 2 ), the height does not exceed 12 feet (3.69 m), and the maximum roof projection does not exceed 24 inches (610 mm).
 
I would think the measurements would be outside the walls. You can measure that without going inside the shed, and thats the size that creates the footprint.
 
e hilton said:
I would think the measurements would be outside the walls. You can measure that without going inside the shed, and thats the size that creates the footprint.
Click to expand...
I would agree with that system to determine the SF.
 
Pcinspector1 said:
I would agree with that system to determine the SF.
Click to expand...

I would support a change in language of the that exemption and support that.... basically building footprint including usable area under roof projection. This would be similar to how ground area (under Oregon's architect licensing laws and that board's administrative rules defines. Maybe we can adopt into code something similar to that. Building Area's definition sounds close to it. I think we should be able to do something on this front that makes the task easier for building officials when they may or may not have any sort of plans to assess from and might not be able to get inside the structure. This is something we should address in the building codes and it's language. I wouldn't be opposed to it. It isn't like HSW risk is changing just because of what may be a 10% difference in size. Whatever we use, it should make sense.
 
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