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Can a Wood-Framed Wall Cantilever Over a Foundation Wall?

jar546

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Can a Wood-Framed Wall Cantilever Over a Foundation Wall?​

Question in Detail:

A building located in Climate Zone 4A requires foundation insulation. We need to detail the connection between a wall plate and a concrete masonry unit (CMU) foundation wall. While we're not using continuous exterior insulation on the wood-framed walls, we prefer to apply it to the foundation walls, including CMU stem walls and slab conditions.

We aim to avoid a 2 to 3-inch outward jog around the building's skirt to accommodate the difference in exterior treatments as required by the 2018 International Building Code (IBC) Section 2304.3.1. A design that features a sill plate cantilevered over the foundation wall to make up for this jog has caught our interest.

Our question is whether this design complies with the code, and if there is a prescriptive allowable sill plate offset.

Attachment(s):

Code Analysis:


This analysis also applies to the 2021 and 2024 IBC.

According to the 2018 IBC Section 1807.1.6.1 and Section 2304.3.1, a wood-framed wall cannot cantilever over the foundation wall. Section 2304.3.1 mandates that the studs must bear on a sill plate with a width at least equal to the width of the studs. Additionally, Section 1807.1.6.1 requires that the thickness of the foundation wall must not be less than the thickness of the supported wall. The combined intent of these provisions is to ensure that the full width of the stud wall bears directly on the foundation, without any cantilevering.
 
We had a similar situation with ICF forms, they did not use to right ICF type for the top course, so they cantilevered the 2x4 sill plate out on top of the ICF foam. They had to engineer a bracket solution to support the sill plate instead of trying to bear on the foam.

Makes proper anchor bolt placement tricky too...
 
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If the wall works structurally with with width that is in direct bearing, I would argue the rest of the stud is furring. The intent is to provide the required load path, If you only need 3 1/2" of the studs to work and you have 2x6 walls, you should be able to hang out 2" over the foundation wall.
But... the code does not explicitly say that. But... the AHJ can allow it if you provide sound engineering.
 

Can a Wood-Framed Wall Cantilever Over a Foundation Wall?​

Question in Detail:

A building located in Climate Zone 4A requires foundation insulation. We need to detail the connection between a wall plate and a concrete masonry unit (CMU) foundation wall. While we're not using continuous exterior insulation on the wood-framed walls, we prefer to apply it to the foundation walls, including CMU stem walls and slab conditions.

We aim to avoid a 2 to 3-inch outward jog around the building's skirt to accommodate the difference in exterior treatments as required by the 2018 International Building Code (IBC) Section 2304.3.1. A design that features a sill plate cantilevered over the foundation wall to make up for this jog has caught our interest.

Our question is whether this design complies with the code, and if there is a prescriptive allowable sill plate offset.

Attachment(s):

Code Analysis:


This analysis also applies to the 2021 and 2024 IBC.

According to the 2018 IBC Section 1807.1.6.1 and Section 2304.3.1, a wood-framed wall cannot cantilever over the foundation wall. Section 2304.3.1 mandates that the studs must bear on a sill plate with a width at least equal to the width of the studs. Additionally, Section 1807.1.6.1 requires that the thickness of the foundation wall must not be less than the thickness of the supported wall. The combined intent of these provisions is to ensure that the full width of the stud wall bears directly on the foundation, without any cantilevering.

We have a metric boatload of raised ranch style houses in this state (and this region). I'd say at least 90% of them have the upper story cantilevered out beyond the lower level by a foot or more on both the front and the back. In a raised ranch, the foundation stem wall is only half height, with the remaining height of the lower level being a wood-framed cripple wall. So, in this design, there is a load-bearing sill plate and wall on the foundation, but the roof and main floor loads are cantilevered.

In fact, it was very common even back in colonial New England for the second story to overhand the first story.
 
We have a metric boatload of raised ranch style houses in this state (and this region). I'd say at least 90% of them have the upper story cantilevered out beyond the lower level by a foot or more on both the front and the back. In a raised ranch, the foundation stem wall is only half height, with the remaining height of the lower level being a wood-framed cripple wall. So, in this design, there is a load-bearing sill plate and wall on the foundation, but the roof and main floor loads are cantilevered.

In fact, it was very common even back in colonial New England for the second story to overhand the first story.
The question was not about cantilevering of a floor, which is allowed by code, but this was about cantilevering the sill plate.
 
The question was not about cantilevering of a floor, which is allowed by code, but this was about cantilevering the sill plate.
I saw that once .. but it was because the foundation sub had the slab out of square by 2 inches in 40 feet! I think the framer split the difference .. in an inch on one end and hanging out an inch on the other.

(Sorry for the thread drift, Jeff!)
 
A design that features a sill plate cantilevered over the foundation wall to make up for this jog has caught our interest.
Is there an option to cantilever the floor framing over the sill plate, the studs wouldn’t be bearing on the plate on the CMU that way.

TBCF 240604 cantilevered floor framing.jpg
 
I guess my question is why reinvent the wheel

Just use the matching depth insulated zip wall sheathing panel, you never have enough insulation in my book.

 
In Canadian code, the wall plates are permitted to project up to 1/3 the plate width.

Note that this is 1/3 the actual plate width, not the required width.
 
Absolutely not. A signed and sealed rubber stamp does not negate a code requirement.
see passage below from the 2021 the ICC code illustrated, an engineered design supersedes prescriptive code requirements.

2304.3 Wall framing. This section addresses minimum prescriptive requirements for wood-framed walls. These provisions include the framing of bottom plates, the framing over openings within the wall, and shrinkage. The shrinkage requirement sets a limit on the height of wood framed walls at no more than two floors and a roof. For all of these provisions, an exception is made when a “specific design is furnished.”
 
see passage below from the 2021 the ICC code illustrated, an engineered design supersedes prescriptive code requirements.

2304.3 Wall framing. This section addresses minimum prescriptive requirements for wood-framed walls. These provisions include the framing of bottom plates, the framing over openings within the wall, and shrinkage. The shrinkage requirement sets a limit on the height of wood framed walls at no more than two floors and a roof. For all of these provisions, an exception is made when a “specific design is furnished.”
A bottom plate is not a sill plate. Specific requirements cannot be waived by an engineer's stamp.
 

Can a Wood-Framed Wall Cantilever Over a Foundation Wall?​

Question in Detail:

A building located in Climate Zone 4A requires foundation insulation. We need to detail the connection between a wall plate and a concrete masonry unit (CMU) foundation wall. While we're not using continuous exterior insulation on the wood-framed walls, we prefer to apply it to the foundation walls, including CMU stem walls and slab conditions.

We aim to avoid a 2 to 3-inch outward jog around the building's skirt to accommodate the difference in exterior treatments as required by the 2018 International Building Code (IBC) Section 2304.3.1. A design that features a sill plate cantilevered over the foundation wall to make up for this jog has caught our interest.

Our question is whether this design complies with the code, and if there is a prescriptive allowable sill plate offset.

Attachment(s):

Code Analysis:


This analysis also applies to the 2021 and 2024 IBC.

According to the 2018 IBC Section 1807.1.6.1 and Section 2304.3.1, a wood-framed wall cannot cantilever over the foundation wall. Section 2304.3.1 mandates that the studs must bear on a sill plate with a width at least equal to the width of the studs. Additionally, Section 1807.1.6.1 requires that the thickness of the foundation wall must not be less than the thickness of the supported wall. The combined intent of these provisions is to ensure that the full width of the stud wall bears directly on the foundation, without any cantilevering.

I would avoid that condition, as it would upset my structural engineer who would tell me "absolutely not."

You have two other options:
1) do a comcheck tradeoff method and ditch the slab insulation
2) Flash the slab edge insulation and furr out your exterior siding slightly if you don't like the look of it. Typically 1-1.5" of insulation won't be that noticeable at grade.
 
Specific requirements cannot be waived by an engineer's stamp.

That depends on the requirement. A structural engineer can't "engineer" a design that negates fire resistance ratings, but a structural design by a licensed engineer always has precedence over prescriptive structural requirements in the code. The engineer can't reduce the code-mandated loads, but he can design a structure to support those loads that doesn't comport with the prescriptive requirements.
 
If the wall works structurally with with width that is in direct bearing, I would argue the rest of the stud is furring. The intent is to provide the required load path, If you only need 3 1/2" of the studs to work and you have 2x6 walls, you should be able to hang out 2" over the foundation wall.
But... the code does not explicitly say that. But... the AHJ can allow it if you provide sound engineering.
if there is sound engineering I would expect that the AHJ would be compelled to accept the solution
 
if there is sound engineering I would expect that the AHJ would be compelled to accept the solution
The question becomes: Who is the final arbiter as to the validity of the engineering? Common sense dictates that it is not the engineer that created the "sound engineering". That same principal stands in the way of a structural observation performed by the engineer that created the engineering. That engineer is not likely to catch his own mistakes.
 
if there is sound engineering I would expect that the AHJ would be compelled to accept the solution

The sticky wicket, of course, is determining if the engineering IS sound.

We have encountered this question at least twice, both of which I have mentioned in other threads. Structural drawings done by a PE and bearing his seal and signature, but I was convinced they didn't work. In both cases the engineers took the position that, as mere building officials, we couldn't question their work. The second actually stated outright that we had to accept his plans because he had put his seal and signature on them. The first took the position that, even though I am also a licensed architect and I have taken graduate-level structural engineering course, I am not qualified to review his work.

Case 1: In the first case (the one in which the PE literally stole the foundation design and details from a design by another PE for a smaller building), we first consulted the other engineer to ask if he had authorized the re-use of his details. He said he had not. When we told him how big the building we were reviewing was, his response was, "I wouldn't guarantee that will stand up."

To resolve that one, we invoked the last sentence of IBC 107.1, which says, "Where special conditions exist, the building official is authorized to require additional construction documents to be prepared by a registered design professional." We did this after consulting with the Corporation Counsel (town attorney). The theory was that a known, demonstrable case of plagiarized documents, when the engineer who prepared the original details expressed reservations about the adequacy on a larger building, constituted "special conditions." We required a peer review by another PE. That peer review resulted in recommendations for several changes in the foundation design, which were made.

Case 2: The second case was the one involving the 92-year-old PE who claimed he took the sizes of the piers for a PEMB directly from the drawings for the superstructure -- which drawings (of course) didn't include any information whatsoever about foundations, they only provided the reactions at each frame base and the baseplate layouts. We had a meeting with the owner and the engineer, we explained our concerns, the engineer (very reluctantly) agreed to make some revisions to the foundation drawings -- and then resubmitted the same drawings, with no changes. The owner told the boss that the engineer decided we had no right to even review his drawings, since he had put his seal on them, so he wasn't going to make any changes. The project was an addition to an HVAC contractor's building, the owner has been around construction long enough to know a little bit, and he acknowledged to the boss that we were right. He hired a different engineer. The new drawings came in on Friday and, at a quick look, they appear to be okay.

Bottom line: As a plan reviewer, even though as an architect I am legally allowed to practice engineering when it is "incidental to my architectural work," that doesn't extend to when I am wearing my building official hat. I'm not going to try to design a building to see if I come up with the same result as the SEOR. However, any building official can request submission of the engineer's calculations, and you can look at them to see if they used the right loads and if they used the right formulas. But that's a two-edged sword. Unless you're qualified as a structural designer, I would advise NOT looking too deeply into an engineer's calculations because, if in a worst case the project ends up in court, an attorney will rip you apart over your qualifications to review structural calculations. Instead, it would be better (IMHO) to strictly limit your review of engineer's calculations (if you request them) to verify that they are for the project you are reviewing (not recycled from a different building) and that they used the appropriate design loads. Don't go down the rabbit hole of trying to second guess the actual engineering calculations.
 
The sticky wicket, of course, is determining if the engineering IS sound.

We have encountered this question at least twice, both of which I have mentioned in other threads. Structural drawings done by a PE and bearing his seal and signature, but I was convinced they didn't work. In both cases the engineers took the position that, as mere building officials, we couldn't question their work. The second actually stated outright that we had to accept his plans because he had put his seal and signature on them. The first took the position that, even though I am also a licensed architect and I have taken graduate-level structural engineering course, I am not qualified to review his work.

Case 1: In the first case (the one in which the PE literally stole the foundation design and details from a design by another PE for a smaller building), we first consulted the other engineer to ask if he had authorized the re-use of his details. He said he had not. When we told him how big the building we were reviewing was, his response was, "I wouldn't guarantee that will stand up."

To resolve that one, we invoked the last sentence of IBC 107.1, which says, "Where special conditions exist, the building official is authorized to require additional construction documents to be prepared by a registered design professional." We did this after consulting with the Corporation Counsel (town attorney). The theory was that a known, demonstrable case of plagiarized documents, when the engineer who prepared the original details expressed reservations about the adequacy on a larger building, constituted "special conditions." We required a peer review by another PE. That peer review resulted in recommendations for several changes in the foundation design, which were made.

Case 2: The second case was the one involving the 92-year-old PE who claimed he took the sizes of the piers for a PEMB directly from the drawings for the superstructure -- which drawings (of course) didn't include any information whatsoever about foundations, they only provided the reactions at each frame base and the baseplate layouts. We had a meeting with the owner and the engineer, we explained our concerns, the engineer (very reluctantly) agreed to make some revisions to the foundation drawings -- and then resubmitted the same drawings, with no changes. The owner told the boss that the engineer decided we had no right to even review his drawings, since he had put his seal on them, so he wasn't going to make any changes. The project was an addition to an HVAC contractor's building, the owner has been around construction long enough to know a little bit, and he acknowledged to the boss that we were right. He hired a different engineer. The new drawings came in on Friday and, at a quick look, they appear to be okay.

Bottom line: As a plan reviewer, even though as an architect I am legally allowed to practice engineering when it is "incidental to my architectural work," that doesn't extend to when I am wearing my building official hat. I'm not going to try to design a building to see if I come up with the same result as the SEOR. However, any building official can request submission of the engineer's calculations, and you can look at them to see if they used the right loads and if they used the right formulas. But that's a two-edged sword. Unless you're qualified as a structural designer, I would advise NOT looking too deeply into an engineer's calculations because, if in a worst case the project ends up in court, an attorney will rip you apart over your qualifications to review structural calculations. Instead, it would be better (IMHO) to strictly limit your review of engineer's calculations (if you request them) to verify that they are for the project you are reviewing (not recycled from a different building) and that they used the appropriate design loads. Don't go down the rabbit hole of trying to second guess the actual engineering calculations.
I get the sense that a building official can always find a justification for rejecting something he doesn't like even if it complies with the building code. This implies the building official can unilaterally modify the building code. Obviously this is illegal.

The argument that the building department cannot review drawings stamped by an engineer is bogus.

The fact that an engineer makes changes to the drawings in response to building department comments does not always imply that the original submission was flawed.

While calculations can be helpful, the real question is whether the design complies with the code.
 
The fact that an engineer makes changes to the drawings in response to building department comments does not always imply that the original submission was flawed.

While calculations can be helpful, the real question is whether the design complies with the code.

Of course. But "complies with the code" also means complies with sound engineering practice. And the code also requires that the construction drawings clearly show that the proposed work will comply with the code.

I hope you wouldn't argue that when the engineer says he took the pier dimensions (which are not shown anywhere on his drawings) directly from the PEMB drawings (which do not include foundations) that we should accept the foundation drawings because the engineer sealed and signed them.
 
Of course. But "complies with the code" also means complies with sound engineering practice. And the code also requires that the construction drawings clearly show that the proposed work will comply with the code.

I hope you wouldn't argue that when the engineer says he took the pier dimensions (which are not shown anywhere on his drawings) directly from the PEMB drawings (which do not include foundations) that we should accept the foundation drawings because the engineer sealed and signed them.
Where in the IBC or IRC does the term "sound engineering practice occur".

I repeat my statement "The argument that the building department cannot review drawings stamped by an engineer is bogus."

A design can comply with the code even if no calculations are provided.

If the drawings did not show the size and location of foundation elements, they are incomplete.
 
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