# load bearing walls



## Den52 (Apr 5, 2022)

I am looking for information on a typical 3 story structure using an 8" Insulating concrete form foundation with 2.5" of EPS on both sides.  The building will be 2x6 construction that is setting on 3.5" of concrete and 2" of the EPS.  I am being questioned whether my wall can handle the load of a 3 story building, because I'm only bearing on the 3.5" of concrete. I have been in construction since 1968 and have built many structures similar in size with 3.5" studs and they're all still standing. This is a code official asking me the question. Is there a place in the IRC that explains this question? I have no problem but I have to satisfy the code official.


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## mtlogcabin (Apr 5, 2022)

You need a minimum 6" concrete wall, because the code does not address concrete walls less than 6 inches thick for a foundation.  Also, to transfer all the loads properly, a 2x6 wall will require a 2x6 sill which would be required to be supported by a 6 inch or wider bearing surface R602.3.4 Bottom (sole) plate.

Studs shall have full bearing on a nominal 2-by (51 mm) or larger plate or sill having a width not less than to the width of the studs.


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## Mark K (Apr 6, 2022)

The description of the situation is not clear.  You really need to be talking with an Architect or Engineer.

If you are really proposing a 3.5 thick stem for the footing, think again.

My sense is that the IRC does not address this situation and thus you will need to comply with the IBC.


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## bill1952 (Apr 6, 2022)

I'll only comment I looked at three ICF web sites and did not find one with a core less than 4" (and of course larger  cores, typically in 2" increments to at least 12").  Just seems there might be some misunderstanding.


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## TheCommish (Apr 6, 2022)

The manufacturer should be able to provide you with technical support for the product, including a listing report that may have the limiting factors for the supported building height.


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## e hilton (Apr 6, 2022)

Sounds like the forms are 8” wide, of which 3” is concrete in the middle with 2.5” foam sides.  I’m thinking the 3.5” concrete is the thickness of the slab.   Maybe.


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## bill1952 (Apr 7, 2022)

Mark K said:


> The description of the situation is not clear.  You really need to be talking with an Architect or Engineer.
> 
> If you are really proposing a 3.5 thick stem for the footing, think again.
> 
> My sense is that the IRC does not address this situation and thus you will need to comply with the IBC.


So this detail from Building Science Corp does not comply with the IRC?


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## e hilton (Apr 7, 2022)

bill1952 said:


> So this detail from Building Science Corp does not comply with the IRC?


Looks like that is explaining insulation, not structural details.


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## bill1952 (Apr 7, 2022)

e hilton said:


> Looks like that is explaining insulation, not structural details.


It shows a 2x6 wall on 3 1/2" of concrete and 2" of foam.  Not dissimilar from original post.  Is it compliant with IRC?


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## mtlogcabin (Apr 7, 2022)

bill1952 said:


> Is it compliant with IRC?


No
2018 IRC
R403.1.6 Foundation anchorage.
Wood sill plates and wood walls supported directly on continuous foundations shall be anchored to the foundation in accordance with this section.

..........*The bolts shall be located in the middle third of the width of the plate*...........

J-Bolt would be too close to the edge of the concrete


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## Paul Sweet (Apr 7, 2022)

A 3-1/2" stem wall that is only 8" high is a lot different than one that is a story high.  I would probably set the face of the stem 1" from the face of the studs and let the drywall & base cover the insulation that projects beyond the face of the studs.

My only concern with the BSC detail would be the compression perpendicular to grain in the plate in a 2 story building with long spans or a trussed roof.


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## mtlogcabin (Apr 7, 2022)

The IRC is prescriptive and does not address foundation walls that are less than 6 inches wide.

TABLE R404.1.2(2)
MINIMUM VERTICAL REINFORCEMENT FOR 6-INCH NOMINAL FLAT CONCRETE BASEMENT WALLS b, c, d, e, g, h, i, j, k

Engineer would be required


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## bill1952 (Apr 7, 2022)

mtlogcabin said:


> The IRC is prescriptive and does not address foundation walls that are less than 6 inches wide.
> 
> TABLE R404.1.2(2)
> MINIMUM VERTICAL REINFORCEMENT FOR 6-INCH NOMINAL FLAT CONCRETE BASEMENT WALLS b, c, d, e, g, h, i, j, k
> ...





mtlogcabin said:


> The IRC is prescriptive and does not address foundation walls that are less than 6 inches wide.
> 
> TABLE R404.1.2(2)
> MINIMUM VERTICAL REINFORCEMENT FOR 6-INCH NOMINAL FLAT CONCRETE BASEMENT WALLS b, c, d, e, g, h, i, j, k
> ...


Is that 6 to 8" stem really a "basement wall"?


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## bill1952 (Apr 7, 2022)

Just googling for details like this, there are many, many details with a stem or
"curb" that is clearly less than 6".  Kind of surprising if it isn't compliant with codes.


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## Mark K (Apr 7, 2022)

The detail is what I suspected.  You do not want a 3.5" stem no matter what the code may allow.  It is too brittle.

You also want the slab on grade to tie into the footing.

This is what you get when the focus is exclusively on thermal issues.  You need a solution that also addresses the structural issues.

I suspect that when you talk to local engineers, they will be aware of alternate strategies.  I believe that one strategy might involve the application of insulation on the outside face of the footing below grade.


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## mtlogcabin (Apr 7, 2022)

All the ESR reports say the same for all of the ICF walls.  4" concrete walls are limited to above grade under the IRC


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## e hilton (Apr 7, 2022)

bill1952 said:


> It shows a 2x6 wall on 3 1/2" of concrete and 2" of foam.  Not dissimilar from original post.  Is it compliant with IRC?


You missed my point.  The diagram is bogus, it was not intended to illustrate a properly engineered foundation.  It was intended to be a visual aid for a story about insulation.  You can’t take random illustrations at face value to support a discussion without considering the context from which it came.


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## Joe.B (Apr 8, 2022)

Den52 said:


> I am looking for information on a typical 3 story structure using an 8" Insulating concrete form foundation with 2.5" of EPS on both sides.  The building will be 2x6 construction that is setting on 3.5" of concrete and 2" of the EPS.  I am being questioned whether my wall can handle the load of a 3 story building because I'm only bearing on the 3.5" of concrete. I have been in construction since 1968 and have built many structures similar in size with 3.5" studs and they're all still standing. This is a code official asking me the question. Is there a place in the IRC that explains this question? I have no problem, but I have to satisfy the code official.


You've gotten several good replies. Are you going to chime back in? We would love to hear more information. From the code official side we hear "I've been doing this for 30 years" (or similar) very often and it can be a red flag. Codes change, designs change, buildings change. There's a reason for that.

If we don't hear back from you many of us will assume that you didn't like the answers you got, and that you do indeed have a problem.


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## Beniah Naylor (Apr 13, 2022)

I think this detail above is what the OP meant, where they used ICF for the basement wall, and then they made the framing on top flush with the foam on the outside of the forms so that siding can cover both the framing and ICF in the same plane. I think the thickness of the concrete is not what is in question, it is the amount of bearing the bottom plate has on the concrete that is in question.

Being an inspector, and confronted with the idea of the front half of a wall bearing on insulating foam... yeah, I'm gonna make you get an engineer. The only saving grace is that you used 2x6s, so an engineer might be able to make it work.

To meet prescriptive code, you have to be fully bearing and keep your anchor bolts in the center 1/3 of the bottom plate - otherwise you will need an engineer.


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## Genduct (Apr 13, 2022)

bill1952 said:


> So this detail from Building Science Corp does not comply with the IRC?
> View attachment 8780


Bill this does not appear to fit his description below:
8" Insulating concrete form foundation with 2.5" of EPS on both sides. The building will be 2x6 construction that is setting on 3.5" of concrete and 2" of the EPS

Structurally your example with a 3.5" X 6" high projection isn't much of a "Column" so no real problem I see with the cantilevered 2x6 plate that covers the insulation caused gap when 2x4 studs is all that is needed.

IMHO


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## bill1952 (Apr 13, 2022)

Genduct said:


> Bill this does not appear to fit his description below:
> 8" Insulating concrete form foundation with 2.5" of EPS on both sides. The building will be 2x6 construction that is setting on 3.5" of concrete and 2" of the EPS
> 
> Structurally your example with a 3.5" X 6" high projection isn't much of a "Column" so no real problem I see with the cantilevered 2x6 plate that covers the insulation caused gap when 2x4 studs ia all that is needed
> ...


I think we agree that this is ok, but does it require an RDP to sign off?


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## Genduct (Apr 13, 2022)

bill1952 said:


> I think we agree that this is ok, but does it require an RDP to sign off?


Seems like it is Not What People are used to seeing, BUT if 2x4's OK for 3 story structure, can the Code Official really find a Code reference that says the owner can't "Waste 2 inches of the 2X6 vs a 2x4 ?

Might take a little explaining, but given that Joe L at Building Science says it is OK..... Well I hope Code Official knows who Joe L is to the world of Bldg. Science best practice


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## mtlogcabin (Apr 13, 2022)

Most ICF forms have a taper block to use on the top course. it only has 1" of Styrofoam at the top so only 1/2' or less hang over the foam


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## Genduct (Apr 13, 2022)

mtlogcabin said:


> Most ICF forms have a taper block to use on the top course. it only has 1" of Styrofoam at the top so only 1/2' or less hang over the foam
> 
> View attachment 8822
> View attachment 8823


Thank You

This is really interesting

Notice the rim board location in relation to the 2x6 plate
Like Joe L's example, it is also somewhat cantilevered over the 2 inch foam!

The rebar schedule and the flared top seems to make a lot of sense.

I wonder about the thin (3.5 in ) of concrete and wonder if the insulation will reduce the moisture that may, over time, rust the rebar, because of low / thin concrete coverage.  Probably using 1/2 stone or a really small aggregate mix.  I don't see the PSI of req'd. mix spec'd.

Given the "Non Traditional" design,  I wonder if the Code Official will ask you to get an Engineer's stamp to validate.  For good reason the AHJ may feel that they are sticking their neck, or some other piece of anatomy,  out to be cut off later.


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## Genduct (Apr 13, 2022)

Genduct said:


> Thank You
> 
> This is really interesting
> 
> ...


PS  17 inch wide footing doesn't sound like is is supporting 3 stories.  Yep, going to need a Design Professional to validate this one.


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## mtlogcabin (Apr 13, 2022)

Genduct said:


> Notice the rim board location in relation to the 2x6 plate
> Like Joe L's example. it is also somewhat cantilevered over the 2 inch foam!


I would move the rim board to the outside edge of the sill plate and then spray foam the rim from the inside.

The 4" wide concrete bearing surface is bothering me more from an anchoring issue than a bearing issue. I just do not believe there will be enough concrete coverage for the anchor bolts to provide the lateral and possible uplift loading requirements. If the J-bolts are off a little or the J portion is not running parallel with the concrete wall to prevent concrete breakout or side-face blowout.


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## Genduct (Apr 13, 2022)

mtlogcabin said:


> I would move the rim board to the outside edge of the sill plate and then spray foam the rim from the inside.
> 
> The 4" wide concrete bearing surface is bothering me more from an anchoring issue than a bearing issue. I just do not believe there will be enough concrete coverage for the anchor bolts to provide the lateral and possible uplift loading requirements. If the J-bolts are off a little or the J portion is not running parallel with the concrete wall to prevent concrete breakout or side-face blowout.


I like the way you think, although there is something to be said for keeping the load from the 2x6 plate almost centered given the relatively thin (3.5 in) wall.
I guess the flared top portion will compensate, but moving the rim make it more of  a non-concentric load.   Again, probably not a big deal

Still, an interesting example.

I guess it is a good thing we are supposed to review and not design and hence can discuss, but not allow our thoughts to dictate.  Here is where we ask for CLARIFICATION !
My approach had been to say "I have some Concerns!" 
Then I am either surprised or confused.
Can you help me understand,,,,,,,,,,,,?

Got to remember the bright double line we are not suppose to cross unless you want to get into a head on collision.

At the end of the day, the good guys like that you may have helped them catch a problem they didn't see and did it in a nice way.   We are not there to embarrass anyone or show off.  Just do our part

You sound to me like someone who approaches the job in a similar way


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## Genduct (Apr 13, 2022)

Genduct said:


> I like the way you think,  although there is something to be said for keeping the load from the 2x6 plate almost centered given the relatively thin  (3.5 in) wall.
> I guess the flared top portion will compensate,  but moving the rim make it more of  a non-concentric load.
> Again, probably not a big deal
> 
> ...


Darned !  Just looked closer at the sketch.  2nd dimension up looks like 6 inch concrete wall, not 3.5.
DUHHHHH   How the heck could we believe it was 3.5    See what I mean ?


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## ADAguy (Apr 27, 2022)

Are you trying to do this without using a DP? No permits required over your last 30 years?


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