# Townhouse firewall foundation



## Buelligan (Jul 11, 2016)

2009 IRC

I have a contractor who wants to amend his plans to eliminate the footing between units. He says "what do I need that for, it only holds drywall?" First of all it will be supporting two one hour walls with 5/8" Type x on each side three stories tall! (UL Design U305) He wants to pour ONE 4" thick slab across ALL 6 units without the separating foundations.

*R302.2 Townhouses.* Each townhouse shall be considered a separate building and shall be separated by fire-resistance-rated wall assemblies meeting the requirements of Section R302.1 for exterior walls.

My interpretation of the above section requires a perimeter foundation for "each" unit including the "common" fire wall. I have never seen an exterior wall built on top of a 4" slab, gable end included. He believes because it has no floor or roof load, there is no requirement for a footing.

*R302.2.4 Structural independence.*
Each individual townhouse shall be structurally independent.
Exceptions:
_*1. Foundations* supporting exterior walls or common walls._
2. Structural roof and wall sheathing from each unit may fasten to the common wall framing.
3. Nonstructural wall and roof coverings.
4. Flashing at termination of roof covering over common wall.
5. Townhouses separated by a common 1-hour fire-resistance-rated wall as provided in Section R302.2.

Now the above section only allows the "foundation" under the common wall to be shared and not "structurally independent", but it still needs to be a foundation, correct?

So again would you consider the "interior slab" acceptable as the "foundation" required for the firewall?

I say absolutely not!!

Also on another note, pertaining to U305. He has been allow to build one wall and then attach the 5/8" drywall for the second wall to it before building the second wall next to it. My understanding is that the drywall MUST be attached to it's corresponding wall and not the wall next to it, correct?

I told him he would have to attach the drywall to second wall first before standing it up next to the first wall. would that be correct?

Thanks!


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## steveray (Jul 11, 2016)

Look at R403.1......And how did you cut and paste those code sections?


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## cda (Jul 11, 2016)

Not a building person
But the wall also does not have to be structurally independent 


Look at continuity to see if that answers your question

302.2.1


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## Buelligan (Jul 11, 2016)

steveray said:


> Look at R403.1......And how did you cut and paste those code sections?



Thank you, I agree and yes that will help. I think the disconnect will be the exception to "exterior" walls. I'm not sure he believes the fire wall to be an "exterior" wall and may read the "structural independence" exception as an exception to any foundation be it "shared" or not.

Also, I just cut and paste from the Folio View program from ICC, the $900 complete collection on CD. I have to add the formatting (bold, underline etc.)


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## Buelligan (Jul 11, 2016)

cda said:


> Not a building person
> But the wall also does not have to be structurally independent
> 
> 
> ...



*R302.2.1 Continuity.*
The fire-resistance-rated wall or assembly separating townhouses shall be continuous from the* foundation* to the underside of the roof sheathing, deck or slab. The fire-resistance rating shall extend the full length of the wall or assembly, including wall extensions through and separating attached enclosed accessory structures .

Yes, you are correct. See R302.2.4 above. But that is not my question.

R302.2.1 above also states "...continuous from the *foundation*...". My concern is this, I do NOT consider a 4" thick slab as a "foundation" under the firewall.


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## Francis Vineyard (Jul 11, 2016)

Also has to meet the provisions for shear walls; R403.1.6


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## Buelligan (Jul 11, 2016)

https://mnq79w.bn1302.livefilestore...IdxG9UrmoQ?width=675&height=348&cropmode=none







Here is a quick diagram that might help.
Hopefully one of these works.


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## cda (Jul 11, 2016)

Buelligan said:


> *R302.2.1 Continuity.*
> The fire-resistance-rated wall or assembly separating townhouses shall be continuous from the* foundation* to the underside of the roof sheathing, deck or slab. The fire-resistance rating shall extend the full length of the wall or assembly, including wall extensions through and separating attached enclosed accessory structures .
> 
> Yes, you are correct. See R302.2.4 above. But that is not my question.
> ...




I guess concrete will burn at some point??


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## cda (Jul 11, 2016)

Buelligan said:


> https://mnq79w.bn1302.livefilestore...IdxG9UrmoQ?width=675&height=348&cropmode=none
> 
> 
> 
> ...





I am use to seeing this stuff like on page 8,9




http://www.buildgp.com/DocumentViewer.aspx?repository=BP&elementid=4286


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## Paul Sweet (Jul 11, 2016)

I agree that the drywall needs to be attached to the second wall before standing it up.

A thickened slab beneath the common walls should be adequate if they are non-bearing walls.


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## mtlogcabin (Jul 11, 2016)

2012 IRC

WALLS. Walls shall be defined as follows:

Load-bearing wall. A wall supporting any vertical load in addition to its own weight.

Nonbearing wall. A wall which does not support vertical loads other than its own weight.

The gable end wall supports a gable end truss which supports 1 foot of the tributary load of the roof.
It is a load bearing wall by definition


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## JBI (Jul 11, 2016)

Actually what the IRC describes between townhouses is a party wall, they just don't call it that.


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## Buelligan (Jul 12, 2016)

Ok, so I got some lessons through all this.

First of all, the "party" wall as described above comes in two flavors. Individual 1 hour walls or as a single or "common" wall ( usually 2-hour but can be 1-hour if sprinkled).

So my first mistake in this description was that he was building a "common" wall, he is not. Therefore, based on 302.2.4 they must be structurally independent because the exception 1 is only for exterior and "common" walls. So not only does he need a footing but they must be structurally independent! But at this point he will have to build a 2-hour "common" wall or dig between the units and build independent foundations. This can be so fun at times.


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## ICE (Jul 12, 2016)

Structurally independent has to do with fire.  One wall can collapse due to fire and not cause the other wall to fail as a result.  A single foundation should serve both equally well.


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## mtlogcabin (Jul 12, 2016)

We require the foundation of each unit to meet the frost depth requirements. If one unit is destroyed and not replaced it leaves the adjoining exposed unit(s) to the possibility of damage by frost.


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## cda (Jul 12, 2016)

Buelligan said:


> Ok, so I got some lessons through all this.
> 
> First of all, the "party" wall as described above comes in two flavors. Individual 1 hour walls or as a single or "common" wall ( usually 2-hour but can be 1-hour if sprinkled).
> 
> So my first mistake in this description was that he was building a "common" wall, he is not. Therefore, based on 302.2.4 they must be structurally independent because the exception 1 is only for exterior and "common" walls. So not only does he need a footing but they must be structurally independent! But at this point he will have to build a 2-hour "common" wall or dig between the units and build independent foundations. This can be so fun at times.





My understanding is townhomes do not have to be """"structurally independent""""


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## cda (Jul 12, 2016)

Buelligan said:


> Ok, so I got some lessons through all this.
> 
> First of all, the "party" wall as described above comes in two flavors. Individual 1 hour walls or as a single or "common" wall ( usually 2-hour but can be 1-hour if sprinkled).
> 
> So my first mistake in this description was that he was building a "common" wall, he is not. Therefore, based on 302.2.4 they must be structurally independent because the exception 1 is only for exterior and "common" walls. So not only does he need a footing but they must be structurally independent! But at this point he will have to build a 2-hour "common" wall or dig between the units and build independent foundations. This can be so fun at times.




Not sure how you cannot get more common than the shared wall between your unit and your neighbor??


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## mtlogcabin (Jul 12, 2016)

cda said:


> My understanding is townhomes do not have to be """"structurally independent""""


It is required but there are exceptions

R302.2.4 Structural independence.
Each individual townhouse shall be structurally independent.

Exceptions:

1.    Foundations supporting exterior walls or common walls.

2.    Structural roof and wall sheathing from each unit may fasten to the common wall framing.

3.    Nonstructural wall and roof coverings.

4.    Flashing at termination of roof covering over common wall.

5.    Townhouses separated by a common 1-hour fire-resistance-rated wall as provided in Section R302.2.


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## FLSTF01 (Jul 12, 2016)

I would certainly allow a common footing and would not require it to be a full depth for frost protection.  Even if the entire other half fell away after a fire, the remaining frost walls and slab would prevent frost from getting under that "common" footing.  Besides, the newly-created exterior wall with nothing but drywall on it would be a bigger problem.


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## Buelligan (Jul 12, 2016)

cda said:


> My understanding is townhomes do not have to be """"structurally independent""""



According to the ICC code opinion, a common wall is an individual unit constructed independent of the structures on either side. Therefore meets the exception 1 under R302.2.4 structural independence. Think block wall or the core wall linked above in post number #9

But in this case the builder is building two separate 1-hour walls supporting the gable truss on each side. Therefore it is NOT a "common" wall and must be structurally independent per 302.2.4 because it DOES NOT qualify for any exceptions under 302.2.4 below

*R302.2.4 Structural independence.*
Each individual townhouse shall be structurally independent.

Exceptions:

1. Foundations supporting exterior walls or _common walls._


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## cda (Jul 12, 2016)

Hummm.........


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## JBI (Jul 13, 2016)

Buelligan, '1. Foundations supporting *exterior walls OR common walls'*. If built as 2 separate one-hour walls they are to be constructed as *exterior walls*, and can therefore share a common foundation wall.


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## Buelligan (Jul 14, 2016)

JBI said:


> Buelligan, '1. Foundations supporting *exterior walls OR common walls'*. If built as 2 separate one-hour walls they are to be constructed as *exterior walls*, and can therefore share a common foundation wall.



That's what I said! But guess what? The ICC code opinion I got was that those ARE NOT exterior walls except in reference to FIRE SEPERATION. The only reference to that "party wall" (be it individual or common) being an exterior wall is in the first code section R302.2.

*R302.2 Townhouses.* Each townhouse shall be considered a separate building and shall be *separated by fire-resistance-rated wall assemblies meeting the requirements of Section R302.1 for exterior walls.
*
This statement does not say to treat that wall as exterior. Just means to build a rated wall meeting a _standard for exterior walls_.

Again I don't disagree with you, but the person at ICC that I spoke with was adamant that exception 1 under structural independence DOES NOT apply to the separate one hour walls. His opinion was that structural independence was written for that purpose. When two load bearing, structurally independent walls are built they need structurally independent foundations as well. At least that's what I took away from the conversation.


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## cda (Jul 14, 2016)

Buelligan said:


> That's what I said! But guess what? The ICC code opinion I got was that those ARE NOT exterior walls except in reference to FIRE SEPERATION. The only reference to that "party wall" (be it individual or common) being an exterior wall is in the first code section R302.2.
> 
> *R302.2 Townhouses.* Each townhouse shall be considered a separate building and shall be *separated by fire-resistance-rated wall assemblies meeting the requirements of Section R302.1 for exterior walls.
> *
> ...





Wonder if you call icc and talk to someone else,,,


What answer you will get????


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## steveray (Jul 14, 2016)

I've never even seen that required in an IBC firewall situation...And I believe firewall continuity only states "from the foundation.....up"...


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## Pcinspector1 (Jul 14, 2016)

If the foundation walls are removed below the first floor and it is completely open like a crawl space like the picture depicts will drywall need to be applied to the underside of the floor assuming it is wood framed?


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## Pcinspector1 (Jul 14, 2016)

This appears to be slab construction, and grade beams would most likely be needed if bearing walls are in play. Maybe the design has all the bearing points from back to front and not using the party walls?


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## Buelligan (Jul 14, 2016)

Pcinspector1 said:


> This appears to be slab construction, and grade beams would most likely be needed if bearing walls are in play. Maybe the design has all the bearing points from back to front and not using the party walls?



You are correct! He wanted to pour a 4" slab with NO grade beams under 3 story  bearing walls in between each unit, carrying a gable truss with some roof load. I said no way. So he came in to amend his plans to a 2-hour non-bearing common wall. Still no grade beams, but according to ICC it is not required, because exception 1 under structural independence applies to this common wall. 

Not sure I completely agree, but that's how it goes some times.


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## my250r11 (Jul 14, 2016)

The few i built when i was still wearing my tools they had thickened grade beams because they were also shear walls with tie downs and sheathing which would require the foundation, don't know if this would help in your situation.


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## steveray (Jul 15, 2016)

The townhouses I have going now are also GWB braced wall.....Good call Mike!....That would be another path to a "foundation" under it through something like 602.10.....?


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## my250r11 (Jul 15, 2016)

R602.11 Wall Anchorage, requires braced walls to be anchored and refers you back to R403.1.6 & R602.11.1 which in hand requires continous footing and anchor bolts.

IMO Shear/Brace Walls are interior load bear walls, the load is not always directly from the top, thus the need for the brace walls but they still are supporting side loads.


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## JBI (Jul 15, 2016)

Braced walls, whether interior or exterior, are intended to resist lateral forces from wind and seismic. 
They are best described as 'prescriptive alternatives to an engineered shear wall'.


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