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drafting duplex

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I am drafting a few duplexes, I've never done one nor actually built one so I was wondering if the interior walls dividing the two units need to be 6" each, or just build a main wall in the middle of the two units at 10"-12".

 

Any suggestions would be greatly appreciated :)

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Check with your local city/county etc. There are probably fire codes that will apply to the party wall.

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Depends on if you are designing structurally independent units or just 1 hour fire separation.

As Eric said check with local authority but ultimately up to you and the client to decide what you are really building.

 

Will the units be individually owned- or just rented by landlord. 

 

1 story or 2- fire rated asemblies for walls only or full separations to roofs searching.

 

Lots of good info from the APA and United Gypsum board association.

 

 

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as stated check with local building dept

 

may require two separate walls with an air gap between them

 

besides fire there are also sound transmission issues

 

Lew

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You can also look up fire rated assembly's and sound rated on the internet, lots to find there 

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Chief calls these Marriage Walls ( a term I am not familiar with? ) but it is basically a Double Wall (Furred Wall Type) , there is a KB Article here :

 

https://www.chiefarchitect.com/support/article/KB-00925/using-marriage-walls.html

 

A Double Wall with 5/8" FIRE Drywall TO THE RIDGE BOARD usually gets you by for Code but Soundproofing as also a big issue , but checking with the Local City ( to the Build ) is important , as many City's also have there Own Fire Code on top of the National Code.

 

M.

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I've heard them called "zero lot line" walls

 

Lew

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If your looking for a true fire separattion we spec a product called shaft wall and from a 2 x 4 wall on each side to put any electric or plumbing into this way there is a true firerated wall between and I beleive it is a 2 hour rating, I uploaded one of my details for that wall

shaft wall.calibz

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Every party wall I ever framed was (2) separate walls. 

Some had fire-rated GWB in the 2" gap space plus sound batting 4x8 sheets.

 

I have a sketch at the point in time in this video

 

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Thank you Chief 58.

Have not had any issue with local Building Depts. with the way I have been showing Firewalls but this is a much better job. Have a great week,Ken.

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We have been involved in the construction of MANY duplexes and here's how we've typically handled that area.  I just copied Ray's CAD block and modified it a bit...

5aa9870454204_Pic1.thumb.jpg.6f8397b80f722537d187c08956d326bb.jpg

PARTY WALL EXAMPLE.calibz

 

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Michael the way you show the party wall example what fire rating would you get not using the shaftwall material, inspectors here want a full firewall between party walls for fire a 2 hour fire protection between each unit, I might be wrong the way you have it if a fire breaks the 5/8 type x sheetrock it could get into the other walls and other apartment, I know on the townhouses I always spec the shaftwall

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33 minutes ago, chief58 said:

Michael the way you show the party wall example what fire rating would you get not using the shaftwall material, inspectors here want a full firewall between party walls for fire a 2 hour fire protection between each unit, I might be wrong the way you have it if a fire breaks the 5/8 type x sheetrock it could get into the other walls and other apartment, I know on the townhouses I always spec the shaftwall

 

The way we've always done it gets a double layer of 5/8" on both units which should give it a 2 hour fire rating.  This double layer continues top to bottom except where solid framing can be included in the fire rating calculation.  I don't know off hand what the fire rating of most lumber is, but as I recall its somewhere in the neighborhood of 1/2 hour per nominal inch meaning we might only put one layer of 5/8" over 2x joists in the center, or if joists/trusses are running perpendicular we might use 4x blocking and no GWB at all. If we're using I-joists then they would get the full 2 layers.  It all really depends on the job though.

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Michael as always thank you for the information

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3 hours ago, Alaskan_Son said:

 

The way we've always done it gets a double layer of 5/8" on both units which should give it a 2 hour fire rating.  This double layer continues top to bottom except where solid framing can be included in the fire rating calculation.  I don't know off hand what the fire rating of most lumber is, but as I recall its somewhere in the neighborhood of 1/2 hour per nominal inch meaning we might only put one layer of 5/8" over 2x joists in the center, or if joists/trusses are running perpendicular we might use 4x blocking and no GWB at all. If we're using I-joists then they would get the full 2 layers.  It all really depends on the job though.

 

Double 5/8" works great for Sound Transmission too, and is usually Cost effective but a diligent Installer of Rockwell  Roxul/Rockwool is needed too...  as Air Cavities/Gaps = Sound Transmission. Make sure to have all penetrations like Electrical Outlets/Switches are Air Sealed too.

 

M.

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19 minutes ago, Kbird1 said:

...but a diligent Installer of Rockwell is needed too...

 

I assume you meant Rockwool (mineral wool)?  Ya...we don't use the stuff around here.  Pretty much always fiberglass for everything.  By the way, one other thing that can be pretty easily and affordably added to the assembly to help reduce sound transmittance even further is RC channel (resilient channel).

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I am always blown away by the support, encouragement and information received by this community :).

You guys are the best and in my opinion you make CA worth more than what it costs. 

 

Thank you all sooooo much.   

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5 hours ago, para-CAD said:

Every party wall I ever framed was (2) separate walls. 

Some had fire-rated GWB in the 2" gap space plus sound batting 4x8 sheets.

 

I have a sketch at the point in time in this video

 

Thank you this is great. 

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3 hours ago, Alaskan_Son said:

We have been involved in the construction of MANY duplexes and here's how we've typically handled that area.  I just copied Ray's CAD block and modified it a bit...

5aa9870454204_Pic1.thumb.jpg.6f8397b80f722537d187c08956d326bb.jpg

PARTY WALL EXAMPLE.calibz

 

Thank you very much for sharing this. 

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1 hour ago, Alaskan_Son said:

 

I assume you meant Rockwool (mineral wool)?  Ya...we don't use the stuff around here.  Pretty much always fiberglass for everything.  By the way, one other thing that can be pretty easily and affordably added to the assembly to help reduce sound transmittance even further is RC channel (resilient channel).

 

Oooops Yes  RockWool  , I think SpellCheck must have gotten me there :)  it was Roxul but is going through a rebranding at the moment....

 

My understanding was that Mineral Wool (Roxul) is better at Sound control and also can have a higher R-Value but I have not looked at any recent innovations in that area ( if there has been any?) so I use it in Sound applications but Fiberglass Batt normally. I actually prefer Blown Cellulose in Ceilings, and it's easy in Remodels for top ups etc. Spray Foam if they can afford it (or needed). In Alaska you may have different methods though.... 

 

https://www.rockwool.com/a/b/hello/

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Just to keep everyone updated:

I have drafted the first duplex, not finished yet but enough for the developer to present a concept. It was actually fairly simple after all of the great suggestions you guys have provided. 

 

By using the "marriage wall" that Mick suggested that simplified a whole lot of things (foundation, roof and framing)

 

Thank you all so very much. 

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In my neck of the woods its typically done the same way @chief58 has described.  I am also from PA.  USG calls it an area separation wall assembly and has some pretty good literature available on their website.  I'll include the link.  They are designed such that one of the units can completely collapse in a fire, and the firewall should remain relatively intact so as to minimize damage to adjoining units.  USG has an article describing a case just like that.  I used it on an addition i built on a twin home a few years back, and it is a simple and effective way to construct a separation.  Easily installed by carpenters as the building is being framed.  I'll attach some photos of it during construction.  Another typical detail on townhouses around here is to use fire treated plywood sheathing on the exterior walls and roof surface for a minimum of 4' on either side of the firewall.  Section R-302 of the IRC goes over everything in great detail.  One homebuilder around here uses an 8" concrete bock wall as the firewall between units.  Key is for whatever system you choose is that its continuous from the foundation to the underside of the roof sheathing, and from exterior sheathing to exterior sheathing.   

 

https://www.usg.com/content/usgcom/en/products-solutions/products/wallboard/wall-systems/usg-area-separation-wall-system.html

IMG_20150610_145143490.jpg

Snyder Addition-0054.JPG

IMG_20150522_134958062.jpg

IMG_20150529_181020686.jpg

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