# Two-Family Wall Separation



## PhilC (Feb 17, 2010)

A two family dwelling offers some breaks in fire separation requirements per section R317.1 of IRC2006 when compared to townhome requirements of of R317.2.  The townhome section makes specific reference to continuity and exterior walls requirements of R302 because they are always considered seperate buildings.  The two-family dwelling section makes no such reference leading me to believe that R302 is primarily directed at townhomes.  Can we assume that a two family dwelling, even with a zero lot line (non condo/private ownership), is exempt from section R302 exterior walls?  Probably not, but it does not seem to be well documented and it seems odd that arbitrary property lines affect life safety mandates.     Thanks


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## FM William Burns (Feb 17, 2010)

Re: Two-Family Wall Separation

My question would be could this be due to the abilities to have more than two dwellings in the townhouse whereas only two are permitted as defined for 1-2 family dwellings and the increased risk associated to multiple hazard?


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## AegisFPE (Feb 17, 2010)

Re: Two-Family Wall Separation

While the language is different, I think the intent is the same.



			
				R317.1 said:
			
		

> Dwelling units in two-family dwellings shall be separated from each other...


  Fundamentally, this does not prescribe such separation to occur only at the interface where the dwelling units are in physical contact.





			
				R317.1 said:
			
		

> ...wall assemblies shall extend and be tight against the exterior wall, and wall assemblies shall extend to the underside of roof sheathing.


This seems to describe continuity similar to that found in R317.2.1.If the code anticipates two-family dwellings to be zero-lot-line, then Table R302.1 could also be considered to prescribe a 1-hour for the wall separating the units.

The "break" for not being a townhome appears to be a 1-hour wall versus a 2-hour wall as prescribed for townhomes.


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## TJacobs (Feb 17, 2010)

Re: Two-Family Wall Separation



			
				PhilC said:
			
		

> A two family dwelling offers some breaks in fire separation requirements per section R317.1 of IRC2006 when compared to townhome requirements of of R317.2.  The townhome section makes specific reference to continuity and exterior walls requirements of R302 because they are always considered seperate buildings.  The two-family dwelling section makes no such reference leading me to believe that R302 is primarily directed at townhomes.  Can we assume that a two family dwelling, even with a zero lot line (non condo/private ownership), is exempt from section R302 exterior walls?  Probably not, but it does not seem to be well documented and it seems odd that arbitrary property lines affect life safety mandates.     Thanks


The answer is in the definition of FSD:

_FIRE SEPARATION DISTANCE. The distance measured from the __building__ face to one of the following:_

_1.	To the closest interior lot line; or_

_2.	To the centerline of a street, an alley or public way; or_

_3.	To an imaginary line between two __building__s on the lot._

_The distance shall be measured at a right angle from the face of the wall._

The entire two family dwelling is a single building.  Use 317.1 for the separation wall between dwelling units in a two family dwelling.  Use 302 for the FSD to the exterior walls of adjacent buildings.

Each dwelling unit in a townhouse is a building.  Use 302 as modified by 317.2 for the FSD to all walls separating dwelling units in a townhouse, and the FSD to all exterior walls of adjacent buildings.

In my opinion fire spread would effect more dwellings in a townhouse thus the greater protection required.


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## Mac (Feb 17, 2010)

Re: Two-Family Wall Separation

FWIW I think "townhouses" are meant be sold to individual owners, and have property lines between the units, thus the distance separations and higher exterior wall resistance ratings.

Although not explicitly clear, the terms in 317.1 "Two family dwellings" read as if two-family dwellings pose a lesser spread-of-fire hazard, or are not intended to have property lines between the units. In the event they are sold to separate owners, I guess that's all the fire resistance they get!


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## FM William Burns (Feb 17, 2010)

Re: Two-Family Wall Separation

Thanks for the clarification regarding the intent of my question 1 hour v. 2 hour.


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## brudgers (Feb 17, 2010)

Re: Two-Family Wall Separation

Two Family Dwellings unlike Townhouses can be stacked.

The requirement is one hour between dwellings regardless of if the separation is horizontal or vertical or both.

Fire separation distance does not enter into it.

And Yes...the requirements are less stringent than for Townhouses.


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## mtlogcabin (Feb 17, 2010)

Re: Two-Family Wall Separation



> "townhouses" are meant be sold to individual owners, and have property lines between the units,


Under the IRC there is NO requirement for for a property line between Townhouses.

3 units or more non-stacked much like the old ROW house developments.

The 2 hour common wall or 2 one-hour walls required to extend to the roof deck and exterior walls is nothing more than creating  smaller fire areas using a fire barrrier wall as outlined in the IBC.


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## TJacobs (Feb 17, 2010)

Re: Two-Family Wall Separation



			
				brudgers said:
			
		

> Two Family Dwellings unlike Townhouses can be stacked.


Correct



			
				brudgers said:
			
		

> The requirement is one hour between dwellings regardless of if the separation is horizontal or vertical or both.


Correct


			
				brudgers said:
			
		

> Fire separation distance does not enter into it.


Incorrect, go back and re-read the OP, FSD applies to the exterior walls to adjacent buildings even in a two family stacked.  He asked if he could ignore FSD and with your simplistic answer he might think he could.



			
				brudgers said:
			
		

> And Yes...the requirements are less stringent than for Townhouses.


Correct


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