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2 family separation vs townhouse separation

jar546

jar546

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Why.............

Why does a townhouse (3 or more) require a 2 hour separation and a 2-family dwelling only require a 1 hour separation if both can be sold separately anyway. What is the difference and why/how was this decision made?

A townhouse is clearly specified as being a "separate building" whereas each side/up-down of a 2-family is considered a "dwelling unit" and is not specified as a separate building like a townhouse is.

Thinking about electrical, do we have to look at 2 family units as 1 building/structure for purposes of grouping disconnects?
 
The real answer: it's based on experience, not rationalized in an ivory tower.

As an aside, four adjacent townhouses are one structure but several buildings.

Some jurisdictions require separate disconnects, some require them all together.

Just a matter of interpretation based on experience and local custom.

And there is nothing wrong with that.
 
Probably the same reason that the IBC has the height and area table. Larger building assumes a greater risk and therefore requires a greater degree of protection.
 
For whatever it is worth, the commentary states "One and two family dwellings account for more than 80% of all deaths and residential property losses. Despite this poor fire record, there is a wide spread resistance to mandating much in the way of fire protection systems or methods because of our society's belief that people's homes are their castles." It goes on to talk about the separation required in Section R317.
 
A two family dwelling is one building with two dwelling units on a single lot. The wall or ceiling/floor assembly simply separates the dwelling units. A townhouse is one of (at least) three attached single family dwellings, typically on separate lots. The walls between units become (effectively) party walls. That's also why the basic requirement for townhouse separation is two one hour walls, each separate building gets its' own zero lot line rated assembly.
 
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