# Duplex 1 hour separation through crawl space



## retire09

In order to comply with the 1 hour separation requirement between units, wouldn't the 1 hour separation have to extend to the foundation under the building if there is a crawl space below?

Can you have a common crawl space below a non-rated floor assembly?


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## pyrguy

Basically the rated assembly should go from foundation to roof deck.

But there are exceptions, YMMV, etc.


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## Coug Dad

Under 2009 Section 709.4 the wall does not extend through the crawl space.  Under 2006 Section 708.4 it is an interpretation because the 2006 excluded sleeping rooms, but not dwelling units.  The 2009 excludes both.  (comment based upon IBC, not IRC)


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## FredK

Your question starts do I need?  Here's how I look at it.

1.  DWELLING UNIT. A single unit providing complete independent living facilities for one or more persons, including permanent provisions for living, sleeping, eating, cooking and sanitation.

2.  SECTION R317  DWELLING UNIT SEPARATION

3. R317.1 Two-family dwellings.

Dwelling units in two-family dwellings shall be separated from each other by wall and/or floor assemblies having not less than a 1-hour fire-resistance rating when tested in accordance with ASTM E 119. Fire-resistance-rated floor-ceiling and wall assemblies shall extend to and be tight against the exterior wall, and wall assemblies shall extend to the underside of the roof sheathing.

4. R317.1.1 Supporting construction.

When floor assemblies are required to be fire-resistance-rated by Section R317.1, the supporting construction of such assemblies shall have an equal or greater fire-resistive rating.

There are some exceptions but I can't comment if those apply.   Depending how it's built the answer is maybe.


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## Francis Vineyard

IRC Crawl Space Openings Part II

IRC crawl space ventilation has minimum opening dimensions and an exception permits these openings on zero lot line. Thus it could be as unlimited openings of crawl space ventilation as applicable between dwelling units including attached single family.

The fire-resistance "from the foundation"  construe that the foundation of wood girders on wood columns or wood walls not required to be fire-resistance?

Francis


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## Indimana

Since it is not a townhouse, It appears 2009 International Residential Code - section 302.3 requires the rating to extend to a foundation - through the crawl space.

"Can you have a common crawl space below a non-rated floor assembly?"

This seems to be a very different question and depends on if there is a required rating involved in the floors and/or walls above. 302.3.1 Two-Family Dwelings /  302.2.1 Townhouses

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## Francis Vineyard

Indimana welcome to the forum. Pardon me for answering with a question.

Fire-separation is between exterior walls, this is a single building, the separation is between dwelling units.

Would you require that there be a foundation (wall) where one is not required for support below a non-rated floor?

*R302.3 Two-family dwellings. *_Dwelling units _in two-familydwellings shall be separated from each other by wall and/orfloor assemblies having not less than a 1-hour fire-resistance
​rating





Francis


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## mtlogcabin

Francis you did not post the complete section

R302.3 Two-family dwellings.

Dwelling units in two-family dwellings shall be separated from each other by wall and/or floor assemblies having not less than a 1-hour fire-resistance rating when tested in accordance with ASTM E 119 or UL 263. Fire-resistance-rated floor-ceiling and wall assemblies shall extend to and be tight against the exterior wall , and wall assemblies shall extend from the foundation to the underside of the roof sheathing.

I believe the fire seperation is required from the foundation to the underside of the roof sheathing unless you choose to use Exception 2 for the attic area


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