# Duplex Supporting Construction Exterior Walls



## Francis Vineyard (Jan 7, 2010)

Two family dwelling, top and bottom unit with outside entry basement garage and heated storage area, is it correct to say that

Supporting walls of the rated horizontal assembly cannot have windows?

Bath, kitchen and dryer ducts required to be rated through penetration?

These walls are rated on both sides not just the interior even though its more than 5 feet from any lot line or other buildings?  However if openings are not allowed it does not make sense to be rated assemly on the outside!

The wall is rated to the foundation?

I’m having a long year in one week, appreciate your help.


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## Mac (Jan 7, 2010)

Re: Duplex Supporting Construction Exterior Walls

Not sure I fully understand the configuration you describe, but my first thoughts are:

Why build rated walls where they are not needed?

Bath and kitchen exhaust ducts can be ducted directly to the exterior (if walls don't require ratings)- unless they discharge through the garage?

 Where the horizontal garage/dwelling space separation is a floor-ceiling assembly, the structure supporting the separation shall also be protected by not less than 5/8-inch type X gypsum board or equivalent. So some walls will need to be rated - but only for exposure from the inside.

Hi Francis!


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## mtlogcabin (Jan 7, 2010)

Re: Duplex Supporting Construction Exterior Walls

If the exterior walls are NOT required to be rated by Table 302.1 and openings are NOT required to be protected by Table 302.1 then the answers are as follows:

Supporting walls of the rated horizontal assembly cannot have windows? False

Bath, kitchen and dryer ducts required to be rated through penetration? If they are penetrating the walls No If penetrating the floor celing assembly Yes

So some walls will need to be rated - but only for exposure from the inside.

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.

I would agree since floor ceiling assemblies are tested from the ceiling side.


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## cda (Jan 7, 2010)

Re: Duplex Supporting Construction Exterior Walls

Francis Vineyard

1. what code are you using and what year edition?????????


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## Francis Vineyard (Jan 8, 2010)

Re: Duplex Supporting Construction Exterior Walls

This is my first top/bottom duplex, in the 2006 IRC it has a “fire-resistance-rated wall supporting a fire-resistance-rated floor assembly” (not Horizontal Assembly, Fire Barriers and Partitions). Although in the garage there only needs to be ½ inch sheet rock on the wall supporting a rated floor but it can have no openings and with non-protected penetrations.

I’m confused!

But with the two dwelling units there can as many (combustible) openings as possible in the lower dwelling walls and only rated from the inside having penetrations protected per R317.3?

Sprinklers anyone?


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