dshall

Attic draft stops, when and why?

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I have a 20' x 20' square building with a flat roof.  I have a mansard roof around the perimeter of building on all 4 sides.  Do you think the attic area within the mansard needs to be fire blocked every 10 feet.  

 

If not every 10 lineal feet,  then is it fir every 1000 sf of attic area....  inquiring minds want to know this important stuff.  I want to know it because I do not have a  life and the darn inspector is asking for it.

 

 

 

 

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I would say Commercial--yes, residential--no

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If you label the mansard roof as a cornice you may be fine without....though its fire-blocking is so easy to fulfill.  If the inspector is asking for it then re-labeling to cornice may not work. 

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3 of the most experienced users and we do not know for sure.

My client just got nailed, he spent money and time putting them in, and why? I do not know.

He will ask the inspector to cite the reason, I will let you know.

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I guess it's up to the local building official if he want to enforce it or not, like most things, did they miss it in plan check?

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I guess it's up to the local building official if he want to enforce it or not, like most things, did they miss it in plan check?

I saw this with commercial projects years ago. This is a two story house. Why don't we put draft stops at 10' in our house attic?

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Do you have a section of the mansard roof detail by chance? Often rim/sole plates and blocking "naturally" create draftstopping. Is there a living space above your mansard roof? That would be a major pre-requisite to be required, not to mention that is why I recommended calling it a cornice (since there is an exception for that too).

(R302.12)

Can you show me what the condition looks like?

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Draft stopping is described in the building codes (IRC/IBC) as follows: 

DRAFTSTOP. A material, device or construction installed to restrict the movement of air within open spaces of concealed areas of building components such as crawl spaces, floor/ceiling assemblies, roof/ceiling assemblies and attics. 

Draft stopping is required to be located in areas where a transition from horizontal to vertical or vertical to horizontal occurs. It is also required in spaces over a prescribed volume or square footage to limit how much air is available to feed a fire. The intent is to starve the fire of oxygen before it can grow to a point that it can cause severe damage to the building or structure. As draft stopping is used to limit air and not stop fire it can be build of almost any material approved by the building codes. We commonly use sheet metal, wood framing members, insulation or expanding foam for draft stopping. 

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Let me see if I can sum this up.

We do not need drafts stops in attics because there is an attic access.

We do need drafts stops in mansards because the mansard attic is an enclosed space without an access.

If I provide an access to the mansard attic area, I do not need draft stops.

Would anybody disagree with what I just said?

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Where are you relating having an attic access with not needing draft-stops?  Id like to see where you are reading that.

 

Unless there is something specific in the CA code the IRC states:

 

R302.12 Draftstopping.

In combustible construction where there is usable space both above and below the concealed space of a floor/ceiling assembly, draftstops shall be installed....

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....

 

 

R302.12 Draftstopping.

In combustible construction where there is usable space both above and below the concealed space of a floor/ceiling assembly, draftstops shall be installed....

 

I do not think there is usable space above the mansard so why are draft stops required at mansard attic but not in the attic on the right picture.

post-50-0-97686500-1463226315_thumb.png

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Doesn't it say "both above and below".  

Alan

 

Yes,  but do you have an answer to my question?

 

We are all citing passages but nobody has answered my question yet.

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The answer is, it depends on if your inspector or plan checker knows what the H*** they are talking about. Verify everything. Sometimes they make up things.

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Actually Scott,  I think the answer to your question depends on EXACTLY where your inspector wants to see draft stop. 

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Actually Scott,  I think the answer to your question depends on EXACTLY where your inspector wants to see draft stop. 

 

 

Michael,  why would you say that?  Is that a quote from a code book?  Post 13 asked what I thought was a very simply question with maybe not an easy answer.

 

Why   don't we all  say,  "I do not understand why the inspector would ask for draft stops in the mansard and not in an attic"

 

Nobody has answered the question in post 13.

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Michael,  why would you say that?  Is that a quote from a code book?  Post 13 asked what I thought was a very simply question with maybe not an easy answer.

 

Why   don't we all  say,  "I do not understand why the inspector would ask for draft stops in the mansard and not in an attic"

 

Nobody has answered the question in post 13.

I haven't seen your entire plan but the reason I said that was because  it might be those "interior" walls or floor system communicating with the roof system where the inspector wants to see draftstop. 

 

Besides that, even IF the inspector wants to see full triangular shaped stops every 10 feet, I'm not so sure that's a bad idea...That roof system is actually a lot different than your typical attic situation.  Your typical attic situation is wide open.  The roof you have drawn up creates a sort of "chase" or path for fire to travel elsewhere (possibly unnoticed and a lot harder for firefighters to access). 

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Scott,

 

In your example is that a deck in the middle?.

The inspector may think you are using open web floor joists. If your are using open web joists then draft stops are required every 1,000sf.

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Is any part of the roof within the 5' of any setback, new codes require them to be 1 hour fire rated.

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Scott,

 

In your example is that a deck in the middle?.

The inspector may think you are using open web floor joists. If your are using open web joists then draft stops are required every 1,000sf.

 

In this case it is a deck.  

 

I am not using open web joists and the attic area is definitely less than 1000 s.f.

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Since the deck is considered usable and you have a usable room below then you meet the definition of requiring draft stops.

You need to isolate the deck floor assembly from the roof attic areas.

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Is any part of the roof within the 5' of any setback, new codes require them to be 1 hour fire rated.

 

That may be it....  the wall is 48" from p.l.,  the eave is 36" from p.l.,  I do have an enclosed soffit at eave.  The eave is stucco.

 

That just might be it Perry,  thanks,  the owner is going to question the inspector,  I will let you know what we find out.

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By the way Scott, you still haven't stated exactly where the inspector wants to see draftstop. Do you even know?  That is a key piece of information. In the sketch you provided I can count at least 6 different places where draftstop could potentially be required depending on the way the structure is constructed.

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Since the deck is considered usable and you have a usable room below then you meet the definition of requiring draft stops.

You need to isolate the deck floor assembly from the roof attic areas.

I do have blocking under mansard walls,  so I assume that would be isolating the deck from roof.

 

Let me ask you this,  suppose that mansard was tall enough for it to be habitable,  I would not need draft stops because....  why.  Because it is habitable?  

 

That is why I think it is tied into being an ACCESSIBLE ATTIC AREA WITH AN ACCESS HOLE vs being a CONCEALED/NON ACCESSIBLE space.

 

Bottom line,  I do not  think there is a very clear statement in the code book that addresses this.....

 

I do appreciate the possible reasons you guys have suggested.

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