Sizing Wood Framing for Fire Code

[KevinChez]

Hi...I designed a small outdoor pavilion (free standing) in CA. The code official is asking if the lumber is sized to meet the fire code. I don't have a fire code so I am searching online and cannot find any info on this.

I have had structures that needed non combustible roofing or be treated with fire retardant. But I have not been asked to "Size the lumber" for the fire code.

Any help is appreciated.

Thank you!

Kevin

 

[phamENG]

Structural timber can be sized for fire resistance. Based on the length of the fire, you determine how much char is anticipated and, therefore, how much of the member is lost. Then you run your calcs with that size lumber and see if it works.

Is there an architect? I usually leave this stuff up to them unless they tell me we're using an assembly that requires de-rating the structure.

 

[jayrod12]

I agree with phamENG on all account. But I would've maybe reversed the order. My first question would be is there an architect? They should be indicating whether the structure requires a fire rating or not.

Based on my (albeit limited) understanding of my local codes, a free-standing building would not require a fire rating unless it was a) too close to the property lines, or b) too close to an adjacent building. However if neither of those things are true, then there shouldn't be a fire rating needed. Where I practice, roofs of single storey buildings do not require a rating.

All that said, you absolutely can size heavy timber framing to provide its own fire rating. I have successfully built one building already, another is under construction, and a third is in permit stages.

 

[KevinChez]

@phamENG: thx for the info. There is no architect. This is an open air outdoor structure. I don't know why I would be required to design it for a fire. If it does endure a fire and is charred I'm sure it will be torn down.

 

[BridgeSmith]

I've heard of some structures requiring the design to show stability with members reduced in size by the char depth (typically 1/2") on the exposed sides, to ensure that a building doesn't collapse and kill the occupants if there was a fire.

I'd be surprised that those provisions would be applicable to an outdoor pavillion, even in crazyfornia.

 

[KevinChez]

This address is also in a flood plane and want verification that the structure has been designed to resist floor forces. There are no walls. Just (4) 10x10 posts supporting the roof. Common sense says "it ain't going nowhere" to quote my contractor friends.

 

[alt0]

Where in CA? Might be subject to WUI requirements (which I think considers anything 4x or thicker as 'heavy timber')

 

[KevinChez]

@alt0: Ojai CA

I am looking for the requirements. It would be helpful if the towns has their design requirements clearly listed on their website.

 

[phamENG]

Ask the code official. Tell them "no, it isn't designed for that - does it need to be?" Maybe they'll say "Nope, I was just curious!" (Sort of doubt it, but you won't know until you ask.)

Flood loads does make sense. Whether wave action or not, you still have to check for hydrodynamic loading of flood waters flowing past it. For a lightweight outdoor structure I could see it being more than seismic loads, even in Cali. (And just because it wouldn't be used during a flood isn't justification...the people in the house next door that collapses when the pavilion folds up and slams into the bearing wall of their house will not be pleased.)

 

[KevinChez]

what I am gathering regarding the fire resistance in Ventura County for an accessory structure is it needs to be non-combustable or ignition resistant materials. There are exceptions for SF and distance from other structures and property line.

Unfortunately it looks like the client didn't do due diligence and may have selected a structure that might not meet the requirements.

They are also asking me if I can do a plot plan. I told them to find an architect, contractor, or surveyor for that one.

 

[SWComposites]

yeah, well, officials are probably a tad bit more sensitized to fire issues here in CA given the incidents over the past few years.

 

[fel3]

In addition to talking to the code official, I suggest talking to the Ventura County Fire Department. They are probably better suited to determining the fire rating requirements for this structure. BTW, I lived and worked in Ventura for five years (1981-1986) and had a friend who was a fire protection specialist (or whatever his title was) with VCFD. He was not a fire protection engineer, but part of his job was setting fire protection requirements for new projects, in between pulling shifts as a real fireman. Unfortunately for this thread, he retired about twelve years ago and he wouldn't be up on the current codes.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[Mike Mike]

California is such an interesting state I have sized timber to meet fire code by NDS chapter 16. Basically take 1 1/2" off each "exposed" side for every hour of resistance and multiply your allowable bending stress by around 3.

 

[BridgeSmith]

Basically take 1 1/2" off each "exposed" side for every hour of resistance and multiply your allowable bending stress by around 3.

That sounds about right. I thought I remembered 1/2" for a 1/2 hour rating, which would seem more than adequate time to evacuate a "small outdoor pavillion", which is usually the criteria for fire codes. Of course, CA may have stricter criteria.

Interesting side note: At the University of Wyoming, the Arena Auditorium roof is a geodesic dome made with timber instead of steel because the fire rating was better. The timbers were large enough to maintain their compression capacity after charring, but the steel would have softened too much and buckled from the heat.