The simple 2X4 double wall R40 insulated design described in your most recent issue was very interesting. I have a question about the impact this design would have on the progression of fire within the wall cavity. I understand that fire blocking is used to slow fire progression vertically within a wall cavity and is required if walls are taller than 8 feet tall. This double wall design would allow fire to spread both vertically and horizontally from wall cavity to wall cavity without a physical wood barrier. Is this a code concern?
Scott Broce
Newberg, Oregon
Edited 11/26/2009 2:54 pm ET by Scott_Broce
Edited 11/26/2009 2:57 pm ET by Scott_Broce
Replies
I don't see the problem as insulation is firerated. Exterior walls don't require fore blocking, at least not here.
Under the IRC 2006 It depends on the height of the wall - if over ten feet you must provide intermediate fire blocking - not terribly common but it happens.
Also required at vertical-to-horizontal intersections such as soffits.
Loose fill insulation can't be counted as fireblocking unless it has been tested in that capacity.
Jeff
Jeff our local BI accept fibreglass as meeting the requirement on exteriors.
Interiors we must use wood or suitable equivalent.
Funny isn't it?
I have a double stud wall in my house and built a few others this way. The two walls are actually 3 1/2 inches apart and the whole shebang is full of fibreglass insulation. I have never given fire a moments thought. If my house catches on fire, I'm getting my family out and calling my insurance agent.
Have a good day
Cliffy
Not sure what code you all use but below is a link to the IRC section that covers fire blocking.
IRC602.8
Of particular interest is the 1. part "10 foot intervals both vertical and horozontal". In building townhouses I have been made to satisfy this 10' horozontal rule in firewalls between units where there was an air space betwween the different layers of the rated assembly, even though the UL rating didn't call for the 10' blocking. I'm sure this fire blocking requirement came from the IRC paragraph cited.
So, your concern is valid.
BTW - the above code reference is something I just googled up and is from some town called Blain MN. I don't know if Blain has modified it, but I 90% sure the part I cited is right out of the IRC.
PS - I hope the above html tag worked... if not I'll re-do it in a subsequent post. This is the first time I've added a link to this new format fourm.
Also BTW - where is the spell checker?