Hi all:
To meet the fireblocking requirements under 602.8 in the 2006 IRC when framing out a basement, the typical practice around my parts is to put up a strip of type x drywall on the ceiling around the perimeter of the room. Then we put up the walls with the top plate going underneath the drywall. All the joints and gaps are filled with fireblock caulk or foam or “rotten cotton” if need be. This is what the inspectors want to see.
Now my question– 602.8 also requires horizontal fireblocking every ten feet. the building officials are just now catching on to this little fact. In a regular wall that can be met with insulation between the studs. In a basement, where there is a gap between the stud and the foundation wall, it is another story. Does anyone have any bright ideas for this area? I’m not thrilled about using a little stub of drywall attached to a stud to bridge the gap, because that would potentially promote mold where the masonry foundation touches the drywall. I’m also not thrilled with stuffing insulation in the gap either, because that could hold moisture. Anybody have a better way?
John Painter
Replies
For the horizontal fireblocking, just add one stud every 10' that either touches the concrete wall (treated stud) or is about 1/4" off the concrete, then caulk to the concrete.
T:
That would work for the walls close enough to the foundation, though not all are. I'd also have to add additional blocking of some sort for the gap by the top and bottom plates, or else notch a wider piece of 2x. I wonder what treated plywood goes for these days and if that would pass muster and count under the "structural panels" clause.
J.
How far off the concrete are you going to be? I'd rather use a 2x8 if I had to than something else. Then the insulator can put insulation at the top.
T:
I'm with you--on a straight run I could use a 2x8 or even 2x10, but this particular job has a lot of zigging and zagging in the walls to accomodate piers, columns, ductwork, etc. It may work out that the ten foot rule will fall in easy spots, or it may not. I'll have to see when I get back there this weekend.
J.
We use regular 5/8" GWB, but you could use DensArmor if if makes you feel better.
Jon Blakemore
RappahannockINC.com Fredericksburg, VA
J:
That's not a bad idea to use cement backerboard, although the cost is a bit more, I think. I just looked up the code again, and it does mention 1/4 cement backer as an option. It is a royal pain to score and snap small sections of that stuff, or at least the hardibacker that I usually use for tile is difficult. What a PIA this code is for a basement! It takes me longer to fit fireblocking around two feet of ductwork and electric than it does to put up 20 feet of stud wall. I wish some manufacturer would come up with a magic spray solution.
J.
It's not cementitious backer board, but rather paperless GWB. It's still gypsum, just a little more itchy to work with.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
I've never heard of that fireblocking requirement...I suppose it's meant to keep fire from moving sideways?
Justin Fink - FHB Editorial
Justin:
Yeah, it is contained under the 602.8, section 1.2 in the 2006 IRC. I guess the point is to sectionalize any fire both vertically and horizontally. However, I've also read that the idea is to contain smoke and vapors, rather than the fire per say. I've been asked by building inspectors to use fire-rated caulk to plug up the holes for plumbing and electric every ten horizontal feet in studs too.
This is one of those things that building officials jump on because it is easy to spot and it makes them feel like they've done something important. Meanwhile, I continue to find all sorts of much more serious violations when I do remodeling jobs on houses only a few years old. The biggest trouble for schleps like me is trying to explain to a homeowner why my quote has an extra $1500 in labor and materials to do this fireblocking. In an economy like ours, there is always an unlicensed and uncaring competitor telling the homeowner to save the cash and not to worry about it.
John