Fire Blocking

Old 09-13-04, 01:47 PM
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Unhappy Fire Blocking

We are finishing our basement and are almost done with the framing of all the interior walls and ceiling (we're putting in a drywall ceiling). I've talked to the city building department about fire blocking and still am not clear on how this is done. One stud wall is about 4" from the cement wall -- do I try to get up back behind the top plate and attempt to nail/screw another piece of wood in there? Will insulation work, and if so, does it have to be secured somehow?

The finished space will be 5 rooms and cover about 1,000 sq ft. I know I'm probably making this more difficult than it has to be, I just can't picture how we're going to be able to get up, in, back behind there. I hear that the smaller gaps can be filled with "great stuff". With this "stuff" adhere to both the cement and the lumber?

Thanks for any help anyone can offer. Anyone have any pictures?? I hear fire stopping isn't always pretty. Thanks.
Old 09-13-04, 03:45 PM
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Fire Blocking

Where your framed walls run perpendicular to your floor/ceiling joists above, fireblocking should be installed between the joists and above the top plate of the framed wall in the form of 2x10s or whatever are the dimensions of your floor joists above.

In other words, you will need to cut individual blocks out of (usually) 2x10s at 14 1/2" long and fasten them between each floor joist over the framed walls.

Where the framed walls run parallel to the floor joists, you can fasten a plate to the top of the framed wall and to the side of the nearest living space joist so that any fire that eripts behind a framed wall will be contained there.

Alternately, you can used unfaced fiberglass insulation stuffed between floor joists in any location above the framed wall.

Some spray foam insulations in the can (those manufacturers after January 2003) are generally fireproof and will also work for smaller areas. Read the fireproofing characteristics on the can before using.
Old 09-13-04, 07:52 PM
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Thanks for your quick reply. There are some areas where this will be difficult,but I'll give it a try. The insulation idea sounds much easier.
Old 09-17-04, 01:45 PM
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Call your city inspector about the use of fiberglass. My inspector didn't allow insulation and told me use 1/2" sheetrock instead of fiberglass. I also had to block of the curtains walls vertically every 10'. Not fun work, but I guess it will be worth it in case of a fire.
Old 09-17-04, 01:56 PM
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Like said check code there for sure on the fire stop. Some will call for 5/8 drywall.Do put R19 in each joist space up there on the sill plate all around the home.
Fiberglass as a fire stop forget it. Some time take some fiberglass and put a small LP torch to it. It wont burn but it sure will melt right away and let a fire through. Thats why we use cellulose insulation all the time.

Old 09-17-04, 02:15 PM
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Packed Fiberglass

Packing unfaced fiberglass as a fireblock is used to prevent oxygen from feeding a fire and is the only approved insulation for fireblocking under the IRC 2003 code (apart from some approved foam sprays).

Cellulose insulation will compact with time and humidity and will allow oxygen to feed a fire rather than dampen it. Cellulose will also burn (albeit slowly) unless treated with fire retatrdent chemicals.

This is why cellulose is not approved for fireblocking.

In fact, it may behoove us to actually define "fireblocking" because it does not seem that everyone understands just what it is.

One such definition is : "“Fireblocking”, is now defined as generic materials, such as lumber, structural wood panels,
gypsum board, cement fiberboard, or particleboard, batts or blankets of glass or mineral wool
installed within concealed spaces to resist, or block, the migration of fire and hot gases for an
undetermined period of time. Fireblocking is used to subdivide or block off the stud cavity inside a
wall, in a soffit over cabinets, between stair stringers at the top and bottom of a run, in an
exterior cornice, in the space between the combustible finish materials and the wall itself.",,,Source:

Please note that cellulose insulation is not at any time considered and approved 'fireblocking' material.

Comparing cellulose with fiberglass in terms of fireblocking is like comparing apples and oranges. Cellulose is not an approved fireblocking material. Dense packed fiberglass least under IRC 2003.

Whether fiberglass is acceptable in your code jurisdiction as a fire block depends upon your local code and code enforcement office.

So do consult them for their authoritative advice in your particular case.

But let us not get confused regarding the differences in the insulating merits of fiberglass insulation vs. cellulose insulation as some innate approval of cellulose over fiberglass in fireblocking when there is none.

Nor forget that while fiberglass can melt under high temperature, cellulose will spread flame and smoke producing other deadly results in a fire while fiberglass will not.

So yes, consult your professional code enforcement office and do not rely on the hearsay evidence that can be found in forums like these.

It may mean your life.

Last edited by homebild; 09-17-04 at 03:20 PM.

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