Fire Blocking

Old 07-27-04, 08:01 AM
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Question Fire Blocking

I am currently finishing a basement and had some questions about fire blocking and when it is needed.

My builder framed out all of my walls in the basement. In 2 cases, the wall is offset from the plane of the concrete wall by about 3-4" (there were water lines attached to the underside of the joists near the wall that they were trying to avoid). The remaining exterior walls are set flush. Every wall in the basement is approximately 8.5' tall and is framed using 2 horizontal 2x4s (attached to the bottom of the joists and the floor) with studs placed 16" OC between.

My questions are:

1. Is any additional fireblocking required on the flush walls?
2. Is there any special fireblocking required on the walls that are offset?
3. For the soffits that go around the duct work and attach to the walls about 12" down, is there special fireblocking needed?
4. I assume there is nothing special that has to be done if the wall just out to go around things like drain pipes, etc.

If you know of a good web site that I could look at to learn more about how to fireblock, that would be great!

Old 07-27-04, 09:13 PM
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It would help to know where you live and under which building code your state operates, but generally speaking if your state subscribes to the International Construction Code version of the IRC (International Residential Code) the answers would be:

1: Additional fireblocking is not required for stud walls placed directly against masonry walls, but any gaps or openings between the top plate and masonry walls needs to be fireproofed.

This fireproofing can be accomplished by stuffing unfaced fiberglass insulation into opening between the wood top plate and the masonry wall OR by applying spray foam insulation is a can in these areas, OR by using any other type of approved fire-rated caulking.

2: Fireblocking for walls that are offset includes the requirement that all floor joists above top plates be blocked with 2x lumber to prevent air flow...

3: Any soffit needs to be fireblocked using either structural lumber of 1 hour rated drywall.

4:You assume wrongly. Any hole, orifice, pipe, duct, wire, conduit or anything else that penetrates a plate or stud or wall needs to be sealed with caulk, foam or insulation that is fire-rated.

The best and most proper way to learn about fire-blocking is to contact your local code enforcement office and have them adivse you.
Old 07-30-04, 08:11 AM
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Homebild pretty much answered your question but here's my two cents. First, your local building inspector makes the final call, the framers must do what he says. It might cost you more...but he's the best person to talk to.
Think of fireblocking like this, any gap that allows air to move from the basement to the first floor is a potential hazard. What I do is cut 2x4 or whatever size is needed and pound them in there pretty hard and nail it. Then I use spray foam insulation in the cracks. So what you can do is look for gaps, feel for moving air, etc. It's all you on but if there was a fire, the difference is possibly a complete loss of your home vs. salvagable. Fireblocks usually don't look "pretty."
Old 08-05-04, 10:20 PM
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"fire blocking" The single greatest source of residential fires, is loose electrical connections.

Some framers, as a practice, continuous block, some use a long standing practice of "3 from a corner, 2 from a window or door", and this is primarily for wall stability, not fire blocking.

The 2 studs, sole plate, and the double top plates, comprise a stud bay. Adding a wall covering to each side, the bay becomes encapsulated. Only by compromising this unit, do you cause it then, to not retain its natural Resistance to flame spread.

<2. Is there any special fireblocking required on the walls that are offset?>

Only if there is to electrical in them.

<3. For the soffits that go around the duct work and attach to the walls about 12" down, is there special fireblocking needed?>

Drywall taping should suffice.

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