The whole idea behind fireblocking is to slow the progression of a fire in parts of the home you can't see, and to contain it to small areas of concealed space. If a fire in a stud wall can move vertically into the floor due to lack of a fireblock, the fire can compromise the structure much faster. If a fire in a wall or chase is able to move to the attic, the fire can quickly propogate. The idea of fireblocking is to use any number of materials and methods to keep that fire from moving in concealed vertical spaces to or from concealed horizontal spaces. The installation of those same materials serves double duty to minimize the ability of a fire to pull oxygen from other parts of the home. If it can't breathe, it can't burn.
How to fireblock framing
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Now, a few scenarios...
This is one that just about every house has. Chases for HVAC vent pipes, plumbing and electrical must be firestopped top and bottom. This picture is not firestopped. See how the vertical chase is open to the horizontal spaces between the floor joists, which allows a fire to move from vertical to horizontal?
This is one that just about every house has. Chases for HVAC vent pipes, plumbing and electrical must be firestopped top and bottom. This picture is not firestopped. See how the vertical chase is open to the horizontal spaces between the floor joists, which allows a fire to move from vertical to horizontal?
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Two ways to deal with this. You can't put wood or insulation in contact with the vent (min 1" clearance), so sheet metal is one way most inspectors accept.
See how the metal was installed at the top of the vertical chase to prohibit vertical to horizontal movement? It is cut nice and tight to the vent and secured at the perimeter.
The way to deal with the first picture is to use 2x10 blocking between the joists at both sides of the chase to prevent the vertical to horizontal movement. In this picture the chase opens to the attic so that wasn't an option.
See how the metal was installed at the top of the vertical chase to prohibit vertical to horizontal movement? It is cut nice and tight to the vent and secured at the perimeter.
The way to deal with the first picture is to use 2x10 blocking between the joists at both sides of the chase to prevent the vertical to horizontal movement. In this picture the chase opens to the attic so that wasn't an option.
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The same thing is required at the floor level to keep a fire from the floor joists from moving vertically into the chase, and vice-versa.
Sheet metal is the standard around here.
Sheet metal is the standard around here.
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When you finish a basement, it is pretty standard to frame your walls out of 2x3's or 2x4's an inch or so away from the existing foundation or framed downwalls that sit on short foundation walls. This picture wasn't taken in a basement, but it clearly illustrates the gap left between the top plates of the walls. The gap between your basement top plate and the foundation will need to be firestopped. Options include very tightly packed fiberglass, wood, and fire foam for small gaps. I'll get into fire foam later.
This picture has not been firestopped yet. I'll definately get a lot of good pictures for finished basements down the road and go into them in depth here.
This picture has not been firestopped yet. I'll definately get a lot of good pictures for finished basements down the road and go into them in depth here.
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Here's a good example of firestopping basics. The studs, when sheetrocked, would be wide open to the attic since the rafters intersect the wall below the top plate. That allows fire to move freely between the wall and the attic.
They'll need to block between the studs with 2x4's just beneath the rafters.
They'll need to block between the studs with 2x4's just beneath the rafters.
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This intersection between the rafters and the walls would have been fine but they added additional 2x's to the underside of the rafters to accommodate additional insulation thickness. The result is a gap left right underneath the top plate.
The insulation will fill the gap, but doesn't comply with the code for this application.
See how they blocked that gap with the on-edge 2x4's right under the top plate?
This is perfectly firestopped.
The insulation will fill the gap, but doesn't comply with the code for this application.
See how they blocked that gap with the on-edge 2x4's right under the top plate?
This is perfectly firestopped.
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The following two pics are very similar situations. The first one has not been fireblocked. See how the studs open up to the attic? Gotta block that. The easiest way is to block between the studs below the opening to the attic. Another way would be to sheet the back side of the opening from the attic using 3/4" ply or sheetrock.
The second pic has been effectively fireblocked.
The second pic has been effectively fireblocked.
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Let's talk plumbing and electric (and other) penetrations of top and bottom plates.
Fire foam is a great way to deal with this. Not regular "Great Stuff", but specific fire foam. Great Stuff does make it, as do others. The annulus between the wood and the pipe or wire needs to be filled. Fire foam expands as it cures so it does a good job of filling the void. The code doesn't mention fire foam as an option but most inspectors will happily accept it since it is listed for the application. Most fire foam is listed to fill gaps up to 1-3/8", but that depends on the brand used.
Here's a pic of some plumbing properly firestopped through the bottom plate.
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For larger holes, wood blocking or really tightly packed fiberglass is appropriate.
Fire foam is a great way to deal with this. Not regular "Great Stuff", but specific fire foam. Great Stuff does make it, as do others. The annulus between the wood and the pipe or wire needs to be filled. Fire foam expands as it cures so it does a good job of filling the void. The code doesn't mention fire foam as an option but most inspectors will happily accept it since it is listed for the application. Most fire foam is listed to fill gaps up to 1-3/8", but that depends on the brand used.
Here's a pic of some plumbing properly firestopped through the bottom plate.
For larger holes, wood blocking or really tightly packed fiberglass is appropriate.
Excellent presentation KC. BOB
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Ok, some more pictures. Finished basement...
This is a situation commonly encountered in basements of homes with truss floors, but the concept can be applied in many situations. The finished basement's stud wall's top plate is situated above the ceiling line. Once rocked, there's a pretty good-sized void between the ceiling and the top plate.
You can see that the framer wisely placed flat 2x4 blocking horizontally just below the ceiling line. He may not have had fireblocks in mind as much as he was thinking about nailers for the sheetrock's top edge, but the blocks serve double duty.
This is a situation commonly encountered in basements of homes with truss floors, but the concept can be applied in many situations. The finished basement's stud wall's top plate is situated above the ceiling line. Once rocked, there's a pretty good-sized void between the ceiling and the top plate.
You can see that the framer wisely placed flat 2x4 blocking horizontally just below the ceiling line. He may not have had fireblocks in mind as much as he was thinking about nailers for the sheetrock's top edge, but the blocks serve double duty.
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This is pretty much the most common fireblocking issue in a finished basement. The wall is built tight to the underside of the floor joists and is rocked on only one side...
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Buuuut, the challenge begins when the wall is furred out from the foundation wall (or framed downwall, whichever) a little bit, which most are.
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