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Termite 01-30-2009 09:17 AM

How to fireblock framing
I'll kick off this new section with a how-to topic I've been thinking of posting for a long time. Firestopping. A lot of municipalities require firestopping in combustible construction per IRC 602.8...New homes, finished basements, and the like. If you're finishing your basement, building a new home, adding soffits to an existing room, or adding an addition, the code requires fireblocking.

This will be a pictorial how-to, and it will take me a while to compile pictures and discuss each one. So, this thing will evolve over the coming weeks. I'll post pics and describe the violation or the fix.

Fireblocking requirements are clear in the code, but the enforcement can be subjective. It is always best to discuss fireblocking requirements and methods with your inspector before doing the work.

So, how do I know what needs to be fireblocked you say? The best description I can give is to tell you to imagine setting off a smoke bomb inside a finished/sheetrocked wall. Is that smoke confined to the wall stud space or can it move to any other spaces like soffits, furdowns, floor joists, dead spaces behind the wall (if only rocked on one side) or anywhere else? If it is confined, you're good. If not, you need to fireblock. Even small spaces around plumbing pipes or holes that wires go through need fireblocking.

I've been in homes that burned that were fireblocked, and I've been in homes that were not. I can tell you that it does work in slowing the progression of a fire. I've even seen properly firestopped stud spaces have fires that ignited and then burned out due to lack of oxygen getting to the space. A fire in a stud space will suck air through a small hole in a top plate with a great amount of vacuum, and it will look like a torch as the oxygen enters the space.

EDIT: Since this thread has covered other fire protection issues as it has evolved, I'm going to try to cover all the fire protection issues covered by the residential code (single residences only), in addition to fireblocking. I'm not going to get into firewalls and fire separation because that is a totally different topic.

Termite 01-30-2009 09:24 AM

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.

AtlanticWBConst. 01-30-2009 10:48 AM

Good Topic for the site, and for "How-to".

Termite 01-30-2009 11:16 AM

The code allows you to use a few different materials for fireblocking. 3/4" plywood or OSB with edges blocked, 2x dimension lumber, two thicknesses of 1x lumber, 1/2" sheetrock, or rock wool or fiberglass unfaced insulation rigidly supported in place. Sheet metal is also widely accepted, although not mentioned in the code.

Termite 01-30-2009 11:18 AM

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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?

Termite 01-30-2009 11:20 AM

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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.

Termite 01-30-2009 11:24 AM

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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.

Termite 01-30-2009 11:30 AM

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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.

Termite 01-30-2009 11:33 AM

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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.

Termite 01-30-2009 11:37 AM

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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.

DangerMouse 01-30-2009 11:40 AM

as i'm doing a lot of this type construction here this spring, this is truly appreciated KC!



Termite 01-30-2009 11:41 AM

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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.

Termite 01-30-2009 11:52 AM

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.

For larger holes, wood blocking or really tightly packed fiberglass is appropriate.

Termite 01-30-2009 11:53 AM

I'm out of pictures! Stay tuned, more to come...

gma2rjc 01-30-2009 04:47 PM

This is a great idea Nathan. KC, I'm glad to see this topic with the pictures.

I've been working on sealing my attic since November and, depending on how you answer my question, I think it's completely sealed. In post #6, where the vent goes up through the attic floor, I had a heck of a time in my attic figuring out what to use to seal the 1" gap between the vent and the wood flooring because that vent gets pretty hot. First I used Great Stuff, then found out it can't be used on surfaces over 140 degrees F. I took all of that out and replaced it with the Great Stuff Fire Blocker foam. That can't be used on surfaces over 140 F either. I cut all of that out and I'm glad I did. The foam that was in contact with the vent was melted. I'll take a picture of a piece of it and post it. A couple nights ago I filled that gap with Rutland 500 degree F fire sealant.

Will the fire sealant serve as a fireblock? Also, to put a piece of the sheet metal like you have around the vent in post #6, can it be done with an existing vent or only when the vent is being pieced together?

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