DIY Home Improvement Forum banner

How to fireblock framing

444K views 219 replies 61 participants last post by  mvcardillo 
#1 ·
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.
 
See less See more
#2 ·
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.
 
#4 ·
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.
 
#5 ·
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?
 

Attachments

#93 ·
Over here you can use fiberglass insulation around hot air ducts just not chimney(type-b vent). I've seen fiberglass shoved into spaces like the picture you posted. Not sure what type of vent that is but you don't want to give people the misconception that they cannot use insulation around ducts. For any electrical running over top or along side ducts, there needs to be insulation between them as well,ad least here in the great white north.

I don't believe firestopping is code(or just not enforced at all) where I'm from as this is the first I've heard of someone going to all of this effort(not to say I disagree with it). I don't believe we have to insulate our ceilings either regardless if its drop ceiling or drywalled. Last basement I finished only had the bedroom ceiling insulated for noise reduction, the rest of the place was drywalled with no insulation in the joists. Inspector did not care and never occured until I read your post that there was more to it. In the case of a ceiling being insulated and drywalled, would you recommend vapor barrier as well, mainly to help hold the insulation in place?
 
#6 ·
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.
 

Attachments

#8 ·
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.
 

Attachments

#9 ·
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.
 

Attachments

#10 ·
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.
 

Attachments

#12 ·
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.
 

Attachments

#13 ·
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.
 
#15 ·
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?
 
#17 ·
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?
Yup, you've got to maintain 1" clearance to type B gas vents. The Rutland sealant is a silicone-based RTV sealant for relatively low heat applications (500-600 degrees), but will work great for what you're using it for. It isn't a code-approved fireblock and isn't listed as such, although it will be much more effective than having nothing at all.

Normally a sheet metal pan is made as the pipe is being assembled so it can be slipped through. But that doesn't mean you can't make a two piece version and come at it from both sides of the pipe. The two halves can be screwed together with sheet metal screws and sealed tight with the RTV.
 
#18 ·
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.
 

Attachments

#21 ·
Fire and oxygen can move freely behind the wall.

First, vertical to horizontal. The gap between the top plate and the foundation must be filled to seal the gap off. Wood is the best bet but often impractical. Fire foam is the easiest assuming the gap isn't too big. Some inspectors will allow tightly packed fiberglass insulation stuffed in the gap.

Second, horizontally. If a fire begins on one side of your basement wall you don't want it moving horizontally all the way across the basement to the other side. The code requires that you take steps to fireblock every 10' horizontally. This is accomplished by utilizing the stud to your advantage. Once again, foam, wood or packed insulation are good methods.

This picture illustrates the potential fire movement that the code is concerned with.
 

Attachments

#23 · (Edited)
Good information

Question, if basement walls are put up only for insulation
No floor, no ceiling, is blocking still required?
I would think it should be, or would be a good idea
Since someone could come along later & put a ceiling in

Should the vertical blocking every 10' be sealed against the cement?
I was thinking a PT 2x would be good every 10' & provide more stability against pushing the wall towards the cement wall
 
#24 ·
ScubaDave, the answer to that is a little subjective...Tough call. I'd say that firestopping would not be required if there were no ceiling. Firestopping is only required for CONCEALED SPACES. If you can stand there and see fire pouring out the top of your wall (and so can the firefighters) I'd say that isn't a concealed space. It is worth considering that by framing walls you're making it very convenient to finish the basement, like you said. A good argument could be made for making the effort to firestop it now in case you (or a future owner) want to finish the ceiling down the road.

The PT 2x is a great thought. That is how many people do it when the gap is significant. When it is a small gap, fire foam is hard to beat.
 
#25 ·
KC - I guess I'm confused about the purpose of fire foam. For example, the Great Stuff Fire Blocker. It wasn't a good idea to use it for sealing around a hot vent that exceeds the foams temperature limit of 140 degrees F. How does it serve as a fire blocker if the heat and flames of a house fire exceed 140 F?
 
#26 ·
KC - I guess I'm confused about the purpose of fire foam. For example, the Great Stuff Fire Blocker. It wasn't a good idea to use it for sealing around a hot vent that exceeds the foams temperature limit of 140 degrees F. How does it serve as a fire blocker if the heat and flames of a house fire exceed 140 F?
Heck of a question, and I've been pondering it for years! Fire will seek out a fuel source...In the case of a small concealed space, oxygen. The foam does a superb job of stopping air movement, which will certainly reduce the chance of a fire moving around. Yes, if a flame hits it it'll fail. Great Stuff and other companies' products have to go through extensive certification and testing to be classified for firestopping or fireblocking, so I feel confident saying it will serve its intended purpose reasonably well. Is wood blocking or packed fiberglass or rock wool more fire resistant? Absolutely. Like I mentioned earlier in this thread, it is always a good idea to check with the local building official before using fire foam, as the code does not list it as an approved fireblock but many building officials will approve it based on its listing.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top