How to fireblock framing - Page 2 - DIY Chatroom

buletbob · 01-30-2009, 09:46 PM

Excellent presentation KC. BOB

**thekctermite** · 01-30-2009, 10:06 PM

Quote:

Originally Posted by gma2rjc

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.

**thekctermite** · 01-30-2009, 10:21 PM

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.

**thekctermite** · 01-30-2009, 10:24 PM

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...

**thekctermite** · 01-30-2009, 10:26 PM

Buuuut, the challenge begins when the wall is furred out from the foundation wall (or framed downwall, whichever) a little bit, which most are.

**thekctermite** · 01-30-2009, 10:38 PM

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.

**thekctermite** · 01-30-2009, 10:46 PM

So, here's where the firestopping goes.

**Scuba_Dave** · 01-30-2009, 11:09 PM

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

**thekctermite** · 01-30-2009, 11:19 PM

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.

gma2rjc · 01-30-2009, 11:35 PM

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?

**thekctermite** · 01-30-2009, 11:47 PM

Quote:

Originally Posted by gma2rjc

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.

**thekctermite** · 01-30-2009, 11:51 PM

By the way, I errantly tend to interchange the words fireblock and firestop. It is a bad habit I developed early in my career, and a lot of people do it so nobody really thinks anything of it in the field. This thread is about fireblocking. Firestopping is a whole other issue that really isn't encountered too much in single family residences. Firestopping is the act of sealing penetrations into and through fire-rated assemblies such as those in the floors and walls of apartment buildings and commercial structures.

DIY_JC · 01-31-2009, 09:18 AM

I am enjoying this thread... so thank you.

One issue I have (and many others do as well) with every house I have owned, is that the fireblocking also makes it near impossible to run wires (coax/speaker/cat5/6 etc) without tearing a house apart to get around/through the fireblocking. It wouldn't be an issue if the builders wired it for what people want/need but unfortunately, most do not. Even if they did, it would most likely be an issue in 5yrs when the technology changes. With that said, how does one circumvent the fireblocking while still providing the necessary protection? Is there a certain size hole that is allowed? Is that any different than the holes drilled for wiring the electrical?

**Scuba_Dave** · 01-31-2009, 11:28 AM

Good point
Can you install a PVC pipe & cap it & does that meet fireblock requirements??

**thekctermite** · 01-31-2009, 11:36 AM

DIY JC, you're right that fireblocking can add obstacles to running wires in dead spaces. That is one drawback, but it can usually be overcome. Drilling holes in the top and bottom plate of a concealed wall is pretty easy to do with a long flexible installers bit...Going horizontal is a challenge. Some homeowners and builders are wise enough to have the forethought to install "Murphy's law pipes" in the home to facilitate installation of wires from floor to floor years down the road. It can be challenging to run wires in a home with no firestopping at all, and hacking into the wall or ceiling can also be necessary.

As for hole size relevant to firestopping, the code is silent. Any penetration through a framing member or block serving as a firestop has to be sealed up reasonably tight to prevent passage of air.

The good thing is that when fishing wires in an existing finished wall, it is impossible to firestop your holes, and nobody's going to fuss about it.

Balancing safety and convenience can often be a challenge when building!