XPS and fire blocking

sparkywannabeFebruary 5, 2009

I am having a disagreement with my city inspector over fire blocking. I am using 2" XPS against the concrete foundation and framing in front of that. All XPS joints tight and taped. The inspector is now saying that since the XPS is flammable, the vertical fire block required per 2003 IRC every ten feet needs to go all the way to the concrete wall. I feel this will compromise the integrity of the XPS system but he is just concerned about meeting the Code. Has anyone run into this before? Any help would be appreciated.

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Section R602.8. Fire-blocking and draft-stopping shall be installed to cut
off all concealed draft openings (both vertical and horizontal) and shall form an effective barrier
between floors, between a top story and a roof or attic space, and shall subdivide attic spaces,
concealed roof spaces and floor-ceiling assemblies. Fire blocking shall be provided every 10 feet
both vertically and horizontally, in concealed spaces of stud walls and partitions and at the ceiling
and floor levels, including soffits, drop ceilings, cove ceilings, stair stringers, around vents, pipes,
ducts, chimneys and fireplaces, and similar openings which afford a passage for fire at ceiling and
floor levels.

I thought this looked familiar.

See here.

I work under a different Code and have not been required to do basement fireblocking in this manner.

Here is a discussion of your question with possible solutions.

I will add to the JLC discussion the extra step your inspector wants--extending the firestop to the foundation wall.

    Bookmark   February 6, 2009 at 11:04AM
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Good news. I talked to the guy in charge of the building department today (not sure of his title) and he said that for a basement remodel they will only require the blocking at the top of the wall. This top blocking will have to meet the concrete. Not ideal, but at least I am not cutting the XPS from floor to ceiling every ten feet. I just hope that at inspection time he still feels the same way.
Thanks for replying and posting this question in another discussion group. I hope to post some pictures soon of my progress.

    Bookmark   February 6, 2009 at 1:25PM
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Can someone explain this in simpler terms?

I just put up slotted XPS. Fur strips sit in the slots every 2 feet. Tapcons go through the strips, through the XPS 1.25" into the concrete. The XPS runs up my poured concrete wall from floor to the top of the concrete. (where the sill is) For most of the area I am attaching drywall directly to the XPS/Fur Strips as reccomended by the manufacturer. For added insulation, I will be framing up against the XPS in a few areas so I can add some extra fg insulation and have wiring run. A dropped ceiling will cover everything.
So, now I am a bit worked up!
What do you mean fireblocks every 10 feet vertically and horizontally? I really spent a lot of time weighing whether I should even use the XPS and chose to do so because of Building Science reccomendations etc. I wanted to eliminate mold possibilities as much as possible. It almost sounds like the code is saying every 10 horizontal feet there should be a brake in the XPS...ie a stud mounted right to the concrete?...is that what a fireblock is? Why the heck was the XPS sold with slots for a continuous run if this is the case?

I thought mounting wood directly to the concrete was not the way to go. Basements are usually only 8 feet tall max so I am unsure how the 10 foot vertical would come into play. I am also confused as to how you satisfied local code....what did you do.

Are you saying that I in the little ledge at the top of my concrete wall (the sill sets back and inch or so as I recall) that I sort of need to cap off the top of the XPS. How does one do that, liquid nail a fur strip to the ledget and let it overhang enough to cover the XPS?

I am confused!!!

    Bookmark   February 6, 2009 at 2:44PM
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I read you links Worthy. I think I would be up to code where the drywall abuts the XPS / fur stips right? Also, I should be ok where I frame so long as the framing is right up against the XPS right?

Where I am lost is what to do at the top of the XPS. Right now its cut off at the top of the concrete wall, ie if you look down you would see 1) the sill sitting on the top ledge of the wall, not covering all of it, a little space of concrete then the top edge of the XPS. What if anything do I need to do here?

I want to be up to code and SAFE.
I also have not spoken with my township...this whole thing could take me a year or more to finish...I'm just working half the basement now....I'd was hoping to have the XPS and drywall up (not even spackled etc) for spring and resume in the fall...not sure how long permits are good for etc...mostly just trying to get the area to be a little warmer and cleaner..and then there is always the horror stories about inspections you here and increased taxes etc. Maybe I should speak with them or call them in....?

    Bookmark   February 6, 2009 at 3:36PM
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If you're having this inspected, it's obviously a good idea to see what the municipality wants.

As the discussion on JLC shows, what is typically required is a horizontal block--as simple as pieces of 5/8" Fire Code drywall screwed into the 1st floor joists above the framed basement wall. And some municipalities may be satisfied with fg as a firestop, though it isn't. If the municipality requires a horizontal fireblock in contact with the concrete, I would prefer to use a more moisture resistant material than drywall, such as the special mineral wools or foam mentioned by the contractors in the JLC discussion.

    Bookmark   February 6, 2009 at 5:50PM
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Oh lord! So how far out from the wall should this drywall go? Does not sound too expensive or hard I guess. Do you feel this really adds to saftey?. If one omitted, having to add later does not sound to hard, just need pop out your ceiling tiles I guess. I already have the fg in the ceiling already. I am still thinking maybe I should have the inspector out----and hopefuly not open a can of worms. Again, I want to be safe but if the flames are climbing up the wall, what does this piece of drywall really add to the equation? Adding a 2 X 4 pt piece around the top of the XPS resting partially on the sill and acting as a cap might not be too bad either...attaching being the difficult part.

BTW, is fire rated drywall typically required in on the walls in basements? Even if not is it worth the extra dollars or just a gimmic?

    Bookmark   February 6, 2009 at 6:45PM
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In my own home, the top of the 1" XPS on the foundation walls is not fireblocked as it was not required to be and I feel perfectly safe.

By the time any fire in the basement breached the drywall, ignited the XPS and then the floor above I figure I'd be long gone. Smoke detectors on every floor, battery and hard-wired.

Still, if your project is being inspected because you took out a permit, you must meet the municipality's requirements. Fire-rated drywall (Type X) is not typically required in residential except for such things as around boilers etc.

    Bookmark   February 6, 2009 at 8:19PM
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Here is a link to a good diagram of fire blocking in a basement.
I am going to block the top of the wall with 2x4. I will try to get a good close up pic for you tonight.

    Bookmark   February 6, 2009 at 11:00PM
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I have pics but need to figure out how to post them.

I would not put in the fire block if this was not going to be inspected. I feel the same way about it as Worthy, I'd like to think I would be long gone. Although I don't have hardwired smoke detectors currently, they are required as part of this basement remodel so when the weather warms a bit I will be in the attic running conduit.

I will have the same situation with furring strips on part of the wall by the stairs where I can not afford to lose the space for framing. I have not figured out exactly what to do there yet but will spend some time this weekend to come up with a solution.

    Bookmark   February 6, 2009 at 11:56PM
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Let me know your solution...for now I plan on using 1 X 4 pt strips (with that foamseal stuff behind--the stuff you use under your pt wood on the floor) and with 1/2" dow blueboard XPS in between...every 2'. Using 1/2 drywall over that appears to come close to aligning with the drywall above the sill heading up the stairs...if it does not end up matching well some sort of piece of molding will need to suffice.

    Bookmark   February 7, 2009 at 11:52AM
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Very nice pdf picture. If adding that vertical strip of drywall to the insde of a 2 X 4 every 10 or so feet really can make a difference, what the hell, it easy enough to do. Now real way to do that with a continuous run of XPS though.

Now, the horizonatl stuff looks like you essentially need to cut a stip of drywall large enough to cover the 2 X 4 + the depth of your XPS and add between to the top.

I assume, technically, the areas I am not framing but rather attaching drywall right to the XPS really should be capped with a skinny strip as well...I'd need to think of how to attach it and if it really would be worth it....I guess it depends of how level I cut XPS....or I might even have enough room to lay a 2 X 4 over the xps and rest the other half on the concrete, maybe some more foamseal underneath...not sure how I'd attach it....sounds like there is little bang for the buck if there is a fire though!

    Bookmark   February 7, 2009 at 12:07PM
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Here are some pics.

As you can see, I had to run a 2x4 along the concrete because my floor joists are lower than the top of the concrete wall. I plan on covering the concrete above the 2x4 with a strip of XPS if it will be acceptable.

    Bookmark   February 8, 2009 at 10:29AM
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THANKS! I see. I'll have to figure a way to 'cap' the XPS as well.

    Bookmark   February 9, 2009 at 5:09PM
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Thanks for the fire-blocking sketch and the pics.

Trying not to be too picky. But your bottom plate should have been resting on a strip of 6 mil poly or XPS or have been pt. And you didn't need king studs around the window as the wall is non-supporting. Excellent detailing at the top of the XPS.

    Bookmark   February 10, 2009 at 11:43AM
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All wood touching concrete is PT, it's hard to tell from the pics. I contemplated putting sill seal or XPS under the plates but decided on just PT. Ripped out basement was finished this way and the wood looked like new after 25 years. In fact, I will use the wood from the old basement finish for fire blocking, minus the pieces with holes bored through it.
I know I didn't need the kings (my dad said the same thing last weekend) but I am adding a sill to the window and wanted a strong frame around it. cost ~$4.

    Bookmark   February 10, 2009 at 12:42PM
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