What is fire blocking? How do I fire block when framing my finished basement?

Not sure how to install fire block? I’m your huckleberry. I know that’s a movie quote from somewhere but I can’t remember where. I think it means I’m your man or something southern macho like that.

how to fire block a basement wall

If you’re reading about fire blocking then I know you must be either:

1. Someone who plans way ahead (kudos to you!)

or

2. Someone who is presently freaking out. Perhaps because you missed a major step in your basement finishing project.

Either way, I know I can help you. During my basement finishing project I was the latter. The guy freaking out.

I remember, it was a Monday. I mentioned to my friend Tom that I was done framing my basement walls and had scheduled my framing inspection for Thursday. He goes, “Cool. You are really doing it.” then casually mentions as he walked away. “Don’t forget fire blocking – they’ll fail you for sure.”

WHAT!!!  What the hell is fire blocking? Can I do it in 3 days?

The purpose of fire blocking is two fold. Starve a fire of oxygen and prevent it from spreading. Ironically, fire blocking material does not have to be fire-proof. It just has to keep the fire from getting fuel (air/oxygen).

basement wall with no fire block

Here’s my best attempt at visually explaining what fire blocking is and where it goes. In this example there is NO fire block. The fire can get air and move freely. (not good)

When you’re finishing your basement, you need to install a fire block in the gap between the top plate of your framed wall and block wall of your house foundation.

basement wall with fire blocking

Ok, same diagram but with fire blocking installed right near the top plate of the wall. That’s it, a little strip of drywall. Not that magical.

Believe it or not, that’s the best explanation I was able to write after 30 minutes of my hamster brain running. Read these other sections and it will make more sense.  I know, you’re probably thinking “what the hell is he trying to say???”

What material can I use as a fire block?

I recommend using drywall as a fire stopping material. You can also use 2x4s, plywood, rigidly packed insulation, fire foam and sometimes sheet metal. I used drywall for my basement. I was a bit short on time so drywall was easiest to cut to the right width and length. It passed inspection without any issues.

How do I “install” fire block?

Fire blocking isn’t something you’ll see at the Home Depot labeled “fire stopping stuff” or “fire block”. It’s just material (drywall in my case) that’s nailed into the gap between your top plate of your framed walls and the foundation of your house.

So you’re going to cut a strip of drywall (or other material) the width of the gap from the block wall to the framed wall, probably 4 to 5 inches. Then push that strip of drywall up into that space.  Take a few nails or screws and secure to the material in there so it doesn’t fall. It doesn’t have to hold Andre the Giant, just its own weight, so a couple of screws or nails should do it.

If you have small enough gap just use some fire foam and it will expand to fill the space. Plus, it fun to squirt.

Fire Block Space around Holes for Pipes or Wires

fire foam used to fire block holes for electrical wiring

photo from : http://joshbasement.blogspot.com (thanks Josh !)

If you drill a hole in the top plate of a wall so you can run plumbing pipes or wiring you need to stuff some rock wool or insulation in the remaining space.

Yes, even a little tiny space. Don’t shortcut it.

If a fire is burning behind your wall and that space is open the fire will suck air into the gap and go burn crazy.

No hole… the fire should just smolder or even go out.  Giving you, your family and your fire department time to react.

Not sure what you can use to fire block? Ask your Inspector!

If you’re not sure about what you can use in your area for fire blocking, ask your inspector. Don’t be afraid to call, they are there to help you! Call them. Here’s what you say. I wrote it down for you.

You:   “Hello, I’m finishing the basement of my house and I have a question about fire blocking .”

Inspector Receptionist:  “Okay, no problem, hang on while I get _____ (Fred).

Fred: “Hello?  What ?  (Fred is a little hard of hearing, due to that one air show he went to where he stood right next to the engine while it “warmed up”.)

You: ” Yes, Hello… Fred… What material do you recommend for fire blocking if I’m finishing my basement? Is it okay to use drywall?

Fred:  “Yes….yeah… drywall is A-okay! Thanks for checking.”

See. That was easy. He even said thanks for checking, so you know you are good to go.

3 Questions, 3 Answers – About Fire Blocking

Q: Do I install fire blocking before or after wall framing?
A:  After. You can also do it as you go along. I didn’t even know about it so for me… after was good.

Q: What if I don’t install fire blocking?
A:  You will fail your framing inspection. Well, you “should” fail. Not a huge deal, you don’t get penalized or anything – you just have to install the fire block before they will pass you. In most areas they’ll come back for another inspection at no extra charge.

Q: What is horizontal fire blocking?  Do I need to worry about it.
A:  So, the fire blocking we’ve been talking about is vertical. It stops fire from moving up. Horizontal fire block stops fire from moving sideways. My county did not require horizontal fire blocking. It wasn’t even mentioned at all in the building codes. Check your code, but it seems like it’s not required in many areas for basement finishing – check your code though.

basement finishing jason 205I hope that helps. I know for me fire blocking was a tricky topic to grasp at first.

You’re doing awesome! Keep going with your basement finishing! It’s going to be so worth it.

If my awesome explanation wasn’t good enough, although I can’t see how that would be, feel free to leave a comment or question below this post.

Cheers – Jason

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Questions and Comments

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  1. Nick says

    I installed fireblocking before framing as recommended by the inspector. I simply cut 8 foot drywall sheets into strips and screwed them to the floor joists (or blocking going the other direction) along where my exterior framing would go. Then the top plate of the wall was screwed to the joists through the layer of drywall.

    I think Jason’s way might be easier in the long run since I may have to shave off drywall and make it even with my top plate where I left it a little too wide.

    You’ll also need to make sure to fireblock any exterior wall framing that runs under a soffit, it’s the same idea, but visually is different and for some reason was hard to wrap my head around.

  2. Jian from Toronto ON says

    Hi Jason, Thanks for everything you posted on your website. I am about to remodel my basement myself. Luckly, I found your website, and now I am learning and digesting from your DIY day by day. The drawings and picture in regard to fire blocking are very helpful.

    • says

      Jian – That is awesome! I’m so glad it’s been helpful, theres more on the way. You’ve got the perfect attitude, make some progress each day, each week and before you know it you’re looking at a great finished basement for a third of the price. Plus a primo set of tools and skills to boot. Have fun! – Jason

  3. Jon says

    FYI
    The walls of my basement came with insulation already on the walls so I’m framing my walls on the outside of the insulation. The inspector here (Colorado) says the insulation on the walls can act as the fireblock so I don’t need to add anything special…YAY!

    • says

      Thats… interesting…. I’m not sure how that qualifies as fireblock for the vertical space? But, if they say ok, then it should be good. No big deal if they aren’t being clear, they’ll just tell you what you need at the framing inspection. – Jason

  4. Dan says

    Jason, I a bit slow…do you mean that the sheetrock should go on all the vertical ceiling boards (and horizontal boards, if required)? Dan

    • says

      Dan – I’m not 100% sure I’m following your question. For fire blocking you do need to install it along the entire perimeter behind your wall, there shouldn’t be any gaps where a fire could spread vertically. If you have a picture email it to me and I can probably comment more better. – Jason

  5. Jeff says

    Hi Jason,
    Is 1/2″ thick drywall acceptable for fire blocking in the stud cavities or does it need to be 5/8″?
    Thanks….Jeff

  6. Jared says

    Hello Jason,

    You post was awesome and just what i needed. I was like you and freaking out that I had finished my framing with no fire-blocking. Thank you so much for your post! I just wanted to say thank you for your drawings and pictures also, they helped me understand exactly what I needed to do.

    You da man!

  7. Ed says

    Hi – Thanks for your article. I understand that 1/2″ drywall would be acceptable to use as fire blocking where I am located. However, it shows the 1/2″ drywall tight to the joists and then extending to the exterior perimeter sill plate, then the top plate of the basement framing fastened through the 1/2″ drywall into the joist above (top plate of basement framing would be under the drywall). Even though the basement wall will not be a load bearing wall it seems odd to fasten through the drywall to catch the joist – do you or anyone on here have any experience with this method and its long term viability?

    • says

      Hello Ed – Although I haven’t seen it done this way too often it would seem to me that should work just fine. It sounds like what you’re describing is that they drywalled the ceiling first then framed the wall. In this way the fire-blocking is already in place? Once the walls were framed you would just have to drywall the walls and you’re good to go. Seems okay.

      Anyone else seen this? Please chime in. Good luck with your project! Cheers -Jason

  8. Tom Bennett says

    Jason, great article and your writing style is very easy to understand and makes perfect sense. Now my wife and I can stop discussing fire blocks on our project…she won. I had to laugh at the very beginning when you talk about the statement “I’m Your Huckleberry”. The movie was Tombstone and it was what Doc Holiday (Val Kilmer) said to Johnny Ringo during the movie. It’s in reference to Huckleberry Fin of the Tom Sawyer books, Huck Fin being Tom’s back up and best friend. Doc was Wyatt Earp’s very good friend in the movie.

    • says

      I’m glad someone has my same level of movie intelligence, knowledge of history and recall. Thank you for the wonderful compliments on my writing, I really appreciate the feedback. Clearly you’re a man of great character and savvy.

      As for the fire blocking – like you I always let my wife win arguments – this makes getting permission for my annual 4 day golfing trip to Orlando that much easier.

      Cheers – Jason

  9. Steve says

    Very entertaining writing style!
    In Colorado, horizontal fire blocking is also required, or draft stopping, especially after these huge fires we’ve had. They’re slightly different, but go together. The principle is that only 100 sq ft of wall or ceiling should be air-flowing. So less than every 12 linear feet of wall, there should be a sealed barrier (on the outside walls, preventing air from flowing along between the basement wall and the framing. Like you’ve said, you can do it with wood (2x or 2 1x) or drywall or structural board, and seal the seams with fire caulk or compressed (packed) fiberglass insulation.
    And you’ve already covered the vertical blocking–separating the cavities in between the floors from the walls, and from each other. With these huge fires, one of the things that happened is that a deck caught fire, the fire entered the area inside the exterior wall under the first floor and…spread like crazy, resulting in the loss of the whole house and fuel for the next house down the street. Embers that could start new fires were flying up to 1/2 mile!

    • says

      Steve – Great info. I didn’t even think about fire creeping in from the outside but you’re 100% right. These seemingly small fire blocking tips can be the difference between a small fire and the total loss of your home. – Jason

  10. frank says

    Hi, Jason,,

    I am not sure I understand correctly

    “Then the top plate of the wall was screwed to the joists THROUGH THE LAYER OF DRYWALLl.”

    any picture will be helpful.

    Thanks

    Frank

  11. Cliff says

    Jason,

    Can you walk us through fire stopping soffits? I can’t seems to visualize it at all. I’m also in Loudoun County so I’m glad to hear I don’t need to fire stop horizontally.

    Thanks,
    Cliff

  12. Geoff says

    Hey Jason,

    I’m wondering about fire stopping for a basement in which we plan on having an open/painted/industrial looking ceiling (In other words… no drywall… just rafters, pipes, wires, etc. shown bare). I’m still in the planning stages of my project so I’m not in a rush but I’d love to hear your thoughts.

    Thanks,
    G

    • says

      Hi Geoff – Okay, here’s the deal with fire blocking your basement with a no drywall ceiling. It’s the same as if you had a drywalled ceiling. Fire blocking is for the ceiling space behind your basement walls (which I’m presuming are going to be drywalled). There will be a 3-5″ space between your concrete wall and the framed-drywall walls. It’s that ceiling space that MUST be fire blocked with drywall or some other material.

      The reason is that that space is hidden. Because the drywall for the wall goes up to the ceiling the space behind it is hidden. IF your design has some kind of openness to the top of the walls then perhaps you would not need fire-blocking. Any concealed space must have fire stopping materials at the top to prevent the spread of fire to the next floor.

      Hope that helps to explain it. It’s a great question – and I really like the no drywall ceiling option – let us know how it turns out.

      Cheers – Jason

  13. Ran Parikh says

    My family member did basement without permit. When he went back to get CO, the city is giving hard time to pass inspection without fire stopping. walls are up and painted. Is there any other way to install fire stopping without destroying walls??

    • says

      Bummer… that’s a common issue that trips people up who don’t get permits. There’s no way that I know of where you can add fire-blocking without removing some drywall.

      This page talks in more detail about some of your options for fire-blocking after drywall has been installed. Good luck! – Jason

  14. Don says

    Jason,

    I am finding myself in trouble before I get these permits started to finish my basement. Last year my pipes were blocked solid from the Kitchen to the Basement from 50 years of bacon grease and who knows what else from the previous owner. My friend and I tore out the Cast Iron and Copper piping and installed PCV in a day but needed support for the new 2″ pipes so we built an open frame, 2×6 studs and 24″ apart along the wall to the existing cast iron stack for the plumbing. My friend and I didn’t know anything about fire blocking until I read what I need to do for finishing my basement this past week. From what I see from the town here in NJ and on other websites, people are attaching 3/8 plywood, Drywall, or a 2×4 before putting up the framing to go between the floor and the Fire blocking. I see what you did in that one picture which looks similar to my situation where you had existing framing but no Fire blocking and you added Drywall and Spray Fire resistant foam underneath the 2×4. Will or did it pass code for you?
    Thanks,
    Don

    • says

      Hello Don – Yes, I used drywall and some spray foam for fire blocking and both methods passed code. I’ve also worked with guys who like to use rock wool, and that has passed. I can’t comment specifically on NJ – but I would guess their allowable methods for fire blocking are similar.

      Hopefully that helps – good luck with finishing your basement! – Jason

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