Fire blocking (and Firestop) Your Basement– Avoid Making These Mistakes6 min read

Fire blocking (and Firestop) Your Basement– Avoid Making These Mistakes6 min read

Any new home constructed must adhere to the draft stopping and fire blocking codes.  What if you are doing a simple basement renovation? I know it’s confusing. So, we will look at everything to make you renovation fireproof.

Gaps, holes, and cracks allow air flow and oxygen is the most needed element for the fire to burn.  Fire blocking attempts to prevent the flow of air and smoke. Thereby stop, control and delay the spread of flame, smoke, and gas.  From one room to another and from one floor to another.

This is another area that is very unclear. Every state and every county rule differ. Some need and enforce it and others just recommend.

However, when you refinish your basement, you will most likely fail the inspection if you don’t have proper fire blocking in place.

It doesn’t matter whether you do it yourself or use a contractor to finish. So if your contractor isn’t pulling the permit, and you are, be forewarned to ask and check this.

Why Fire block?

Good question.

Have you ever noticed a fireplace closely? You will see a chimney going all the way to the roof. You need that, so you don’t have smoke all over the room.

Now, this is needed to vent the smoke and raise any fire above and not into the room.

That’s just designed that way, intentionally.

What happens in a fire accident? The fire tries to find gaps or holes on the floor above. And smoke and flame start to raise through those voids to the floor above.

This puts the whole house in danger instantly the moment you have a fire somewhere.

What if you seal all the holes and block all the gaps?

Essentially, you are compartmentalizing your walls and floors above. What it does it this.

Chokes the hell out of that spot with its own smoke, supply no oxygen and in any case delay the spread of fire.

In a nutshell, you are creating a barrier. For the fire started in the basement or the cellar (or crawlspace) to get up through the next level and spread to the rest of the house.

It’s per code in a lot of areas to put these.  Anyhow, time is your friend here before firefighters can act.

Fire statistics to know

Some fire damage statistics if you are still not sold on fire blocking.

There were near 1.3 million fire accidents as of the latest collected statistics (2017). And it resulted in more than 2000 deaths and 10000 injuries.

And cumulatively the damages accounted for a total loss of $23 billion.

It’s more devastating that you can think.  You may not be able to stop it completely.

Because We are still using wood products which is just the fuel that fire needs.

We should indeed be using concrete to make the building stronger, fireproof and hurricane proof.

However, we can stop the other critical ingredient – airflow-, right?

Difference between Fire block and Firestop

IRC section R302.11 states “In combustible construction, fire blocking shall be provided to cut off both vertical and horizontal concealed draft openings and to form an effective fire barrier between the stories, and between a top story and the roof space.”

The terms are interchangeably used by novice and experts.  However, there is a slight difference.

Fire blocking and Draft stopping:Draft stopping and fire blocking to stop flame and gas spread

Fire block’s objective is to -as the name states- block the flame and gas to easily move through the cavities of the house construction.

However, there is no restriction on the material used.

As long as it is as per the recommended guidelines set by IRC.

Wood is a known burning product and is a fuel as we all know.

However, we can use it as a fire block product to stop the flame from going up or sideways.

And it must be rated by the hours it can withhold the fire without spreading.

What does 1-hour fire mean?

Very simply this. Based on the combination of building materials used, the room can resist or contain the fire for 1-hour before spreading to the other side of the wall.


Firestop, on the other hand, has a different objective – To stop the fire from passing through the penetration, based on the materials used.

It provides the same level of fire protection that a fire-rated wall or ceiling provides to any ceiling or floor that is penetrated.

Penetration is due to pipes and wires.  In a commercial environment, office cables and wires pass through several walls (a.k.a Multi-cable transits or MCTs).

The type of material used might burn when exposed to fire, however, it will not hold and spread the fire.

So, in short, Firestop is a system of different components used in conjunction to provide fire-resistance.

The various fire stop components or materials are used to seal joints, holes, and openings, which then stops the fire spread.

The holes in the walls and ceiling are typical vulnerable spots in the event of a fire.

Well, as a typical example of a firestop vs fire block on foam the attached video shows the difference.  I don’t think I will have to explain anymore.

Approved Fire block Construction Materials (Fire Blocking)

  • Construction Lumber
    • Regular construction lumber – 2-by-4 or a 2-by-6 (1-1/2 in. in real thickness)
    • Two layers of 1-by lumber. (but with staggered joints)
  • Plywood, OSB and Particleboard
    • A ¾-in. board (Plywood, OSB or Particleboard). In addition, seems must also be covered by one of the approved fire block material or have staggered joints.
    • One layer of 3/4-in. particleboard with 3/4-in. particleboard covering any seams.
  • Wall Materials (Drywall and Cement board)
    • Fire rated Drywall that is at least one-half inch thick (1/2-in.)
    • Cement board that is at least a quarter inch thick (1/4-in.)
  • Insulation Materials (Fire block Insulation and Foam)
    • Fiberglass insulation secured tightly (Batts or blankets insulation)
    • Cellulose insulation (at approved thickness)
    • Spray foams that are approved for fire blocking

gap behind studs and concrete wall fireblocked using a 2by


Fire block and firestop are two different concepts and use different materials.  In any case, the underlying theme is to not spread the fire as much as possible.

In a residential setting and especially when finishing your basement, you are most likely going to fire block.

Because in a lot of jurisdictions fire block is all the inspectors would require you to adhere to.

It doesn’t matter whether you use a burning construction material like wood or a non-burning material like cement board.

As long as you use the minimum recommended dimension, it will stop the gas and flame from spreading to the vertically and horizontally.

Even if your local authority doesn’t require (which is the case with a lot of towns in the US) it’s to your safety.

Stay Protected!

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  1. On long runs with OSB, plywood, or partcle board, it sounds like I need to use two thicknesses in order to stagger or back any seams. Is that correct?

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