Intumescent Strips in fire doors

Fire Door Intumescent Strips: Is More Ever Enough?

If you’re looking for a bespoke fire door, you need to be sure that every component of the door is built to ensure compliance and, of course, safety. That’s easier said than done unless you are fully conversant with timber fire doorset manufacture.

Today, there is a surge in demanding taller or wider doorsets to make a statement in the aesthetic or functional role within the building, and this means that manufacturers have to work harder to achieve the demands of the fire resistance whilst meeting higher expectations.

The core and frame design is limited to what fire resistance they can provide, and it is the application of intumescent product that provides the fire certification. In this blog, we will explore whether adding more intumescent material equals more safety.

Read on!

What is an Intumescent Strip?

An intumescent strip, or intumescent seal as it is also referred, is a piece of material fitted around a doorway that expands to stop the passage of fire from penetrating a door when exposed to heat.

It is a key component of the fire doorset.

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What does Intumescent material do? How does it work?

The material the strips are made from is a very poor conductor of heat, which makes it unlikely to burn and allow the fire to spread through the gaps in the door. Not only that, but intumescent material swells on contact with heat, thereby sealing your fire door in place and preventing it from warping and allowing the fire to come through.

Often, the core component is an Ammonium phosphate, Hydrated sodium silicate or Intercalated graphite-based material. However, these can be brittle and is unsightly.

To overcome this, it is normally encased in a PVC shroud. The PVC shroud can be any colour (even wood grain effect is available). The PVC does not affect the intumescent material when it is working.

How Do I Specify Intumescent Strips?

Unless you have extensive knowledge in door core characteristics and doorset manufacture then please do not.

It is our responsibility, as the doorset manufacturer to ensure that the correct intumescent detailing, (size, quantity, and location of the intumescent strips) is correct.

We calculate this based on a complex detail of information that includes (but is not always limited to) the size of the leaf, the desired fire rating, the action of the door (single or double swing), the proposed ironmongery and on occasion the location of the doorset within the building.

We often refer to this as the intumescent recipe.

If All Things Remain Constant Can I Use What I Used Last Time?

Possibly but not always. If you intend to make a doorset up on-site, we would always recommend speaking to the manufacturer about specific situations.

As a manufacturer, our biggest nightmare is listening to a time served joiner tell us “it’s 10 x 4mm in FD30 doorsets and 20 x 4mm in FD60 doorsets. That’s the way I’ve always done it”.

Possibly in some situations he might be right, but often he has just manufactured a doorset that will fail. A failing doorset costs a life.

Ironic as it is, we don’t stock 10 x 4mm intumescent strip as a standard component in our factory.

My Doorsets Are Very Tall. Do We Increase The Intumescent Recipe?

Possibly but not always. We assessed a situation last year where the doorset had doubled the intumescent profile.

Too much intumescent strip can be as harmful as not enough. For example, when the heat contacts with the doorset, the intumescent strip is designed to fill the gap between the door leaf and the doorframe.

As we noted before, the intumescent strip holds the leaf in place for the period of fire resistance.

Too much intumescent strip filling the gap can actually push the leaf out of the doorframe allowing the fire and smoke to pass freely through.


Let’s go back to the original question,

Is More Ever Enough?

Hopefully by now, you will see that there is no correct answer. Too little or too much will cause doorset failure.

It all comes down to your unique requirements. At RW Joinery, we listen to your vision and will create a fire doorset that not only looks great, but is safe, too.

If you’d like to discuss your project in more detail, why not talk to an expert today? Simply fill out the form below or call us on 0161 480 8722.

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