What Is An Intumescent Strip?

An intumescent strip is a piece of fire-resistant material, which is fitted around a fire door or frame. In the event of a fire, the strip will expand, preventing the fire from spreading. Depending on the product, an intumescent strip will be fire resistant for up to 30 or 60 minutes.

They are installed into a groove around the door or frame, and are self adhesive. You can use a router to create a space wide enough to insert the intumescent strip. We have written a guide on how to fit intumescent strips that you can follow.

There are many different specifications applicable to intumescent strips, and it’s important to understand which type you need for your door. For further help and advice, you can contact our team. 

How does an intumescent strip work?

Intumescent strips are plastic extruded strips with a core of intumescent material. When exposed to heat, the intumescent chemicals react. The intumescent strip swells up and seals the door closed, preventing the fire from getting through the gaps.

Some intumescent strips also contain a smoke seal, such as Lorient Fire & Smoke Seals, which prevents cold smoke from passing through the fire door. This is important because it prevents toxic smoke from entering the rest of the building, reducing the risk of damage or injury. 

Intumescent strips & fire doors

All fire doors require intumescent strips - some will require fire only products and others will require fire and smoke protection. Building Regulations or your architect will inform you of the specifications needed to suit your fire doors.  You can also check the door manufacturers test reports as these will specify the products that have been used to achieve the fire rating - normally this would be either 30 minutes (FD30) or 60 minutes (FD60). One of the most recognised standards for fire doors would be BS476 and all of our intumescent strips would comply with these standards.

If the specification required refers to smoke protection, a fire and smoke strip will need to be installed.  These may be referred to as FD30S or FD60S Doors.  On these doors, it may also be necessary to install a drop down seal to achieve the smoke rating.

Fire and smoke intumescent strips combine the fire protection with a smoke seal.  The smoke seal is either a brush pile or a fin (or flipper) which must make contact between the door and the frame to prevent the spread of smoke.  The intumescent strips with a fin, like the Lorient DS range, also has an acoustic rating to reduce the travel of sound through doorsets.