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Some of the most common questions about Intumescent Strip answered by a Technical Expert


What is intumescent strip?

Intumescent strip is a plastic extrusion containing a core of intumescent material.  It can be either plain (fire only) or supplied with a brush or fin (fire and smoke) to give cold smoke protection.  Some of the fin products also have an acoustic rating.


What do intumescent strips do and where are they used?

Intumescent strips provide fire (and sometimes cold smoke) protection to the edges of fire doors, also known as fire resisting doorsets.  They are used to stop the passage of fire and smoke through a doorway between fire compartments in a building.  They are also vital at preventing the passage of smoke into escape routes.


How do intumescent strips work?

Like all intumescent products, intumescent strips are activated by heat.  When the strips start to get warm from the heat of the fire, they start swelling up.  This seals the gap between the door and the frame, and stops fire and hot gases passing through.  They also firmly 'jam' the door in place, preventing it opening in the event of a flashover or small explosion.


How do I fit intumescent strips?

Intumescent strips are typically mounted in the edge of the door, although they can be fitted in the frame.  They are very easy to fit - simply rout out a groove 4mm deep and wide enough to take the strip round the door edge, peel off the self-adhesive release liner on the back of the intumescent strip, and push into the groove.  You can also use Surface Mounted Intumescent Strip which requires no routing, and therefore is ideal for retro-fitting intumescent strip to a fire door.


Do I need intumescent strip on the bottom of a door?

No.  However, you may want to consider an Automatic Drop Seal, which will protect against smoke, draughts, noise and even insects!


How do I know if I need intumescent strip on my door?

Your Fire Officer or Building Control Officer will have the final say in this, but it's pretty safe to say that a fire door is useless without intumescent strip, so if you have a fire door you do need to fit intumescent strip to it.


How do I choose between Fire Only or Fire & Smoke intumescent strip?

Again, it's mostly up to the Fire Officer or Building Control Officer.  But if in doubt always go for the Fire & Smoke option (the ones with a brush or a fin).  They are only a small amount extra and, as we always say, "Better safe than sorry!"


What's the difference between the bush pile and the rubber fin Fire & Smoke intumescent strips?

A brush pile is the traditional way of protecting against cold smoke.  It's inexpensive, effective and quiet in operation.  However, rubber fins are also able to give an acoustic rating, reducing noise transmission through the doorset.  When the fins run down the edge of the strip, they are also able to 'fly past' hinges and lock/latch mechamisms, providing a continuous cold smoke seal round the door.


Which size intumescent strip do I need?

There's 3 common widths available - 10, 15 and 20mm.  The typical rule of thumb used is that you use 10 or 15mm strips on 30 minute fire doors, whilst 20mm is required on 60 minute fire doors.  However, we do recommend checking the door manufacturer's specifications as it's really important you use the correct width of strip.

Standard Intumescent Strips

Extended Brush Intumescent Strip Surface Mounted Intumescent Strips