Intumescent door edge seal is a critical component in a fire door.

In the heat of a fire, the intumescent material will expand to fill the gap between the door and the frame, thus ensuring the fire integrity of the whole doorset. The longer the door is required to resist the fire, the more intumescent material is needed. Hence there are several different sizes of seal available.

As standard, the seals are all 4mm deep, but the widths vary to accommodate different amounts of intumescent material. The most commonly used widths are 10mm, 15mm and 20mm. In general, the 10mm and 15mm widths are used for FD30 doors, whilst the 20mm width is used for FD60 doors.

The seals should be fitted centrally in the edge of the door, or in the frame opposite the centre of the door edge. If you are using 2 strips along the edge of the door, these should be centred on the centre of the door edge.

However it is very important that, if possible, you consult the test evidence of the door itself and be guided by this.

For instance, very often in door fire assessments a 15mm wide strip is required even for FD30 doors. For this reason we would recommend using 15mm seals on an FD30 door if in doubt.

Extra intumescent is also generally required for double doors, and when a door leaf is extra large. In fact, any doorset other than a standard single action single door should be treated with caution.

In these cases it’s extra critical to consult the door test evidence. This will usually give guidance for pretty much every scenario. For instance, the Warrington Fire Field of Application report for the Strebord 44 and 54 doors has over 150 pages of guidance about what seals should be used in every different scenario!

Below are some potential pitfalls to watch out for;

1. Installing seals that are smaller than required – there simply isn’t enough intumescent material to hold the fire at bay for long enough
2. Fitting seals in the incorrect position – seals should be centred around the middle of the door edge. If they aren’t, you risk the intumescent material forcing the door open when it expands.
3. Using seals that are much larger than required can even have the same effect of forcing the door leaf open and compromising the fire integrity
4. Using larger seals is not a solution to compensate for large gaps around the door! If door edge gaps are too large, the door is unsafe and needs adjusting or replacing.