Choosing the Correct Intumescent Seal
An intumescent seal forms an important part of many fire-rated timber door assemblies.
Under normal conditions the strip sits discreetly within a groove in the door edge or frame. When exposed to the elevated temperatures generated during a fire, the intumescent material expands, helping restrict the passage of fire and hot gases through the gap around the door.
The correct seal must be selected according to the fire-door test evidence, required fire resistance, seal dimensions, door construction, smoke-control requirements and permitted installation position.
Fire-Only or Fire & Smoke Seal?
Not all intumescent seals perform exactly the same function.
A fire-only intumescent seal is designed primarily to expand under fire conditions and help protect the perimeter gap around the fire door.
A combined fire and smoke seal incorporates an additional smoke-control element, such as a brush pile or flexible fin, which helps restrict the passage of smoke through the door gap during normal-temperature smoke conditions.
Where smoke control is required, a fire-only strip should not automatically be substituted for the specified fire and smoke seal.
Brush Pile Fire & Smoke Seals
A brush-pile intumescent seal combines the intumescent material with a flexible pile that helps restrict smoke movement through the perimeter gap.
These seals provide a traditional solution for timber fire doors and frames and can also contribute to acoustic sealing where they form part of an appropriate door assembly.
They are available in several widths, allowing the seal dimensions to be matched to the requirements of the tested doorset.
Side-Fin Fire & Smoke Seals
A side-fin fire and smoke seal incorporates a flexible fin alongside the intumescent carrier.
The fin helps provide smoke and acoustic sealing while offering a streamlined alternative to a traditional brush-pile seal.
The integral fin design can also provide a neat solution around door hardware and in high-use environments where durability and resistance to disturbance are important.
Choosing the Correct Seal Size
Intumescent strips are commonly available in widths such as 10mm, 15mm, 20mm and 25mm, but the correct size should not be selected simply according to the fire rating printed on the door.
The required width, thickness, location and number of seals depend on the tested fire-door construction.
For example, different door leaves and doorsets may require different seal configurations to achieve the intended fire performance.
Always refer to the door manufacturer's installation instructions, fire test evidence or certification before routing the door or frame.
FD30 & FD60 Fire Door Seals
Intumescent seals are commonly used as part of FD30 and FD60 timber fire-door assemblies, representing nominal fire-resistance periods of 30 and 60 minutes respectively.
However, achieving the required fire resistance depends on the complete doorset — including the door leaf, frame, hinges, latch or lock, door closer, glazing where present, perimeter gaps and intumescent protection.
The seal should therefore be treated as one component of the complete tested assembly rather than as a product that independently gives a door its fire rating.
Installing Intumescent Strips
Intumescent seals are normally installed into a correctly sized groove routed into the door edge or timber frame, according to the doorset specification.
The rebate should be clean, correctly dimensioned and free from dust before the seal is installed.
Roundtower Hardware's current intumescent seals are supplied with self-adhesive backing to simplify installation, but the adhesive does not remove the need for the groove size, position and overall installation to comply with the relevant fire-door evidence.
Intumescent Seals & Door Ironmongery
Fire-door hardware should be considered together rather than as a collection of unrelated components.
Hinges, locks, latches, door closers and other ironmongery can interrupt or influence the fire-door construction, and some hardware may require additional intumescent protection.
Care should therefore be taken when routing or cutting seals around ironmongery so that the approved fire-door configuration is maintained.
Frequently Asked Questions
What is an intumescent strip?
An intumescent strip is a fire-protection seal fitted around the edge of a fire door or within the door frame.
When exposed to high temperatures, the intumescent material expands and helps seal gaps around the door.
What is the difference between an intumescent strip and a smoke seal?
An intumescent strip reacts to heat during a fire, while a smoke seal is designed to restrict the passage of smoke through the door gap before those high temperatures are reached.
Combined fire and smoke seals provide both functions within one profile.
Do I need a smoke seal on a fire door?
That depends on the required door specification.
Where the door is specified to provide smoke control as well as fire resistance, a suitable combined fire and smoke seal may be required.
Always follow the requirements for the particular fire-door assembly.
What size intumescent strip do I need?
The correct size depends on the tested or certified fire-door specification.
Common widths include 10mm, 15mm, 20mm and 25mm, but you should not select the width based on fire rating alone.
Check the door manufacturer's instructions or relevant fire-door evidence.
Can I replace an old intumescent strip?
Yes, damaged or missing seals can be replaced, but the replacement should match the required size, type, position and performance specification for the fire door.
Do not automatically replace a fire and smoke seal with a fire-only strip.
Where are intumescent strips fitted?
They are commonly fitted into a groove in the edge of the timber door leaf or within the door-frame rebate.
The permitted location depends on the particular doorset specification.
Are intumescent strips used on FD30 and FD60 doors?
Yes, intumescent seals are commonly specified as part of both FD30 and FD60 timber fire-door systems.
The dimensions and configuration required can differ between doors, so the relevant test evidence should always be followed.
Can intumescent seals be cut to length?
Intumescent seals supplied in longer lengths can generally be cut during installation to suit the door dimensions.
They should be fitted neatly and continuously in accordance with the manufacturer's and doorset's installation requirements.
Need Help Choosing an Intumescent Seal?
The correct seal will depend on your fire-door construction, required fire resistance, smoke-control requirements and specified seal dimensions.
Roundtower Hardware supplies intumescent fire door strips and combined fire and smoke seals throughout Ireland, including brush-pile, side-fin and fire-only options.
Browse our collection online or contact our team with your fire-door specification if you need help identifying the appropriate product.
