Knowledge Base

Our digital knowledge base is a selection of resources for customers to help them properly select and install intumescent strips, acoustic door seals and perimeter door seals while meeting relevant building regulations.


Recently Asked Questions

  • Should I put the intumescent strip in the door or frame?

    You should follow the door manufacturer’s instructions regarding intumescent seals. It is important to use the type, dimensions and location of seal that is detailed, as a change to any of these could negate the likely fire resistance performance of the doorset.

  • How can you tell if a fire door needs a smoke seal?

    The cold smoke rating has now been formalized into the BS 5588 standard.

    This ‘S’ decal is used in the FD rating; for example, FD 30S means the fire door has a minimum of 30 minutes resistance AND a smoke sealed door. For smoke seals here we are talking about ‘cold smoke seals’ which handle smoke which has moved away from the fire.

    More than half the ratings are now required to be the latest ‘S’ type door which under the British Standard 476 Part 31:1 criteria. The seals must be able to perform to a minimum leakage rate of 3 cubic metres of smoke passing through 1 metre of door edge per hour.

  • What is an intumescent product and what is its application?

    Intumescent materials intended for use with the operating gaps in fire doors are usually marketed as strips either manufactured as such or cut from sheets that are fixed with adhesive into grooves in the door leaf edge or in the door frame opposite the door leaf edge. For other purposes in connection with glazing or installation, other forms of intumescent material such as putty, mastic or preformed and malleable components may be more suitable.

    Often the intumescent strip is housed in a pvc casing, which provides protection from moisture and a more pleasing appearance. Plain colours, wood grains and metallic finishes are available. It is usual that pvc casings are self-adhesive protected by peelable tape.

    These seals are commonly available in a thickness range of 3 ~ 4mm and in widths ranging between 10 and 30mm. The thickness of the intumescent content is between 2 and 4mm. Other proprietary brands are supplied in aluminium carriers that are generally thicker and require a deeper groove. Some brands provide combined low-pressure ammonium phosphate with graphite.

  • What do intumescent strips do?

    The word intumescent means to swell or expand, which is exactly what an intumescent strip does: it swells up when hot, filling the void between two surfaces to create a fire seal.

  • What is the difference between the various types of intumescent seals?

    In essence, all intumescents do the same job, but not necessarily in the same way! You’ll need to know which specifications you require; consult our technical team to discuss this area in depth.

  • Why do I need intumescent seals in my fire door?

    With the advent in 1972 of BS 476: Part 8 and the requirement for positive pressure in the furnace, the introduction of the cotton fibre pad to measure integrity made it necessary to employ intumescent materials in virtually all timber fire door designs.

    These expand on heating to close off operating gaps around door leaves through which hot gas and flames could otherwise pass to the unexposed face of fire doors and cause integrity failure early in a fire test.

  • Does the plastic not burn to create a failure?

    The type of PVC used in intumescent strips are not very flammable and will not sustain flame.

  • What is Intumescent?

    The dictionary definition of Intumescent means ‘to swell, or become swollen’.

    As a product any material which expands under the single introduction of heat may be called intumescent however there is a lot more to the technology than just its reaction.

  • Where do I need to protect Ironmongery?

    The simple answer is to check the door manufacturers’ specification and test evidence. If they have protected ironmongery then you will also need to; if not, then you are clear to work without it. In best practice, ironmongery products are described as ‘hot spots’ in a door.

    The best way to protect against early failure is to either put a layer of intumescent behind the hinge or wrap the ironmongery in a thin layer of intumescents. This is known to be an excellent insulator and resists the passage of fire through the affected area.

  • What size of cutter should be used for a standard intumescent strip?

    Most of the major manufacturers make just about a perfect sized width with very little tolerance. Therefore, a 10mm x 4mm strip will need a full 10mm cutter set to 4mm depth.

    The products are made to have a friction fit as well as the self-adhesive tape applied.

    The strips have a tolerance of as little as ± 0.2mm which ensures the strip will fit! Best practice for these strips is a tight fit. The fire-only versions of the Norseal Advantage Range gives the compression gap at the base, allowing for that tighter than usual fit.