Which Door Seal Do I Need? A Guide to Different Types of Door Seals

Which Door Seal Do I Need? A Guide to Different Types of Door Seals

Choosing a door seal sounds straightforward until you look at what the door actually needs to do. It may need to resist fire and restrict smoke spread, reduce sound transfer between rooms, keep out draughts and weather, or meet several of these requirements at the same time. The type of door matters too. A seal designed for a timber fire door will not necessarily suit a glass, steel, or sliding door.

Then there is the seal itself. Intumescent seals, smoke seals, brushes, fins, perimeter seals and automatic drop seals all do different jobs, although some products combine several functions. The right starting point isn't the shape or size of the seal, but the performance the door needs.

What does your door seal need to do?

Door seals close or control the gaps that inevitably exist around an operational door. Which gaps need sealing, and how effectively, depends on the door and its intended performance.
For a fire-resisting doorset, the priority may be maintaining fire resistance and restricting smoke passage. An acoustic door needs effective sealing around the perimeter and threshold because gaps allow sound to pass through. External doors may need protection against draughts, water, and weather, while doors in healthcare and other specialist environments may have additional requirements for hygiene, accessibility, and ease of operation.

One seal may satisfy several requirements but never assume it. The specification should be based on appropriate evidence for the required performance.

Intumescent seals for fire doors

Ask for "intumescents" in the door industry, and most people will know exactly what you mean. Intumescent seals are widely used around fire-resisting doors and are designed to expand when exposed to heat, helping to seal the gap between the door leaf and frame and maintain the integrity of the doorset during a fire.

There is, however, no universal intumescent seal for every fire door. Different intumescent materials can activate at different temperatures and expand at different rates and pressures. The size, material and position of the seal therefore need to correspond with the evidence for the particular door construction. Simply adding an intumescent seal to an ordinary door does not turn it into a fire door, nor should a different seal be substituted simply because it fits the same groove.

This is particularly important with pairs of doors, where seal behaviour at the meeting stiles can affect how the two leaves perform during a fire. For new fire doors and doorsets, refer to the relevant test evidence, certification and information provided by the manufacturer when establishing which intumescent seal is required.

What is the difference between an intumescent seal and a smoke seal?

Although the terms are sometimes used interchangeably, intumescent and smoke seals perform different functions. An intumescent material reacts when exposed to fire temperatures. A smoke seal is intended to restrict the passage of cold smoke through the gaps around a closed door before those temperatures are reached.

Where both fire resistance and smoke control are required, the doorset may use a combined intumescent and smoke seal or separate products, depending on its specification and supporting evidence. A perfectly intact intumescent strip does not necessarily provide cold smoke control. At the same time, a damaged smoke-control element may affect the performance of a combined seal even though the intumescent material itself appears undamaged.

Brush seals or fin seals: what is the difference?

Smoke seals are commonly available with either a brush or flexible fin. Brush seals have been used for decades and remain an effective solution in suitable applications. However, the brush itself creates friction as the door opens and closes, and the spaces between the filaments make it less effective where acoustic containment is also required.

Flexible fin seals create less resistance as the door opens and closes and generally restrict sound better than brushes, particularly when several fins are used. They are also easier to keep clean, which can be an advantage in hospitals and other hygiene-sensitive environments.

That doesn't mean fins are always the right choice. It depends on what the door needs to achieve and how it needs to operate.

Acoustic door seals

Sound exploits gaps around a door, so the acoustic performance of the door leaf alone tells only part of the story. Effective acoustic sealing usually requires addressing the gaps around the perimeter and at the threshold.

Acoustic perimeter seals are designed to maintain contact between the door and frame when the door is closed. Depending on the product and application, the same sealing system may also provide smoke or fire performance. The threshold is particularly important, so acoustic specifications often combine perimeter seals with an automatic drop seal.

Threshold seals and automatic drop seals

The gap beneath a door presents a different challenge from the gaps around its head and jambs. The door still needs to swing freely over the floor, so a fixed seal cannot simply fill the available space in every application.

An automatic drop seal is fitted into or onto the bottom of the door and lowers when the door closes, forming a seal against the floor or threshold. When the door opens, the seal retracts so that it does not drag across the floor. Depending on the product and supporting evidence, drop seals can contribute to acoustic, smoke and other sealing requirements.
Consider threshold sealing as part of the complete door set, not an afterthought. The gap, floor finish, threshold detail and required performance all affect the appropriate solution.
Weather seals for external doors

External doors have a different set of sealing problems. Wind, rain, draughts, and temperature changes all need to be considered, and seals may be required around both the perimeter and threshold.

The right weather seal depends on the door construction, location and degree of exposure. A sheltered entrance will have different requirements from an external door exposed to driving rain, for example. Effective weather sealing therefore means treating the gaps around the entire door rather than focusing on one edge in isolation.

Door seals for glass doors

Glass doors need a different approach to sealing because there is no timber door edge or frame to route out for a conventional seal. The seal is often visible too so that a bulky solution can spoil the appearance of an otherwise minimal glass door.

Seals designed specifically for glass doors include options for the perimeter and threshold. The right product will depend on the thickness and type of glass, how and where the seal can be fixed, and what it needs to achieve. That might be reducing sound transfer, controlling smoke or closing the gap beneath the door.

What seals can be used on sliding doors?

Sliding doors cannot be sealed in the same way as conventional hinged doors because the door leaf needs to move laterally past the surrounding structure. Sealing must therefore accommodate that movement while controlling the gaps around the door when it is closed.

Different solutions are available for the vertical edges and threshold, and the right combination depends on the door construction and the level of acoustic, smoke, or other performance required. This is another situation where selecting a seal purely by its dimensions can lead to the wrong result.

Can one door seal do more than one job?

Yes. Many modern door seals are designed to provide more than one type of performance. A perimeter seal might provide both acoustic and smoke containment, for example, while a combined fire and smoke seal incorporates an intumescent element alongside a flexible smoke seal.

That does not mean that one function automatically guarantees another. A product intended primarily as a smoke seal should not be assumed to provide the acoustic performance required for a particular project, and an intumescent seal should not be assumed to provide smoke control unless it has been designed and evidenced to do so.

Where several performance requirements apply to the same door, look for a sealing system with appropriate evidence for each.

How do I choose the right door seal?

Start with the door, not the seal. Establish what the doorset must achieve, whether that is fire resistance, smoke control, acoustic containment, weather protection, or a combination of requirements.

Next, consider where sealing is required. The head and jambs, meeting stiles on pairs of doors and the threshold can present different problems and may need different products. For fire-resisting doors in particular, check the relevant test evidence and certification rather than assuming that a particular size or type of intumescent seal is interchangeable with another.

Door operation matters too. Seals should not introduce unnecessary resistance or make a door difficult to use, particularly where accessibility is a consideration. Finally, look at the complete doorset. Even a well-chosen seal cannot compensate for an unsuitable door construction, excessive gaps or a sealing system that fails to address another part of the door.

Need help specifying a door seal?

With so many different types of door seals, and an increasing number of doors required to meet several performance requirements at once, choosing the right product isn't always as simple as matching a seal to a gap.

Norseal's technical team can help identify a suitable sealing solution for fire and smoke, acoustic, threshold, weather, glass and specialist door applications. Tell us about the door, the performance you need to achieve and the evidence available, and we can help you work through the options.

Door seal FAQs

What type of door seal do I need?

Start with what the door needs to do. Is the priority fire protection, smoke control, sound reduction or keeping out weather? From there, consider the door itself, where the gaps need sealing, and which products deliver the right performance for the job.

What are intumescent seals?

Intumescent seals are used on fire-resisting doors and expand when exposed to heat. The correct material, size, and position should match the evidence for the door or door set; fitting an intumescent strip does not, by itself, make a door fire resistant.

Is an intumescent seal the same as a smoke seal?

No. Intumescent seals react to heat during a fire, while smoke seals restrict the passage of cold smoke around a closed door. Where both functions are required, you may use separate or combined fire and smoke seals.

What is the difference between brush and fin smoke seals?

Brush and fin seals can both provide smoke control in suitable applications. Flexible fin seals can offer lower friction and better acoustic containment than traditional brush seals, but the correct choice depends on the required performance and the supporting test evidence for the door.

Do acoustic doors need seals at the bottom?

Effective acoustic sealing normally needs to address the threshold as well as the head and jambs. Automatic drop seals are commonly used because they seal against the floor when the door closes and retract when it opens.

Can one door seal provide fire, smoke and acoustic performance?

Some door seals are designed and tested for more than one performance requirement. Don't assume performance in one area guarantees another; check the evidence for each requirement.

Can I use any intumescent seal that fits the groove?

No. Intumescent materials can differ in activation temperature, expansion and pressure. For fire-resisting doors, the seal should match the relevant test evidence, certification, or the door manufacturer's specification.

Can door seals make a door harder to open?

Yes. Some seals create more resistance than others and can make a door harder to open. This is especially important for doors that must meet accessibility requirements, where a low-friction seal can help keep opening forces down.

What seal should I use on a glass door?

Use a sealing system designed for the glass thickness, fixing method, available clearance and required performance. Glass doors may need acoustic, smoke, perimeter or threshold sealing without conventional routed-in seals.

Can sliding doors be sealed?

Yes, but sliding doors need seals that accommodate lateral movement. The right perimeter and threshold solution depends on the door construction and whether you need acoustic, smoke, or other performance.