Choosing an Automatic Drop Seal
An automatic drop seal is fitted into or onto the bottom edge of a door and lowers towards the floor when the door closes.
A small actuator makes contact with the frame as the door approaches the closed position, causing the seal to descend and close the gap beneath the door. When the door opens again, the seal automatically retracts.
This makes automatic drop seals particularly useful where acoustic performance, smoke control or draught reduction is required without creating a seal that continuously rubs across the floor.
Acoustic Door Drop Seals
The gap beneath a door can significantly influence the acoustic performance of the complete door assembly.
Even where the door leaf itself provides good sound insulation, an uncontrolled gap at floor level can allow sound to pass through.
An acoustic drop seal closes this gap when the door shuts, helping the complete door set achieve better acoustic separation.
Drop seals are therefore commonly considered for offices, meeting rooms, hotels, apartments, healthcare facilities, bedrooms and other sound-sensitive spaces.
The acoustic performance of the complete door set will depend on the door leaf, frame, perimeter seals, drop seal and installation rather than the drop seal alone.
Drop Seals for Fire & Smoke Doors
Automatic drop seals can also form part of a fire and smoke door specification.
Where smoke control is required, the seal beneath the door helps restrict smoke movement through the threshold gap when the door is closed.
Selected drop seals are also tested for use within fire-door assemblies.
However, the suitability of a particular drop seal should always be confirmed against the specific fire-door test evidence, certification and permitted installation arrangement.
A drop seal should be treated as one component of the complete tested doorset rather than as something that independently gives a door its fire rating.
Rebated Drop Seals
A rebated drop seal is recessed into a routed channel within the bottom of the door.
This provides a discreet installation because most of the mechanism is concealed once fitted.
Rebated drop seals are particularly suitable where a clean architectural appearance is required and are commonly installed during door manufacture or while the door is being prepared for its ironmongery.
The groove dimensions must correspond with the particular drop-seal profile.
Compact Drop Seals
A compact automatic drop seal can be particularly useful where there is limited space available within the bottom of the door.
The Norseal NOR810S in our range uses a smaller profile than the standard NOR810, reducing the amount of material that needs to be routed from the door.
This can be useful for door manufacturers and installers where a more compact installation is required.
Drop Seals & Door Thresholds
A drop seal can operate against the finished floor or against a compatible door threshold.
For the best result, the surface beneath the seal should provide a suitable and reasonably consistent contact area.
Where the floor changes level or finish beneath the doorway, a threshold can provide a defined surface for the drop seal to meet.
The complete arrangement should be considered together, particularly where acoustic, smoke, weather or accessibility performance is required.
Choosing the Correct Drop Seal Length
Automatic drop seals are available in different lengths to suit different door widths.
The selected seal should suit the width of the door and the manufacturer's permitted cutting or adjustment range.
Many drop seals can be shortened during installation, but there will normally be a limit to how much material can be removed without affecting the mechanism.
Always check the individual product instructions before cutting.
Frequently Asked Questions
What is an automatic drop seal?
An automatic drop seal is a door-bottom seal that lowers when the door closes and retracts again when the door opens.
This allows the gap beneath the door to be sealed without the gasket continuously dragging across the floor.
What is a drop seal used for?
Drop seals are commonly used to help improve acoustic sealing, smoke control and draught reduction beneath doors.
The exact performance depends on the drop seal and the complete door assembly.
Do drop seals help reduce noise?
Yes. Closing the gap beneath the door can significantly improve the acoustic sealing of a doorset.
For high acoustic performance, the drop seal should normally be considered together with suitable perimeter seals and an appropriately rated door and frame.
Can a drop seal be used on a fire door?
Selected automatic drop seals are tested for use in fire-door applications.
Always check the individual product's test evidence and confirm that the installation is compatible with the particular fire-door specification.
What is the difference between a drop seal and a threshold?
A drop seal is fitted to the door and moves automatically, while a threshold is fixed at floor level.
The two products can be used together where the threshold provides the surface onto which the drop seal closes.
Does a drop seal drag across the floor?
Normally no.
The seal retracts when the door opens and only lowers as the door approaches the closed position. This is one of the main advantages of an automatic drop seal compared with a permanently projecting door-bottom seal.
Can an automatic drop seal be cut to size?
Many automatic drop seals can be shortened within a permitted range.
The amount that can be removed varies by model, so always follow the manufacturer's cutting instructions.
Can drop seals be used on double doors?
Selected drop seals can be used on both single and double-leaf timber doors.
The overall sealing arrangement at the meeting stiles and threshold should also be considered when specifying a double-door set.
Need Help Choosing a Drop Seal?
The correct drop seal will depend on your door width, door construction, acoustic requirements, smoke-control requirements and fire-door specification.
Roundtower Hardware supplies Norseal automatic drop seals in Ireland in a variety of lengths and profile sizes for residential and commercial timber doors.
Browse our range online or contact our team if you need help identifying the correct drop seal for your door set.
