Functional doors, also known as special doors, are used when standard doors fail to meet the desired requirements such as sound or thermal insulation. What matters to the consumer is the test certificate supplied with a functional door. It confirms that, according to testing by a commissioned institute, the functional door meets the described properties such as sound insulation or burglary resistance class. In order to meet the requirements placed on a door, the necessary components are integrated into the door leaf. As a result, functional doors differ visually from standard doors either not at all or only slightly.
Climate category for functional doors
An important aspect when buying a functional door is the climate category to which it is assigned. This criterion has no connection with the thermal insulation of a special door, but refers instead to the hygrothermal stress placed on a door. If the ambient temperature or air humidity is too high, the material built into the door reacts by changing its shape and warping. In this case, a sound-insulating or thermally insulating door would lose part of its functionality. This applies to all door types with the exception of the fire door, as separate regulations apply here.
Special doors for thermal insulation
Special doors for thermal insulation support the energy efficiency of a house and are available in several climate category classes. If a climate category is chosen that does not match the ambient temperature, the door warps and loses its functionality. Doors for thermal insulation are preferably fitted as part of an energy-efficiency refurbishment or, ideally, in new-build construction, and additionally reduce heat loss. These special doors are available as internal and external doors and are filled with insulating material. A drop-down bottom seal, which adjusts exactly to the floor level, complements their functionality. The insulating effect is stated as a thermal transmittance value, which should be in the region of 1.2W/m2K.
Special doors for sound insulation
Modern sound-insulating doors are used as apartment entrance doors in multi-family buildings, where they shield residents from external noise. As an internal door, these doors screen off rooms and at the same time prevent sound from escaping the room. In this way, these special doors reliably give a room the privacy it needs. The door leaf of a high-quality sound-insulating door is always at least two layers, and ideally multiple layers, in construction. Sound-insulating doors make use of the spring-mass principle. The individual layers form the largest possible mass, while the filling material fitted between them serves as the spring. Door leaves constructed in this way achieve sound insulation of 35 to 45 decibels. As sound penetrates the smallest gaps, good doors have special drop-down seals on the lower edge of the door.
Special doors for damp and wet rooms
These special doors are used only when the door leaf of an internal door is exposed to extremely high air humidity or heavy splash water over a long period. Typical areas of use for wet-room doors are shower rooms in indoor swimming pools, sports halls or also in hospitals. Wet-room doors are made exclusively of uPVC and feature corrosion-protected hardware.
If the door leaf is exposed to higher air humidity or splash water only for a short time, a damp-room door is sufficient. Like the wet-room door, the functional door designed for damp rooms is also equipped with corrosion-protected hardware.
Special doors as burglary protection
Burglar-resistant functional doors are characterised by substantially reinforced components in the area of the general weak points of a door leaf and the hardware. In addition, these special doors have integrated locking systems which, when the door lock is closed with the key, create a connection between the door leaf and the door frame that reaches deep into the frame. Burglar-resistant doors are classified according to DIN EN 1627 into six resistance classes, RC1 to RC6. For the private sector, according to the police, a door of class RC3 is sufficient. Only commercial businesses should protect their premises against burglary with functional doors of classes RC4 to RC6.
Special doors as fire and smoke protection
The fire door, referred to in technical jargon as a fire-protection closure, is always a self-closing door made of heat-resistant material. All the building-code requirements necessary for this are governed by DIN 4102. This includes the testing of these doors. This is because fire doors receive their valid approval exclusively from the Institute for Building Technology and must be marked as such with a plaque.
The smoke-protection door is different: indoors, in the event of a fire, it protects residents from toxic smoke for approximately ten minutes. These doors are normal internal doors fitted with special seals. However, as this door type provides no appreciable protective function, it is only rarely installed in living spaces.
