Drop down door seals restrict the passage of noise, smoke and air underneath timber and glass doors. They can be surface mounted or integrated with the door. When a door closes, they drop automatically to create a seal.
In the event of a fire, intumescent strips will seal the gaps around the perimeter of the door set on three edges between the frame and the door.
A gap of up to 10mm is permissible underneath a fire door. However, if Building Regulations specify that smoke protection is required, then the maximum gap underneath the door reduces to 3mm. In this case, a drop down seal may be required to maintain the integrity of the fire door.