Gap under doors

[Guest Dave]

Hi, the steel doors in our building have gaps under the doors 8-9mm. Some of the steel doors have drop down seals on them but some don’t. Is a 10mm gap on steel door acceptable or should it be less?

[Neil ashdown]

For metal fire doors there is no standard for this so it must be as required by the particular door manufacturer. However, generally I would work on 10mm max for a fire door and where smoke protection is required seal the gap to the floor with a threshold seal/plate combination. If it is impractical to fit a threshold seal then the gap should be 3mm max.