Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Replies 2 replies
  • Subscribers 38 subscribers
  • Views 864 views
  • Users 0 members are here
Options
You may also be interested in

Fire detection on perforated raft ceilings

Mikkywakky

We have an office project where perforated raft ceilings have been used, suspended from a concrete slab. Smoke detection has currently been installed in the void above; however, the perforations in the ceiling do not meet the requirements of BS 5839-1 2025 so this should be treated as a solid ceiling. 

The following is an image of the ceiling which shows 150mm gaps between the raft sections.

We understand that detection will be required below the ceiling but should this be provided for each raft section on the basis that smoke would rise up between each raft, or is there an allowable gap between the rafts where they can be treated as a continuous ceiling?

Parents
  • 0
    BS 5839‑1 treats perforated rafts as solid ceilings unless perforations meet the standard’s criteria for smoke passage. With 150 mm gaps between rafts, these are effectively separate ceiling sections, so detectors should be installed below each raft or positioned to ensure coverage per spacing rules. A continuous ceiling assumption isn’t valid unless gaps exceed the minimum defined in BS 5839‑1 Annex guidance.
Reply
  • 0
    BS 5839‑1 treats perforated rafts as solid ceilings unless perforations meet the standard’s criteria for smoke passage. With 150 mm gaps between rafts, these are effectively separate ceiling sections, so detectors should be installed below each raft or positioned to ensure coverage per spacing rules. A continuous ceiling assumption isn’t valid unless gaps exceed the minimum defined in BS 5839‑1 Annex guidance.
Children
No Data

Community Rules & Guidelines