Quantity rules for smoke barriers (GB/T 50854-2024 Table N.3.1, m2) and compliance check of the droop depth against the smoke reservoir (GB 51251-2017)

Topic Positioning

Quantity-calculation rules and takeoff caliber for smoke barriers (BOQ code 011303003, "other ceiling decoration"), and the compliance benchmark of their droop depth against the smoke-reservoir thickness.

Core Conclusions

1. Quantity rule (GB/T 50854-2024 Table N.3.1) Smoke barriers are a "other ceiling decoration" (code 011303) BOQ item (011303003), unit m2, rule "computed by area per design-shown dimensions"; item characteristics describe "1. form 2. material", work content "1. installation, fixing 2. actuator installation (if any)"; the "form" may be described as retractable, fixed, etc. (Table N.3.1 clause notes). Takeoff caliber: area = arrangement length x droop depth, both per design dimensions (length along the barrier run, depth along clear height); not by opening area or vertical projection, and multi-section assemblies total per design overall dimensions. Example: design 1.7 m x 1.3 m (1700 x 1300 mm) -> single-panel area = 1.7 x 1.3 = 2.21 m2; identical panels accumulate as "single area x count", count per the drawings.

2. Droop-depth compliance check (GB 51251-2017; does not change measurement) Depths of smoke-barrier separation facilities shall not be less than the prescribed smoke-reservoir thickness; in spaces with ceilings, where ceiling openings are uneven or the opening ratio is <= 25%, the plenum height does not count into the reservoir thickness (Clause 4.2.2). Reservoir thickness: natural exhaust >= 20% of clear height and >= 500 mm; mechanical exhaust >= 10% and >= 500 mm; and the reservoir bottom shall be above the minimum clear height for safe egress, computed per Clause 4.6.9 (Clause 4.6.2). Retractable barriers shall also meet the technical requirements of GA 533.

3. Construction-check benchmark (design/acceptance caliber) T/BCQMS 02-2024 Clause 7.15.4: barriers shall be of non-combustible material; single-section width of rigid barriers <= 2000 mm, flexible <= 4000 mm; the gap between retractable barriers and structure (column or wall) <= 60 mm; continuous barriers of two or more sections shall have no gaps between sections and overlap >= 100 mm; the manual button shall be fixed 1.30-1.50 m above the floor, operable and visible; with ceilings the droop is >= 500 mm below the ceiling with sealing above by smoke-barrier material; without ceilings >= 500 mm below beams or slabs, and greater than the exhaust-fan inlet height.

Applicable Boundaries

• The measurement rule applies to building/decoration works under the GB/T 50854-2024 BOQ caliber; reservoir and construction requirements are design/acceptance compliance calibers for checking design dimensions, not changing quantities.
• "1.7 x 1.3"-type takeoff presupposes both figures are design dimensions (length x depth); where drawing dimensions mean something else (e.g., including plenum sealing), adjust per the design notes.
• The construction-check section cites a Beijing association standard; other regions follow local acceptance/fire standards; retractable barriers additionally need product-standard checks and separate pricing of "actuator installation".
• Quota assembly: some regions lack dedicated smoke-barrier sub-items — convert from similar material/structure sub-items or compile supplementary sub-items.

Further Reading

• GB/T 50854-2024 Standard for Measurement of Building and Decoration Works, Appendix N, Table N.3.1 "other ceiling decoration" (code 011303, incl. 011303003) and clause notes (form description).
• GB 51251-2017 Technical Standard for Smoke Management Systems of Buildings, Clauses 4.2.2 (barrier depth and reservoir), 4.6.2 (reservoir thickness), 4.6.9 (minimum clear height).
• GA 533 Smoke Barriers (retractable barrier performance); T/BCQMS 02-2024 Beijing Changcheng Excellent Quality Evaluation Standard, Clause 7.15.4.