Quantity calculation rules for roofing and waterproofing works: tiled roofs by sloped area, waterproofing upturns merged, drainage components by length/count (Beijing DB11/T 2382-2024 Clauses 4.10.19 to 4.10.28 + GB/T 50854-2024 Appendix J)

Topic Positioning

Quantity calculation rules for roofing and waterproofing works: the measurement bases for tiled/profiled-sheet roofs, roof waterproofing, drainage pipes and components, wall/floor/foundation waterproofing, protective layers and joint sealing, and movement joints. The primary evidence is Beijing DB11/T 2382-2024 "Construction Consumption Standard" Clauses 4.10.19 to 4.10.28, linked with the BOQ basis of Appendix J (roofing and waterproofing works) of GB/T 50854-2024 "Standard for Calculation of Quantities of Building and Decoration Works".

Core Conclusions

1. Tiled roofs, profiled-sheet and other roofs (4.10.19)

• "Tiled roofs, profiled-sheet and other roofs shall be calculated by the sloped area of the dimensions shown on the design drawings; the areas occupied by roof chimneys, vent-cowl bases, flues, small dormer windows and valley gutters shall not be deducted, and the overhanging eaves of small dormer windows shall not be added."
• Polycarbonate-panel roofs and daylighting roofs are calculated by area per the design dimensions shown, without deducting individual holes of not more than 0.30 m2; membrane-structure roofs by the horizontal projected area of the design dimensions; elevated fiber-cement ventilation slabs (on stool-type supports) by horizontal projected area, with the accompanying steel gratings and steel cover plates by length.

2. Roof waterproofing (4.10.20)

• Sloped roofs by the sloped area; flat roofs (including slope-forming to falls) by the horizontal projected area;
• The areas occupied by roof chimneys, vent-cowl bases, flues, small roof dormer windows and valley gutters are not deducted, and the corresponding upturned areas are not added;
• The upturned parts at roof parapets, expansion joints and skylights shall be merged into the roof quantity;
• Waterproofing of valley gutters, eaves gutters, overhanging eaves and canopies is taken by the developed area shown on the design drawings and merged into the roof quantity.

3. Drainage and components (4.10.21 to 4.10.23)

• Downpipes and air-conditioning drainage pipes by length per the design dimensions; hoppers, bends, drainage outlets and FRP short pipes by the numbers shown on the design; roof vent (breather) pipes, weep (discharge) pipes, vent cowls and roof access hatches by the numbers shown on the design.

4. Walls, floors, foundation waterproofing and associated rules (4.10.24 to 4.10.26, 4.10.16)

• Wall waterproofing by area per the design dimensions, without deducting individual holes of not more than 0.30 m2; the sides of pilasters and wall buttresses are merged into the wall quantity; membrane waterproofing batten strips by length.
• Floor waterproofing by area, without deducting partition walls and individual columns, buttresses, chimneys and holes each of not more than 0.30 m2 in area; upturned parts with a height not exceeding 300 mm are merged into the floor quantity.
• Clause 4.10.16: "Floor waterproofing with an upturn height not exceeding 300 mm shall be executed under the corresponding floor-waterproofing items; where the upturn height exceeds 300 mm, the corresponding wall-waterproofing items shall be executed."
• Foundation waterproofing by area, the upstand-beam parts merged by developed area; pile-head waterproofing by count; waterproof fabric by area; waterstops by length.
• Waterproof protective layers by area; joint sealing by length; movement joints by length (4.10.27 to 4.10.28).
• Related bases: Clause 4.10.9 - the construction consumptions of waterproofing works already include laps and the additional layers and edge termination at internal/external corners, post-cast strips, sump pits, elevator pits etc.; Clause 4.10.11 - waterproofing of valley gutters, eaves gutters, overhanging eaves and canopies may be executed under the corresponding roof-waterproofing items, and balcony waterproofing under the corresponding floor waterproofing/damp-proofing items.

5. BOQ linkage (GB/T 50854-2024 Appendix J) "The setting of quantity-list items of roofing, the content of item feature descriptions, the units of measurement and the quantity calculation rules shall follow the provisions of Table J.1.1." (roofing code 010901)

Applicable Boundaries

• The above rules come from the body of Beijing DB11/T 2382-2024 and serve the consumption-standard (quota) measurement basis; the BOQ basis follows GB/T 50854-2024 Appendix J - the two bases run in parallel and must not be mixed.
• "No deduction" is limited to the items listed in the provisions; the 0.30 m2 hole-deduction threshold applies only where the clause so states (e.g. polycarbonate-panel/daylighting roofs, wall waterproofing, floor waterproofing); other parts follow their own provisions.
• The 300 mm upturn line determines two things at once - whether the upturned part merges into the floor quantity, and whether the floor- or wall-waterproofing sub-items apply; measurement and item selection must stay consistent.

Further Reading

• DB11/T 2382-2024 Clauses 4.10.9, 4.10.11, 4.10.16, 4.10.19 to 4.10.28 (original text); waterproof layers, protective layers, drainage (water-storage) and filtration layers of planted roofs: Clauses 8.2.10 to 8.2.11 as referred to by Clause 4.10.12.
• GB/T 50854-2024 Appendix J "Roofing and Waterproofing Works", Table J.1.1 and the quantity calculation rules of each section, and Clause J.6.1 on item feature descriptions.