Horizontal extension of bathroom floor waterproofing at door openings (at least 500mm outward and 200mm to each side): distinguishing it from the 250mm wall-upturn criterion, with threshold-stone / curb water-stop details and BOQ item coding

Topic Positioning

Horizontal extension requirements and criteria for the waterproofing of bathroom floors at door openings: the code criteria for outward extension length and width to each side (not less than 500mm / 200mm), how to distinguish them from the easily confused "wall upturn height of 250mm", plus the accompanying water-retaining details (threshold stone / curb / level difference) and the BOQ item coding rules.

Core Conclusions

1. Primary criterion for the door-opening extension. JGJ 298-2013 "Technical Specification for Waterproofing of Residential Interior Work", clause 5.4.1 (original text): "The waterproofing of floors shall extend horizontally at door openings, with an outward extension length of not less than 500mm and a width of not less than 200mm to each side." The same criterion also appears in: DB11/T 1811-2020 "Technical Specification for Waterproofing of Kitchens and Bathrooms" clause 5.7.2 (adding "and turning up the walls to not less than 300mm above the indoor finished floor"); DB33/T 1147-2018 "Technical Specification for Building Waterproofing" clause 5.5.14 (also requiring that "threshold stones shall be bedded full in polymer-modified cement waterproofing mortar"); DBJ 43/T 302-2025 "Technical Standard for Prevention of Common Quality Defects of Residential Projects" clause 5.1.4 (applicable to floor waterproofing of "bathrooms without wet/dry separation", and requiring "measures at the doorway to prevent water spilling out").

2. Where "250" comes from - the wall upturn height, not the door extension. GB 55030-2022 "General Code for Waterproofing of Buildings and Municipal Engineering", clause 4.6.4 (original text): "At the interface between water-use and non-water-use floors, measures shall be taken to prevent water flowing into non-water-use rooms. The upturn height of wall waterproofing in shower areas shall not be less than 2000mm and not lower than the shower head. The upturn height of wall waterproofing at wash-basins and other water points shall not be less than 1200mm. The upturn height of wall waterproofing at other wall areas shall not be less than 250mm." GB 50352-2019 "Unified Standard for Civil Building Design", clause 6.13.3, puts both figures in one sentence (original text): "The upturn height of the waterproofing along walls should not be less than 250mm; at door openings the waterproofing may be extended horizontally outward, with an extension width of not less than 500mm and a width of not less than 200mm to each side." - 250mm governs wall upturns while 500/200mm govern door-opening extension; they are different checkpoints and cannot substitute for each other; no current standard contains a rule of "250mm outward extension at the door".

3. Measurement in practice. (1) Outward: measure not less than 500mm from the doorway (threshold stone / wall edge) toward outside the door; (2) Sides: taking the two jamb edges as the datum, extend not less than 200mm beyond each side (the extension is convex in plan; total width = clear door width + 2 x 200mm minimum); (3) Termination: DB11/T 1076-2023 "Standard for Quality Acceptance of Residential Decoration Engineering", clause 7.1.7 item 4, requires that "the floor waterproofing shall extend onto the walls at both sides of the door opening".

4. Accompanying water-retaining details (which, together with the door extension, constitute the "measures preventing water spilling out / flowing into non-water-use rooms"). GB 55030-2022 is a full-text mandatory code; clause 4.6.4 ("measures shall be taken to prevent water flowing into non-water-use rooms") is a mandatory requirement, and its commentary lists interface measures including "the water-use room being lower than the non-water-use room, installing a threshold stone bedded in waterproofing mortar, and extending the waterproofing into the non-water-use room". DB11/T 1811-2020 clause 5.7.8: "A threshold stone should be installed at the bathroom doorway, and beneath it a curb of the same width as the wall should be formed with dry-mix cement mortar." Clause 5.2.4 of the same specification: "Bathroom floors should be not less than 20mm lower than the floors of adjacent rooms, or a water-stop threshold should be formed; where barrier-free design applies, they should be 15mm lower than the finish of the adjacent room and transitioned by a ramp." GB 50352-2019 clause 6.13.3: floors requiring waterproofing should be 15.0mm lower than adjacent floors. The commentary to DB33/T 1147-2018: horizontal extension of the waterproofing combined with full-bed polymer cement waterproofing mortar bedding of the threshold stone can "prevent the capillary action of water".

5. Rationale and quantity take-off. Commentary to JGJ 298-2013 clause 3.0.1: the outward extension at doorways is intended "to avoid leakage of wastewater through rooms without waterproofing into rooms on the floor below". Quantity basis: GB/T 50854-2024 "Standard for Method of Measurement of Building and Decoration Works", Annex J, item J.6.8 (original text): "Where the upturn height of floor waterproofing exceeds 300mm, it shall be coded under the corresponding wall waterproofing item." That is, the door-opening extension is merged into the floor waterproofing quantity (to the dimensions shown on the design drawings), and only the portion turned up more than 300mm is coded as wall waterproofing; a separate "door-opening extension" BOQ item is generally not billed.

6. Practical judgment: where a site detail or price build-up uses "250mm outward extension at the door", it falls short of the not-less-than-500mm requirement of JGJ 298-2013 and most local standards and should be corrected through drawing review / designer confirmation; it must not be copied as it stands.

Applicability Boundaries

• The primary criterion addresses residential interior waterproofing (the scope of JGJ 298-2013); public buildings follow GB 55030-2022 and GB 50352-2019.
• 500/200mm are "shall not be less than" lower limits; GB 50352-2019 uses "should not be less than". Local standards apply by the project's administrative region; DB11/T 1811-2020 adds the stricter requirement that "the extension turns up the walls to not less than 300mm above the indoor finished floor"; individual projects follow the design documents and the local drawing-review requirements.
• The "no wet/dry separation" qualifier appears only in DBJ 43/T 302-2025; the national criteria set no such precondition.
• For barrier-free design, the level difference between the bathroom and the adjacent room follows DB11/T 1811-2020: 15mm with a ramp transition, instead of 20mm.
• Quantity take-off follows the measurement standard / quota agreed in the contract.

Further Reading

• JGJ 298-2013 clause 5.4.1 (door-opening extension), clause 3.0.1 and its commentary (principle of combining prevention with drainage, preventing water spilling out)
• GB 55030-2022 clause 4.6.4 and its commentary (full-text mandatory code)
• GB 50352-2019 clause 6.13.3 (where 250mm and 500/200mm appear in one sentence)
• DB11/T 1811-2020 clauses 5.7.2, 5.7.8 and 5.2.4
• DB11/T 1076-2023 clause 7.1.7
• DB33/T 1147-2018 clause 5.5.14 and its commentary
• DBJ 43/T 302-2025 clause 5.1.4
• GB/T 50854-2024 Annex J, item J.6.8