Indoor/outdoor boundaries for water-sewer, heating, gas, and fire-water pipes: scope of the 1.5m-outside-wall rule, manhole/valve attribution, and railway vs Beijing system differences

Topic Positioning

The indoor/outdoor boundary rules for water-sewer, heating, gas, and fire-water piping in building installation, the BOQ attribution of valves and wells at the boundary, and the second-level interface to municipal pipes — covering the national measurement caliber (GB/T 50856-2024) and railway (TB/T 10832-2024), Beijing (DB11/T 1835-2021, DB11/T 2382-2024), and Shenzhen (SJG 77-2020) differences.

Core Conclusions

1. National caliber — GB/T 50856-2024 Annex K K.9.1 (verbatim):

1. Water supply: 1.5m outside the building face; at the entrance valve where set;
2. Drainage: the first exit inspection well;
3. Heating: 1.5m outside the building face; at the entrance valve where set; with an outdoor entrance unit, at the circulation-pipe tee;
4. Gas: underground entries at the first indoor valve; above-ground entries at the first tee outside the wall. Points: the 1.5m rule applies only to water and heating; drainage divides at the first exit well; gas by entry type.

2. Boundary component attribution (SJG 77-2020, 6.1.4, verbatim):

1. Indoor/outdoor water systems at 1.5m outside the face (or the entrance valve); the valve belongs to 6.3 water/sewer works;
2. Indoor/outdoor drainage at the first exit inspection well; the well belongs to 6.16 outdoor installation works. I.e., valves to water/sewer works, wells to outdoor installation works; the two sides often sit in different chapters — prevent duplication or omission.

3. Second-level interface to municipal pipes (SJG 77-2020, 6.1.5, verbatim):

1. Water systems at the municipal connection point; connection work belongs to 6.16 outdoor installation;
2. Drainage at the municipal connection manhole; the manhole belongs to 6.18 municipal-support installation.

4. Fire-water pipes — GB/T 50856-2024 Annex J J.11.1:

1. Sprinkler pipes: 1.5m outside the face (or the entrance valve); pump-room pipes in high-rises at the pump-room outer wall;
2. Hydrant pipes: water-supply rules — 1.5m outside the face (or the entrance valve). Beijing DB11/T 2382-2024, 6.9.2: fire-system indoor/outdoor pipes at 1.50m outside the building face; overhead fire piping within plant areas executes the fire-works items.

5. Railway difference — TB/T 10832-2024 Vol. 11 volume notes (verbatim): (1) Water: at the entrance meter or junction well; direct entry at the building face. (2) Drainage: at the first exit inspection well (or septic tank). Note: railway has no 1.5m band — water at the meter/junction well; only direct entries use the building face (no 1.5m); drainage at the first exit well or septic tank.

6. Beijing construction caliber — DB11/T 1835-2021 (for new/rebuilt outdoor city water and sewer pipes in Beijing): Indoor/outdoor water and sewer lines divide at outdoor wells or gate valves: drainage — the pipe from the first inspection well (incl.) out of the building is external; water — the pipe beyond the first gate-valve well (incl.) before entry is external; reclaimed-water works may follow the water-pipe provisions.

Applicable Boundaries

• "1.5m outside the face" applies only to water, heating, and fire water; drainage (wells) and gas (valve/tee) have their own rules — no mixing.
• Boundary rules follow the executed standard system: railway TB/T 10832-2024 (no 1.5m); Beijing locals; Shenzhen SJG 77-2020; national GB/T 50856-2024 for BOQ measurement. Cross-system use causes itemization and pricing errors.
• The two sides of a boundary often sit in different chapters (water/sewer vs outdoor installation vs municipal support) — fix the boundary, then the attribution, to avoid duplication or omission.
• Construction-technical calibers (DB11/T 1835-2021) and pricing calibers (SJG 77-2020, DB11/T 2382-2024) serve different purposes; contracts fix the executed standard.
• Heating entrance-unit forms and gas entry type (underground/above ground) move the boundary — judge per drawings.

Further Reading

• GB/T 50856-2024 Annex K K.9.1; Annex J J.11.1.
• SJG 77-2020, 6.1.4, 6.1.5.
• TB/T 10832-2024 Vol. 11 volume notes, Chapter 3 outdoor pipe laying.
• DB11/T 1835-2021 general provisions.
• DB11/T 2382-2024, 6.9.2.