Drainage & Sewer System Inspection

Per UNI EN 12056 & DM 37/08, the building drain (horizontal pipe inside the building) must be minimum 3" for a single toilet, 4" for two or more toilets or the building sewer. Slope must be 1/4" per foot for 3" pipe, 1/8" per foot for 4" pipe. Pipe material must be approved (PVC Schedule 40, ABS, or cast iron). Cleanouts required every 100 feet and at every change of direction >45°.

1. Verify building drain pipe size: 3" minimum (4" recommended for whole house)

2. Check slope with level: 1/4"/ft for 3" pipe, 1/8"/ft for 4" pipe

3. Confirm pipe material is approved (PVC Sch 40 most common, cast iron for noise reduction)

4. Verify cleanouts: at base of each stack, every 100' horizontal, at direction changes

5. Check all joints: PVC primer + cement, ABS cement, no-hub bands for cast iron

6. Verify building sewer connection to municipal sewer or septic (proper depth and slope)

7. Check for proper bedding material around building sewer (sand or pea gravel)

- Insufficient slope — sewage backs up, solids settle and block pipe (bellies)

- Missing cleanouts — impossible to clear blockages without cutting pipe

- Improper joints — leaks allow root infiltration, soil contamination, sewer gas

Per UNI EN 12056 & DM 37/08, branch drains must be sized for the fixture units they serve: 1.5" (1–3 DFU), 2" (4–8 DFU), 3" (20+ DFU with toilet). Every fixture must connect through a properly sized trap. Branch drains must slope minimum 1/4" per foot. Maximum horizontal distance from trap to vent per pipe size: 1.5" = 6', 2" = 8', 3" = 12'.

1. Verify each branch drain pipe is sized for the fixture units it serves

2. Check slope: minimum 1/4" per foot on all branch drains

3. Confirm each fixture has a proper P-trap (not S-trap)

4. Measure trap arm length — must not exceed code maximum before vent connection

5. Verify no cross-connections between fixture drains that could cause cross-contamination

6. Check that laundry standpipe is 18–30" above floor (trap below floor)

7. Verify floor drain trap primer connection (if code-required to prevent trap dry-out)

- Trap arm too long — trap siphons dry, sewer gas enters living space

- S-trap used (gravity siphons water seal) — must be P-trap with proper vent

- Laundry drain too small (1.5") — cannot handle washer discharge rate, overflows

Per UNI EN 12056 & DM 37/08, every fixture trap must be vented. Main vent stack must extend through the roof (6" minimum above roof in normal climates, 12" in snow areas, 10' from any operable window). Vent must be minimum 1.25" for single fixture, 2" for bathroom group, 3" minimum for main stack. Vents must be installed to drain back to the drainage system by gravity.

1. Verify main vent stack extends through roof at proper height

2. Check vent flashing at roof penetration — properly sealed and integrated with roofing

3. Confirm each fixture has a vent within code distance of trap

4. Verify vent pipe sizes meet code minimums for fixture units served

5. Check vent routing: rises above flood rim before going horizontal

6. Verify no vent is trapped (horizontal section that could accumulate moisture)

7. Confirm vent termination is at least 10' from operable windows/air intakes

- Vent termination too close to window — sewer gas enters home

- Vent flashing improperly installed — roof leak at penetration

- Undersized vent — gurgling at fixtures, slow drainage

- Trapped vent — frozen condensation blocks airflow in winter

Per UNI EN 12056 & DM 37/08 and local sewer authority, the building sewer lateral must connect to the public sewer main at the proper depth and with approved fittings. Minimum pipe size is typically 4" (6" in some jurisdictions). Pipe material for the sewer lateral must be approved for below-grade use (PVC SDR 35, ductile iron). Backwater valve may be required in flood-prone or low-lying areas.

1. Verify sewer lateral pipe size meets municipal requirements (4" minimum typical)

2. Confirm pipe material is approved for underground use (PVC SDR 35 most common)

3. Check connection to main is at proper depth and angle per sewer authority specs

4. Verify slope: 1/8" per foot minimum for 4" pipe (1/4" preferred)

5. Check for backwater valve if required (prevents municipal sewer backup into home)

6. Confirm sewer lateral was inspected by camera before backfill (no bellies, root intrusion)

7. Verify proper bedding and backfill around sewer pipe (sand/gravel, no rocks)

- Sewer lateral has belly (low spot) — collects waste, recurring clogs

- Root intrusion at joints — trees planted too close to sewer line

- No backwater valve in flood area — sewer backup during heavy rain

- Pipe crushed by heavy equipment during backfill

Per UNI EN 12056 & DM 37/08, the complete DWV system must be tested before use. Air test: 5 PSI for 15 minutes. Water test: filled to highest point, 10' head minimum, 15 minutes. Camera inspection of sewer lateral recommended to verify no damage during construction. Final test must be witnessed by plumbing inspector before closing walls/floors.

1. Perform air test or water test on complete DWV system (per local code preference)

2. Run water through each fixture — verify proper drainage and no leaks

3. Check each trap holds water (pour water, wait 24 hours, check water level)

4. Camera inspect sewer lateral from cleanout to main connection

5. Verify all cleanouts are accessible and properly capped

6. Test backwater valve operation if installed

7. Document all test results and obtain inspector sign-off

- Air test leak — often at cleanout plug, test plugs, or cemented joints

- Camera reveals belly in sewer lateral — must be corrected before backfill

- Trap seal evaporates in unused fixtures — install trap primers for floor drains