4.3 DWV Materials, Fittings, Joints, Supports & Underground Installation
Key Takeaways
IPC Table 706.3 allows a sanitary tee only for a horizontal-to-vertical change, and a short-sweep fitting for a vertical-to-horizontal change only in 3-inch and larger pipe or a 2-inch-or-smaller fixture drain.
Double sanitary tees may not receive back-to-back water closets or pumping-action fixtures, unless each water closet's outlet is at least 18 inches in horizontal developed length from the tee (IPC 706.3).
PVC DWV joints need a purple ASTM F656 primer and a solvent cement that is not purple and conforms to ASTM D2564 (IPC 705.10.2), while ABS uses ASTM D2235 cement with no primer requirement (IPC 705.2.2).
IPC 707.1 prohibits cement or concrete joints, mastic or hot-pour bituminous joints, rolling O-rings between different pipe diameters, saddle fittings, and solvent joints between different plastics except one ABS-to-PVC joint at the building drain and sewer connection.
Table 308.5 supports cast-iron pipe every 5 feet horizontally (10 feet with 10-foot lengths) and 15 feet vertically, and ABS and PVC every 4 feet horizontally and 10 feet vertically.
Why this section matters
General Knowledge and System Installation questions often ask whether a fitting, joint or support is legal. The 2021 IPC answers in Tables 702.1–702.4, Table 706.3, Section 705 (joints), 707 (prohibited joints) and Table 308.5.
Materials (702)
| Use | Table | Main materials |
|---|---|---|
| Above-ground soil, waste and vent | 702.1 | ABS (ASTM D2661 solid, F628 cellular core, F1488 composite); PVC (ASTM D2665 solid, F891 cellular core, F1488); cast iron (ASTM A74 hub and spigot; ASTM A888 and CISPI 301 hubless); copper pipe; copper tube Types K, L, M and DWV; galvanized steel; glass; PVDF; polyolefin; stainless steel (ASME A112.3.1) |
| Underground building drainage and vent | 702.2 | ABS, PVC, cast iron, copper Types K, L, M and DWV, PE (ASTM F714), PVDF, polyolefin, stainless 316L. No galvanized steel underground |
| Building sewer | 702.3 | The above plus sewer-and-drain PVC (SDR 35, ASTM D3034), ABS sewer pipe (D2751), concrete, vitrified clay, polypropylene. Copper K or L only |
- 702.5: Where waste water is hotter than 140°F, the drainage pipe must be rated for that temperature.
- 702.6: Chemical waste systems are separate and must be corrosion resistant for the chemicals involved.
- 702.4: Fittings must suit the pipe material and meet Table 702.4. Threaded drainage fittings must be the recessed drainage type (706.2), such as ASME B16.12 cast-iron drainage fittings. These give a smooth waterway with built-in pitch.
Fittings and change of direction (706)
Section 706.2 prohibits fittings with ledges, shoulders or reductions that retard flow. Section 706.3 requires fittings that guide flow in its direction, as listed in Table 706.3:
| Fitting | Horizontal to vertical | Vertical to horizontal | Horizontal to horizontal |
|---|---|---|---|
| Sixteenth, eighth or sixth bend | Yes | Yes | Yes |
| Long sweep | Yes | Yes | Yes |
| Wye | Yes | Yes | Yes |
| Combination wye and eighth bend | Yes | Yes | Yes |
| Quarter bend | Yes | Only for a 2-in-or-smaller fixture drain | Only for a 2-in-or-smaller fixture drain |
| Short sweep | Yes | 3 in and larger, or a 2-in-or-smaller fixture drain | Only for a 2-in-or-smaller fixture drain |
| Sanitary tee | Yes | No | No |
- Sanitary tees are only for flow from horizontal to vertical, such as a fixture arm entering a stack. Laid on its back in a horizontal line, a sanitary tee directs flow across the pipe and invites stoppages.
- At the base of a stack, a long sweep, a combination wye and eighth bend, two eighth bends, or (for 3 inches and up) a short sweep are all acceptable.
- Double sanitary tees may not receive the discharge of back-to-back water closets or of fixtures or appliances with pumping action, such as clothes washers and dishwashers. One water closet's discharge can blow across into the opposite fixture. Exception: back-to-back water closets are allowed where the horizontal developed length from each closet outlet to the double sanitary tee is 18 inches or more.
- 706.4: Heel-inlet quarter bends are acceptable, except where the quarter bend serves a water closet, and a low-heel inlet may not be used as a wet-vented connection. Side-inlet quarter bends are acceptable for drainage, wet venting and stack venting.
Joints (705)
| Material | Joint | Key rules |
|---|---|---|
| PVC | Solvent cement | Clean, dry joint; purple ASTM F656 primer; solvent cement not purple, conforming to ASTM D2564; joint made while the cement is wet, per ASTM D2855 (705.10.2) |
| ABS | Solvent cement | ASTM D2235 cement (705.2.2). The code does not require primer |
| PVC and ABS | Mechanical (elastomeric seal) | ASTM C1173, D3212 or CSA B602. Underground only unless approved (705.2.1, 705.10.1) |
| PVC and ABS | Threaded | Schedule 80 minimum, with plastic dies |
| Cast iron, hub and spigot | Compression gasket | ASTM C564 gasket tested to ASTM C1563, compressed when the pipe is fully inserted (705.3.2) |
| Cast iron, hub and spigot | Lead and oakum | Pack oakum, pour lead at least 1 inch deep in one pour, no more than 1/8 inch below the hub rim, caulk tight. No coating until tested (705.3.1) |
| Cast iron, hubless | Shielded coupling | CISPI 310, ASTM C1277 or C1540 sleeve and shield with a center stop, installed per the manufacturer (705.3.3) |
| Copper | Solder, braze, mechanical | ASTM B32 solder and B813 flux; AWS A5.8 brazing (705.5, 705.6) |
| Galvanized steel | Threaded | Compound on male threads only (705.8.1) |
| Push-fit DWV | Push-fit | Listed to ASME A112.4.4 |
Joints between different materials (705.16)
- Use mechanical joints of the compression or sealing type conforming to ASTM C1173, C1460 or C1461, with approved elastomeric seals.
- Copper to cast-iron hub: use a copper or copper-alloy ferrule soldered to the copper, then caulked or compression-jointed into the hub (705.16.1).
- Copper to galvanized steel: use a copper-alloy or dielectric fitting (705.16.2).
- Plastic to plastic of a different type: use an approved adapter. The only allowed solvent joint between ABS and PVC is one joint where the building drain meets the building sewer, using ASTM D3138 transition cement (705.16.4).
- Plastic to cast-iron hub: use a caulked joint or a mechanical compression joint.
- Slip joints in drainage follow 405.9 (705.17).
Prohibited joints and connections (707.1)
- Cement or concrete joints.
- Mastic or hot-pour bituminous joints.
- Joints made with fittings not approved for the installation.
- Joints between different pipe diameters made with elastomeric rolling O-rings.
- Solvent-cement joints between different types of plastic, except the 705.16.4 ABS-to-PVC transition joint.
- Saddle-type fittings.
A threaded cleanout opening may not be used to add a fixture or extend piping, unless another cleanout of equal size is provided (708.1.12).
Supports, bracing and restraint (308)
| Material (Table 308.5) | Horizontal | Vertical |
|---|---|---|
| Cast-iron pipe | 5 ft (10 ft where 10-ft lengths are installed) | 15 ft |
| ABS and PVC | 4 ft | 10 ft* |
| Copper tube, 1-1/4 in and smaller | 6 ft | 10 ft |
| Copper tube, 1-1/2 in and larger | 10 ft | 10 ft |
| Steel pipe | 12 ft | 15 ft |
| Stainless steel drainage | 10 ft | 10 ft* |
| Lead pipe | Continuous | 4 ft |
* Mid-story guide for sizes 2 inches and smaller.
- 308.6, sway bracing: On horizontal drainage pipe 4 inches and larger, where a fitting changes direction more than 45 degrees, provide rigid bracing so the upstream pipe cannot move in the direction of flow. A change into a vertical pipe does not need this.
- 308.7.1, restraint: For drain pipe larger than 4 inches, restrain all changes of direction and all changes in diameter greater than two pipe sizes, using braces, blocks or rodding as the coupling maker specifies. This matters because hubless couplings can pull apart under the thrust of a surge.
- 308.4: Hangers must be attached to the structure in an approved way. 308.3: Hangers must carry the pipe's weight and contents and must not cause galvanic action.
Underground installation
Follow Section 306:
- Give continuous support, with bell holes at joints.
- Remove rock to 3 inches below the pipe and bed on tamped sand.
- In soft soil, over-excavate two pipe diameters.
- Backfill in 6-inch tamped layers to 12 inches over the crown, bringing it up evenly on both sides.
- Never block pipe up to grade.
- Where the manufacturer's bedding rules are stricter (common for plastic pipe), follow them (306.2, 306.3).
Also remember these:
- Underground drains in filled or unstable ground need the materials in 703.2.
- A drain crossing under a footing needs a relieving arch or a sleeve two sizes larger (305.3).
- A trench beside a footing may not cut into the 45-degree bearing plane (307.5).
Exam traps
- Sanitary tee: horizontal to vertical only.
- Short sweep at the base of a 3-inch or 4-inch stack is permitted by Table 706.3. Quarter bends there are not.
- Primer: purple primer is required on PVC. ABS has no primer requirement.
- Bedding over rock: at least 3 inches of tamped sand, per 306.2.2.
Under IPC Table 706.3, for which change of direction may a sanitary tee pattern fitting be used?
Any change of direction on 3-inch and larger pipe
Horizontal to vertical only
Horizontal to horizontal only
Vertical to horizontal only
Two water closets are installed back-to-back on opposite sides of a wall and connect to one vertical stack. Under IPC 706.3, when may they share a double sanitary tee?
Never; back-to-back closets always need separate fittings
Only if each closet outlet is 18 inches or more from the tee
Only if the stack is 4 inches or larger at that floor level
Always, because water closets are self-venting fixtures
Which joint is specifically prohibited in sanitary drainage piping by IPC 707.1?
A shielded hubless coupling with a center stop on cast-iron pipe
One ASTM D3138 solvent joint between ABS building drain and PVC building sewer
A saddle-type fitting clamped over a hole cut in the drain
A compression gasket conforming to ASTM C564 in a cast-iron hub
Sections you finish are checked off in the contents.