6.1 Drainage Fittings, Changes of Direction, Joints & Prohibited Connections
Key Takeaways
Sanitary tees are permitted only for horizontal-to-vertical changes of direction; wyes, combination wye and eighth bends, long sweeps and sixteenth, eighth and sixth bends are permitted in all three directions (Table 706.3).
Quarter bends and short sweeps may be used vertical-to-horizontal or horizontal-to-horizontal only on fixture drains 2 inches or smaller; short sweeps 3 inches or larger are also allowed vertical-to-horizontal (Table 706.3 notes a and b).
Double sanitary tees may not receive back-to-back water closets or pumping fixtures unless the horizontal developed length from each closet outlet to the fitting is at least 18 inches (706.3).
Heel-inlet quarter bends are acceptable except where the bend serves a water closet, and a low-heel inlet may not be used as a wet-vented connection (706.4).
Prohibited joints include cement or concrete joints, mastic or hot-pour bituminous joints, rolling O-rings between different pipe diameters, solvent joints between different plastics (except 705.16.4), and saddle fittings (707.1).
Why fittings are regulated
Drainage depends on gravity and momentum. A fitting that turns flow too sharply in the wrong orientation slows the water, drops solids, and can push air back toward traps. IPC 706.1 requires approved drainage fittings for all connections and changes of direction. 706.2 prohibits fittings with ledges, shoulders or reductions that could slow or block flow. Threaded drainage fittings must be the recessed drainage type. 706.3 requires fittings to guide sewage and waste in the direction of flow, using Table 706.3.
Table 706.3: fittings for changes in direction
| Fitting pattern | Horizontal to vertical | Vertical to horizontal | Horizontal to horizontal |
|---|---|---|---|
| Sixteenth bend (22-1/2°) | Yes | Yes | Yes |
| Eighth bend (45°) | Yes | Yes | Yes |
| Sixth bend (60°) | Yes | Yes | Yes |
| Quarter bend (90°) | Yes | Note a | Note a |
| Short sweep | Yes | Notes a and b | Note a |
| Long sweep | Yes | Yes | Yes |
| Sanitary tee | Yes (note c) | No | No |
| Wye | Yes | Yes | Yes |
| Combination wye and eighth bend | Yes | Yes | Yes |
- Note a: permitted only for a 2-inch or smaller fixture drain.
- Note b: 3 inches or larger. A short sweep 3 inches or larger may be used vertical to horizontal.
- Note c: see 706.3 for the limit on double sanitary tees.
Combination fittings, side inlets and increasers are judged by the flow pattern they create.
What this means in practice:
- Branch into a stack (horizontal to vertical): a sanitary tee is the usual fitting.
- Base of a 4-inch stack (vertical to horizontal): use a long sweep, a short sweep (3 inches or larger), a wye with an eighth bend, a combination wye and eighth bend, or two eighth bends. A 4-inch sanitary tee or a regular quarter bend is not allowed, since quarter bends are limited to 2-inch fixture drains.
- Horizontal branch joining a horizontal drain: use a wye or a combination wye and eighth bend. A sanitary tee laid on its side is never allowed horizontal to horizontal.
Double sanitary tees and back-to-back fixtures (IPC 706.3)
Double sanitary tee patterns shall not receive the discharge of back-to-back water closets or of fixtures or appliances with pumping action discharge. The short-turn pattern lets one closet's flush shoot across into the opposite inlet.
Exception: back-to-back water closets may connect to a double sanitary tee if the horizontal developed length between each water closet outlet and the fitting is 18 inches or greater.
Back-to-back water closets are normally connected with a double combination wye and eighth bend, or with a double fixture fitting designed for that use.
Heel- and side-inlet quarter bends (IPC 706.4)
- Heel-inlet quarter bends are acceptable except where the quarter bend serves a water closet.
- 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.
Drainage pipe materials (IPC 702)
| Use | Table | Examples of listed materials |
|---|---|---|
| Above-ground drainage and vent pipe | 702.1 | ABS and PVC (solid, cellular core or composite wall), cast iron (ASTM A74, A888, CISPI 301), copper or copper-alloy (Type K, L, M or DWV), galvanized steel, glass, polyolefin, PVDF, stainless steel |
| Underground building drainage and vent pipe | 702.2 | ABS, cast iron, PVC, copper and others listed for underground use |
| Building sewer pipe | 702.3 | ABS, cast iron, concrete, PVC sewer pipe, polypropylene, vitrified clay and others |
| Fittings | 702.4 | Must match the pipe material standard |
- 702.5: where wastewater will be hotter than 140°F, the sanitary drainage pipe must be rated for the highest wastewater temperature.
- 702.6: chemical waste systems must be separate and of corrosion-resistant material (see Section 4.3).
- 303.3: plastic pipe and fittings must be third-party certified to NSF 14.
Joints (IPC 705)
| Material | Joint method and key rule |
|---|---|
| ABS (705.2) | Solvent cement meeting ASTM D2235. Mechanical joints with elastomeric seals are installed only underground unless otherwise approved. |
| PVC (705.10.2) | Purple primer meeting ASTM F656, then solvent cement that is not purple, meeting ASTM D2564 or listed CSA standards, applied to all joint surfaces. Virginia deleted the model exception that let some DWV joints of 4 inches or smaller skip primer, so primer is required in Virginia. Solvent joints may be above or below ground. |
| Cast iron, hub and spigot, caulked (705.3.1) | Firmly packed oakum or hemp, then molten lead poured in one operation to at least 1 inch deep, not more than 1/8 inch below the hub rim, caulked tight. No paint or coatings until tested and approved. |
| Cast iron, compression gasket (705.3.2) | Gaskets meeting ASTM C564, tested to ASTM C1563. |
| Cast iron, hubless (705.3.3) | Coupling with an elastomeric sleeve (with center stop) and a metal shield meeting CISPI 310, ASTM C1277 or C1540. |
| Copper (705.5 and 705.6) | Solder joints per ASTM B828 with ASTM B813 flux and ASTM B32 solder; brazed or mechanical joints are also listed. Ream tube ends to full diameter. |
| Different materials (705.16) | Mechanical compression or mechanical-sealing joints with elastomeric seals, or the specific methods in 705.16.1 to 705.16.7 |
Joints between different materials:
- 705.16.1: copper to cast-iron hub pipe uses a copper or copper-alloy ferrule, or a compression joint.
- 705.16.2: copper to galvanized steel uses a copper-alloy or dielectric fitting.
- 705.16.4: different plastics join with an approved adapter. The only solvent joint between ABS and PVC allowed is a single joint at the end of the building drain and the start of the building sewer, using solvent cement meeting ASTM D3138.
- 705.17: drainage slip joints follow 405.9: only on the trap inlet, trap outlet and within the trap seal.
Prohibited joints and connections (IPC 707.1)
- Cement or concrete joints.
- Mastic or hot-pour bituminous joints.
- Joints made with fittings not approved for the specific installation.
- Joints between different diameter pipes made with elastomeric rolling O-rings.
- Solvent-cement joints between different types of plastic pipe, except as 705.16.4 allows.
- Saddle-type fittings.
To add a branch to an existing drain, cut in an approved wye or tee with approved couplings. Strapping a saddle over a hole is never allowed.
Other connection rules
- 704.2: no reduction in size in the direction of flow (4-by-3 closet flanges and bends are not reductions).
- 704.3: branches connect at least 10 stack diameters downstream of a stack base or horizontal offset.
- 1101.6: storm drainage uses the same Table 706.3 fittings.
- 708.1.12: a threaded cleanout opening may not be used to add a fixture or extend piping unless another cleanout of equal size is installed.
Which fitting is permitted at the base of a 4-inch soil stack where the flow turns from vertical to horizontal?
A 4-inch sanitary tee
A 4-inch double sanitary tee on its side
A 4-inch regular quarter bend
A 4-inch long-sweep quarter bend
Two floor-mounted water closets are installed back to back on a vertical stack. Under IPC 706.3, when may a double sanitary tee receive them?
Only where each closet outlet is at least 18 inches of horizontal developed length away
Whenever the stack is 4 inches or larger, because the barrel can absorb both flushes
Never; a double sanitary tee may not be used anywhere on a vertical stack
Whenever both water closets are 1.28 gpf models, because their flushes are small
A plumber makes a solvent-cement joint on PVC DWV pipe in Virginia. Which statement is correct?
Primer may be omitted on PVC DWV pipe 4 inches and smaller with listed one-step cement
Purple ASTM F656 primer is required; Virginia deleted the 705.10.2 exception
ABS solvent cement may be used on PVC pipe as long as the joint is above ground
Saddle fittings may be solvent-welded onto PVC drains to add new branch connections
Sections you finish are checked off in the contents.