Cast Iron

Cast iron soil pipe and fittings carry wastewater, vent air, and storm water by gravity through a building's drain system. This category covers the three systems used in cast iron plumbing: service weight hub and spigot, extra heavy hub and spigot, and no-hub pipe, along with the gaskets and couplings that join them. As a cast iron DWV material, it is listed in the major US model plumbing codes and remains common in commercial, multifamily, and high-rise construction. The dense pipe wall absorbs the sound of flowing water, which keeps drain noise down near occupied rooms, and the material is noncombustible, so it does not add fuel to a fire inside walls and chases. Properly installed cast iron drain pipe can stay in service for decades. 

Cast iron soil pipe is made in sizes from 1-1/2 to 15 inches for hubless systems and 2 to 15 inches for service weight and extra heavy, so one material can run from a single fixture branch to the main building drain. Pipe, fittings, couplings, and gaskets are grouped by system below, so a complete drain, waste, and vent installation can be sourced from one category.

Cast Iron Systems by Type

Extra Heavy CI Pipe & Fittings

Extra Heavy CI Pipe & Fittings have a thicker wall and a larger outside diameter than service weight pipe of the same nominal size. Extra heavy cast iron is specified where local code, an engineer, or the job calls for added wall strength, such as underground building drains, deep burial, or heavy-load areas. Pipe and fittings use hub and spigot ends sealed with extra heavy compression gaskets.

No-Hub Pipe Fittings & Couplings

No-Hub Pipe Fittings & Couplings use plain-end pipe and fittings joined with stainless steel shielded couplings that clamp a neoprene sleeve over each joint. No hub cast iron installs faster than hub and spigot, needs less space at the joint, and lets a section be removed by loosening its couplings, which suits stacks, branches, and tight chases. Cast iron couplings come in standard and heavy-duty versions, each tightened to the manufacturer's torque value.

Service Weight Pipe Fittings Gaskets

Service Weight Pipe Fittings Gaskets cover the most widely used hub and spigot weight for residential and commercial drainage. Service weight cast iron joins with a neoprene compression gasket: the gasket seats inside the hub, the spigot is lubricated, and a pipe puller or assembly tool drives it home to form a watertight seal. Service weight gaskets fit service weight hubs only and do not interchange with extra heavy gaskets.

Choosing Cast Iron Pipe and Fittings

Selecting cast iron pipe and fittings starts with size, weight, and joint type.

Size and weight. Size each line from fixture unit loads and slope in the governing plumbing code, then choose the weight. Service weight covers most drainage work; extra heavy goes where code or the engineer requires it.

Joint type. Hub and spigot joints suit underground runs and building drains, where compression gaskets give a rigid, sealed connection. No-hub joints suit above-grade stacks and branches, where speed, space, and future access matter. Many cast iron drain systems use both: hub and spigot below the slab and no-hub above it.

Transitions. To tie new no-hub pipe into existing hub and spigot, cut the old pipe square and join the plain end with a no-hub or transition coupling rated for both outside diameters. A new spigot can also enter an existing hub with a compression gasket of the matching weight. Extra heavy pipe has a larger outside diameter than service weight and no-hub pipe, so joining it to either takes a transition coupling sized for both diameters. In most sizes, a cut length of service weight pipe accepts a standard no-hub coupling on its plain end.

Cutting. A soil pipe snap cutter makes a clean, square cut on site without sparks. A cutoff saw with an abrasive or diamond blade also works. Remove burrs and confirm the end is square before coupling.

Fittings. Common cast iron pipe fittings include 1/4, 1/8, and 1/16 bends, sanitary tees, wyes, combination wye and 1/8 bends, P-traps, test tees, and cleanout fittings. Match each fitting to the system's end type and weight, and pair floor and wall access points with Drains & Cleanouts that have matching cast iron connections.

Standards. In the US, hub and spigot pipe and fittings are made to ASTM A74, hubless pipe and fittings to ASTM A888 and CISPI 301, no-hub couplings to CISPI 310 or ASTM C1277, and compression gaskets to ASTM C564. Check product markings against the project specification.

Testing. Most codes require a water or air test of the drain, waste, and vent system before it is concealed. Place test tees at stack bases and branch points where the inspector will need access.

Support. Cast iron is heavy, so hangers and riser clamps must be spaced as the code requires. Larger no-hub runs need bracing at changes of direction to resist thrust. Hangers & Struts cover supports for horizontal runs and vertical stacks.

Frequently Asked Questions

Where can I buy cast iron soil pipe and fittings for a commercial drain, waste, and vent job?

This category groups cast iron soil pipe with matching fittings, couplings, and gaskets for service weight, extra heavy, and no-hub systems. Confirm the system type and sizes on the drawings, then order pipe and fittings from the matching subcategory.

What do I need to order for a no-hub cast iron drain line?

Order hubless pipe, the fittings for each change of direction or branch, and one coupling per joint. Add hangers, riser clamps, and bracing for larger sizes. A snap cutter and a torque wrench set to the coupling manufacturer's value complete the install.

What's the difference between service weight and extra heavy cast iron pipe?

Extra heavy pipe has a thicker wall and a larger outside diameter than service weight cast iron of the same nominal size. Service weight covers most drainage work. Extra heavy is used where code or the engineer requires more wall strength. Their gaskets are not interchangeable.

Should I use no-hub or hub and spigot cast iron for a drain stack?

No-hub is the usual choice for above-grade stacks and branches because it installs faster and needs less space at each joint. Hub and spigot with compression gaskets is common below the slab. Follow the project specification and local code.

 Is cast iron or plastic drain pipe better for a multi-story commercial building?

Cast iron is quieter because its dense wall absorbs flow noise, and it is noncombustible. Plastic is lighter and simpler to handle. Many multi-story projects specify cast iron for stacks near occupied space. Penetrations through fire-rated assemblies need listed firestopping with either material.

How do I connect new no-hub cast iron pipe to existing hub and spigot pipe?

Cut the existing pipe square, then join the plain end to the new no-hub pipe with a no-hub or transition coupling rated for both outside diameters. A new spigot can also go into an existing hub using a compression gasket of the matching weight.

What gasket do I need for service weight cast iron hub and spigot pipe?

Use a neoprene compression gasket sized for service weight pipe and made to ASTM C564. Seat it inside the hub, lubricate the spigot, and drive the joint home with a pipe puller or assembly tool. Extra heavy gaskets will not fit service weight hubs.

What's the right way to cut cast iron soil pipe on a job site?

A soil pipe snap cutter gives a clean, square cut without sparks. A cutoff saw with an abrasive or diamond blade also works. Deburr the cut and check that the end is square before installing a coupling or gasket.

How can I reduce drain noise in an apartment building's waste lines?

Use cast iron drain pipe for stacks and horizontal drains that run near living space, since its mass dampens the sound of flowing water. Support the pipe with proper hangers and riser clamps so it does not rest directly on framing.

A no-hub cast iron joint is leaking. Should I replace the coupling or the pipe?

Check coupling torque first, then confirm both pipe ends are square, fully seated against the sleeve's center stop, and aligned. Replace the coupling if the shield, clamps, or sleeve are damaged. Replace the pipe only if it is cracked.

FAQ 11: What sizes does cast iron soil pipe come in?

Hubless pipe and fittings are made from 1-1/2 to 15 inches. Service weight and extra heavy hub and spigot pipe and fittings are made from 2 to 15 inches. Common pipe lengths are 5 and 10 feet.

What standards should cast iron DWV pipe and fittings meet in the US?

Hub and spigot pipe and fittings are made to ASTM A74. Hubless pipe and fittings follow ASTM A888 and CISPI 301. No-hub couplings follow CISPI 310 or ASTM C1277, and compression gaskets follow ASTM C564. Cast iron DWV products are marked with the standard they meet.

 Can I use no-hub couplings to join extra heavy cast iron pipe?

Not with a standard coupling in most cases. Extra heavy cast iron has a larger outside diameter than hubless pipe, so the joint needs a transition coupling sized for both diameters. Check the coupling's listed diameter range before installing.

How long does cast iron drain pipe last, and is it still used in new construction?

Properly installed cast iron can stay in service for decades. It remains an approved drainage material in the major US model plumbing codes and is widely used in commercial, multifamily, and high-rise buildings for its sound control and fire performance.

Which cast iron fittings go into a typical drain system?

Common cast iron pipe fittings include 1/4, 1/8, and 1/16 bends, sanitary tees, wyes, combination wye and 1/8 bends, P-traps, test tees, and cleanouts. Each fitting must match the system's end type, either hub and spigot or no-hub, and its weight.