Type L vs Type K copper comes down to wall thickness and location. Both are ASTM B88 tube with the same outside diameter, but Type K is thicker (0.065 in. vs 0.045 in. at 3/4 in.). In NYC, only Type K is allowed underground, and Type L is the interior standard. Type M isn't listed.
NYC Repipe & Repair publishes these figures with named sources so every number can be checked before you call anyone, including us.
Every NYC repipe is copper, because the city’s plumbing code doesn’t allow PEX or CPVC for water distribution. That moves the real material question one step down: which type of copper. Types K, L and M look the same from outside, and the difference only shows in the wall, in the price and in the code.
The difference is wall thickness
All three types are copper water tube made to ASTM B88. For a given size, they share the same outside diameter, so the same fittings fit all three. What changes is how much copper is in the wall, and therefore the inside diameter and pressure rating.
| Nominal size | Outside diameter | Type K wall | Type L wall | Type M wall |
|---|---|---|---|---|
| 1/2 in. | 0.625 in. | 0.049 in. | 0.040 in. | 0.028 in. |
| 3/4 in. | 0.875 in. | 0.065 in. | 0.045 in. | 0.032 in. |
| 1 in. | 1.125 in. | 0.065 in. | 0.050 in. | 0.035 in. |
Source: ASTM B88 dimensions as published by Engineering ToolBox. Color codes: K green, L blue, M red, per the Copper Development Association.
At 3/4 in., the size of most house risers and mains, Type K has about 44% more wall than Type L, and Type L about 40% more than Type M. That margin is what the soil, the frost line and decades of corrosive water work against.
Where NYC code puts each type
The 2022 NYC Plumbing Code assigns copper by location (NYC Plumbing Code ch. 6):
- Water distribution inside the building (Table 605.4). Copper tubing Types K and L, along with brass, copper and copper-alloy pipe, ductile iron and stainless steel. Type L is the working standard for risers and branches in a whole house repipe, an apartment repipe or a building riser replacement.
- Underground water distribution (Table 605.4.1). Copper Type K only, plus brass, ductile iron and stainless steel. Type L isn’t listed for burial.
- Water service pipe from the street (PC 605.3). Governed by DEP rules rather than the plumbing code table; in practice, the buried service is Type K. See water line replacement and lead service line replacement.
Joints are set by code too. Copper is soldered with lead-free solder, since everything carrying drinking water must meet NSF/ANSI 372 (PC 605.2), or joined with permanent press fittings made with a manufacturer-certified tool. Removable push-fit fittings are prohibited (PC 605.9).
Why Type M isn’t listed in NYC
Type M is the thinnest copper water tube, and it’s widely used for interior plumbing in other parts of the country. NYC’s Table 605.4 names Types K and L and leaves Type M out (NYC Plumbing Code ch. 6).
It matters because of the water. NYC’s supply is soft and corrosive: DEP’s annual water quality report puts the average Langelier index at −2.21, meaning the water tends to dissolve metal (DEP’s annual water quality report). A thinner wall gives pitting less metal to get through. Older copper systems, especially in postwar houses on Staten Island, where 68% of one- to four-family homes were built in 1960 or later, are where thin copper and pinhole leaks turn up. Pinhole leaks in copper pipes covers when that means a repipe.
Cost: does Type L or K change the price much?
Not much on a whole job. Labor is roughly 70% of a repipe’s cost nationally (HomeAdvisor), and the type of copper is a small part of the material line. What moves an NYC price is fixtures, stories, walls and access. A full copper repipe typically runs $12,000 to $35,000 for a house and $3,000 to $8,000 for an apartment, and a buried service line $8,000 to $25,000 (repiping cost guide). For your building, use the repipe cost estimator.
The bigger price question in NYC is copper versus PEX, and that’s settled by code. Copper vs PEX in NYC explains why PEX prices from national guides don’t apply here, and pipe lining vs repiping covers the other shortcut that isn’t allowed.
What to check on your quote
- The pipe is named as Type L copper (ASTM B88) for distribution, not just “copper”.
- Any underground piping and the service line are Type K.
- Joints are solder or permanent press, never push-fit.
- Transitions to old galvanized use an ASSE 1079 dielectric union (PC 605.24.1).
- The job is filed as a Limited Alteration Application in DOB NOW: Build by a NYC Licensed Master Plumber; see does repiping require a permit in NYC.
The free pre-hire checklist turns this into one page to hand each contractor.
Bottom line
Type K is the heavy-wall copper for buried pipe and service lines; Type L is the NYC standard for everything inside the walls; Type M isn’t listed for NYC water distribution. If a quote doesn’t name the type, ask. Call (929) 659-6658 for a free on-site estimate and a written, itemized price that names it.