Type L or Type M copper? The simple homeowner guide 🛠️

Choosing copper for a water line or repair often boils down to type L or type M copper. This quick guide explains the difference, when code prefers one over the other, and how to size a project correctly—plus a short sidebar comparing type S mortar vs type N for masonry so all your specs live in one place. 🔧

Copper tube types are about wall thickness and duty rating. Thicker walls handle abuse and pressure better—but cost more and are harder to bend.

Always follow your local plumbing code and the manufacturer’s instructions. Some jurisdictions limit where type M can be used for potable water.

Type M copper tubing demonstrating its lightweight and flexibility

Type L or Type M copper: what changes and why it

matters

Type L has a thicker wall than type M. The thicker wall gives type L better resistance to impact, pinholes from localized corrosion, and slightly higher pressure capacity. Type M is lighter, easier to cut, and typically less expensive—good for low-risk, protected runs when allowed by code.

Quick comparison for domestic water

Feature	Type L	Type M
Wall thickness	Medium-heavy	Medium-light
Typical uses	Interior potable lines, distribution trunks, exposed mechanical rooms, some exterior runs in protected locations	Interior potable branches in protected walls, hydronic heating loops where permitted
Durability & abuse tolerance	Higher	Lower
Cost & weight	Higher cost; heavier	Lower cost; lighter
Common code stance	Allowed broadly for potable water	Allowed in many areas inside dwellings only; some codes restrict or prohibit for certain uses
Best pick when unsure	Choose Type L if you need a safer, more durable default

If the line will be exposed, in a workshop/utility area, near concrete, or subject to movement, type L is the safer choice. Use type M only where it is protected and explicitly permitted.

Copper pipe type L vs M: choosing the right tube for your project

1. Check code first. Some cities require type L for all potable water; others allow type M only inside conditioned spaces and walls.

2. Think abuse, not just pressure. Impacts from storage, tools, or expansion can stress thin walls; thicker type L buys margin.

3. Consider water quality. Aggressive or acidic water can shorten the life of thinner tube; use type L or treat the water.

4. Plan transitions carefully. If you are mixing copper with PEX, use the correct fittings and support to avoid kinks and stress.

5. Size by flow, not by habit. Keep velocities moderate to reduce noise and erosion; upsizing a branch is cheaper than opening walls later.

Installation notes that prevent callbacks

• Support spacing: Strap or clip per code so the tube cannot rub and wear.

• Soldering/Brazing: Clean and flux lightly; avoid overheating which can anneal tube and weaken fittings.

• Isolation: Use dielectric unions when joining to dissimilar metals that may corrode.

• Concrete contact: Sleeve or wrap copper that passes through slabs or masonry.

Sidebar: type S mortar vs type N (quick masonry reference)

You also asked about type S mortar vs type N—use this as a compact reference.

Mortar	Typical use	Why choose it
Type S	Below-grade walls, retaining walls, exterior areas with wind or seismic forces	Stronger bond and higher compressive strength; better for structural or high-load applications
Type N	Above-grade exterior walls, veneers, chimneys, general masonry	Balanced workability and flexibility; good for everyday brick and stone where loads are lighter

Rule of thumb: Type S for strength and weather; Type N for most above-grade walls and veneers where flexibility matters.

FAQ

In one sentence: should I use type L or type M copper? Choose type L when you want durability or when code is strict; use type M only for protected interior runs where it is explicitly allowed.

 Is copper pipe type L vs M about pressure only? No—wall thickness and abuse tolerance are the bigger day-to-day differences for homeowners.

 Can I mix L and M on the same line? Yes, if code allows; keep type L on exposed or high-risk sections and support all transitions properly.

 When would I skip copper entirely? Long runs in aggressive water or seismic zones may favor PEX with proper fittings and support.

 Type S mortar vs type N—when do I pick each? Use type S for structural or below-grade work; use type N for most above-grade walls and veneers.

Conclusion

When the question is type L or type M copper, decide by code, risk, and location. If the line is exposed, subject to wear, or you want a safer default, choose type L. If the run is protected inside a wall and your jurisdiction permits it, type M can save cost and time. Keep the installation clean and supported, and your system will run quietly for decades.