New Pipe Sizing Standard ICC 815 and 2024 IPC Section 305.8 Changes for Homeowners

Plumbing pipe sizing is one of those behind-the-wall details most homeowners never think about. That changes when you’re planning a renovation, repipe, or new build and hear that the rules for how pipes are sized in your home are getting their biggest update in decades. Pipe sizing methods have roots in mid-20th-century assumptions, and ICC 815 is a major modernization effort aimed at matching modern fixtures and real-world usage patterns.

Yes, there is a real new standard in development. The ICC 815 standard introduces a new methodology for calculating what size water pipes your home needs. And the 2024 International Plumbing Code (IPC) also brought new provisions that directly affect homes in the DFW area, particularly rules protecting buried pipes from the expansive clay soil that causes so many slab leaks in Plano and Collin County.

Will it affect your existing home? Typically only when work requires a permit or inspection. Is it already enforced in Texas? Adoption is city-by-city — Plano’s 2024 code set took effect August 1, 2025, and Frisco’s 2024 IPC becomes effective March 1, 2026. Will it change what your next plumbing project costs? Possibly, and the surprise is that it could cost less, not more.

Here’s what this article covers: why the current pipe sizing method is outdated, what the ICC 815 standard actually changes, how the 2024 IPC affects North Texas homeowners specifically, when DFW cities will adopt these updates, and what you should do right now if you’re planning a plumbing project in 2026.

Why Pipe Sizing Standards Are Finally Changing

Every water pipe in your home was sized using a method with roots in mid-20th-century research. That method, called the Water Supply Fixture Unit (WSFU) system, assigns a fixed number to each fixture (toilet, shower, faucet) and adds them up to determine pipe diameter. The problem: those numbers were based on how people used water decades ago, when fixtures consumed far more water than they do today.

Older toilets commonly used 5 or more gallons per flush. Showerheads pushed 5+ gallons per minute. Dishwashers and washing machines ran full-blast cycles that lasted far longer than modern units. The fixture-unit tables assumed all of those high-flow fixtures could run simultaneously at peak demand.

Today’s fixtures use a fraction of that water. Low-flow toilets run at 1.28 gallons per flush. WaterSense showerheads top out at 2.0 gallons per minute. The result is that the old tables dramatically overestimate how much water your home actually needs at any given moment.

That overestimation means homes built under current codes often have pipes larger than necessary. Oversized pipes aren’t just wasteful in terms of material cost. They can also create water quality concerns: water sits stagnant in oversized pipes longer, which can contribute to increased bacterial growth potential and higher concentrations of dissolved metals from pipe walls. This is one of the factors driving the push for updated sizing methods, though any new approach must also account for risks from higher velocities in smaller pipes.

What the ICC 815 Standard Actually Changes

The ICC 815 standard introduces a modern sizing methodology intended to reflect today’s fixture flow rates and real-world usage patterns, rather than relying on the legacy assumptions baked into the old fixture-unit tables. Instead of assuming every fixture could run at full blast simultaneously, the new method uses probability-based calculations that account for how people actually use water in a home.

ICC is developing the methodology with academic partners, primarily the University of Miami, and drawing on global building-services data. It sits alongside other modernization efforts in the industry, including IAPMO’s Water Demand Calculator. The core tool is a software platform called DRIPS (Design of Robust International Plumbing Systems), which models real-world water demand patterns to calculate pipe diameters that deliver adequate pressure and flow to every fixture.

What changes in practice:

• Smaller trunk lines. A home that currently needs a 1-inch main water line might only need 3/4-inch under the new calculations. Branch lines could drop from 3/4-inch to 1/2-inch for some fixture runs.
• Potential water quality improvements. Smaller pipes mean water moves faster and sits less, which can reduce stagnation time. ICC is actively evaluating risks like higher velocities and biofilm impacts to ensure the new method improves sizing without creating new problems.
• Lower material costs. Smaller pipe diameters use less copper or PEX per foot, and smaller fittings cost less. For a whole-house repipe, the material savings can be meaningful.
• Designed to maintain performance. The new sizing is intended to account for actual peak demand. The calculations factor in realistic simultaneous usage so that fixtures still deliver adequate pressure and flow during normal use.

One concern homeowners raise: won’t smaller pipes mean lower water pressure? Static pressure is determined by your municipal supply and your pressure regulator. However, pipe diameter does affect pressure drop through friction losses as water flows through the system. The new standard aims to right-size pipes so that friction losses stay within acceptable limits at realistic peak demand, delivering adequate pressure and flow at each fixture.

What the 2024 IPC Means for Texas Homeowners

The 2024 International Plumbing Code introduced several updates, but one provision stands out for every homeowner in the DFW area: new protections for buried pipes in expansive soil.

North Texas sits on expansive clay soil that swells when wet and shrinks when dry. This seasonal cycle puts enormous stress on any pipe buried under or near your foundation. It’s a common contributor to slab leaks in Plano, Allen, McKinney, and across Collin County, especially in homes built from the 1970s onward with copper supply lines under the slab.

The 2024 IPC adds Section 305.8, which establishes requirements for protecting plumbing components in expansive soil conditions. Key provisions include:

• Flexible expansion joints. Where plumbing transitions from the building to buried conditions beyond the foundation perimeter, the code requires adequately flexible expansion joint provisions to accommodate soil movement.
• Void space isolation. For isolated foundations in expansive soil, buried plumbing in the active zone must be suspended with void space isolation rather than sitting directly in contact with moving soil.
• Foundation penetration protection. Where pipes penetrate foundations or transition between structural elements, the code addresses controlled movement to prevent joint failures from soil-induced stress.

For a DFW homeowner, these provisions address the exact failure mechanism that causes thousands of slab leaks every year in North Texas. Staggs Plumbing has been recommending PEX reroutes above the slab for homes with repeated copper slab leaks since well before this code update. The 2024 IPC essentially codifies what experienced plumbers in expansive clay regions already know works.

When These Changes Take Effect in Plano and DFW

Understanding code adoption timelines prevents confusion. Here’s how it works: the International Code Council publishes a new model code every 3 years (the 2024 IPC is the latest). But a model code has no legal authority until a state or municipality formally adopts it.

Texas plumbing code adoption is a mix of state rules and local ordinances — the edition in effect depends on your city and its amendments. The Texas State Board of Plumbing Examiners (TSBPE) has authority to adopt plumbing codes at the state level, but individual municipalities maintain significant autonomy. Cities can adopt newer code editions ahead of the state, add local amendments, or move on their own timeline. Plano’s 2024 code set took effect August 1, 2025, and Frisco’s 2024 IPC becomes effective March 1, 2026. Other DFW cities may follow on their own schedules.

The ICC 815 pipe sizing standard is on a separate track. It’s being developed as a standalone referenced standard, meaning it could be adopted independently of the full IPC cycle. Some jurisdictions may adopt ICC 815 before the rest of the 2024 IPC, while others will wait for the full package. There is no adoption date for ICC 815 yet.

The bottom line: If you’re in Plano, the 2024 IPC is already the law. If you’re in another DFW city, check with your building department — adoption timelines vary by city. Before pulling a permit, call your city’s building department to confirm which code edition is currently in effect.

How This Affects Your Next Plumbing Project

The impact depends on what you’re planning. Here’s a breakdown by project type:

New construction. Once the new standards are adopted locally, your builder’s plumber will size pipes using the updated methodology. You may see smaller water supply pipes specified on your plans. This is normal and reflects the updated calculations, not cost-cutting.

Whole-house repipe. If you’re replacing aging copper or galvanized pipes with PEX, a plumber who understands the new sizing approach can right-size your system. This may reduce material costs compared to sizing under the old tables, since smaller-diameter pipe and fittings cost less per foot. Right-sized pipes may also reduce water stagnation time.

Kitchen or bathroom remodel. For a partial remodel, pipe sizing for the new fixtures will follow whatever code is in effect when your permit is pulled. If you’re remodeling under current code, the old fixture-unit method applies. If the new code is adopted before your permit, the new method applies.

Repairs and replacements. Replacing a single fixture or fixing a leak generally follows a “like-for-like” principle. You won’t need to resize your entire system for a faucet replacement or a spot pipe repair.

What to Do Right Now (And What to Ask Your Plumber)

If you’re planning a plumbing project in 2026, here are the specific steps to take:

1. Ask about code awareness. When you get quotes, ask: “Are you familiar with the 2024 IPC changes and the ICC 815 pipe sizing standard?” A plumber who stays current on code updates can advise you on whether your project should account for upcoming changes.
2. Discuss pipe sizing rationale. For a repipe or new construction, ask your plumber to explain why they’re specifying particular pipe diameters. Under either the old or new methodology, you deserve to understand the reasoning.
3. Check your municipality’s adoption status. Before pulling a permit, call your city’s building department and ask which plumbing code edition is currently enforced. This takes 5 minutes and eliminates guesswork.
4. Consider future-proofing. If your project is in the planning stage and won’t break ground until late 2026 or 2027, ask your plumber whether sizing to the new standard now (even if not yet required) makes sense for your situation.
5. Prioritize expansive soil protection. For any work involving pipes under or near your slab in Plano or the broader DFW area, ask specifically about flexible piping materials and proper bedding. With 40+ years of experience working through North Texas clay soil, Staggs Plumbing (TX License #17697) has navigated every major code cycle since the original BOCA/SBCCI codes through current IPC adoption, pulling permits and coordinating inspections on every qualifying job.

Frequently Asked Questions

Staggs Plumbing has been navigating plumbing code transitions in the DFW area since 1981, with 40+ years of hands-on experience through every major code update. If you’re planning a renovation, repipe, or new build and want to make sure your project is sized right under current or upcoming standards, call 972-833-8660 to talk through your project with a licensed team (TX #17697, A+ BBB rated) that stays ahead of code changes so you don’t have to.