PEX Pipe Sizes Explained for Lake Forest Homes: 1/2, 3/4 and 1 Inch Lines and Where Each Belongs
The right PEX size keeps showers steady and fixtures strong. How 1/2, 3/4 and 1 inch lines are used in a repipe and what we size for Foothill Ranch, Portola Hills and…
Not every pipe in a repipe is the same size, and getting the sizes right is a big part of whether your new system feels better than the old one. Lake Forest homes range from 1970s houses near the lakes to Foothill Ranch and Portola Hills homes from the 1990s and 2000s, and each layout needs a sizing plan that matches its fixtures and run lengths.
How PEX is sized
PEX is sold by nominal size, matched to copper tube sizing, so a 1/2 inch PEX line and a 1/2 inch copper line serve similar roles. The inside diameter of PEX is a bit smaller than copper of the same nominal size because of wall thickness, which is one reason fittings and routing matter. Common residential sizes are 3/8, 1/2, 3/4 and 1 inch.
Where each size belongs
- 1 inch: often used for the main from the meter or pressure regulator into the house, especially for larger homes or long runs.
- 3/4 inch: trunk lines feeding groups of fixtures, the water heater supply and lines to large showers or multiple bathrooms.
- 1/2 inch: branch lines to individual sinks, toilets, showers and the laundry.
- 3/8 inch: occasionally for a single low-flow fixture over a short run, as allowed by code.
Factors that change the plan
Code uses fixture counts and run lengths to set minimum sizes, but real homes add other factors. A two-story Foothill Ranch home with three bathrooms upstairs needs adequate trunk size to keep the upper floor from dropping when someone downstairs starts the washer. Long runs to a far bathroom lose pressure, and too many fittings add restriction. Homes with a pressure regulator near the main start with a set pressure, so the sizing has to deliver good flow from that point. Larger showers, soaking tubs and tankless water heaters each have their own flow needs.
Trunk-and-branch or manifold
In a trunk-and-branch layout, larger lines feed smaller branches. In a manifold layout, a central manifold sends individual 1/2 or 3/8 inch lines to each fixture. Many Lake Forest repipes use a hybrid with multiport tees. We choose based on the floor plan, attic access and where the main enters.
Local notes
Lake Forest is served by Irvine Ranch Water District and El Toro Water District depending on the neighborhood. Repipe permits go through the City of Lake Forest, and many HOAs, including communities around the lakes, have rules about work hours and contractor parking.
Related reading
If you are replacing plastic pipe, read our CPVC pipe replacement guide, and see whether SharkBite fittings are reliable for permanent work. Homeowners nearby can visit Irvine, Mission Viejo and Rancho Santa Margarita, or see the full service area at repipeinc.com.
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Repipe OC, 23821 Hillhurst Drive, Laguna Niguel, CA 92677, (949) 524-2362, CSLB #1087885 C-36.
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Written by Repipe OC · CSLB #1087885 C-36 · 23821 Hillhurst Drive, Laguna Niguel, CA 92677 · (949) 524-2362