What to Expect During New Construction Plumbing: A Complete Guide

Whether you're a general contractor breaking ground on a commercial project or a homeowner building custom, understanding the plumbing process helps you plan better, avoid delays, and make informed decisions. New construction plumbing is one of the most critical phases of any build — it happens early, it touches every room, and mistakes are expensive to fix after the walls go up.

At Texas Divine Plumbing, new construction is our primary focus. Here's a detailed walkthrough of what happens at each stage, what Texas building codes require, and what you should expect from your plumbing contractor.

Phase 1: Design and Planning

Before any pipe is cut, the plumbing system needs to be designed. This phase begins with the building's blueprints. An experienced plumbing team reads the architectural and mechanical drawings to map out every supply line, drain line, vent stack, and fixture location in the building.

For commercial projects, this is where the complexity really lives. A restaurant kitchen has very different plumbing demands than an office suite or a car dealership service bay. The design must account for fixture count, hot water capacity, grease trap requirements, drainage calculations, and backflow prevention — all before the permit application is submitted.

In Texas, plumbing permits are required for all new construction. The Texas State Board of Plumbing Examiners oversees licensing, and local municipalities handle permits and inspections. Your plumbing contractor must hold a valid Master Plumber license to pull permits in the state of Texas. At Texas Divine Plumbing, Hector holds this license and oversees every project.

What happens during design:

• Blueprint review and plumbing layout design
• Fixture count and sizing calculations
• Material specification (copper, PEX, PVC, cast iron — each has its application)
• Coordination with other trades (HVAC, electrical, structural)
• Permit application with local building department
• Material procurement and supply chain scheduling

This is also where having strong supply chain management matters. Our Rice MBA, Alexis, handles procurement to ensure materials arrive on schedule and at competitive prices. Delays in material delivery are one of the most common causes of construction schedule slippage, and proactive procurement prevents them.

Phase 2: Underground Rough-In (Slab Work)

Before the concrete slab is poured, underground plumbing must be installed. This is called the underground rough-in or "slab plumbing," and it's one of the most critical phases because once the concrete is poured, changes become extremely expensive.

During this phase, the plumbing crew installs drain lines, sewer connections, and any under-slab water supply lines. In Texas, most commercial and residential buildings use slab-on-grade foundations (no basements), which means all underground plumbing must be precisely placed according to the blueprint — there's no crawl space to access later.

What's installed underground:

• Main sewer line connection to municipal system
• Drain lines for all ground-floor fixtures (toilets, sinks, floor drains)
• Cleanout access points for future maintenance
• Grease trap connections (commercial kitchens)
• Water supply stub-ups through the slab

Texas soil conditions add a layer of complexity. The expansive clay soils found throughout Houston, Dallas, and San Antonio shift seasonally, putting stress on underground pipes. Experienced plumbers account for this by using appropriate pipe materials and joint configurations that can tolerate minor ground movement.

After the underground rough-in, a municipal inspector verifies that all work meets code before the general contractor can pour the slab. This is a required inspection — the building department will not allow the slab pour until plumbing passes.

Phase 3: Top-Out Rough-In (Above Slab)

Once the slab is poured and the building's framing is up, the plumbing crew returns for the top-out rough-in. This is when supply lines (hot and cold water), drain-waste-vent (DWV) piping, and vent stacks are run through walls, ceilings, and floors to connect each fixture location.

For multi-story commercial buildings, this phase is particularly involved. Supply lines must maintain adequate pressure to upper floors. Drainage must be pitched correctly to flow by gravity. Vent stacks must extend through the roof to prevent air locks in the drainage system.

Key activities during top-out:

• Running hot and cold water supply lines to all fixture locations
• Installing drain and vent piping within wall cavities
• Connecting vent stacks through the roof
• Installing water heaters, expansion tanks, and pressure regulators
• Setting gas lines for gas-powered water heaters (if applicable)
• Installing fire suppression connections (commercial)

Coordination with other trades is essential during this phase. Plumbing, HVAC, and electrical all compete for space within wall cavities and above ceilings. An experienced plumbing team knows how to work in concert with these trades to avoid conflicts — and how to resolve them quickly when they arise.

Phase 4: Inspection and Pressure Testing

After the top-out rough-in, the plumbing system undergoes its second municipal inspection. The inspector verifies pipe sizing, material compliance, proper venting, slope on drain lines, secure connections, and overall code compliance.

Pressure testing is a critical component. Supply lines are pressurized to verify there are no leaks. Drain lines are tested with water or air to confirm the entire waste system is tight. Any failures must be corrected and re-inspected before the project can proceed to the finish phase.

In Texas, the International Plumbing Code (IPC) serves as the base code, though individual cities may adopt amendments. Houston, Dallas, San Antonio, and Austin each have local amendments that experienced plumbers must know. This is one reason why hiring a licensed Master Plumber who works across the Texas Triangle matters — we know the code variations in every city we serve.

Phase 5: Finish (Trim-Out)

After walls are closed up, painted, and finished, the plumbing crew returns for the final phase: installing all visible fixtures and making final connections. This is the trim-out, and it's what building occupants will actually see and use every day.

What gets installed during trim-out:

• Toilets, urinals, and bidets
• Sinks, faucets, and supply valves
• Garbage disposals and dishwasher connections
• Shower valves, heads, and tub fixtures
• Commercial-grade fixtures (sensor faucets, flush valves)
• Final water heater startup and testing
• Backflow preventer testing and certification

For commercial projects, this phase often includes specialty fixtures: commercial kitchen equipment connections, medical gas systems (in healthcare facilities), or specialized drainage for laboratory or industrial settings.

Phase 6: Final Testing and Handoff

The last step is a comprehensive test of every fixture and system in the building. Every faucet is turned on. Every toilet is flushed. Every drain is tested. Water heaters are verified for temperature and pressure. Backflow prevention devices are certified. The municipal building department conducts a final inspection, and upon passing, the plumbing system receives its certificate of occupancy approval.

At Texas Divine Plumbing, we walk through every project with the building owner or general contractor at completion. We explain the system, point out cleanout locations and shut-off valves, and provide recommendations for ongoing maintenance. Our goal is to hand over a system that works flawlessly on day one and continues working for decades.

Choosing the Right Plumbing Contractor for New Construction

New construction plumbing is a specialty. Not every plumber who can fix a leaky faucet can handle a ground-up commercial build. When selecting a plumbing contractor for new construction, look for:

• A valid Texas Master Plumber license
• Proven experience with your building type (commercial, residential, industrial)
• Strong blueprint reading capabilities
• Reliable supply chain and material procurement
• Good communication and coordination with other trades
• References from general contractors and building owners