Most homeowners imagine plumbing as something that happens inside finished walls — pipes hidden behind tile, under sinks, and above ceilings. But some of the most important plumbing decisions in any new construction project happen long before a single wall goes up, and even before the concrete slab is poured. Everything starts underground.

At Cordova’s Plumbing LLC, we’ve handled new construction plumbing throughout Richmond, VA and the surrounding area for over 10 years. The underground layout phase is one of the most technical and consequential parts of the entire build — and getting it right the first time is essential. Here’s how we plan and install bathroom and kitchen drain systems before the walls ever go up.

Reading the Blueprint and Translating It to the Ground

Before any pipe goes into the ground, the licensed plumber studies the architectural plans in detail and translates every bathroom, kitchen, and utility room into precise measurements on the actual jobsite.

• Every fixture — toilet, shower, bathtub, sink, floor drain — has a specific location in the plans that must be replicated exactly on the ground before excavation begins
• Plumbers use string lines, chalk lines, and measuring tapes to lay out fixture positions directly on the subgrade, ensuring each stub-out lands in precisely the right spot relative to the future walls
• The location of the main sewer connection and the direction of the building’s slope determine how all drain lines must be routed underground
• Load-bearing elements like footings, piers, and grade beams are identified early so pipe routes avoid structural conflicts
• Coordination with the concrete contractor is critical at this stage — both trades must agree on layout before gravel is placed and forms are set

A mistake in translation from blueprint to ground means a toilet, shower drain, or kitchen sink ends up in the wrong position — a problem that is extraordinarily expensive to fix once concrete covers it.

Establishing Slope and Routing the Drain Lines

Once fixture locations are confirmed on the ground, the plumber designs the underground drain network — the system of pipes that will carry waste from every fixture to the main sewer line.

• Drain lines must maintain a consistent downward slope of at least ¼ inch per foot of horizontal run to allow waste to flow by gravity without clogging
• Each fixture connects to a branch drain line, which feeds into progressively larger collector lines that route toward the building’s main sewer exit point
• Fittings like wye connectors, elbows, and sanitary tees are selected and positioned carefully to maintain smooth flow and avoid turbulence that can cause blockages
• The depth of the pipes at each point is calculated precisely — too shallow and they conflict with the slab thickness; too deep and they become difficult to connect to above-ground plumbing later
• Gravel is compacted beneath and around the pipes to provide stable bedding that prevents settling or shifting before and after the slab is poured

The underground drain network is essentially a map of the entire building’s plumbing system — every future fixture location, every connection point, and every flow path is determined at this stage.

Setting Stub-Outs for Every Fixture

With the drain lines in place, the final step before the slab is setting the stub-outs — the short vertical pipe sections that rise above the gravel and mark exactly where each future fixture will connect.

• Each stub-out corresponds to a specific fixture: toilets, showers, bathtubs, bathroom sinks, kitchen sinks, laundry drains, and floor drains each require their own precisely positioned stub-out
• Stub-out heights are calculated so they end up at the correct elevation once the concrete slab is poured around them
• Caps are placed on each stub-out to keep concrete, debris, and moisture out of the drain system during the pour
• The entire underground system — drain lines, fittings, and stub-outs — is pressure-tested and inspected by the local building authority before any concrete is placed
• Once the inspection passes, the concrete contractor pours the slab, locking the entire underground system permanently in place

Those vertical pipes sticking up through the gravel are not just placeholders — they are the permanent anchor points for every plumbing fixture in the finished building, set with precision that has to be right the first time.

Final Thoughts

Underground plumbing layout is where the entire plumbing system of a new home is born. Every decision made at this stage — where pipes are placed, how they slope, how stub-outs are positioned — directly determines where bathrooms and kitchens can be built and how well the finished plumbing system will perform for decades to come.

There is no phase of new construction plumbing where experience and precision matter more. Once the concrete is down, what’s underneath it stays there — which is exactly why choosing a licensed, detail-oriented plumbing contractor from the very beginning of your build is one of the most important decisions you’ll make.

Planning a new construction project in Richmond, VA? The team at Cordova’s Plumbing LLC brings the experience, licensing, and precision your build deserves — from underground layout to final fixture installation.

📞 Call us at (804) 974-5484 or contact us online to schedule an inspection today.