EPISODE
32

Custom Home Plumbing, HVAC & Electrical Rough-In

The mechanical rough-in phase is when a framed custom home begins receiving the systems that make it functional. Plumbing supply and drain lines are installed, HVAC equipment and ductwork are laid out, electrical wiring and boxes are positioned, and low-voltage connections are planned for technology throughout the house.

This work takes place after the home’s structural shell has been framed but before insulation and drywall cover the walls and ceilings. That timing makes the mechanical stage one of the most important opportunities to inspect the work, confirm practical details and document what will soon be hidden.

In Episode 32 of Building With Breven, Steven Byrnes explains what homeowners can expect during the mechanical rough-in for a custom home. This phase is step four in the complete seven-step custom home building process, following the framing, cornice and roof-decking phase.

What Is the Mechanical Rough-In Phase?

Mechanical rough-in is the stage when a builder and trade contractors install the primary systems inside the framed walls, floors, ceilings and attic. The term generally includes:

  • Plumbing supply, drain and vent lines
  • Central heating and air-conditioning equipment and ducts
  • Electrical wiring, boxes and breaker-panel connections
  • Low-voltage wiring for internet, security, audio and smart-home equipment
  • Certain pest-control systems installed before the walls are closed

The permanent fixtures and finishes usually do not go in yet. For example, plumbers may install shower valves and prepare toilet connections without setting every finished fixture. Electricians install wires and boxes, but decorative lights, switches and outlet covers come later.

The goal is to put each hidden system in the correct location, test it and resolve problems while the framing remains open. Once the project moves into insulation and drywall, changes and repairs become more disruptive.

What Happens During Plumbing Rough-In?

Plumbing rough-in—sometimes called plumbing top-out—connects the water-supply, drain and vent systems that serve the home. Much of the underground plumbing may already have been installed and tested during the foundation stage. At this point, the plumbing contractor extends the system through the framed structure to the planned fixtures.

Water-supply lines

Many new homes use PEX tubing for water distribution. PEX is flexible and can expand and contract more readily than rigid piping, an advantage when Central Texas experiences unusually cold weather. The exact materials and system design should still follow the approved plans, local requirements and the project team's specifications.

One common configuration is a trunk-and-branch system. A larger main line carries water into the home, while smaller branches serve individual fixtures. Depending on the installer, colored tubing may help distinguish hot, cold and main supply lines, although color conventions can vary.

During the open-wall stage, homeowners and builders can confirm practical details such as:

  • The positions and heights of showerheads and controls
  • Whether shower valves can be reached without standing under cold water
  • Connections for bathtubs, sinks and other planned fixtures
  • Hose-bib and outdoor water locations
  • Toilet placement in relation to the framed walls
  • Any special plumbing required by selected appliances or equipment

Selections matter here. A fixture or appliance with unusual supply, drain or clearance requirements should be identified before the wall is closed.

Drain, waste and vent lines

The plumbing contractor also connects the drain system serving sinks, tubs, showers and toilets. Wastewater normally relies on correctly sloped piping to move toward a municipal sewer connection, septic system or another approved on-site solution.

Because gravity and slope are critical, the system should be checked before finishes conceal it. Tub and shower drains must align with their fixtures, waste lines need proper routing, and the venting system must be installed according to the applicable design and code requirements.

How plumbing rough-in is tested

Supply lines can be placed under water or air pressure and monitored using a gauge. If the pressure drops unexpectedly, the team can investigate for a leak. Maintaining a test during later work may also help reveal whether a drywall fastener or another trade accidentally penetrates a line.

The drain system may be isolated and filled with clean water for a head test. A meaningful drop in the water level can indicate that the system is not watertight and requires further investigation. These tests help the project team identify problems before water service is fully activated or the walls are covered.

Testing procedures and acceptance criteria vary by jurisdiction and project, so homeowners should confirm the required inspections with their builder rather than treating a visual check as a substitute for professional testing.

What Happens During HVAC Rough-In?

HVAC stands for heating, ventilation and air conditioning. During HVAC rough-in, the contractor begins installing the equipment, ducts, supply registers, returns, drain lines and control wiring needed to condition the home.

In many Central Texas custom homes, the project uses a ducted central HVAC system. Air handlers or related equipment may be placed in the attic or in dedicated mechanical closets. A larger or multi-level home may require more than one system or zone, depending on its size, layout, ceiling heights, insulation, windows and calculated heating and cooling loads.

HVAC design should follow a plan

HVAC is not simply a matter of placing ducts wherever space is available. Proper design considers:

  • The volume and layout of conditioned rooms
  • Ceiling heights
  • Local climate
  • Window performance and solar exposure
  • Insulation levels and the building envelope
  • The amount of supply air each area needs
  • Return-air locations and airflow paths

In a cooling-dominant climate such as Central Texas, supply and return locations are commonly planned around delivering cool air effectively from above. The specific layout, however, should be based on the home's design and load calculations—not a generic arrangement copied from another project.

Supply ducts, returns and unrestricted airflow

Supply ducts carry conditioned air into rooms, while return ducts bring air back to the system. Together they create a circulation pattern that supports even temperatures and comfort.

Flexible insulated ductwork can help contractors route air through complex framing, but it should not be compressed, sharply bent or pinched into undersized spaces. Restrictions can reduce airflow, lower comfort and place unnecessary strain on the equipment. During the open-wall inspection, the builder should review whether ducts are supported, connected and routed without obvious damage or constriction.

Condensate drainage and equipment protection

Cooling equipment produces condensation, and that water must drain safely. An attic installation may include a primary drain, a secondary drain and an emergency pan or other protection appropriate to the system and applicable requirements.

Drain placement deserves attention because an overflow above finished ceilings can cause significant damage. The project team should verify the routing and protection before access becomes more difficult.

Thermostat locations

Thermostat wiring is also installed during rough-in. A thermostat should be positioned where it can read a representative indoor temperature. Locations directly beneath a supply register or beside another unusual heat source can produce misleading readings.

Homeowners may have some flexibility in selecting a convenient and visually appropriate location, provided it also supports accurate system control.

What is a duct-leakage test?

A duct-leakage or duct-blaster test measures how much air escapes from the duct system. Testers temporarily seal the registers, connect calibrated equipment and pressurize or depressurize the ducts. The resulting measurement helps identify leakage at connections, boots, plenums or other parts of the system.

Even when ducts are located inside a spray-foamed or conditioned enclosure, reducing leakage can support better system performance. An open-wall test also makes many repairs easier because the installer can reseal a connection or correct damaged ductwork before finishes are installed.

What Happens During Electrical Rough-In?

Electrical rough-in includes running cables, positioning electrical boxes and preparing circuits for lights, switches, outlets and hardwired equipment. This is also the ideal time for an electrical walkthrough with the builder because framed rooms allow homeowners to understand the actual placement more clearly than a floor plan alone.

During the walkthrough, compare the electrical plan with how the home will be used. Questions to consider include:

  • Are switches positioned conveniently near the correct entrances?
  • Are fan and light controls divided in a practical way?
  • Are lighting boxes centered where the selected fixtures will hang?
  • Are there outlets where countertop appliances will be used?
  • Does the pantry, closet or utility area need a nonstandard outlet?
  • Is wiring planned for under-cabinet or accent lighting?
  • Are outdoor living areas equipped for the intended fans, lights and appliances?
  • Is capacity planned for an EV charger or another 240-volt appliance?

Some additions or relocations may require a change order. However, making a well-considered adjustment during rough-in is generally easier than opening finished drywall later.

Main panels and subpanels

A custom home may use a main electrical panel along with one or more subpanels. Large loads such as certain ranges, dryers, HVAC equipment and vehicle chargers may require dedicated higher-voltage circuits, while standard lighting and receptacle circuits are distributed through the system as designed.

Homeowners should understand where the panels will be located and whether they remain reasonably accessible. Final panel design, circuit sizing and installation must be handled by qualified professionals according to the approved electrical plans and applicable codes.

Plan Low-Voltage Wiring Before Drywall

Low-voltage planning has become increasingly important as homes use more connected devices. Depending on the project, the low-voltage contractor may install wiring for:

  • Internet and Ethernet connections
  • Wi-Fi access points
  • Security cameras and alarm devices
  • Doorbells and access controls
  • Whole-home audio and speakers
  • Media rooms and surround sound
  • Televisions and other audiovisual equipment
  • Smart-home controls and compatible appliances

Wireless technology does not eliminate every wiring need. Some televisions, cameras, access points and smart appliances perform better—or may only support certain functions—when hardwired. Homeowners should review equipment selections before rough-in so the project team knows where to route cables, install boxes or leave accessible wire for future devices.

Planning ahead can also reduce visible cords and prevent avoidable wall repairs after move-in.

Can Pest-Control Preparation Happen During Rough-In?

Some builders include pest-control preparation before insulation and drywall. The approach depends on the location, building method, lender requirements and pest risks associated with the property.

In Central Texas, this may include a borate treatment applied to accessible framing or an in-wall pest-management system installed while stud cavities remain open. Some systems use small tubes routed through selected wall areas and connected to exterior service ports.

These products and procedures should be evaluated with the builder and a qualified pest-control provider. Homeowners should confirm what is included, what documentation will be provided and what ongoing service may be required after closing.

Why a Pre-Drywall Inspection Matters

A pre-drywall inspection happens after major rough-ins are substantially complete but before insulation and wallboard conceal them. It gives the builder, applicable inspectors and—when arranged—the homeowner's independent inspector an opportunity to review visible components.

Items commonly reviewed at this stage include:

  • Plumbing supply and drain testing
  • HVAC duct routing, connections and condensate provisions
  • Electrical boxes, wiring paths and panel preparation
  • Low-voltage wiring and planned device locations
  • Visible penetrations, clearances and protection plates
  • Consistency with the plans and approved changes

The purpose is not to encourage homeowners to perform their own technical inspection. It is to make sure questions are raised while qualified trades can still reach the work easily. Inspection scope and required approvals vary, so coordinate timing and access through the builder.

Document Everything Behind the Walls

Before insulation and drywall begin, take a detailed photo or video record of every room. A slow walkthrough—including walls, ceilings, floors and mechanical areas—can become a valuable reference after the home is finished.

That documentation can later help answer questions such as:

  • Is plumbing located behind this section of wall?
  • Where does an electrical cable or low-voltage line run?
  • Can a television, shelf or large piece of artwork be mounted here?
  • Where were future speaker or technology wires left?
  • Which framing member provides support for an attachment?

A 360-degree camera can provide broad coverage, but an organized phone video and clear still photographs can also be useful. Label the files by room and keep them with the home's plans, selections, inspection reports and warranty records.

Mechanical Rough-In Checklist for Homeowners

Before the project proceeds to insulation and drywall, review the following with your builder:

  • Confirm that plumbing and appliance selections are finalized.
  • Review shower controls, hose bibs and specialty water connections.
  • Ask which plumbing tests have been completed and documented.
  • Confirm HVAC equipment, supply, return and thermostat locations.
  • Ask whether duct-leakage testing is required or planned.
  • Complete the electrical walkthrough before wiring changes become difficult.
  • Verify special outlets, lighting, outdoor power and dedicated circuits.
  • Finalize internet, security, audio, television and smart-home wiring.
  • Confirm the pre-drywall inspection schedule and access procedure.
  • Photograph and record the open walls before they are covered.

The details should be coordinated through the builder and documented when they affect cost, schedule or scope. Following Breven Homes' custom home process helps keep those decisions organized from planning through construction.

Frequently Asked Questions About Mechanical Rough-In

What does mechanical rough-in include in a custom home?

Mechanical rough-in generally includes plumbing pipes and drains, HVAC equipment and ducts, electrical wiring and boxes, and low-voltage cabling. The exact scope depends on the project's plans, systems and local requirements.

When does mechanical rough-in happen?

It normally occurs after structural framing and the exterior shell are far enough along to support the work, but before insulation and drywall cover the framing cavities.

Should homeowners attend the electrical walkthrough?

When the builder offers one, the electrical walkthrough is valuable because homeowners can verify switch, outlet and lighting locations in the actual framed rooms. Any requested changes should be reviewed for cost, code compliance and schedule impact.

What should be checked during HVAC rough-in?

The project team should review equipment and thermostat locations, supply and return paths, duct condition, condensate drainage and required testing. Technical evaluation should be performed by qualified contractors or inspectors.

Why test plumbing before drywall?

Pressure and drain-system tests can reveal leaks while the piping is accessible. Finding a problem before insulation and drywall can reduce the amount of finished material that must be removed for repairs.

Is a pre-drywall inspection required?

Required inspections depend on the jurisdiction and project. Homeowners may also discuss an independent inspection with their builder. The important point is to coordinate it before the walls are covered.

Why should homeowners photograph the open walls?

Photos and video create a record of plumbing, wiring, ducts and framing that may later help with mounting items, planning upgrades, maintenance and troubleshooting.

Build With a Clear View of What Is Behind the Walls

Mechanical rough-in is more than a collection of pipes, wires and ducts. It is the point when planning decisions become the hidden infrastructure of the finished home. Careful coordination, appropriate testing and a thorough pre-drywall review can help the systems work together as intended.

To learn more about each stage, explore the Building With Breven podcast series. If you are planning a custom home in Central Texas, contact Breven Homes to discuss your project and the process from design through completion.