Understanding Home Construction: Plumbing, Heating, and Electrical Work

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After the framing and often while installing the siding, the builder begins to rough in or place the plumbing, heating, and electrical systems in the walls of the house behind the drywall or interior paneling. In many new homes, the builder also installs a central cooling system.

In addition, some common low-voltage components of the home—such as telephones, cable televisions, burglar alarms, intercoms, doorbells, thermostats, and smoke alarms—are usually prewired at this point. Many modern homes may also have a central vacuum or other specialized features that require some pre-wiring before the builder installs the dry wall or paneling. Today, the builder can even integrate these electrical-power and signal-wiring systems into a SMARTHOUSE wiring system controlled by a central computer.

Once the builder has had the subcontractors rough in the plumbing and electrical systems and before the drywall or paneling goes up, the local municipal inspectors examine the roughed-in portion of these systems for compliance with local codes.


At the plumbing rough-in stage, the builder needs to know the exact location of all plumbing fixtures because the plumber will now install the plumbing lines for both the hot and cold water supply and the sewage. (See photo 4.1.) To install the plumbing lines, the plumber usually drills large holes through joists, studs, bottom plates, and subflooring. Local building codes detail specifications for the size, location, and number of these holes. The actual plumbing fixtures will be installed later as the house nears completion.

Usually the plumber also installs the tubs and shower bases at this point. In many areas, inspectors require the plumber to seal the entire plumbing system and pressurize the supply pipes to check for leaks. If any leaks appear at the rough-in inspection, the builder must then call the plumbers back to fix them.

In some areas, after installing the plumbing lines, the builder may fill the holes with some type of hardening foam. This increases the energy efficiency of the exterior walls. It also helps to keep out pests, such as mice and roaches, and prevent the spread of fire from one floor to another. The builder may install this foam at the same time as the insulation, after putting up all the mechanical systems. In some municipalities, however, inspectors require the builder to install the foam separately before the insulation, so the inspector can easily verify that the builder has properly filled all holes.

A few other points about the plumbing may interest you. You may notice that portions of the sewage pipes extend up through the roof. These are the vent pipes discussed in Section 3. The sewage vents balance air pressure on both sides of traps, which prevent sewer gas from entering the house through sink drains, and allow the gas to vent to the outside. Collars installed around these vent pipes at the roof prevent water leakage.

As part of the plumbing system, the builder may also place one or more hose bibs outside the home for watering the lawn or washing the car. The location of these bibs can vary, so the builder and homeowner will want to work together to select these locations.

Heating and Cooling Systems

The central heating and cooling ductwork is generally installed after the plumbing. (See photo 4.2.) The installation of these two systems takes so much work by so many people that the builder may avoid scheduling them at the same time. The choice of which step comes first is usually the builder’s and subcontractor’s preference.

A house can have a room heating or cooling system with a separate unit and thermostat in each room. For example, an electric-resistance baseboard heating system has individual heaters and thermostats in each room. As an alternative, a house can have a central heating and cooling system with one unit, thermostat, and distribution system to carry heat and cool air throughout the house. The most common types of central heating and cooling systems are a natural gas furnace with an electric air conditioner or an electric heat pump that provides both heating and cooling.

4.2 Ductwork

Natural Gas

The typical natural gas heating and cooling system has a gas furnace with a separate electric cooling compressor mounted outside of the house. The system also comes as a packaged unit that the builder can mount on the roof or other outside locations. Functionally the two types of gas systems are identical.

In the summer, the system pulls warm air from within the house into return air ducts and passes it across a set of cooling coils. The cooling coils contain a gas similar to the gas in your refrigerator. This gas absorbs the hot air in the house and cycles it to a compressor located outdoors. The cooled air is then distributed throughout the house through the sup ply ducts.

In the winter, the air handler pulls cool air from within the house and passes it through a gas heating unit. The warm air is then recirculated through the same ductwork used for cooling in the summer.

Like your refrigerator, an electric cooling system is a closed system requiring little or no maintenance. Although it may need recharging at some point, if properly maintained, this system should give years of trouble-free service.

The gas furnace and air conditioning system share a common blower, a common thermostat system, and common ductwork, so they seem like one system when they are really two distinct systems. If a house has this kind of system, the builder has a certified gas plumber run gas lines, which look like plumbing lines, to the furnace.

Electric Heat Pump

A heat pump is essentially a reversible air conditioner. The heat pump may look and sound like a stand-alone compressor or packaged unit. While the gas furnace blows hot air in the winter and the air conditioner blows cool air in the summer, the heat pump, which operates on electricity, is a single system designed to both heat and cool.

Heat pumps follow the principle that outdoor air contains heat or thermal energy even in the winter. During the winter months, the heat pump extracts heat from the outdoor air and circulates that heat through the house. In the summer, the system is reversed. The heat pump removes heat from indoor air, discharges the heat outdoors, and circulates the cooled air through the house.

Heat pumps are efficient systems in moderate climates if the home is properly insulated. Additionally, the heat pump contains back-up or emergency electric heating coils that automatically turn on if the outside temperature falls below about 25 to 30 degrees.

Ceiling fans can also be an integral part of a home’s cooling system, particularly for warm spring and fall evenings. If the extensive use of ceiling fans is planned for a new home, the builder will have the electrician prewire switch controls for the fan and optional light kit.

Electrical Wiring

Since installation of the plumbing and ductwork can require large cuts in the wall and floor systems, builders usually leave the rough-in of the electrical wiring until last. In most jurisdictions, the utility company is responsible for setting the meter and installing the line to the transformer and electricians are responsible for running electrical lines from the meter into the home. In some areas, however, electricians may also furnish the meter. (See photo 4.3.)

4.3 Electrical Meter Box Ready for Meter Installation

As the first step, the electrician installs a service wire that leads from the meter into the breaker box. The breaker box distributes electricity by circuits or wires to outlets in each room of the house, as well as the thermostat, light switches, the doorbell, appliances, the intercom, and the security sys tem. Most electricians try to locate the meter and breaker box as close as possible to one another in a convenient location in the house.

The electrician next sizes the breaker box to handle the electrical load expected for the home. Most single-family detached homes with no special requirements call for a breaker box with at least a 200-amp capacity. However, if the homeowner plans to add on to the home or run any special circuits later, the service should be upgraded accordingly.

Upgrading the electrical system at this time is not nearly as costly as upgrading the service at a later date.

From the breaker box, the electrician then runs wires for all of the circuits in the home. The electrician usually threads these wires through holes drilled in the stud walls and joists or staples wires to the framing in inaccessible areas.

You may notice that the wires for different circuits come in different sizes and types. Most outlets have a 120-volt ser vice. In general, the higher the amperage expected for a given circuit, the larger is the wire needed to conduct that amperage. Also, certain appliances in the home will require a 240-volt service. These appliances may include the hot water heater, dryer, range, heat pump, and air conditioner.

Breakers of various ratings protect all of the circuits in a home and are designed to trip when they detect an over loaded circuit. This prevents the wire or the appliance from getting hot and starting a fire. However, the breakers also allow a brief period of overload before tripping, since most appliances, particularly those with motors, run for a short time at a high amperage before settling down to their normal levels.

Circuits that carry currents to bathrooms and outdoor outlets or appliances need more sensitive breakers to reduce the danger of electrical shock in areas where plumbing and water are commonly found. For those circuits, the electrician uses ground-fault circuit-interrupters, which trip the moment a faulty appliance such as a hairdryer is grounded.

The notion of an electrical circuit may seem a little confusing. Some appliances like refrigerators, dryers, or ranges are such a drain on the electricity that they need their own circuits. On the other hand, circuits for bedrooms can typically handle several receptacles and lights. If the house has high wattage circuits for such things as overhead fans, waterbed heaters, or window air conditioners, the electrician may need to decrease the number of outlets on a circuit accordingly. However, with normal loads, just a few circuits can handle the low-usage areas of the home.

As a final step in the electrical wiring, the electrician mounts the boxes for the outlets, switches, and fixtures before the builder moves on to the insulation of the house.


After the builder has had the plumbing, heating, and electrical components roughed in but before the drywall or paneling goes up, the builder installs the wall insulation.

Eventually, the floors and ceilings also need insulation. (See photo 4.4.) However, if access to the floors and ceiling is available through a crawl space and attic, then the builder can insulate these areas later.

Wall Insulation. The most common wall insulation is fiberglass or rock wool (mineral wool) made of very fine fibers spun from molten rock or glass. This type of insulation may come either as faced or unfaced flexible blankets or as rigid or semi-rigid boards. Finally, fiberglass or rock wool may come in a loose fiber form, which the insulation subcontractor can blow or pour into cavities like attic spaces.

Blankets used for insulation generally have a kraft paper or aluminum foil facing that may serve as a vapor retarder to prevent moisture from collecting in the walls. The blankets are the width and length of the cavity between the studs and the paper extends an inch or so on either side of the studs to serve as a stapling edge.

If the builder decides to install unfaced fiberglass insulation in the stud walls, the inner face of the wall should be covered with a material such as polyethylene to serve as a vapor retarder. Vapor retarders must always face the conditioned space—in on walls, down on ceilings, and up on floors. However, a vapor retarder is not always necessary on the ceiling if the attic space is well ventilated.

Attic Insulation. The builder normally installs the attic insulation after the gypsum board is installed on the ceiling. On flat attic spaces, the insulation subcontractor uses either fiberglass blankets or a blown insulation made of fiberglass, mineral wool, or cellulose. Either approach provides effective insulation for attic areas.

Blown fiber insulation has the advantage that it can fill nooks and crannies of the attic that the insulation subcontractor can't reach with blankets. However, blown insulation requires heavy equipment and can also be messy to install, which explains why many builders try to complete this phase soon after the gypsum board is installed in the ceiling.

Ceiling Insulation. Spaces above vaulted ceilings require fiberglass blankets as insulation, which the builder needs to install before the drywall. (See photo 4.4.) The ceiling insulation provides a blanket to keep the home warm in winter and cool in summer. Vaulted ceilings present one additional challenge for the insulation subcontractor. Ventilation of the space between the insulation and the roof sheathing is every bit as important as the insulation of that space.

Proper ventilation for the insulation of ceilings, as well as attics, provides the following for a house:

• allows moisture to escape

• maintains the R-value of the insulation (The R-value indicates the level of resistance to heat flow in a building material. The higher a material’s R-value, the more effective insulation it provides.)

• prevents condensation from collecting within the insulation or on the bottom of the sheathing

• prevents mold and rot

• cools the roof in the summer

In colder climates, proper ventilation of roof cavities also keeps the roof cold in the winter and thus reduces the melting of snow on the roof and ice damming at the eaves.

The insulation subcontractor can combat the buildup of moisture in ceiling spaces by installing insulation baffles that provide an air channel from the eave vent, through the space between the rafters. The insulation subcontractor nails these baffles to the underside of the roof sheathing before installing the insulation.

With this type of insulation, you can see that the continuous eave and ridge vent system is virtually a must in homes with vaulted ceilings. On the other hand, homes with flat ceilings can use eave vents, gable louvers, ridge vents, or other types of vents to provide ventilation.

Floor Insulation. The builder installs the floor insulation between the floor joists by using short pieces of stiff wire, sometimes called dogs or tiger teeth, which press the batts up against the subflooring. In heated basements, the walls are usually insulated instead of the floor.

In crawl spaces in very cold climates, the builder may also install some form of foundation wall insulation. This typically involves plastic foam insulation boards or fiberglass blankets applied to the inside of the foundation wall within the crawl space. For spot insulation the builder may have a plastic foam sprayed into the cracks around windows and doors, pipe openings, and other air leakage points. The builder may also have a plastic sheeting spread on the ground within the crawl space to control moisture.

All of this begs the question, “How much insulation is enough?” First, of course, local climate conditions determine the amount of insulation a house requires. In addition, in some areas, local building codes require minimum amounts of insulation in a house. Generally, insulation is inexpensive for the job it does, and it usually pays to go for the most insulation possible. However, remember that energy conservation is more than just pouring on the insulation.

Multi-pane windows with low-E glass, careful caulking and weather-stripping of doors and windows, and use of south-facing windows and high-efficiency heating and air conditioning equipment are also important. The home builder and public utility company can provide sound advice on the level of insulation required for a house in a particular climate.

The house is now a maze of plumbing pipes, wires winding through studs, ducts for heating and cooling, and insulation of all kinds. As a final step, the builder now roughs in the specialty components of the house.

Miscellaneous Rough-in

Before the drywall goes up, the builder roughs in such common specialty components as the wires for telephones, doorbells, intercoms, security systems, and cable televisions. Again, as another alternative, SMARTHOUSE wiring integrates all of these wires into one system.

Virtually all homes have telephones, and having the electrician pre-wire the appropriate rooms at the rough-in stage is an inexpensive way to ensure that the homeowner has phone service wherever required. Wiring two phone lines at the same time is usually no more expensive than wiring one. In this way, the homeowner will have access to wiring for that home office or teenager who wants a phone later on.

Cable television is a different challenge. Pre-wiring for cable ensures that unsightly cables don't run along the baseboard or through holes drilled in the carpet. However, pre-wiring cable service to every room of the house is not as feasible as pre-wiring for phone service. With both telephone and cable service, the homeowner should specify exactly where the outlets should go to match furniture placement and lifestyle choices.

Many homes today are also fitted for burglar alarms. These come in a variety of styles and models, and the builder can recommend a suitable alarm company. Pre-wiring for a basic alarm system is much less expensive than wiring for the system after the home is finished, even if the homeowner plans to have the system installed later. Many alarm companies pre-wire on a cost basis and anticipate that homeowners will purchase the system soon after closing.

Other specialty items that the builder may rough in at this point include such amenities as a central vacuum (see photo 4.5), intercom, smoke alarm, built-in multiroom stereo system, computerized climate control, and controls for a swimming pool. Also, an automatic sprinkler system controlled

from the garage, certain types of ceiling lighting, icemakers, a sauna, and a whirlpool tub can be added to the list of amenities that a builder may rough in at this stage in even moderately priced homes.

4.5 Central Vacuum

All of these amenities are listed to make a point. If the homeowner plans to add any of these features after the home is completed, the builder should really do the preliminary rough-in for these features at this stage of construction. Although the builder can't dig the hole for the swimming pool planned for next year, completing the prewiring or pre plumbing for this type of additional amenity is much less expensive at this phase.

So, while the process may vary somewhat, to rough in the plumbing, heating, and electrical systems of the house, the builder first installs the plumbing and then the heating and cooling systems. After completing these steps, the builder next puts in the electrical wiring and begins to place the insulation in the walls, attic, ceilings, and floors. At this point any specialty components for the house are also roughed in before the builder moves on to the interior finish.

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