reading plumbing plans

PLUMBING

Reading Plumbing Plans

SECTION 2 / SpecificsPLUMBING 321

INTRODUCTIONThe first thing that a technician should do upon receiving a set of plans for a building is to review them, scan-ning each plan to get an overview of the building. Understanding the mechanical, electrical, and plumbingplans is very important because the three trades will be working in the same area to install their equipment,and coordination of their work will be required. Studying each of the plumbing systems one at a time will helpthe technician understand the entire system more thoroughly.

The major systems found in a complete plumbing plan are as follows: sanitary drainage system, plumbingvent system, domestic hot and cold water system, roof drainage system, fire protection sprinkler system, andcompressed air system. In a hospital or medical building, plumbing includes the medical gas systems (oxygen,medical air, nitrogen and vacuum). All of these systems will occupy the same space that is allotted for themechanical and electrical systems. It is essential, therefore, that the systems be understood and coordinated.The set of plans in this book is typical for a small building, with only one sheet required for the plumbing sys-tem. This chapter will focus on the plumbing plan for this building.

LOOKING FOR SPECIFIC SYSTEMSOn the plan, the size and location of each piping system is shown. The domestic cold water piping includesthe service piping to the building and the distribution piping inside the building. The water heater and thedomestic hot and cold water piping are shown.

The heavier lines represent the drain lines. The lines connected to the plumbing fixtures are the sanitarywaste lines. The sanitary piping is located underground except for the part that turns up to connect to theplumbing fixtures.

The roof drainage piping is connected to the roof drains. This piping is extended, usually above the ceiling,to a point where it can be turned down and installed below the floor. These lines are drawn the same as the san-itary drain lines, and they can be identified as storm drain lines because they are connected to the roof drains.

Another piping system is the plumbing vent piping. This piping is connected above the trap on each fixtureto let air enter and leave the piping system when water is introduced into the drainage system. (Remember thatwater and air cannot occupy the same space.)

READING THE PLUMBING PLANSThe floor plan shows the location of the plumbing fixtures, and the fixtures are numbered to correspond tothe numbers in the Plumbing Fixture Schedule. The schedule has the name of the fixtures, the manufacturerand model number of each fixture, and the connection size for all the piping connected to the fixture. Thereis a space for notes that pertain to the fixtures.

The domestic cold water piping is shown with a light solid line having long dashes and a dot. The domestichot water is shown with the same weight line as the domestic cold water lines except that the line is a series oflong dashes with two dots. These piping systems have all the fittings and valves needed for a complete system.

The sanitary drainage piping is shown as a heavy solid line. All the various fittings and related equipmentassociated with the drainage piping are shown. The plumbing vent piping is shown with a series of dashes. Theweight of these dashes is the same as the weight for the sanitary drain line.

The roof drainage system consists of a series of roof drains with related piping and fittings. This piping isshown with the same weight lines as the sanitary drain lines.

Notes are used to direct the technician during the installation. Because this is a small job, the specificationsare shown on the drawing. These specifications are titled “Plumbing Notes and Specifications.”

A plumbing riser diagram on the plan shows the method for installing the various piping systems servingthe plumbing fixtures. The pipe sizes are shown on this diagram along with the method for connecting them.This diagram has the sanitary piping, vent piping, and domestic hot and cold water. Each vent riser is identi-fied with an “R” number or riser number.

The connection to the water heater is included. A larger connection detail for the water heater is shown inthe upper left-hand corner of the drawing. This detail shows the piping and fittings necessary for connectingthe piping to the heater.

Two other details are shown on the plan. The installation of the exterior clean-out is shown with notes aboutthe installation. The other detail shows the method for installing the emergency roof drain. The purpose of thisdrain is to drain water off the roof if the other drains fail, or if for some reason water builds up on the roof toa depth of three inches.

PLUMBINGThe plumbing section is sometimes included as a separate part of the mechanical section. In this chapter,plumbing will be treated as an entirely separate section. The plumbing section usually includes the foundationor basement, floor plan, roof plan, elevations, sections and details, and equipment schedules.

Plumbing work outside the building is shown on the site plan. This site plan is usually bound with the othersite plans. Sometimes, the plumbing site plan is bound as the first sheet of the plumbing section.

In addition to the plumbing work site plan, the plumbing section usually includes the following:

1. The Foundation Plan—shows piping that is installed under the first floor. The piping is located in the crawlspace (if there is one), or under the floor slab of a concrete floor on grade. Piping consists of hot and colddomestic water, sanitary sewer or drainage piping, and special services piping such as fuel gases, medicalgases, or process piping.

2. Basement Plan—piping serving the basement (underfloor piping) is shown on a basement floor plan if thereis a basement; however, notes on the plan specify whether the piping is located under the basement flooror at the basement ceiling level.

3. Floor Plans—each floor plan shows plumbing fixtures and equipment served by the plumbing system. Eachpiece of equipment and/or plumbing fixture has a symbol referring the print reader to the schedule sectionto see exactly what equipment/fixture is specified.

Piping serving the plumbing equipment/fixtures is usually shown on the floor plan where the piping isto be installed. In other words, if the piping is located above the second floor ceiling and servesequipment/fixtures on the third floor, the piping is drawn on the second floor, showing all runouts and riserpiping that turn up to the third floor. The plan is noted to say that piping shown on this plan is to be locatedabove the second floor ceiling. In some cases, the engineer/drafter shows the piping for the equipment/fixtures on the same floor plan on which the equipment/fixtures are shown. To prevent confusion, the engineer/drafter adds notes that explain where the piping is to be installed.

4. Roof Plan—all plumbing work required on the roof or through the roof is shown on the roofing plan. Thisincludes plumbing vents through the roof, roof drains (if required), gutters (if required), and special plumb-ing equipment to be mounted on the roof.

5. Elevations, Sections, and Details Plans—these drawings, usually drawn to a larger scale, show details andgive information necessary for proper installation of the plumbing system, equipment, and fixtures. An iso-metrically drawn piping diagram is not uncommon for the detail sheet.

6. Equipment and Fixture Schedules—schedule sheets usually contain the schedules for plumbing fixtures,plumbing equipment, piping, piping connections, plumbing symbols, and plumbing abbreviations.


All residences have a plumbing system that consists of a water supply system; a water distribution system; anda drain, waste, and vent (DWV) system. The water supply system provides a source of water to the structure,and the water distribution system provides hot and/or cold water to each of the fixtures requiring water in thestructure. After the water is used, the drain, waste, and vent system is used to dispose of the water into amunicipal sewage system or an onsite disposal system.

While not defined as plumbing, plumbers sometimes install gas piping. The gas piping system supplies fuelgas to the gas-fired fixtures, which might include water heaters, furnaces, ranges, and clothes dryers.

PLUMBING MATERIALSThe materials most often used for plumbing are copper, plastic, cast iron, and black iron. A brief descriptionof each is given in the paragraphs that follow.

Copper is frequently used for plumbing because it resists corrosion. However, it is relatively expensive.Copper pipes and fittings may be threaded or smooth for soldered joints.

Plastic materials are used in the water supply, water distribution, and DWV systems. These materials arelightweight, noncorrosive, and easily joined. While plastics are allowed in each area of a plumbing system, theplastics used in a water distribution system must have a minimum temperature rating of 180°F (82°C). Plasticsare not suitable for some applications where high strength is required.

Cast iron is commonly used where DWV piping passes through the foundation and outside the building,where it is buried. Cast iron is strong and has excellent resistance to corrosion. Cast iron is not generally usedfor water supply or water distribution systems in residential construction.

Black iron is used almost exclusively for gas piping. Black iron pipes and fittings are threaded, so they canbe screwed together. Brass fittings are frequently used to join black iron pipe.


Fittings

A wide assortment of fittings is used for joining pipe,making offsets at various angles, controlling the flowof water, and gaining access to the system for service.Most fittings are made of the same materials as thepipe. Plumbers must be familiar with all types of fit-tings so they can install their work according to thespecifications of the designer.

Couplings, Plumbing Figure 1, are used to join twopipes in a straight line. Couplings are generally usedonly where a single length of pipe is not long enough.

Union, Plumbing Figure 2, allows piping to be dis-connected without having to cut the pipe. A unionconsists of three parts, with one part being attachedto each pipe and a nut to secure the connection.Then the two parts of the union are screwed together.When it becomes necessary to disconnect the pipe,the two halves of the union are unscrewed.

Elbows, Plumbing Figure 3, are used to makechanges in direction of the piping. Elbows turneither 90°, 45°, or 22.5°.

Some fittings have a hub on each end to accept theoutside diameter of the pipe. Others, called street fit-tings, have a hub on one end, and the other end is thesame as the outside diameter of the pipe. Street fit-tings can be joined directly to other fittings, with nopipe between them.

Tees and wyes, Plumbing Figure 4, have three con-nections to allow a second pipe to join the first fromthe side. Tees have a 90° side connection. A sanitary teehas a curve in the side connection to help direct theflow. Wyes have a 45° side connection.

Cleanouts, Plumbing Figure 5, allow access tosewage plumbing for cleaning. A cleanout consists ofa threaded opening and a matching plug. Whencleaning is necessary, the plug is removed and a draincleaning cable, also known as a snake or auger, is runthrough the line. Cleanouts are installed in eachstraight run of DWV at the base of drainage stacks,where pipe changes direction more than 45°, andseveral other areas dictated by plumbing codes.


PLUMBING Figure 1. Acoupling is used to perma-nently join lengths of pipe.

PLUMBING Figure 2. A union allows the piping to bedisconnected easily.

PLUMBING Figure 3. Street 90° elbow and 45° elbow.

PLUMBING Figure 4. Sanitary tee and wye.

PLUMBING Figure 5. A cleanout allows access to thesystem.


Valves, Plumbing Figure 6, are used to stop, start,or regulate the flow of water. The faucets on a sink orlavatory are a type of valve. A valve can be used toisolate one part of a system from the rest. Everybuilding must have an isolation valve, and mostplumbing fixtures must have an isolation valvelocated near the fixture. Bathtubs and showers do nottypically require separate isolation valves.

DESIGN OF SUPPLYPIPINGIn most communities, water is distributed through asystem of water mains under or near the street.When a new house is constructed, the municipalwater department taps (makes an opening in) thismain. The supply piping from the municipal tap tothe house is installed by plumbers who work for theplumbing contractor.

The main supply pipe entering the house must belarger in diameter than the individual branchesinstalled from the main to each point of use. Thereare two basic reasons for this. First, water developsfriction as it flows through pipes, and the greater sizereduces this friction in the long supply line. Second,when more than one fixture is used at a time, themain supply must provide adequate flow for both.Generally, the main supply pipe for a one- or two-family house is 3/4-inch or 1-inch pipe.

At the point where the main supply enters thebuilding, a water meter is installed. The water metermeasures the amount of water used. The municipalwater department relies on this meter to determinethe proper water bill for the building. The mainwater shutoff valve is located near the water meter.

The cold water distribution piping continuesthroughout the house, which also provides the watersupply to a water heater. The piping system exitingthe water heater creates the hot water distributionsystem serving the entire house. The size of eachpipe providing water to each fixture is dictated by thespecific fixture requirements and the plumbing code.Plumbing Figure 7 shows the wate distribution sys-tem for a house.

When a valve is suddenly closed at a fixture, thewater tends to slam into the closed valve. This causesa sudden pressure buildup in the pipes and may causethe pipes to hammer (a sudden shock in the supplypiping). For quick closing valves, water hammerarresters are required by most plumbing codes. Thewater hammer arrester has a piston that transmitsshock waves from the system to a gas-filled chamber,Plumbing Figure 8. When a valve is suddenly closed,the gas chamber acts as a shock absorber. Althoughwater cannot be compressed, gas can be. When thepressure tends to build up suddenly, the gas in thearrester compresses and cushions the resulting shock.

DRAINAGE WASTEAND VENT SYSTEMThe main purpose of a drainage system is to evacuatewastewater and solids from a building. A drain isinstalled at each fixture, and all individual drains areconnected to eventually create a building drain thatexits the building. The building drain connects to abuilding sewer, which conveys the wastewater andsolids to a municipal sewer, septic tank, or otherapproved point of disposal. The purpose of a vent isto allow air circulation within the system to equalizepositive and negative pressures within the piping.Each fixture must be protected by a vent to ensuresafe operation of the drainage system. A vent can ter-minate independently through a roof or be con-nected with other individual vents to create a branchvent before terminating through a roof. A ventingdevice known as an air admittance valve (AAV) isaccepted by some codes. When a plumbing fixture isoperated and water drains out of the system, negativepressure causes the valve to open, allowing air toenter as needed to equalize the pressure. When theflow stops, gravity closes the valve, preventing theescape of sewer gases through the valve. An AAVeliminates the need for venting through a roof.

TrapsThe sewer contains foul-smelling, germ-ladenedgases that must be prevented from entering the house.

PLUMBING Figure 6. Each branch should include ashutoff valve.


WATER HAMMERARRESTERS

WATER HAMMERARRESTERS

COLD WATER

HOT WATER

PLUMBING Figure 7. Hot- and cold-water piping.

If wastewater simply emptied into the sewer from thepipe, this sewer gas would be free to enter the build-ing. To prevent this from happening, a trap is installedat each fixture. A trap is a fitting that naturally fillswith water to prevent sewer gas from entering thebuilding, Plumbing Figure 9. Not all traps are easilyseen. Some fixtures, such as water closets (toilets),have built-in traps, Plumbing Figure 10.

VentsAs the water rushes through a trap, it is possible for asiphoning action to be started. (The air pressure enter-ing the fixture drain is higher than that on the otherside of the trap. This forces the water out of the trap.)

To prevent DWV traps from siphoning, a vent isinstalled near the outlet side of the trap. The vent isan opening that allows air pressure to enter the sys-tem and break the suction at the trap, PlumbingFigure 11. Because the vent allows sewer gas to passfreely, it must be vented to the outside of the building.Unless protected by an AAV all of the fixtures arevented into one main vertical pipe, through the roof,Plumbing Figure 12.

PLUMBING PLANSFor residential construction, the architect does notusually include a plumbing plan with the set of work-ing drawings. The floor plan shows all of the plumb-ing fixtures by standard symbols. These symbols are


Pistonmoves &

compressesair cushion

Permanent,pressurizedair cushion

Pistonat rest

Pressure spikegenerated byvalve closure

Water flowsthrough system

PLUMBING Figure 8. Water hammer arrestor.

PLUMBING Figure 9. A trap fills with water to preventsewer gas from entering the building.

PLUMBING Figure 10. A water closet has a built-intrap.

PLUMBING Figure 11. Venting a trap allows air toenter the system and prevents siphoning.


PLUMBING Figure 12. DWV system.


PLUMBING Figure 13. Typical manufacturer’s rough-in sheet. Courtesy of Universal-Rundle.

easily recognized, because they resemble the actualfixture. The dimensions of the fixtures are providedby the manufacturer on rough-in sheets, PlumbingFigure 13.

If the building and the plumbing are fairly simple,plumbers may prepare estimates and bids, and com-plete the work from the symbols on the floor planonly. For more complex houses, the plumbingcontractor usually draws a plumbing isometric,

Plumbing Figure 14, or a special plumbing plan.This sheet includes more details than would normallybe found on a plumbing plan for a single-familyhousing unit. The extra detail is included here tohelp you understand the plumbing plan.

Plumbing plans show each kind of piping by adifferent symbol. Common plumbing symbols areshown in the Appendix. It will help you understandthe plumbing plan if you trace each kind of piping


PLUMBING Figure 14. Single-line isometric shown in PLUMBING Figure 12.

from its source to each fixture. For example, trace thegas piping for the Town House. The gas lines canbe recognized by the letter G in the piping symbol.The gas supply is shown as a broken line until it isinside the garage. Broken lines are used to indicatethat the pipe is underground or concealed by con-struction. Although it is not noted on this plan, theplumbing contractor should know that the buildingcode requires the gas line to be run in a sleeve whereit passes through the foundation and the concreteslab, Plumbing Figure 15. Just inside the garage wall,the broken line changes to a solid line. At this point,a symbol indicates that the solid line (exposed pip-ing) turns down or away. Here, at this point, the gaspiping runs above the concrete slab and along thegarage wall. A callout on this line indicates that thediameter of the pipe is 3/4 inch. At the back ofthe garage, the gas line has a tee. Both of the outletsof this tee are 1/2 inch in diameter. One side of the teesupplies the forced air unit (F.A.U.). The other side of

the tee continues around behind the F.A.U. toanother tee, and then to the water heater. The sideoutlet of the second tee supplies a log lighter in thefireplace. This branch is shown on the first floorplumbing plan. Notice that the log-lighter branch isreduced further to 1/4-inch diameter.

You should trace each type of piping in a similarmanner to be sure you understand it. Using coloredpencils to trace the different types of pipingmay eliminate some of the confusion on crowdeddrawings.

Refer to the details on the drawing for clarificationof the complex areas. As you trace each line, look forthe following:

• kind of plumbing (hot water, cold water, waste)• diameter• fittings• exposed or concealed• where line passes through building surfaces


PLUMBING Figure 15. Sleeve for running gas piping under and through concrete. Local codes specify the designof sleeves used for gas piping. This figure shows only the basic concept.


SUMMARY• Understanding mechanical, electrical, and plumbing plans is necessary for each tradesperson.• The plumbing plan includes sanitary drainage, plumbing vents, domestic hot and cold water, roof drainage, fire

protection sprinkler, and compressed air systems.• In a hospital or medical facility, the medical gases (oxygen, medical air, nitrogen, and vacuum) are part of the

plumbing.• The plumbing plan shows whether piping is underground or above ground and includes the connections and

location of piping.• The Plumbing Fixture Schedule identifies the manufacturer, model number, and other pertinent information

about each fixture.• Certain line weights and configurations denote various types of piping.• The riser diagram shows how various piping systems are to be installed.• Details show specific information on connections, installation, and fittings.

reading plumbing plans

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