15.1
SECTION 15
PLUMBING AND DRAINAGE
FOR BUILDINGS AND OTHER
STRUCTURES
FACILITIES PLANNING AND
LAYOUT
15.1
Water-Meter Sizing and Layout
for Plant and Building Water
Supply
15.1
Pneumatic Water Supply and Storage
Systems
15.8
Selecting and Sizing Storage-Tank
Hot-Water Heaters
15.11
Sizing Water-Supply Systems for
High-Rise Buildings
15.14
PLUMBING-SYSTEM DESIGN
15.23
Determination of Plumbing-System
Pipe Sizes
15.23
Design of Roof and Yard Rainwater
Drainage Systems
15.29
Sizing Cold- and Hot-Water-Supply
Piping

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Source: HANDBOOK OF MECHANICAL ENGINEERING CALCULATIONS
15.2
ENVIRONMENTAL CONTROL
FIGURE 1 Pressure loss in displacement-type cold-water meters.
The standard establishes maximum output or delivery classifications for each
meter size as follows:
5
⁄
8
-in—20 gal /min (15.9 mm—1.26 L/s)
3
⁄
4
-in—30 gal /min (19 mm—1.89 L/s)
1-in—50 gal /min (25.4 mm—3.1 L/s)
1.5-in—100 gal /min (38.1 mm— 6.3 L/s)
2-in—160 gal /min (50 mm—10.1 L/s)
3-in—300 gal /min (75 mm—18.9 L/s)
4-in—500 gal /min (100 mm—31.5 L/s)
6-in—100 gal /min (150 mm—63 L/s)
The standard also establishes the maximum pressure loss corresponding to the stan-
dard maximum capacities as follows:
15 lb /in
2
(103 kPa) for the
5
⁄
8

in Fig. 2b.
2. Choose the type of storage method for the system served
Fig. 3 shows three different arrangements for water storage at above-ground levels.
The reservoir in Fig. 3a serves only the plant and domestic water needs. It does
not have a provision for emergency water for fire-protection purposes.
The constant-head elevated tank in Fig. 3b has an emergency reserve for fire-
fighting purposes. Local faire codes usually specify the reserve quantity required.
The amount is usually a function of the building size, occupancy level, materials
of construction, and other factors. Hence, the designer must consult the local ap-
plicable fire-prevention code before choosing the final capacity of the constant-head
storage tank.
A vertical cylindrical standpipe is shown in Fig. 3c. While storing more water
on the same ground area, this type of tank is sometimes thought to be visually less
attractive than the elevated tanks in Fig. 3a and 3b.
The alternative to the tanks shown in Fig. 3 is an artificial lake, if space is
available at the plant site. Such a solution has its own set of requirements: (1)
Sufficient land area; (2) Suitable soil characteristics for water retention; (3) Fencing
to prevent accidents and vandalism; (4) Approval by the local zoning board for
construction of such a facility; (5) Treatment of the water prior to use to make it
suitable for process and human use. A final decision on the choice of storage
method is usually based on both economic factors and local zoning requirements.
3. Show how the water supply would be connected to a wet-pipe
sprinkler system
The most common types of fire-suppression systems rely on water as their extin-
guishing agent. Hence, it is essential that adequate supplies of water be available
and be maintained available for use at all times.
The minimum recommended pipe size for fire protection is 6 in (152.4 mm).
Where a pipe network is used for fire protection, a looped grid pattern is designed
for the plant or building, or both. It is often cost-effective to use larger pipe sizes
in a grid because the installation costs are relatively the same. Table 1 shows the

ing to back flow from a building’s internal water system. Hence, sizing of building
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15.5
FIGURE 3 (a) Elevated water-storage reservoir. (b) Constant-head elevated water-storage tank
having an emergency reserve for fire-fighting use. (c) Vertical standpipe for water storage. (Mueller
Engineering Corp.)
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15.6
ENVIRONMENTAL CONTROL
TABLE 1
Table for Estimating Demand
Supply systems predominantly for
flush tanks
Supply systems predominantly for
Flushometer valves
Load Load
Water supply
fixture units
(WSFU)
Demand
gal/min L/ s
Water supply
fixture units

140 52.5 3.31 140 77.0 4.86
160 57.0 3.60 160 81.0 5.11
180 61.0 3.85 180 85.5 5.39
200 65.0 4.10 200 90.0 5.68
250 75.0 4.73 250 101.0 6.37
300 85.0 5.36 300 108.0 6.81
400 105.0 6.62 400 127.0 8.01
500 124.0 7.82 500 143.0 9.02
750 170.0 10.73 750 177.0 11.17
1000 208.0 13.12 1000 208.0 13.12
1250 239.0 15.08 1250 239.0 15.08
1500 269.0 16.97 1500 269.0 16.97
2000 325.0 20.50 2000 325.0 20.50
2500 380.0 23.97 2500 380.0 23.97
3000 433.0 27.32 3000 433.0 27.32
4000 525.0 33.12 4000 525.0 33.12
5000 593.0 37.41 5000 593.0 37.41
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15.7
FIGURE 4 Wet-pipe sprinkler system service piping with typical fittings and devices. (Mueller
Engineering Corp.)
water supply systems is a matter of vital concern in protecting health and is reg-
ulated by codes.
Other important objectives in the design of water-supply systems are: (1) to
achieve economical sizing of piping and eliminate overdesign; (2) to provide against
potential supply failure due to gradual reduction of pipe bore with the passing of

FIGURE 6 Pneumatic well-water system for building service. (Mueller Engineering Corp.)
Calculation Procedure:
1. Determine the maximum water flow required for cold-, hot-, and
process services
Use the procedures given later in this section to determine the flow rate and pressure
required for the building served. With a well-pump supply, Fig. 6, the pump should
have a capacity to 1.5 times the maximum water flow required. Such a capacity
will ensure that the pump does not operate continuously.
A booster system such as that shown in Fig. 7 is used when the city or private
utility water system pressure is undependable—i.e., the pressure may be consis-
tently, or intermittently, lower than that required by various fixtures in the system.
The booster pump discharge pressure is set so that it equals, or exceeds, that re-
quired by the fixtures or processes in the building. Water quantity supplied by the
utility, public or private, is sufficient to meet the building demands. However, the
utility pressure can vary unpredictably. As a rule of thumb, the pump must be
capable of delivering a pressure at least 25 percent over that required in the plumb-
ing supply system.
2. Find the required air compressor discharge pressure for the system
Well-water systems generally do not have the capacity to handle a building’s peak
water service demands. Hence, a storage tank of sufficient capacity to handle this
demand is installed, Fig. 6, either underground or in the building itself. Once the
water is in the storage tank, the well pump has served its purpose. A booster pump,
Fig. 6, supplies the needed volume and pressure for the building water supply.
Since it is undesirable to have the booster pump operate continuously to supply
needed water, a pressure tank and air compressor are fitted, Fig. 6. The air com-
pressor maintains pressure on the water in the pressure tank sufficient to deliver
water throughout the building at the desired pressure and in suitable quantities. Air
pressure in the pressure tank is often set at 25 to 50 lb/ in
2
(173 to 345 kPa) higher

backwards out of the pressurized building water system.
In a tall building a rooftop water storage tank can replace the booster system
for the lower floors where there is sufficient head to operate the fixtures at the
needed pressure. In a high-rise building the booster pump raises the water pressure
sufficiently to overcome the static and friction pressure of the water-consuming
fixtures on the upper floors. The booster system can also be designed to pump
water into the rooftop storage tank for delivery to the lower floors.
Related Calculations. Pneumatic water systems find use in a variety of build-
ings: residential, commercial, industrial, etc. While they are more expensive than a
simple metered system supplied at a suitable pressure and flow rate, pneumatic
systems do ensure adequate water flow in buildings to which they are fitted. Where
water flow is a critical concern, duplicate pumps, compressors, and tanks can be
fitted.
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15.11
Data in this procedure come from Mueller Engineering Corporation and L. C.
Nielsen: Standard Plumbing Engineering Design, McGraw-Hill. SI values were
added by the handbook editor.
SELECTING AND SIZING STORAGE-TANK
HOT-WATER HEATERS
Size a domestic hot-water storage-tank heater for an office building with public
toilets, pantry sinks, domestic-type dishwashers, and service sinks when the usable
storage volume of the tank is 70 percent of the tank volume and the following
numbers of fixtures are fitted: 16 lavatories; 6 sinks; 2 dishwashers; 2 service sinks.
Use ASHRAE and ASPE information and representative hot-water temperatures
and hot-water demand data in the computation.

ϭ
162
ϫ
0.30
ϭ
48.6 gal/h (184 L /h).
3. Compute the storage capacity required for the hot-water heater
ASHRAE also publishes storage capacity factors for hot-water heaters in the ref-
erence cited above. For office buildings, the published storage capacity factor is
2.0. This is the ratio of storage-tank capacity to probable maximum demand per
hour. Thus, for this heater, storage capacity without considering the usable storage
volume
ϭ
48.6
ϫ
2.0
ϭ
97.2 gal (368 L).
Since 70 percent of the tank volume is the usable storage volume, the storage
factor
ϭ
1/0.70
ϭ
1.43. Then, storage capacity of the tank
ϭ
97.2
ϫ
1.43
ϭ
138.99

heaters.
Typically, the maximum temperature for domestic hot water serving lavatories,
showers, and sinks is approximately 120
Њ
F (49
Њ
C) at the fixture. The maximum
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15.13
FIGURE 9 Water heater fitted with thermal expansion tank. (Heating / Piping / Air
Conditioning magazine)
desired water temperature from a fixture for personal use can be obtained by blend-
ing hot and cold water; mixing faucets are preferred over separate hot- and cold-
water faucets. Or, thermostatic mixing valves may be installed near the point(s) of
use. For bathing, a temperature-compensated shower valve should be used. The
preferred type is a balanced-pressure model with a high-temperature limit.
ASHRAE lists hot-water utilization temperatures for various types and uses of
equipment. Facilities requiring a higher water temperature than that required for
personal use may have a separate hot-water heating system for the higher temper-
ature water if there is a significant load. Otherwise, a booster heater often is used,
as with a commercial dishwasher. The lowest temperature generally used is 75
Њ
F
(24
Њ
C) for a chemical sanitizing glass washer, while the highest temperature is

relief valve may be installed. Temperature-relief valves and combination
temperature/pressure-relief valves must be installed so that the temperature-sensing
element is located in the top 6-in (15.2-cm) of the storage tank.
The temperature-relief valve opens when the stored-water temperature exceeds
210
Њ
F (99
Њ
C). Its water discharge capacity should equal or exceed the heat input
rating of the heater.
A thermal expansion tank, Fig. 9, should also be provided in the cold-water line
adjacent to the heater whenever the system thermal expansion is restricted. Check
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15.14
ENVIRONMENTAL CONTROL
valves, pressure valves, and backflow preventers, when used on the cold-water line
to the heater, restrict expansion of the water when it is heated. This results in
excessive pressure buildup and can lead to tank failure. ASME construction is
required on all heaters greater than 200,000 Btu /h (58.6 kW) gas input or 120 gal
(455 L) storage. Additional data on sizing such hot-water heaters is available in the
ASPE Data Book, published by the American Society of Plumbing Engineers. Use
the steps in this procedure to select and size storage-tank hot-water heaters for the
10 types of applications listed in step 2 above, and for similar uses.
This procedure is the work of Joseph Ficek, Plumbing Designer, McGuire En-
gineers, as reported in Heating / Piping /Air Conditioning magazine, October, 1996.
SI values were added by the handbook editor.
SIZING WATER-SUPPLY SYSTEMS FOR

C). The tank is to have a submerged heat exchanger.
The most extreme run of piping from the public main to the highest and most
remote outlet is 420 ft (128 m) in developed length, consisting of the following:
83 ft (25.3 m) of water service, 110 ft (33.5 m) of cold water piping from the water
service valve to the hot water storage tank, and 227 ft (69.2 m) of hot water piping
from the tank to the top floor hot water outlet at the kitchen sink. Plans of the
entire water supply system are available.
The building has a basement and seven above-grade stories. The basement floor
is 3 ft 8 in (1.1 m) below curb level, the first floor is 5.0 ft (1.5 m) above curb
level, and the public water main is 5.0 ft (1.5 m) below curb level. Each of the
above-grade stories is 9 ft 4 in in height from floor to floor. The highest fixture
outlet is 3 ft above floor level.
Fixtures provided on the system for the occupancies are as follows:
1. There are 17 dwelling units on each of the second, third, fourth, fifth, sixth, and
seventh floors; and each dwelling unit is provided with a sink and domestic
dishwashing machine in the kitchen, and a close-coupled water closet and flush
tank combination, a lavatory, and a bathtub with shower head above in a private
bathroom.
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15.15
2. This first floor is occupied for administrative and general purposes, and has the
following provisions for such occupancy: one flush-valve supplied water closet
and one lavatory in an office toilet room; one flush-valve supplied water closet,
one flush-valve supplied urinal and one lavatory in a men’s toilet room; two
flush-valve supplied water closets and one lavatory in each of two women’s toilet
rooms; a sink and domestic dishwashing machine in a demonstration kitchen;

have control. You must have as much pertinent information as possible before the
design job is started.
2. Prepare a schematic elevation of the building water-supply system
Figure 10 shows a schematic elevation of the building water-supply system being
designed in this procedure. This drawing was developed using the building and
system plans. All piping connections are shown in proper sequence for the system.
The developed lengths for each section of the basic design circuit are determined
from the building and system plans. Fixtures and risers are identified by combi-
nations of letters and numbers. Those fixtures and branches having quick-closing
outlets are specially identified by an asterisk. Important information for establishing
a proper design basis are shown on the left side of Fig. 10.
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15.16
FIGURE 10 Plumbing system for high-rise building designed in the accompanying procedure.
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PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES
15.17
FIGURE 10 (Continued)
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15.18
ENVIRONMENTAL CONTROL
FIGURE 10 (Continued)

2
؆
(12.7 mm) 4.5 0.284
Sink faucet,
3
⁄
4
؆
(19 mm) 6.0 0.378
Bath faucet,
1
⁄
2
؆
(12.7 mm) 5.0 0.315
Shower head,
1
⁄
2
؆
(12.7 mm) 5.0 0.315
Laundry faucet,
1
⁄
2
؆
(12.7 mm) 5.0 0.315
Ball cock in water closet flush tank 3.0 0.189
1
؆

two of these hose bibs will be used at the same time. Show this on the design
sheet, along with the flow in gal/min (L/ s). Obtain the normal demand for these
fixtures from Table 2.
6. Size the individual fixture supply pipes to water outlets
Use Standard Code Regulations to size these pipes, as given in Table 11, later in
this section of the handbook. Choose the minimum sizes recommended in Table 11.
7. Using velocity limitations established for the design, size the remainder of
the system
The velocity limitations adopted for this system are 8 ft/s (2.4 m/s) for all piping,
except 4 ft/s (1.2 m/s) for branches to quick-closing valves as noted by asterisks
on Fig. 10. Size each line using the total fixture units of load corresponding to the
total demand of each section. For those sections of the cold-water header in the
basement which convey both the demand of the intermittently used fixtures and the
continuous demand of hose bibs, the total demand in gal /min (L/ s) was converted
to equivalent water-supply fixture units of load and proper pipe sizes determined
for them. Proper sizing could also have been done simply on the demand rate in
gal/min (L/ s).
8. Calculate the amount of pressure available at the topmost fixture
Assume conditions of no flow in the system and calculate the amount of pressure
available at the topmost fixture in excess of the minimum pressure required at such
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15.20
ENVIRONMENTAL CONTROL
TABLE 3
Pressure Calculations for Basic Design Circuit
Minimum at public main 75.0 lb/in
2

Developed length of circuit from public main to top outlet 420 ft
Equivalent length for valves and fittings in circuit (based on sizes
established on velocity limitation basis)
363
ft
Total equivalent length of circuit 783
ft
Maximum uniform pressure loss for friction in basic design circuit
(32.1 lb/in
2
/783 ft)
0.04 lb/in
2
/ft
or 4.0 lb/in
2
/100 ft
a fixture for satisfactory supply conditions. The calculated excess pressure is the
limit to which friction losses may be permitted for flow during peak demand in the
system. Then, excess pressure
ϭ
75 lb /in
2
Ϫ
8 lb/in
2
Ϫ
(65.67 ft to highest outlet
ϫ
0.433 lb/in

2
(40 kPa)
for the peak demand flow rate of 227.6 gal/min (862.6 L/ min). Note this on the
design sheet, Fig. 10. The rated pressure loss for flow through the horizontal hot-
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15.21
water storage tank, i.e., entrance and exit losses, is assumed to be about 1.6 ft head
(0.49 m), 0.7 lb /in
2
(4.8 kPa).
11. Calculate the amount of pressure remaining
We must now calculate the amount of pressure remaining and available for dissi-
pation as friction loss during peak demand through the piping, valves, and fittings
in the basic design circuit. Deduct from the excess static pressure available at the
topmost fixture (determined in step 8) the rated friction losses for any water meters,
water softeners, or water heating coils provided in the basic design circuit, as de-
termined in step 10.
Thus, the amount of pressure available for dissipation as friction loss during
peak demand through the piping, valves, and fittings in the BDC is: 38.6
Ϫ
5.8
Ϫ
0.7
ϭ
32.1 lb /in
2

2
/ft, or 4.0 lb/in
2
/100 ft (0.9 kPa/ 100 m). This is the
pipe friction for the BDC. Apply it for sizing all the main lines and risers supplying
water to fixtures on the upper floors of the building.
14. Set up a pipe sizing table showing the rates of flow for the system
Set up the sizing table showing the rates of flow based on the permissible uniform
pressure loss for the pipe friction calculated for the basic design circuit determined
in step 13. In Table 4, the flow rates have been tabulated for various sizes of brass
pipe of standard internal diameter that correspond to the velocity limit of 4 and 8
ft/s (1.2 and 2.4 m /s), and to the friction limit of 4.0 lb/in
2
/100 ft (0.9 kPa/ 100
m) of total equivalent piping length. The values shown for various velocity limi-
tations were taken from the data cited in step 7. Values shown for friction limitations
were taken directly from Fig. 11. This chart is suitable, in view of the water-supply
conditions and a ‘‘fairly smooth’’ surface condition.
15. Adjust the chosen pipe sizes, as necessary
All the main lines and risers on the design sheet have been sized in accordance
with the friction limitation for the basic design circuit. Where sizes determined in
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15.22
ENVIRONMENTAL CONTROL
TABLE 4
Sizing Table for System
Red brass pipe, standard pipe size

1
⁄
4
16.8 18.3 75.0 36.6 22.5
1
1
⁄
2
36.3 25.2 130.0 50.4 33.0
2 92.0 41.6 291.0 83.2 66.0
2
1
⁄
2
181.0 61.2 492.0 122.4 112.0
3 335.0 92.0 842.0 184.0 288.0
4 685.0 158.0 1920.0 316.0 380.0
Note: Apply the column headed ‘‘Velocity limit, l
Ј ϭ
4 ft/s,’’ to size branches to quick-closing valves. Apply the
column headed ‘‘Velocity limit, l
Ј ϭ
8 ft/s,’’ to all piping other than individual fixture supplies. Apply the column
headed ‘‘Friction limit,’’ just for sizing piping that conveys water to top floor outlets. Where two columns apply
and two different sizes are indicated, select the larger size.
FIGURE 11 Water-piping pressure-loss chart.
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PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES

with a separate head. Size the waste and vent stacks and the building house drain
for this system. Use the National Plumbing Code (NPC) as the governing code for
the plant locality. The branch piping and house drain will be pitched
1
⁄
4
in (6.4
mm) per ft (m) of length.
Calculation Procedure:
1. Select the upper-floor branch layout
Sketch the layout of the proposed plumbing system, beginning with the upper, or
second, floor. Figure 12 shows a typical plumbing-system sketch. Assume in this
plant that the second-floor urinals, water closets, and lavatories are served by one
branch drain and the showers by another branch. Both branch drains discharge into
a vertical soil stack.
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15.24
ENVIRONMENTAL CONTROL
FIGURE 12 Typical plumbing layout diagram for a multistory building.
2. Compute the upper-floor branch fixture units
List each plumbing as in Table 5.
Obtain the data for each numbered column of Table 5 in the following manner.
(1) List the number of the floor being studied and number of each branch drain
from the system sketch. Since it was decided to use two branch drains, number
them accordingly. (2) List the name of each fixture that will be used. (3) List the
number of each type of fixture that will be used. (4) Obtain from the National
Plumbing Code, or Table 6, the number of fixture units per fixture, i.e., the average

7).
4. Size the upper-floor stack
The two horizontal branch drains are sloped toward a vertical stack pipe that con-
ducts the waste and water from the upper floors to the sewer. Use Table 7 to size
the stack, which is three stories high, including the basement. The total number of
second-floor fixture units the stack must serve is 42
ϩ
9
ϭ
51. Hence, for a 4-in
(102-mm) stack, Table 7 must be used.
5. Size the upper-story vent pipe
Each branch drain on the upper floor must be vented. However, the stack can be
extended upward and each branch vent connected to it, if desired. Use the NPC,
or Table 8, to determine the vent size.
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