How to Guide

55
20 3.0 3.5 4.5 5.0 6.0 6.5 7.0 7.0 8.0 8.0
50 7.0 9.0 11.0 13.0 14.0 15.5 17.0 18.0 19.0 20.0
100 13.0 18.0 22.0 26.0 29.0 31.5 35.0 37.0 40.0 42.0
Plastic piping expands and contracts at a much greater rate
than comparable metallic systems. Engineers, designers and
installers should use resources such as the American Society of
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Volume 4, Chapter 11 (www.aspe.org) and the applicable local
plumbing code to install stacks with adequate compensation
for expansion and contraction. For vertical stacks in multi-
story applications, compensation for expansion, contraction
or building settling is often accommodated by the use of
offsets or expansion joints. Secure above-ground vertical
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to maintain proper alignment and to support the weight of
the piping and its contents. Support stack at base, and if over
two stories in height, support stack at base and at each floor
with approved riser clamps. Stacks should be anchored so that
movement is directed to the offsets or expansion joints. If using
expansion joints always follow the installation instructions and
recommendations of the joint manufacturer. Compensation for
thermal movement is usually not required for a vent system.
Compensation for expansion and contraction in underground
applications is normally achieved by snaking the pipe in the
trench. Solvent cemented joints must be used.
The following table shows recommended offsets and loop
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Max. Temp. Variation °F, Between Installation
and Final Operation
10° 20° 30° 40° 50° 60° 70° 80° 90° 100°
Loop Offset In Inches
Loop Length
In Feet
Thermal Expansion in DWV and Storm
Drainage Stacks
Thermal Expansion in Underground
Systems
DESIGN & ENGINEERING DATA
Change of Direction
Long Run of Pipe
Hanger or Guide
L
Restraint
2L/5
L/5 6”
MIN
6”
MIN
Loop
L
(Figure 1)
(Figure 3)
L
L /4
L/2
L/4
Offset
(Figure 2)
Failure to compensate for expansion and contraction
caused by temperature change may result in system
failure and property damage.
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addressing all aspects of design and installation of thermal
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available on this topic. The American Society of Plumbing
Engineers (www.ASPE.org) Data Book, Volume 4, 2008,
Chapter 11 is an excellent resource for engineers on designing
for thermal expansion.