Pipe Expansion, Support and IPC/UPC Differences

Pipe moves. A straight run that was cut and hung in a cold building grows as hot water passes through, and it shrinks again at night. If nothing lets it move, the force goes somewhere: into a fitting, a hanger, or a wall. On small jobs, the bends in the run take care of it. On long runs, tall risers, and hot systems, someone has to plan for it. That person is you. You also need to know which code you are under, because a hanger spacing or a test that passes in one state can fail in another.

What You Will Be Able to Do

• Calculate how much a run will grow for copper, PVC, CPVC, and PEX
• Choose offsets, loops, anchors, and guides to absorb the growth
• Apply hanger spacing rules for the code on your job
• Calculate thrust at a bend in a pressure line
• Find the rules that change between IPC and UPC jobs
• Decide what governs when the code and a maker's instructions differ

How Much Pipe Grows

Growth depends on three things: the material, the length, and the change in temperature. The temperature change that matters is the difference between the coldest and hottest the pipe will ever be, starting from the temperature when it was installed.

These rates are in inches of growth for 100 feet of pipe and a 100 F change.

Copper's rate comes from the Copper Development Association's coefficient. The plastic rates come from pipe makers. Use the number on your product's data sheet. PEX with an aluminum layer grows far less, so read the sheet for that product.

Growth = rate x (length divided by 100) x (temperature change divided by 100).

Worked example. A copper hot water main runs 80 feet. It was hung at 60 F and will run at 140 F, a change of 80 F. 1.1 x 0.8 x 0.8 is about 0.7 inches. The same run in PEX at 11 inches would grow 11 x 0.8 x 0.8, or about 7 inches. That is why PEX is never pulled tight.

Worked example. A CPVC line 120 feet long at about 4 inches goes from 70 F to 150 F, a change of 80 F. 4 x 1.2 x 0.8 is about 3.8 inches. If a straight run is held at both ends, that growth has to bow the pipe or stress the fittings.

Cold matters too. A PVC line glued on a hot day shrinks when it cools. Long buried runs need to snake in the trench. A joint that was made under strain may pull apart at the first cold night.

Ways to Absorb Movement

Let It Bend

Pipe will flex a little where it changes direction. The leg that runs off to the side of a long run acts like a spring, as long as nothing holds it stiff. This is the cheapest answer, and it covers most buildings.

Avoid pinning a branch tight against a wall close to the main it comes from. When the main grows, the branch cannot move, and the tee takes the stress. The fix is to leave the branch room to swing, or to use a longer leg.

Offsets and Loops

Where the run is long and straight, add a change of direction on purpose. An expansion offset uses two bends. A loop uses four, in the shape of a U. Leg length depends on the pipe's size, material, and how much it moves. A larger pipe or more growth calls for a longer leg. Read the length from the table in the Copper Tube Handbook, or from the plastic pipe maker's design data. Do not guess it, and do not shrink it to fit.

Anchors and Guides

Movement only stays under control if you decide where it goes.

• An anchor holds the pipe still at one point. It takes real force, so tie it to structure.
• A guide lets the pipe slide along its length, but holds it in line.
• A hanger carries the weight. It must let the pipe slide.

Place an anchor in the middle of a long run and growth splits both ways. Place a loop or offset between two anchors, and let guides keep the pipe straight. A hanger clamped hard to a pipe acts as an anchor you did not plan.

Expansion joints and flexible connectors do exist, but they need the right rating and proper anchors. An engineer usually selects them.

Risers

Tall risers grow up and down. A riser clamp at each floor carries weight. Branches that leave a riser should have room to move as the riser grows. Check for any contact with the edges of floor sleeves. Pipe rubbing on a concrete edge makes noise, and in time it can wear through.

Hanger Spacing

Each model code has a table of the longest allowed space between supports. These are common values, and they are a maximum.

Notice where 1-1/2 inch copper falls. It can hang at 10 feet under the IPC and at 6 feet under the UPC. Vertical pipe is usually supported at each floor, and no more than 10 feet apart. PEX and plastic may need mid-story guides, depending on the code and the size. The UPC table also calls for expansion provisions on long plastic drain runs. Check the table in the edition you are using.

Heat softens plastic, so hot lines may need closer support than cold ones. Add a hanger close to a heavy valve or fitting, and at each change of direction. Do not count on a pipe holding up a valve.

Hanger Materials

• Use copper-coated, plastic-coated, or isolated hangers on copper. Bare steel against copper in damp areas causes galvanic corrosion.
• Use hangers wide enough to avoid cutting into plastic. Keep hangers loose enough for the pipe to slide.
• Use insulated supports on insulated pipe, so that the hanger does not crush the insulation.
• Follow your code's rod and anchor sizes, and hang from structure. Do not hang from another trade's pipe or duct.

Thrust in Pressure Lines

Water under pressure pushes on every bend and capped end. Soldered, solvent-welded, and press joints hold together on their own. Gasketed pipe does not. Bell-and-spigot joints on buried mains can pull apart unless a thrust block or a restraint holds them.

Thrust at a bend = 2 x pressure x pipe area x sin(half the bend angle). For a 90-degree bend, that works out to 1.414 x pressure x area.

Worked example. A 4-inch line has an area of about 12.6 square inches. At a test pressure of 100 psi, a 90-degree bend sees 1.414 x 100 x 12.6, or about 1,780 pounds of force. A capped end sees 100 x 12.6, or about 1,260 pounds. That is why a test on a buried line should not start until the blocks are cured and restraints are in place. An engineer or the water supplier's standards set the block size, based on soil. Do not guess.

Knowing Your Code

The two main model codes are written by different groups. The International Code Council writes the International Plumbing Code (IPC). IAPMO writes the Uniform Plumbing Code (UPC). States adopt one or the other, or write their own, and then cities may amend it. Some states also use the International Residential Code for houses. Before you bid or lay out a job in a new place, find out:

1. Which code and which edition has been adopted?
2. What state and city amendments apply?
3. Who is the authority having jurisdiction (AHJ)?
4. Does the job have a spec or an engineer who asks for more?

Common Differences to Check

A fitter who moves between states should write the differences on a card and read each new jurisdiction's amendments first. If a detail matters and the code is not clear, ask the AHJ before you build. Get the answer in writing when you can.

When the Normal Method Does Not Apply

A senior fitter knows when a usual rule stops being enough. Stop and get engineering input when you see any of these:

• Runs that are very long, or very hot, with little room to offset
• Risers in tall buildings, where pressure and growth both climb
• Pipe crossing a building expansion joint, which needs a listed flexible assembly
• Seismic zones, where bracing is often required
• Lines above sensitive spaces, such as data rooms
• High-pressure or non-water service

Which Rule Wins

You may find that a code and a maker's instructions differ. In general:

• The code is the legal minimum. You can go beyond it.
• Listed products must be installed according to their listing and instructions. Those are part of what the code accepts.
• When two rules differ, the stricter one is usually safe to follow. A closer hanger spacing from a maker still meets a code maximum.
• If they truly conflict, ask the AHJ and the maker, and get it in writing.

Worked example. A PEX maker asks for supports every 32 inches, and your code agrees. A second tube maker's sheet shows closer spacing on hot runs. You use the closer spacing. It meets the code, it meets the listing, and your warranty stays good.

Common Mistakes

Check Your Understanding

1. A copper line runs 150 feet from 60 F to 120 F. How much does it grow?

The change is 60 F. 1.1 x 1.5 x 0.6 is about 1 inch.

2. An owner says a 50-foot PEX hot line is badly installed, because it bows between supports once the water runs at 130 F. It was hung at 50 F. What do you tell them?

Bowing is not a defect by itself. At 11 inches of growth for each 100 feet and 100 F, 11 x 0.5 x 0.8 is 4.4 inches, and that has to go somewhere. Check that the supports meet the spacing rules and that the tube is free to move.

3. You are hanging 1-1/2 inch copper on a UPC job, and the foreman says 10 feet is fine. What do you say?

Check the table, because that is a common IPC value. Under the UPC, 1-1/2 inch copper is usually hung at 6 feet.

4. A 6-inch gasketed water main has an area of about 28 square inches and will see 150 psi. How much force is on a capped end?

150 x 28 is about 4,200 pounds. It needs a proper thrust block or a restraint.

5. A long hot water main has one straight 90-foot run. Where do you want the anchor, and what goes between anchors?

Pick anchor points on purpose, and put an offset or a loop between them. Guides then keep the pipe in line as it moves.

Key Takeaways

• Growth is rate x length x temperature change. PEX grows about ten times more than copper.
• Plan movement with bends, loops, anchors, and guides.
• A tight hanger is an accidental anchor.
• Hanger tables differ. Know which one applies to your job.
• Pressure pushes on bends, so gasketed pipe needs restraint.
• Find the code, edition, and amendments first, and follow the stricter rule.