Reuben's Home Inspection Blog


What causes banging water pipes?

Originally posted at:

Have you ever heard a banging noise coming from your water pipes when the water is turned off quickly?  It usually sounds like the pipes are banging on something inside the walls... and that's exactly what's happening.  When the flow of water is turned off very quickly, a small shockwave is created inside the pipe, which can cause the pipe to shake, and often bang on the wall studs or floor joists.

I recently replaced the water tubing running to my kitchen sink as part of an experiment to get hot water faster at my kitchen sink.  Before I secured the new tubing in place, I tested out the water line to make sure I was happy with the results, and found I had created perfect conditions for a banging pipe.

That pipe banging on the wood was happening just from turning the hot water on and off at the kitchen sink.  How many times do you suppose that pipe will bang on the floor joists before something gives way and the pipe starts leaking?  I don't intend to find out.  Just watching that video makes my skin crawl.

This banging is referred to as 'water hammer', and as you might imagine, it can lead to damage at the water lines.

Water hammer diagram

The Minnesota State Plumbing Code actually addresses water hammer - here's what it says:

4715.1750 WATER HAMMER.

In all building supply systems in which devices or appurtenances are installed which cause noises due to water hammer, protective devices or approved mechanical shock absorbers shall be installed as close as possible to the quick-acting valve causing the water hammer. Where mechanical devices are used the manufacturer's specifications shall be followed as to location and method of installation.

There are two ways to deal with water hammer - install protective devices or shock absorbers.  Protective devices are devices that hold the pipes secure.  As soon as I secured the flexible water tubing at my own house, the tubing couldn't move any more, and the sound went away.  In new installations, clamps and protective devices are standard.

Suspension Clamp

Shock absorbers are more commonly referred to as 'water hammer arresters'.   Water hammer arresters can help to prevent water hammer in homes where the water pipes aren't accessible.  In many older houses in Saint Paul, you'll find a huge galvanized pipe installed vertically, right next to the water meter in the basement.  This was a primitive shock absorber, which was supposed to help prevent water hammer because the riser created an air chamber in the pipe which would compress when there was a shockwave.   The idea was that this pipe would help prevent water hammer throughout the entire house.  In reality, these weren't effective.  The shockwave started right at the fast closing fixture, and affected everything in it's wake.

Primitive water hammer arrester

Because the shockwave that creates water hammer gets created right at the quick-closing valve, a much better location for a shock absorber is right at the faucet or valve.  The photo below shows a couple of early edition shock absorbers installed just above the washing machine connectors.

Primitive shock absorbers

These early-edition water hammer arresters worked fine until all of the air was absorbed in to the water... which might take as little as a few weeks.  After the air is absorbed in to the water, these 'air chambers' become waterlogged and useless.  The animation below shows what would happen to these early-edition water hammer arresters over time.

The simple solution is to install a manufactured water hammer arrester; a small sealed air chamber that's designed to prevent water hammer.  The animation below shows how they work.

If you need water hammer arresters to help prevent banging pipes at your washing machine, you can buy a pair of them for under $25 at Amazon, and they don't require any special tools or knowledge to install.  

Special thanks to Sioux Chief Manufacturing for providing the animations and diagram above, and thanks to Portland Home Inspector Ken Meyer for providing the photos of the primitive water hammer arresters / air chambers.

Reuben Saltzman, Structure Tech Home Inspections


Comment balloon 23 commentsReuben Saltzman • June 26 2012 03:30AM


Reuben, this is great information...always wondered about homes with banging water i know how to talk to the plumber effectively!

Posted by Ginny Gorman, Homes for Sale in Southern RI and beyond (RI Real Estate Services ~ 401-529-7849~ RI Waterfront Real Estate) over 7 years ago

Reuben, this is great information for a problem I have personally experienced. Thanks for posting today.

Posted by David Burrows, No Pressure, Just Seriously Devoted to Real Estate (Classic Realty) over 7 years ago

Reuben: I have wondered about this and now know the reason for banging pipes.  Good information for the masses...suggested!

Posted by Anita Clark, Realtor - Homes for Sale in Warner Robins GA (ColdwellBanker SSK Realtors ~ 478.960.8055) over 7 years ago

I am sure lots of homeowners will find this helpful since it is a common complaint that has escaped diagnosis.

Posted by Sally K. & David L. Hanson, WI Real Estate Agents - Luxury - Divorce (EXP Realty 414-525-0563) over 7 years ago

Another problem I have run into is the safety hoses for the washer. They are designed to stop flow if there is a break in the line, but when the HE machine fills, the hoses create a water hammer effect. 

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) over 7 years ago

Great post again Reubs.  Suggested, as always, as I do to almost every inspector post!

Hey, I heard they have newer shock absorbers than those oldie, but goodie, galvanized "appurtenances."

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 7 years ago

Ginny - thanks, this should be an easy fix for the plumber.

David - I hope you got it taken care of.

Anita - thanks!

Sally & David - I've had a lot of customers ask me about this issue too.

James - no kidding?  I haven't noticed.  I'll have to start paying attention to that.

Jay - thank you, sir.  Yes, the new water hammer arresters are far superior.  I recommend Sioux Chief - their stuff is all made here in America.  

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 7 years ago

Once again, Reuben, you address something I have never heard about but I will keep my ears open! Very detailed information as usual.

Posted by Peggy Chirico, REALTOR® 860-748-8900, Hartford & Tolland County Real Estate (Prudential CT Realty) over 7 years ago

Hi Rueben.

A very informative post about the problems that many home owners have to this day.

Great presentation with all the video's.

Keep up the great posts. We all learn from them.

Best, Clint Mckie

Posted by Clint Mckie, Desert Sun Home, Comm. Inspection 1-575-706-5586 (Desert Sun Home, commercial Inspections) over 7 years ago


Great illistration of the water hammer. I like how the animation shows how air disolves into the water and over time the air cushion dissipates. 


Posted by Donald Hester, NCW Home Inspections, LLC (NCW Home Inspections, LLC) over 7 years ago

Rueben, never heard of this fix for what is an annoying problem at the very least.  Thanks Rueben

Posted by Chris Smith, South Simcoe, Caledon, King, Orangeville Real Esta (Re/Max Chay Realty Inc., Brokerage) over 7 years ago

Peggy - you'll notice it now :)

Clint - thanks!

Donald - I loved that clip too.  They did a great job with that.

Chris - It's especially nast when it's your own house ;) 

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 7 years ago

Thanks for the Ah-ha moment!
Featured you in my Weekly Post!

Posted by Kathy Streib, Home Stager - Palm Beach County,FL -561-914-6224 (Room Service Home Staging) over 7 years ago

OMG I had no that explains a lot.  Mystery solved...and now hopefully, we can spread the word to reduce the damage.

Posted by Debbie Gartner, The Flooring Girl & Blog Stylist -Dynamo Marketers (The Flooring Girl) over 7 years ago

Good morning Reuben,

Wow..I can see why Kathy had a Ah-ha moment on this post! I'm so glad I came over to check this post out..a great explanation for a very common problem I think we have all experienced at one time or another. I suggested! Can't believe this post is not featured :).

Posted by Dorie Dillard CRS GRI ABR, Serving Buyers & Sellers in NW Austin Real Estate (Coldwell Banker United Realtors® ~ 512.750.6899) over 7 years ago

I have heard the term “water hammer” for many years but never really knew what it was. Lucky me, I guess, since I never had personal experience with the problem.

Thanks, Reuben, for the good information.

Posted by John Juarez, ePRO, SRES, GRI, PMN (The Medford Real Estate Team) over 7 years ago

Reuben, thanks for the plumbing tutorial. Next time I go into new construction before drywalling I look for these features.


Posted by Adrian Willanger, Profit from my two decades of experience (206 909-7536 over 7 years ago

Kathy - thanks for reading, and thanks so much for the mention!

Debbie - exactly, that's the goal :)

Dorie - thanks for the suggestion!

John - up until right before I wrote this post, I had never had a problem with it either ;)

Adrian - right on.  Thanks for reading.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 7 years ago

Okay Rueben, so I have a knocking pipe sound when my lawn sprinklers are on. So I am assuming same theory even though most of the pipes are outside? Just find where it comes into the wall of the house? 

Posted by Shar Sitter, Home Staging and Redesign Minneapolis/ St. Paul, M (Rooms With Style) over 7 years ago

Shar - with a sprinkler system, it might be tough to fix the issue... but in theory, yes.  Have one person manually operate the system, getting the valves to open and close, and have someone else watch the pipes, assuming this portion of the home is unfinished. 

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 7 years ago

Thanks Reuben. Yes...the lower level is unfinished and I will make sure the knocking is fixed when we go to finish it off. :)

Posted by Shar Sitter, Home Staging and Redesign Minneapolis/ St. Paul, M (Rooms With Style) over 7 years ago

Good stuff :)

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 7 years ago

That is really annoying to say the least & a very good explanation of what happens.

Posted by Lyn Sims, Schaumburg IL Real Estate (RE/MAX Suburban) over 7 years ago