How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
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Why is old galvanized steel water pipe a problem for homebuyers?
Sunday, October 21, 2018
Galvanized steel pipe was often used for water supply piping in homes until the early 1970s. It is rarely used today because corrosion problems limit it’s useful lifespan to between 40 and 60 years. Rust-corrosion accumulates inside the pipe and causes a plumbing version of arteriosclerosis, with the gradual hardening-of-the-arteries narrowing the diameter of the pipe in horizontal runs to the size of a soda-straw in places. Essentially, it rusts from the inside out. This restricts the flow of water to faucets and showers and, eventually, the corrosion causes the pipe to spring leaks--usually the first place being in the ground under the home’s concrete floor slab, or near the water heater due to an electrolytic reaction to copper fittings speeding up the corrosion.
The photo at the top of the page shows the end of an abandoned section of galvanized pipe in a laundry room wall, where it was cut-off at the juncture with a washing machine faucet. As you can see, the water flow was severely reduced from the buildup of rusty crud in the pipe. Surrounding it is the cream-color plastic pipe that replaced it, called CPVC.
Sometimes the corrosion is painfully obvious on the exterior of the pipe, as in the photo below.
But, because the bulk of the corrosion is happening inside the pipe, it may not be obvious until the interior corrosion eats entirely through the pipe. The two photos below show a section of galvanized pipe that was recently replaced. The side view does not indicate any distress but, looking into the open top end is a different story.
Several insurance companies will not insure an older home (over 40-years) with original galvanized water piping still in place. Others do not require replacement, but will set an extremely high deductible for water damage or want certification of the condition of the pipe by a licensed plumber. The cost of re-plumbing the average home’s water supply piping starts at about $5,000 and, usually, the new piping is run through the attic, then down to the plumbing fixtures, leaving the original galvanized pipe abandoned in place.
Galvanic corrosion, an electrolytic reaction between galvanized and adjacent copper pipe, can cause early pipe failure of some portions of a home’s galvanized steel piping. It usually occurs at pipe connections near the water heater. To learn more about it, see our blog post What's that powdery crust on the pipe connections at the water heater?
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