For professional home inspectors, “corrosion” is a word that often ends up written inside the pages of a home inspection report—especially when checking out older properties in which components haven’t been repaired or replaced for years. But what does corrosion mean? Is it the same thing as “rust”? And when should you be concerned if it rears its ugly head during your search for a new home?
Corrosion is defined as the deterioration of metal (or other material) by chemical or electrochemical reaction resulting from exposure to weathering, moisture, chemicals, or other agents or media, as noted by InterNACHI, the International Association of Certified Home Inspectors. During this natural process, a refined metal (iron or copper, for example) changes its properties due to its environment, converting to another form such as oxide, sulfide, or hydroxide. The result is the degradation of the material, failed systems, and, in many cases, costly damage.
Most common is the occurrence of “rust,” a type of corrosion in which water and oxygen combine to cause iron or its alloys to form iron oxide—a reddish-brown compound you knew all too well if you owned a car in the 1970s. Rust will sometimes appear greenish when oxygen is not a major factor in its production. Either way, the presence of rust is more than a cosmetic concern; it can be an indication that a component is at risk of failure. So when your home inspector highlights a rusty pipe on the report, this isn’t something you should ignore and hope goes away.
For more than 27 years, the certified inspectors at A-Pro Home Inspection have become well-acquainted with corrosion in all its unsightly and destructive forms. Here is a checklist of some of the most common instances of corrosion found during a home inspection.
Pipes: Because of their ongoing contact with water, it’s no secret that plumbing pipes are the number-one component that suffers the effects of corrosion. Supply pipes made from galvanized steel, popular in pre-1960s homes, are notorious for rusting from the inside-out from years of exposure to minerals in the water. This can lead to several unpleasant problems: leaking, particularly at threaded joints; lower water pressure; difficult repairs due to damaged threading; and mineral and rust deposits appearing in your morning shower and boiled pasta.
Your inspector will also report on corroding copper pipes, which will be identified through observation. There are several factors that can accelerate copper pipe corrosion, including high oxygen levels in the water and low pH levels (high acidity). Low pH levels can dissolve the pipe’s protective inner oxide layer, making the pipe vulnerable to rust and leaks. A minuscule, undetected leak can lead to increased water bills over many months before it is discovered. Like with galvanized pipes, failure to address copper pipe issues can invite severe leakage and possible failure of the plumbing system.
Water Heater: Even though modern water heaters are made to prevent corrosion, improper installation can result in a galvanic reaction that can lead to problems. For example, galvanic corrosion can result when two dissimilar metals (e.g., steel and aluminum) are touching each other, such as at the heater’s water inlet and outlet fitting. Oftentimes, a plastic ring is used to prevent the two incompatible metals from making contact. If the plastic fails or if none is used, corrosion—and possible leakage—could occur at the connection fitting. Similarly, a galvanized stainless steel fitting between copper pipe fittings—with the help of the presence of an electrolyte, i.e., water—can spur galvanic corrosion. Even without an active leak, corrosion buildup on a water heater will be noted by the inspector.
The same is true for other places in a home where mismatched metals are incorrectly employed, including:
- Wrong fasteners used to secure metal roofing
- Galvanized steel fasteners used with copper
- Copper or lead flashing used with galvanized or aluminum roofing materials
Electrical: When possible, your inspector will report on the presence of rust and corrosion on any part of the electrical panel, including wires—a potential fire hazard. Corrosion is a sign of past—or possibly current—moisture issues. Observations may include rust on the panel surface, screw connectors on circuit breakers, bus bars, and the connection of the service entrance cable to main breakers/fuse connectors.
Other common areas of corrosion in a home include metal window wells; window and door frames; steel lintels above doors and windows; joint hangers; and garbage disposals.