Window Well Corrosion

by Nick GromickoCMI®

A home inspector will occasionally come across a window well that is corroded.  This may perplex the inspector if the other window wells at the same home have not suffered from any corrosion.  The issue may not be moisture at that particular window.  The window well may be corroded because of electrolysis.  
Electrolysis occurs when dissimilar metals are in contact in the presence of an electrolyte, such as water (moisture). The contact of the dissimilar metals causes a galvanic action, which results in the deterioration of one of them – in this case, the window well.  The window well is acting like a sacrificial anode to the steel reinforcement grid (cathode).
Metal window wells are often made of galvanized metal, which is steel that has a thin coating of zinc oxide.  This  protects the steel from corrosion.  However, if the anchors used to fasten the window well to the poured concrete foundation are too long and come in contact with the steel reinforcement bars inside the concrete, the window well will corrode.
Electrolysis may also occur if the window well is attached to or in contact with a steel window buck (frame).
Although such a test is beyond the scope of a home inspection, there is a specialized voltage meter that can be used to confirm that a window well is in contact with the foundation reinforcement, which is often used as the ground for the home's electrical system.  
You can't simply paint the window to prevent corrosion. Painting may help cosmetically after a repair has been made, but it won't stop the process of electrolysis.  The corrosion will eventually cause the window well – a means of egress in a fire – to lose its structural integrity.  Repairs typically consists of remounting the window wells so that they aren't in contact with the foundation's steel reinforcement.