Metal Clad Window Failure

During a severe storm a three story house suffered severe water damage. This damage was not caused by flooding; it was caused by large amounts of water entering the top floor of the home as a result of openings to the outside. Read Consulting performed a failure analysis of the property and determine the root cause of the damage. The failure analysis included an inspection of the home and a review of photographs taken of the residence immediately after the storm, and the cause of the water intrusion was determined. Severe rot resulted in the formation of openings in the third floor windows. The windows in this house were expensive metal clad wood windows. Failure analysis determined that moisture had reached the wood structure through seal openings in the exterior metal cladding. This caused swelling of the wood and further opening of the seals; thus the amount of water intrusion was excaserbated. In addition, the moisture was "trapped" in the wood and caused accelerated deterioration. In essence, the wet wood would be at temperatures in excess of 125°F during the warm, hot days. This accelerated wood deterioration (i.e. the wood "composted"). In addition, this degradation was not noticeable because the metal cladding covered the wood. Due to rot, the windows became extremely weak and failed during the storm. The upper left photo shows a window that was so rotten that during the storm, the glass pane slipped down and left a 2" gap at the top. The upper right window failed when the bottom part of the top sash fell away creating an opening. These two windows represent the types of failures discovered on the third floor. These allowed large amounts of water into the home and caused severe damage throughout the house.

Evaluation of Hurricane Windows

Window Expert has been involved in a large case involving the failure of hurricane windows. These windows are made from two layers of glass with a thick layer (0.05") of a flexible polymer.
The lesson from this effort has been that the polymers selected for producing windows that meet Miami Dade County requirements must have the required properties. However, Miami Dade does not specifically require the amount of accelerated aging that will prove that a window will be reliable for ten to twenty years (polymer degradation). As an experienced manufacturing engineer, I reccomend that anyone developing a system of this type be aware of the extreme environmental stresses that must be endured by these windows. The important environmental stresses include high temperature, high humidity (this includes the potential for standing water) and exposure to ultra violet light. A series of accelerated life tests should be developed to evaluate the long term reliability of these windows. MIL Std 883 is a good starting point for developing these tests.