Moisture, Condensation and Mold: Typical Window Problems

By Jean W. Tamisin and Richard A. Weber  
OTHER PARTS OF THIS ARTICLEPt. 1: Avoiding Water Penetration in WindowsPt. 2: This PagePt. 3: Repair or Replace the Windows: Making the Right Decision

One of the most common window problems is moisture penetration and related damage to interior finishes. Moisture accumulation can also lead to mold development and subsequent health risks. For these reasons, moisture ingress is one of the most litigious problems related to window systems.

With barrier-type systems, problems associated with moisture ingress are typically related to ineffective exterior seals, either from improper original installation or aging of the materials. For drainage systems, interior water penetration can occur through poorly functioning internal system seals or water overflowing horizontal members, such as sills. Internal drainage systems should include watertight joints and seals, end caps at terminations, and drainage holes to allow water to exit the system. Sill members of drainage systems also should be designed to accommodate anticipated water height within the system, which is based on design wind pressures. Defects in any one of these components or seals can result in interior leakage.

Other problems associated with windows are air leakage and condensation. These problems, particularly cold drafts, can affect occupant comfort and can result in interior moisture damage. Air leakage can occur as a result of high winds or building pressurization problems and is typically due to poor internal seals or gaskets. As gaskets age and are subjected to movement, increased air infiltration typically occurs.

A typical condensation problem is evident if there is moisture at the interior surface of the glass unit or sill framing members independent of rain. Condensation occurs when the interior surface temperature of the window assembly falls below the dew point of the adjacent air. The potential for interior condensation increases in buildings in cold climates particularly if the interior is humidified during cold weather.

Condensation on metal frames can also result from poor placement of the window within the exterior wall where thermal bridging can occur. For example, where the window is installed outside of the wall insulation system for the adjacent cladding, cooling of interior portions of the window frame can occur during cold exterior temperatures.

Other potential problems with window performance include failure of structural elements or connections, glass failures and breakage, fogging of insulated glass units, and failure of coatings.

When deciding whether window systems should be repaired or replaced, consider the following questions to understand the condition of the existing system.

  1. Is the existing window system, including connections, structurally adequate and does it accommodate building movements and structural loadings? This is critical from a safety as well as a performance standpoint.
  2. Is the system effective at controlling water leakage and moisture migration?
  3. Is the system effective in resisting unwanted air infiltration and condensation?
  4. What is the condition of the system components? Check the frame, sash, glazing, hardware, weather stripping, sealants, and exterior paint or other surface coatings.
  5. Are problems widespread or isolated? It may be possible to address problems on a window-by-window basis.
  6. Is it possible that the adjacent wall system is contributing to the problems experienced?
  7. Is the building historically significant?

One of the first steps in answering these questions is to determine the nature and extent of existing problems. Perform surveys of the interior and exterior of the systems to determine locations of water-related damage and potential conditions on the exterior that may cause such damage. Check with staff to identify locations, extent and frequency of occurrence of observed water leakage. This survey can help determine if the problems are primarily concentrated at specific locations or are systemic to the entire building.

To understand fully how the window system performs under various conditions, field testing is often recommended. This is particularly important when investigating the source of water leakage or air infiltration problems. Testing can be performed in accordance with standards published by ASTM International and the American Architectural Manufacturers Association to evaluate the performance of an installed window.

Performance testing of windows, as well as of the surrounding wall, also provides baseline data that can be used in the future when testing is performed to evaluate trial repairs or replacement approaches. In conjunction with field testing, it is beneficial to create inspection openings through interior finishes to monitor for leakage during testing and to verify the condition of anchorage. When necessary, various components of the window system can be disassembled to observe internal conditions. This effort, combined with determining the interior air conditions and surrounding wall interface construction, can be critical when investigating condensation problems.

Continue Reading: Can These Windows Be Saved

Avoiding Water Penetration in Windows

Moisture, Condensation and Mold: Typical Window Problems

Repair or Replace the Windows: Making the Right Decision

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  posted on 3/1/2009   Article Use Policy

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