Repair or Replace the Windows: Making the Right Decision

Once the full extent and nature of the existing problem is known, a determination can be made regarding repair or replacement. No matter what the age or construction type of the windows, maintenance is necessary over time to preserve the system’s materials and ensure serviceability of the assembly. However, when extensive repairs or maintenance are required, the costs and difficulty of continuing repairs and their overall effectiveness should be compared to the cost and performance improvements gained by replacement.

Repair is typically preferable to replacement unless the following conditions exist:

• There is excessive deterioration of the system.
• The effectiveness of the repairs is questionable.
• The cost of repairs approaches the cost of replacement, or life-cycle costs of replacement proves cost-effective based on lower energy and maintenance costs.
• Ongoing maintenance cannot be practically achieved with repairs.

For windows on any structure, repairs should be designed to address distress conditions and deficiencies while maintaining the project cost constraints. Typical repairs may consist of the replacement of sealants, anchorage, operating vents/sashes/hardware, weather stripping/gaskets, and installation of storm systems for improved condensation and air infiltration resistance.

When addressing water leakage issues, pay careful attention to design and implementation of drainage system repairs to avoid obstructing water drainage paths. Often, drainage systems are unintentionally converted to ineffective barrier systems during repairs, such as when drainage holes are sealed over. This can lead to an increase in moisture-related problems. It is also not unusual to convert drainage systems to barrier systems intentionally due to the costs associated with repairing internal seals of window systems.

However, with this approach, additional sealant is often needed to achieve an effective barrier. It is essential that these seals are properly maintained to ensure a watertight system, which will likely increase costs over time. The cost of maintaining exterior seals should be factored into the decision to convert a drainage system to a barrier system.

Other factors to consider in the repair design are the feasibility of implementing the repairs, the level of disruption of building operations, the desired life expectancy and maintenance requirements, and cost.

For windows on historic structures, replacement may be precluded or strictly limited, and local, state or federal authorities may restrict the types of repairs that can be performed. Generally, retaining and repairing the existing historic fabric is recommended. Preferable approaches include repair, selective replacement of components, and maintenance work such as painting or sealing, in lieu of replacement. In instances of severe deterioration where windows are to be replaced, the new system should be appropriate to the original building character.

For replacement systems, the window system should be designed and detailed to address critical performance and aesthetic criteria. These criteria include structural capacity, water penetration, air infiltration, and thermal performance.

Once an initial repair or replacement design has been developed, mock-ups are typically recommended prior to finalizing the design. Mock-ups of proposed repair or replacement systems should be erected on the building to evaluate constructability, performance and aesthetics. Testing of the mock-up is recommended to verify the effectiveness of the repair or replacement design. If the potential for condensation is a concern, monitoring the mock-up during a representative winter season can be very valuable. Laboratory mock-ups can also be beneficial if the replacement system requires custom configurations or has unique or difficult interface detailing with the adjacent wall systems.

In some cases, both repair and replacement options can be included in mock-ups to allow side-by-side comparison of aesthetics and effectiveness during testing/monitoring. Also, whether repairing or replacing the window system, the project should include a well-defined field quality control program to help ensure a successful installation.

It can be difficult to determine whether a window can be saved or not. Making the right decision requires considering an array of factors, and should be preceded by conducting a detailed assessment of existing conditions as well as the systems and options available. This information is essential to determine the appropriate course of action.

Jean W. Tamisin is an associate with Wiss, Janney, Elstner Associates, Inc. (WJE) in Northbrook, Ill. Richard A. Weber is an associate principal with WJE in Northbrook. Tamisin and Weber specialize in the investigation and repair of the building envelope, including problem-solving related to repair and replacement of window systems. David S. Patterson and Deborah Slaton of WJE also contributed to this article.

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