The majority of the windows at the Motherhouse, a religious residential facility in Monroe, Michigan, renovated by Susan Maxman & Partners, were wood double-hung windows with single glazed true divided lights that were very energy inefficient. In order to make an informed decision to either refurbish or replace the windows, a number of criteria were developed by which to evaluate the alternatives.

Windows were restored, left, and replaced at the Motherhouse by Susan Maxman & Partners Photos courtesy of Susan Maxman & Partners

Thermal performance of the windows was a given and a key element in the Sister's goal of sustainability. UV protection and glare were important considerations for the failing eyesight of many of the aging Sisters. The windows had to be easy for the Sisters to operate and clean. The look of the windows was one of the significant character defining elements of the building and was important to both the State Historic Preservation Office and the Sisters.

Construction waste, manufacturing waste, and energy spent in transportation were part of the project's sustainable design goals. Other client concerns included budget, energy efficiency life, and expected life of windows selected over available alternatives. Life cycle costs, however, were not evaluated. Design criteria included the following:

Thermal Performance:

• U-values in summer and winter
• Shading coefficient
• Air infiltration

Visual Health:

• UV transmittance
• Glare reduction

Function:

• Ease of operation
• Ease of cleaning
• Ease of installation
• Maintenance

Aesthetics:

• Historical accuracy
• State Historic Preservation Office Acceptance
• Sight lines

Sustainability:

• Waste material generated
• Manufacturing waste
• Green materials

Cost:

• First costs including screens

Window Life:

• Life of window in years

Alternative Options

Eight alternatives were developed and analyzed during the design phase. A ninth was suggested during the bid phase. A matrix was developed which compared the seven alternatives to the criteria:

1. Keeping the existing single-glazed windows
2. Refurbishing the existing with a double-glazed energy panel
3. Refurbishing the existing with a low-E double-glazed energy panel
4. Refurbishing the existing with double-glazed heat-mirror glass was not possible for the existing windows.
5. New aluminum clad wood windows with double-glazed low-E glass
6. New aluminum clad wood windows with double-glazed heat-mirror glass
7. New aluminum windows with double-glazed low-E glass
8. New aluminum windows with double-glazed heat-mirror glass
9. Refurbishing the existing frames and replacing the sash with double-glazed low-E glass.

Analysis and Solution

In general, refurbishing the existing windows with new double-glazed low-E glass ranked higher in all categories. The project was bid with this alternative. The bids for this alternative came in higher than the estimate. One of the bidders, however, proposed the idea of using double glazed replacement sash with low-E glazing in the existing frames. The cost was closer to the estimated price for the alternative with the refurbished sash. This solution met the Sister's combined goals of sustainability and preservation and was accepted pending approval of a mockup.

The existing windows in the cloisters were lowered and the sash replaced with new steel windows. What was once an inwardly focused residence has been transformed into a new home for the Sisters that is strongly connected to the outdoor environment.

Karin Tetlow is principal of Restorative Partners and writes frequently about design and construction.