Preservation Tech Notes: Windows 2 Installing Insulating Glass In Existing Steel Windows

Historic Preservation

Building Manager Tools

Historic Buildings

Historic Preservation Library

Portfolio Management Resources

Preservation Desk Guide

Preserve America

Project Management Tools

Realty Specialist Tools

Technical Resources

GSA Technical Preservation Guidelines

Historic Preservation Technical Procedures

NCR Preservation Note Series

Preservation Technology

Historic Preservation - Technical Procedures

Spectitle:	Preservation Tech Notes: Windows 2 Installing Insulating Glass In Existing Steel Windows
Procedure code:	0851002S
Source:	Preservation Tech Notes, National Park Service, Pad
Division:	Doors And Windows
Section:	Steel Windows
Last Modified:	02/24/2012
Details:	Preservation Tech Notes: Windows 2 Installing Insulating Glass In Existing Steel Windows PRESERVATION TECH NOTES: WINDO= WS Number 2 INSTALLING INSULATING GLASS IN EXISTING STEEL WINDOWS Charles E. Fisher Preservation Assistance Division National Park Service This standard includes the bulk of information contained in the original Preservation Tech Notes developed by the National Park Service and the Center for Architectural Conservation at Georgia Tech. The Preservation Tech Notes are case studies of exemplary projects designed to provide specific examples of sound preservation techniques. To obtain a complete copy of The Window publications, including figures and illustrations, please contact: Historic Preservation Education Foundati= on P.O. Box 77160 Washington, DC 20013-7160 The Window Handbook, jointly prepared by the National Park Service, Preservation Assistance Division and the Center for Architectural Conservation at Georgia Tech, also contains all of the Tech Notes on Windows and is available for purchase from the Historic Preservation Education Foundation for $32.00. The Window Workbook is available for $49.00. The two publications together can be purchased for $72.00. MERGENTHALER LINOTYPE BUILDING Chicago, Illinois *INTRODUCTION* The Mergenthaler Linotype Building is a six-story printing loft building located in the South Loop Printing House National Register District in Chicago. The masonry building was constructed in 1883 and altered in 1917 with the addition of steel multipane hopper windows on the side and rear elevations. Recently renovated, the building now has residential condominiums in the upper stories and commercial space on the first floor. The historic steel windows on the otherwise plain secondary elevations are a significant architectural feature, clearly visible from the street. The 15 large 20-light windows on the side of the building measure 6' wide by 7' high with a center-pivoting hopper, while the 9 smaller 12-light windows are the same height but only 3'9" wide. On the rear elevation, there are an additional 38 steel windows of 15 lights, measuring 3' by 7'. The individual lights are 14" by 20", a size common to pre-World War II steel sash. During the renovation work on the building, the windows were repaired at the site and insulating glass was used in place of the existing single panes to improve the energy performance of the windows and the marketability of the condominium units. *WINDOW PROBLEMS* The architect for the project, Kenneth Schroeder, AIA, with the Chicago firm of Kenneth Schroeder and Associates, was confronted with a series of problems in dealing with the steel windows. As is commonplace, lack of routine maintenance had led to rusting and mild corrosion of portions of the windows. Some of the sections, especially the hopper units, were bent, bowed or racked and a number of the =AC" wire glass panes were broken. In converting the building to residential use, ways of improving the thermal comfort of the occupants were explored and cost- effective means were studied for reducing energy consumption. Furthermore, a design had to be selected for additional windows that needed to be created in order to satisfy air and light requirements for the new use. Four possible approaches to the windows were examined: - Repair and repaint the existing windows; - Repair existing windows and install insulating glass; - Replace existing windows with custom-made, double-glazed steel sash; or - Remove existing units and install new aluminum double- hung thermal sash. The following were specific considerations in assessing the four window alternatives: 1. Any window alteration would have to be compatible with the historic character and configuration of the existing steel windows. 2. Work on the windows beyond repair and repainting - including the possibility of all new replacement units - would have to be cost-effective in terms of increasing the marketability and value of the condominiums. 3. The existing wire glass would have to be replaced with clear glazing since the wire glass was considered inappropriate for the new residential use. 4. Any work on the windows would have to be accomplished within a tight time schedule. 5. Addition of screening was desirable but not critical because the downtown area was not particularly insect- prone. Of the four possible window treatments, the two replacement options - custom-made steel sash of a matching design, and bronze anodized aluminum double-hung sash - were too expensive for the project; the latter was less expensive but still cost on the average between $400-450 per window. Furthermore, the use of double-hung sash in the large openings would have changed the historic character of the building. For the required new window openings, a manufacturer of steel windows was located who offered a stock unit similar to the original design but with noticeable differences in the horizontal proportions and overall dimensions. These stock units were significantly less expensive than the custom steel windows and were selected for use in new openings since they were compatible with the heavy commercial style and character of the historic windows. *WINDOW REHABILITATION SOLUTION* The decision to repair the existing windows was based largely on the costs involved. Reglazing the windows using 3/8" insulating<= br> glass ran approximately $12 per double pane, while reconditioning the frames and hardware and repainting added another $50-75 to the average cost of each window. The average cost of $250 per window for this work was significantly lower than any of the proposed replacement units, and most of the repair cost was a result of the reglazing. Only about half of the glazing cost was directly attributable to the use of insulating glass since from the outset, the residential use of the building tended to dictate from a marketing perspective that the existing wire glass be replaced. Thus it was decided that in lieu of only repairing and reglazing with clear =AC" glass, which would have been the cheapest of the four identified window options, sufficient benefits could be derived by using double glazing to improve the window's energy performance. In deciding what type of glazing to install, the depth of the T- shape muntin bar was a constraining factor. Since at least the 1930s, companies have been manufacturing double-glazed steel windows. In such cases however, the depth of the muntin bars was usually greater than the 1=AC" found on the windows in the Mergenthaler Linotype Building. By using 1/8" glass instead of the =AC" wire glass, it was possible to use insulating glass in the existing windows, though an optimum distance between the double panes in terms of energy performance could not be obtained. Thus it was decided that the cost of double glazing alone was justified considering the advantages derived from increased energy performance and reduced likelihood of condensation forming on the windows despite the new residential use. The double glazing also created no significant weight problem since =AC" wire glass was being<= br> removed. *PREPARATION AND CLEANING WORK* After the metal glazing angles and glass were removed, the old frames were scraped off and existing paint layers and rust were removed using sand under air pressure. After cleaning, sections from several old windows that had been removed were welded into the remaining windows to replace missing or deteriorated metal pieces. At the same time, racked metal sections, especially the center- pivoting hopper units, were realigned by applying heat and pressure. All the metal was then painted with an anti-corrosive paint. *GLAZING AND HARDWARE* The original wire glass had been held in place by glazing angles bolted to the muntin bars. In removing the glass it was decided, due to deterioration of the glazing angles and the labor- intensiveness of reinstallation, that new spring glazing clips and steel sash glazing compound would be used instead. The insulating glass had been delivered to the site, vacuum sealed and with a continuous glazing edge. After the bed putty was applied to the sash, the insulating glass was installed with glazing clips and face putty. New replacement handles and chains were readily found for hopper units where such pieces were broken, deteriorated or missing. After the windows were painted and caulked, there still was air infiltration around the hopper units, so adhesive-backed foam was added as weather stripping around the hopper unit. *PROJECT EVALUATION* There were no real unforseen problems with the window work and the job was finished on time and within budget. Screens were not added to the windows although it would be possible do to so if an individual resident felt there was a need. Condensation on the windows has not been a problem due to the use of insulating glass; reduced air infiltration after repair, caulking and weather stripping; the presence of a good heat source near the windows; and the southern exposure of the large windows. On the whole, the reconditioned windows are performing well and are providing the desired improvements in personal comfort. There was no real problem in marketing the condominiums and residents have capitalized on the interior design opportunities provided by the large windows and the loft space. The Mergenthaler Linotype Building rehabilitation has shown that the repair and upgrading of historic steel windows can improve energy performance in a cost-effective manner and that the light on the interior space from the large thin frame steel sash can be an amenity in residential conversions of loft buildings. Similar rehabilitation projects have shown that there are a variety of ways - both traditional and innovative - to preserve the character and design of historic steel windows and to have them function satisfactorily. *PROJECT DATA* BUILDING: - Mergenthaler Linotype Building 531 South Plymouth Chicago, Illinois DEVELOPER: - Harper Realty 134 South LaSalle Street Chicago, Illinois PROJECT DATE: 1979 ARCHITECT: - Kenneth Schroeder, AIA Kenneth Schroeder and Associates 714 South Dearborn Chicago, Illinois PROJECT COSTS: - The average cost for repairing each window, installing insulating glass, reconditioning the hardware and finishing<= br> was $250. END OF SECTION

Last Reviewed 2012-02-24