THE CALAMINE CURE FOR TROUBLED WINDOWS
Evolving Roles for Windows Clad in Sheet Metal.
By John M. Corbett

FULLY CLAD. The full effect of this Toronto storefront is made possible by the artisan's ability to express every detail in 20 ounce red copper, including the window sash.

Wood windows clad in sheet metal, so called calamine windows, were historically intended as a defense against fire, but in this era of depleted woodlands and degraded lumber quality, this technique may continue to prove useful for the protection it provides against the damage done by time and rot. A well made custom sheet metal window is a more durable exterior element than any built with second growth lumber, whatever its species. They are not, however, cheap, so they will not be flooding the replacement window market. To find out where these windows are proving useful or necessary, we spoke to Cameron Forbes of Heather & Little, Limited of Toronto, Ontario. Heather & Little has built hundreds of these windows for historic projects, mostly reproductions for important public buildings built in the first part of the last century.

These fire resistant windows were distributed widely among buildings both splendid and utilitarian. In public buildings, they enabled designers to incorporate windows into trim schemes of the same material thus making them an indispensable part of the historic design. For the renovation of the 1924 Investment Building in Washington, DC, Heather & Little furnished numerous missing elements necessary to complete the façade restoration, including seventy plus copper clad calamine windows, fixed and casement. This beaux arts limestone structure featured deeply sculpted copper string courses and cornices which were carried on in elaborate molded window surrounds and the windows themselves. The windows and their surrounds appear as a unified design entity. Similarly, they reproduced a 15 foot by 35 foot tall window for the 1914 Harris Theater on 42nd Street to replace an original destroyed by a misdirected demolition crew. This massive window dominated the narrow, sculpted brick façade and was an integral part of an elaborate copper trim scheme. Heather & Little worked from a dumpster full of debris and reused 70% of the original wood core as both an armature and a template.

The price of custom calamine windows will deter their use in many applications but another historic Heather & Little project suggests a way to mitigate their cost. In 1991 they produced 80 double hung windows in 26 gauge zinc coated steel for a post office in Collingwood, Ontario. These were replacements for existing windows which had been originally produced without wood cores since the weight of the glass itself did not require additional support. Much of the rigidity of these windows derives from the cumulative strength of the assembled tubular sheet metal and the fixing of the glass. Coreless windows can be made energy efficient by filling the cavity with foam and by installing a thermal break in the design. By omitting the wood core, the cost of the millwork plus the labor of working the sheet metal around it is saved. Custom sheet metal windows will never be cheap, but they offer a combination of looks, durability and low maintenance that address specialized building issues.

DETAILS. These samples show sheet metal installed over a range of wood profiles. While not inexpensive, the process of drawing out these moldings does not require major up front expenditures and is feasible for custom short runs. They are smooth finished and without brake creases.

Other recent projects suggest new replacement applications for this technique beyond reproduction of historic calamine windows. For the fire damaged cupola of the 1880 old Harbour Commission building in Montreal, Heather & Little furnished replacements in 20 ounce copper for moldings and trim. Also replaced were four round windows seven feet in diameter. Curved wood moldings of this size in exterior applications can be quite unstable, and prone to rot, unless fabricated from the most carefully selected grade of lumber available. While not historically original, such a substitution can serve the building by reducing failures and the need for maintenance. There are many exterior features that are no longer viable in wood in today's environment of uncertain lumber quality and aversion to maintenance. Red copper accepts any finish as reliably as wood, if properly prepared. And, like the original "Kalamein" windows, (see below) they are fire resistant.

The cost of reproducing copper clad wood windows likely decided the fate of 700 historic double hung calamine windows in the 1917 wing of the Massachusetts State House in Boston, a job that Heather & Little never got. This building is part of an historic complex dating back to 1790. It at first seemed that as original historic fabric that these windows held a very strong hand. It was planned to reproduce half the windows and to restore the rest, but after much soul searching and budget wrangling, the decision was made to replace them all with new wood windows at, Cameron Forbes estimates, about one quarter of the cost. They simply didn't contain enough history to justify the cost differential.

Historic or not, with half of the windows scheduled unrestorable after just eighty some years, it would seem that their replacement cycle payout was only fair. To see if this is predictive of future performance, we must take into account the design and context of the original windows. The window contractor for the entire project, Richard Muckle of Muckle & Associates of Lawrence, MA, had the opportunity to deconstruct the windows and to analyze their failure. He observed that most of the sheet metal joints were coped and then simply butted and filled with solder, offering little resistance to thermal movement or to the shocks and stresses of operation. The original artisans can't explain their choices, unfortunately, but the materials consultant for the project, William Finch of Finch & Rose in Beverly, MA, emphasizes that metal cladding was never intended as a strategy for extending the life of an installation but solely a measure taken to reduce the amount of readily combustible material in building interiors. While these butted joints may conceivably have contributed to a flatter, cleaner look, Cameron Forbes notes that such a joint is not as strong as the lapped and sweated joints Heather & Little installs today. They have benefited from the gift of 80 years of hindsight, of course, and design all work to address today's desire for low maintenance and extended replacement cycles.

THE MEANING OF THE WORD

A century ago, wood windows were first clad in zinc coated or zinc plated steel, with the object of making them fire resistant, and marketed under the trade name "Kalamein". This name refers to calamine, the mineral which furnishes the ore from which zinc, the eighth metal known to man, is extracted. The reason it took man so long to get to zinc (India, c.1200 AD), is that it evaporates when heated, instead of melting. For millennia before that, however, calamine in its natural state was used in the production of brass (copper and zinc) and calamine lotion. While the trade name "Kalamein" seems no longer to be maintained, the terms "kalamein", "kalamien" and "calamine" persist, referring to the general practice of cladding architectural elements in sheet metal of any composition.

---

Custom Sheet Metal Specialists:

---

Skyart Studio and Gallery, Meriden CT, Copper Weathervanes.

---

Vulcan Supply Corp., Westford VT, Catalog architectural sheet metal.

---

Heather and Little, Ltd., Markham ON, Canada, Custom architectural sheet metal.

---

C.G. Bostwick Company, Hartford CT, Roofing & Sheet Metal. CT.