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Working with superstructures: The framework for Ontario's heritage buildings

The Elgin and Winter Garden Theatre Centre (Toronto). In 1987, a basement is excavated under the lobby corridor, and the grand staircase is suspended in the air.

Photo: The Elgin and Winter Garden Theatre Centre (Toronto). In 1987, a basement is excavated under the lobby corridor, and the grand staircase is suspended in the air.

By

Ontario Heritage Trust

Buildings and architecture, Tools for conservation

Published Date: May 19, 2005

Last issue, we discussed the importance of a solid foundation when preserving heritage structures. In this issue, we see how a buildingʼs skeleton holds everything together. Find out more about the techniques of handling frames, walls and floors – and their repairs – in Well-Preserved. Download Well-Preserved here.

The following excerpt appears in Well-Preserved: The Ontario Heritage Foundation’s Manual of Principles and Practice for Architectural Conservation (Third Revised Edition), by Mark Fram (Boston Mills Press, 2003).

All walls bear at least their own weight, and often a portion of the loads of the floors and roof above. Nevertheless, most buildings in Ontario from small to large are constructed as a structural frame with a relatively light cladding rather than according to the more traditional European practice of bearing-wall construction. Log construction is essentially a case of bearing walls supporting a small and relatively light roof structure. In many areas, a masonry or clapboard exterior on a house with rather thick walls probably covers an older log structure. Cladding fashionably upgraded the appearance and protected the logs from weathering (as well as stopping drafts).

Most other bearing-wall structures are of stone masonry with timber floors and roofs. Such bearing walls consist of two faces of relatively well-cut stone (sometimes one face is brick) with a core of rubble, sometimes bonded by mortar. Most bearing-wall structures in Ontario are churches; massive walls support elaborate and heavy roof structures.

Brick exteriors are often just cladding; plentiful supplies of timber and sawn lumber for framing made the load-bearing brick walls of European practice obsolete, even in urban areas, where some early building regulations required brick exteriors to prevent the spread of fires. Brick veneer allowed for much larger openings than brick bearing walls and was far more suitable for the complex forms . . . Nevertheless, idiosyncratic examples of double- or even triple-thick brick bearing walls seem to occur everywhere. The modern practice of backing a brick face with concrete block did not become common until the 1920s.

Timber frames have come in several varieties. The traditional mortise-and-tenon framing of relatively heavy timber beams and joists arrived from Europe and the United States with each wave of immigration, with subtle variations in practice from group to group. But cheap sawn lumber and machine-made nails made platform- and balloon-framing an instant success by the mid-19th century, pushing traditional heavy-timber construction out of domestic and commercial use. Most such lightweight framing uses “sticks” of small dimensions for wall studs and floors joists, with wooden laths, floorboards and occasional diagonal braces or bridging to make the entire assembly solid. Much more rare was the use of post-and-beam construction, with rigidly braced joints.

Wrought iron as a structural material, used for engineered structures such as bridges and gas-holders and some framing in large public buildings, was a rarity in 19th-century Ontario. Steel supplanted wrought iron late in the century. Steel’s strength permitted much of the eclectic stone and masonry constructions . . . to be “draped” on a hidden framework that carried most of the load. Steel-reinforced concrete frames appeared soon afterward.

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