Humans have been building with wood since devising their earliest forms of primitive shelter. Unlike stone, wood proved a far more workable material that could be assembled by individual or small groups of workers. While it did not produce monumental architecture, it also did not demand decades of labour by a vast workforce. Quick and easy to construct, wood buildings proved to be durable and resilient while offering warmth and natural beauty. From the earliest European settlements to this day in Canada, wood accounts for most of our housing, and more recently we have witnessed the introduction of mass timber buildings that deploy a diverse palette of engineered wood products. It is predicted that a sustainable built environment will be founded on buildings that are constituted from an even higher proportion of bio-based materials than we use in conventional construction today, hence much of Canada's promise and destiny will continue to depend on her forests and the wood products they produce.

With our environment in mind, the advance of the contemporary "green" building movement continues to evolve, but a new vernacular of 21st century architecture with a sustainable ecological footprint has yet to fully emerge. While we seek to fashion reliable and robust recipes for our everyday buildings, ranging from apartments and stores, to schools and offices, there is much to learn from the resilient and adaptable warehouse and light-factory buildings that line the streets of Canada’s historic manufacturing districts.

In the same way that light wood-frame house construction evolved into prescriptive codes and standards, mill construction pointed the way to the future of mass timber buildings whereby a series of formulaic design guidelines for common building archetypes would eliminate the need for alternative solutions to demonstrate code compliance. Complementary innovations in prefabricated modular building envelopes would enable rapid installation and subsequently, the periodic maintenance, retrofit and eventual replacement of enclosures over the building life cycle. Design for economy, efficiency, durability, flexibility/adaptability, resilience and low whole life carbon are key to the future of sustainable architecture. Our heritage "brick and beam" buildings did much of the heavy lifting needed to develop a contemporary sustainability framework for buildings crafted from wood.

This publication about Historical Tall Wood Toronto catalogues a cohort of such buildings that have endured and, in many ways, outperformed the vast majority of 20th and 21st century architecture. But this achievement can only be appreciated by taking the long view and considering the life cycle of buildings - the sort of design thinking that was baked into our historical tall-wood buildings, lessons learned that we must rediscover.

The term "mill construction" describes a type of building construction where interior framing and floors are of timber, arranged in heavy solid masses, and smooth flat surfaces, so as to expose the least number of edges and corners, and to avoid concealed spaces which may be reached readily by flames in case of fire. Heavy timber beams and columns were sized to maintain sufficient strength after exposure to fire and experience has shown these to be much safer for evacuating occupants and fire fighters than many other types of construction. Traditionally, this building typology featured load bearing masonry exterior walls with regular punched windows that combined to provide a durable building enclosure with a useful service life often exceeding one hundred years.

This evolved building typology originally responded to the needs of the Industrial Revolution before the advent of electrification, hence passive measures for daylighting and natural ventilation were privileged in these buildings. Unlike the specialized office, commercial and manufacturing buildings we construct today, the tall wood buildings were mixed use buildings that catered to manufacturing, mercantile and office occupancies that housed a diversity of uses and activities under one roof. Many have since been converted into highly desirable loft condominiums and professional offices, with very few major alterations required, other than subdividing occupancies, replacing windows, restoring wood surfaces, and updating mechanical, electrical and plumbing services.

What "brick and beam" buildings have taught us about sustainable architecture is that it is founded on the 3-Ls: long life (durability, resilience); loose fit (adaptability, flexibility, contingency); and low impact (emissions, ecological footprint). The stock of historical tall-wood buildings in Toronto, as well as many other parts of Canada and the United States, are a living testament to a proven approach that integrated the 3-Ls. Some recent mass timber buildings have largely duplicated the mill building typology because it is highly sought after real estate that is preferred by people over the more conventional modern building types.

There are some critical attributes of mill construction buildings that deserve to be imitated in today's buildings - why be original when we can be good? Innovation does not need to discard proven design strategies and construction techniques when striving for continual improvement. In this regard, an examination of this typology reveals a building DNA that can serve as a benchmark against which today’s designs may be compared.

Most notably:

• Regular, rectilinear floor plans and structural grids that are simple and economical to construct;

• Post and beam structures with long, clear spans that allow for flexible interior partitioning;

• Punched windows that provide vertical segments of non-combustible exterior masonry to receive fire-rated demising walls that enable the fire separation of adjacent occupancies;

• The even arrangements of fenestration with large operable openings that promote natural ventilation, daylighting and equitable access to views;

• Generous floor-to-floor heights that accommodate suspended mechanical, electrical and plumbing (MEP) services;

• Redundant means of vertical access and egress that satisfy fire safety requirements for numerous uses and occupancies;

• Robust, low maintenance interior masonry wall surfaces that accommodate a variety of finishes, the addition of thermal insulation and the integration of services;

• Raised main floor levels that render a tall inhabitable basement with large windows above grade; and

• Single-level concrete foundations that do not encourage automobile use by avoiding underground parking.

But not all aspects of the “brick and beam” buildings were sustainable by today's standards. Using brick as a structural wall material entails a large upfront carbon footprint and the building enclosure is not thermally efficient. Single glazing in steel window frames may have been durable and easy to maintain, but it compromised thermal comfort and increased space conditioning energy demands. To the credit of mill construction buildings, their robust armatures have proven easy to retrofit with the addition of thermal insulation and energy efficient windows. Modern heating, cooling and ventilation systems could be installed with ample headroom for ducts, piping and wiring. The ease of retrofit offered by brick and beam building is unmatched in any other building typology standing today. This typology has been able to gracefully transition from industrial facilities to professional offices and studios, and subsequently to a variety of residential occupancies.

In the life cycle of human settlements and the built environment, this building typology has demonstrated it is sufficiently durable and resilient, such that it can be run down for many decades, after which its robust armature enables revitalization for another cycle of occupancy. This is vital because cities need building stock that can be worn out and devalued so it becomes affordable to communities, such as artists and start-up entrepreneurs, providing a combined live/work/maker space that is eventually gentrified, but only after affordably incubating one or more generations of the creative class.