In the Face of a Changing Climate, Our Buildings Need Thermal Resilience.

The Thermal Resilience Design Guide from Ted Kesik could be a new standard.

Dr. Ted Kesik, Professor of Building Science at the University of Toronto, with Dr. Liam O’Brien of Carleton University and Dr. Aylin Ozkan of U of T, have just released aThermal Resilience Design Guide. In the introduction he explains the reason:

Aging energy infrastructure and extreme weather events due to climate change can lead to extended power outages that cause buildings to be much too cold or hot to inhabit. Intelligent enclosure design can take advantage of passive measures to futureproof buildings.

Passive house or Grandma's house?/Public Domain

For many years on TreeHugger I talked about Grandma's house, about learning how people built before what Steve Mouzon calls the Thermostat Age, when we could just spin a dial to change the temperature. I thought that every building should be designed with high ceilings, natural ventilation and thermal mass to keep cool in summer; in winter, one should put on a sweater and turn down the thermostat.

Then I discovered Passivhaus or Passive House, and it changed my thinking completely. It came with a really thick blanket of insulation, high quality windows, a tight envelope and a ventilation system to deliver fresh, clean air instead of getting it through leaky walls and windows. You didn't have to put on a sweater and, if you needed cooling, you didn't need much.

But to design for true thermal resilience, you have to be a bit of both, a bit of Grandma's house and a bit of Passive House. First, you have to consider:

Thermal Autonomy

Kesik, Ted, Liam O’Brien and Aylin Ozkan. Thermal Resilience Design Guide, Version 1.0./Public Domain

Thermal autonomy is a measure of the fraction of time a building can passively maintain comfort conditions without active system energy inputs.

This is where you design your building to need as little heating and cooling as possible, for as much of the year as possible. Doing this reduces energy consumption, extends the life of mechanical equipment, and reduces peak demand on the energy grid, an important consideration if we are going to electrify everything.

Passive Habitability

Passive habitability is a measure of how long a building remains habitable during extended power outages that coincide with extreme weather events.

This is how we used to design things before the Thermostat Age. Ted notes:

Since the beginning of human history, passive habitability has driven the design of buildings. It is only since the Industrial Revolution that widespread access to plentiful and affordable energy caused architecture to put passive habitability on the back burner. Climate change is influencing building designers to rethink building reliance on active systems that became dominant during the 20th century.

We have covered this on TreeHugger before, noting that super-insulated and Passivhaus designs laugh at the Polar Vortex and also stay cooler longer in summer.

The third factor in Thermal Resilience is fire resistance.

Kesik, Ted, Liam O’Brien and Aylin Ozkan. Thermal Resilience Design Guide, Version 1.0./Public Domain

So how do you achieve all this? Again, with a mix of Passive House and Grandma's House. This section summarizes it: a lot of insulation, minimizing of thermal bridges, very tight and continuous air barriers to control infiltration.

With windows, high quality windows, placed carefully to control solar gain. But he really stresses the window-to-wall ratio (WWR) which is often overlooked or undervalued. "Too little glazing will reduce opportunities for daylighting and views, and too much glazing makes it difficult to achieve high-performance in terms of comfort, energy efficiency and resilience."

kesik, Ted, Liam O’Brien and Aylin Ozkan. Thermal Resilience Design Guide, Version 1.0./Public Domain

As the graph makes very clear, even the very best windows drag down the performance of a building and "highly glazed buildings can never be thermally resilient." And you can't just think of the elements on their own: "The optimal overall effective R-value of the entire building enclosure is more important than the amount of insulation provided in specific components, such as walls or roofs."

This all works well for dealing with cold weather resilience, but Dr. Kesik reminds us that, "while cold weather thermal resilience helps protect buildings against frost damage and freezing water pipes, the evidence indicates human health, in particular morbidity and fatality, are much more significantly impacted by exposure to extended heat waves."

Bris de soliel at the Salvation Army/ Lloyd Alter/CC BY 2.0

That brings us back to Grandma's house, with her shading devices and natural ventilation. Brise soleil like Le Corbusier used, exterior sunglasses like Nervi, shutters and exterior shades, all help keep out the sun but can allow for ventilation.

From a thermal resilience perspective, natural ventilation is primarily a passive measure that needs to be integrated with shading devices to manage overheating due to solar gains and extremely high outdoor temperatures.

kesik, Ted, Liam O’Brien and Aylin Ozkan. Thermal Resilience Design Guide, Version 1.0./Public Domain

This drawing shows it clearly: a single window is pretty much useless for ventilation. High ceilings with high and low openings are far more effective. Even if they are on one wall, high and low openings can provide good ventilation, which is why I loved my tuneable double-hung windows.

Then there is thermal mass. I had pretty much discounted it except in climates with big diurnal swings, thinking that lots of insulation was much more important for comfort and resilience. But Dr. Kesik writes:

Highly insulated and thermally lightweight buildings can rapidly overheat in the absence of effective solar shading, and if they are relatively airtight tend to cool down slowly unless they are adequately ventilated.

It doesn't take a lot of thermal mass to make a difference, 2 or 3 inches of concrete topping can do it. "A hybrid approach to configuring the thermal mass of a building can be very effective where low embodied energy materials, such as mass timber, are selectively combined with thermal mass elements such as concrete floor toppings."

kesik, Ted, Liam O’Brien and Aylin Ozkan. Thermal Resilience Design Guide, Version 1.0./Public Domain

In the end, the thermally resilient building most closely resembles the Passive House concept, but integrates some ideas from Grandma's house or even her ancestors: "The sad reality remains that many indigenous and vernacular forms of architecture from centuries ago provided a higher level of thermal resilience than many of our contemporary architectural expressions." It aims for ventilation autonomy, getting fresh air through natural ventilation for as much of the year as possible, and thermal autonomy, minimizing heating and cooling, which both lead to greater resilience.

Dr. Kesik concludes by noting that the guide "is intended to promote more robust and resilient passive features in buildings and to help everyone proactively address the challenges of climate change adaptation." But it is also a careful mix of the old ways of doing things that worked without electricity or thermostats, and the new thinking that has come out of the Passivhaus movement. Perhaps I didn't have to choose between Grandma's House and Passive House, but can have a bit of both.