What is Sustainable Design? Part Four: Sustainable Materials The George and Kathy Dembroski Centre for Horticulture, Toronto Terri Meyer Boake BES, BArch, MArch, LEED AP Associate Director School of Architecture University of Waterloo Past President of the Society of Building Science Educators Member OAA Committee on Sustainable Built Environment
Materials First! Aldo Leopold Legacy Centre, Wisconsin The Bird’s Nest, Beijing Materials need to be part of the very initial thoughts as a building is conceived. A building’s design is intrinsically linked to its materiality.
Materials can be classed as those that RETAIN HEAT and those that REJECT HEAT
HEAT RETENTION is useful if we wish to store the free energy from the sun in the material
HEAT REJECTION is also called INSULATION.
INSULATING materials are used to retard the heat flow through the building envelope
INSULATION at VERY HIGH LEVELS is essential in all elements of a cold climate building envelope
THERMAL BRIDGES are points in the building envelope where there insulation is completely lacking
THERMAL BRIDGES ARE TO BE AVOIDED as they result in heat loss and normally degradation of the building envelope at the point of breach (evidenced by condensation, mould, mildew or rust)
Insulation Different types perform different ways, as a function of their materiality and thickness. More is more… Some are less environmentally harmful than others. Soybean based spray Fiberglass batt Styrofoam R values of batt insulation Spray cellulose insulation Rigid fiberglass
Heat Storage Capacity of Materials The specific heat of materials is different than their ability to store this heat. This is referred to as their “ thermal mass ” or “ heat storage capacity ”. Thermal mass is the ability of a material to hold heat and slowly release it back into the environment giving a flywheel effect. We often make a choice, depending on the climate, if we need to store heat to have it released later in the day, when the sun is down and things have “cooled off”. Materials with a high thermal mass are helpful in the heating of building interiors in cold climates. We need to select materials with a high heat storage capacity but that are not conductors (like metal).
Thermal Mass IslandWood, Seattle Exposed concrete floors are becoming increasingly common in sustainable buildings. The concrete is both structural and acts as an excellent storage material for free solar energy that comes in through the windows. It can be made less harmful by replacing some of its cement content with “flyash” which is a waste product of the steel industry. The concrete can be stained with different colours if desired.
Microclimate is the “mini climate zone” around your building as modified by local conditions.
Things that naturally change your microclimate are :
amount of sun received over the day
wind and natural breezes
The natural materials of the site
Things that YOU select also change the microclimate :
material choices: paving, roofing, wall materials and planting
colour of materials
In a cold climate select materials to INCREASE HEAT in the WINTER and DECREASE HEAT ABSORPTION in the SUMMER
Solar Access and Microclimate The micro climates in the backyards on either side of the walkway are different as a result of solar access, even though materially they are identical. Bain Avenue Coop, Toronto
The front of the house has more paving and less tree cover, which make it hotter. The black asphalt roof also raises the general heat level of the site. East elevation West elevation There are different microclimates on the front vs. the back of the house due to materials, amount of shade and orientation (sun).
The Effect of “Found” Site Natural Materials Natural materials and the natural site landscape and configuration will affect the heating or cooling potential of the site. Replacing natural “soft” materials with “hard or impervious” materials will increase the heat retention potential of the site. Pervious materials are preferred as they allow rainwater to be naturally cleaned and cycled without being directed into the storm and sanitary systems. Heat retention makes for a warm microclimate and can increase the cooling requirements of buildings in the summer months.
The Effect of Roofing Choices The choice of roofing material critically impacts heat retention. - Dark materials absorb heat, which is redirected to the urban atmosphere, where greenhouse gasses trap it in place. - Light materials reflect the heat (aka “ cool roofs ”). - Green roofs stay cool, produce oxygen and absorb rain water, reducing pressure on the sewer system.
Cool Roofs Theory Cool roof materials have two important surface properties: a high solar reflectance or albedo and a high thermal emittance . Solar reflectance is the percentage of solar energy that is reflected by a surface. Thermal emittance is defined as the percentage of energy a material can radiate away after it is absorbed. Vernacular architecture in hot climates normally finish roofs in light colours to reflect heat as well as to provide a clean surface for water collection.
Green Roofs Green roof technology started in Germany over 30 years ago. Proprietary systems are being looked at with some seriousness in Canada at this point. Green roofs reduce urban heat island effect and decrease carbon dioxide levels in the city. They also can provide a higher level of insulation (but not necessarily). Green roof treatments can cover the entire roof, or just a smaller part, depending on the requirements and limitations of the project. Vancouver Public Library Children’s Museum, Boston
Imagine the environmental benefit and resultant cooling if all of those roofs were either green roofs or cool roofs…. It would help to mitigate Urban Heat Island Effect.
“ Paving” or the displacement of pervious, green surfaces, with hard surfaces, is a primary cause of negative changes to the local microclimate.
Paving can not only cause heat retention, and overheat the urban environment, but it can also impact water runoff and absorption into the site.
Paving selections need to simultaneously:
Allow for water to be absorbed into the earth (pervious)
Be durable for winter traffic conditions and snow removal
Create a cool microclimate to prevent heat island effect
Phoenix, Arizona: shopping centre with (white) roof and pavement...
Permeable Paving Different materials are available that allow for a level of durability for traffic, yet also let water drain through. Issues of snow removal must be accounted for when choosing materials. Permeable concrete is also an option.
The Effect of Other Material Choices Other materials on site, whether they are chosen for walls or accessory structures, will affect the overall tendency of the site to retain heat and create a hot environment. Shading your walls will help to prevent heat gain. However, in very cold climates, where the sun angle is very low, material choice can be used TO hold heat in the building and warm up outside spaces.