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What are Passive Sustainable Strategies?

Buildings are responsible for between 30-40 percent of emissions globally. Emissions stem from the products we build with, the methods in which we build, and how a building is operated post-construction. Sustainability is a critical consideration during design as the architecture and construction industries work to reduce the carbon footprint of a building’s lifecycle.

Active sustainable design strategies include the installation of heating, cooling and ventilation systems, the light fixtures that are used, and other systems that utilize purchased energy. Passive sustainable design strategies work to reduce the dependency on active strategies by utilizing ambient energy sources and include building orientation and massing, passive daylighting, and passive heating and cooling.

Our team is currently designing a multi-use building addition in Ohio, situated on a main road and adjacent to a river to the west. This building, “Building B,” is an addition to an existing office building; the new program includes museum display space, display storage, pre-function and event space. Throughout the design process, passive strategies have remained at the forefront of our conversations as we strive to maximize daylight in and views out while mitigating the sun’s heat. Follow along as we discuss passive sustainable strategies and relate them to our current design project.

Building Orientation and Massing

Building orientation refers to the direction a building faces. Massing is the overall shape and size of the building, including proportions of solid to void. Two buildings with identical floor area and volume but different massing can drastically differ in energy performance.

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Building orientation and massing should consider location and climate of the building, take advantage of site conditions, and use the shape and size of the building to maximize passive energy from the sun and wind. In the northern hemisphere, orienting a building east-west allows for more façade to face the north, taking advantage of desirable indirect sunlight while allowing for greater control of the south sun and minimizing the effect of the harsh light and heat from the sun in the east and west. Building B is massed rectangularly in a way that minimizes surface area-to-volume to avoid unwanted heat loss and gain. The north façade is mostly glass, filtering in desirable daylight. The remaining facades are designed to reflect and carefully control harsh sunlight. As we move through design, the building program will continue to inform massing decisions and vice versa.

Passive Daylighting

Controlling direct sunlight is essential in reducing unwanted effects of glare and solar heat gain. Simultaneously, encouraging diffused natural light from the sky (indirect sunlight), which is the desired natural indoor lighting, increases human visual comfort and decreases electrical energy costs.

Passively controlling sunlight helps maintain thermal comfort in a building. This can be done with a variety of strategies, including carefully placed openings, use of special façade elements, interior and exterior material choices, and interior-space planning. A building’s geographic location and climate should inform strategies applied with consideration for all seasons of the year and times of the day. For example, an appropriately sized overhang on a south-facing façade in the northern hemisphere can block out unwanted direct light and solar gain during 75 percent of the year, while allowing for direct heat gain during the winter months to help offset the active heating load required.

Windows facing away from the sun’s path provide the most diffused lighting. Building B takes advantage of the northern light by implementing a large span of glazing on the north façade. Evenly distributed openings and continuous strip openings are best for controlling light into a space.

A sawtooth fin approach to Building B’s west façade orients glazing to the north in a stepped approach, providing a solution to mitigate heat gain. West-facing opaque, light-colored stone panels reflect the harsh western sun, offering a dynamic appearance. At the east and south facades, strategically placed horizontal windows allow light to reach a greater depth while minimizing heat gain.

North / east elevation

West elevation

Passive Heating and Cooling

Smart passive strategies use building design to minimize the use of mechanical systems for heating and cooling. Passive heating uses the energy of the sun to keep occupants comfortable. The sun’s heat can be stored by thermal mass. Walls with high sun exposure can capture and store heat during the day and release the heat at night. High thermal mass materials include brick, concrete and stone.

Passive cooling uses strategies include natural ventilation, air cooling, and shades to maintain thermal comfort. Wind and stack ventilation are types of natural ventilation that use outside air to help cool a building. Wind ventilation uses the force of wind to pull air through a building while stack ventilation uses temperature differences to move hot air up and out of a building.

Material and color of the building envelope impact heat gain and energy efficiency. Lighter material colors reflect the sun’s light and discourage heat gain while darker materials absorb the sun’s light and heat.

The primary material of Building B’s façade is a light-colored stone panel with the potential to function as a thermal mass. While natural ventilation is a strategy that is widely used in our climate zone, it is not appropriate to the program of our building that requires a high level of temperature and moisture control. Our west façade fins function as shades from the harsh western sun, effectively keeping the building cooler on hot days.

Photo credit: Sun, Wind, and Light, by G.Z. Brown and Mark DeKay

Each building is unique and requires careful consideration of site, program, climate, and the desired aesthetic when designing with passive sustainable strategies in mind. Choosing passive strategies that suit the project early in the design process will positively impact the building’s lifecycle cost by reducing the need for and use of mechanical systems to condition spaces later.



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