2d diagram of sun analysis

Solar Diagrams: Balancing Natural Light

Flavin Architects designs natural modern homes that respond to the location and angle of the sun throughout the year. Our homes connect the homeowner to nature and foster a more comfortable interior environment. By considering climatic data and diagrams of the sun’s path, our designs decrease energy use.

Sun path diagrams are a metric for designing a home and act as a visual aid to convey the architect’s design decisions to the homeowner. Great tools for creating these diagrams are readily available online. For example, suncalc.org provides the solar data of a site and tracks the sun as it moves across the sky from dawn to dusk. The length of shadows can be determined for any specific day and time. This aids Flavin Architect’s ability to design in response to the sun.

Understanding the position of the sun allows us to build passive measures into the design of a home. Passive measures for sun control include a consideration of the proper placement, orientation, and shape of a home. Architectural features like sun shading and overhangs are likewise established early, during the planning stage of design. The goal is to shade the home during the hottest days of the year while allowing light to warm the home during colder, shorter days.

We track the four most important days of the year, the summer solstice, the autumnal and vernal equinoxes, and the winter solstice. Our team uses this information to create a site-specific diagram which overlays a plan of our design. A new home in Newton, MA, provides our example below. The red path indicates the path of the sun at the summer solstice. The sun rises at 5:08am and sets at 8:25pm. On the winter solstice, the sun will rise at 7:10am and set at 4:16pm, indicated by the blue path. The difference between the summer and winter sunsets shows the range of location across which the sun will set over the year. Similarly, the potential view of the sunrise is charted on this diagram. This allows us to plan the location and orientation of spaces in and around a home. If the homeowner wants to view the sunrise from the master suite and the sunset from the screen porch, we can ensure that wish is prioritized early in the space planning phase of design.

sun diagram annually
3D Site Sun Diagram

The summer solstice has a sun path that is long and approaches the center of the diagram in the middle of the day. The center of the diagram below marks the zenith. The closer to the zenith the sun path comes, the higher the sun is in the sky. The orange and green paths represent the equinox. The shortest day of the year is the furthest from the zenith, showing the sun’s low altitude. Noon is indicated by the hollow circle at the center of each sun path. With this diagram, we can track the azimuth of the sun (the rotational angle about the zenith). In this example, throughout the year the azimuth of the sun at noon shifts from south-east to slightly south-west.
solar analysis diagram
Site Sun Diagram

Sun control is most efficient when located outside the conditioned envelope of a home. If sun control occurs only inside, as with blinds or curtains, the heat from the sun increases the demand on the mechanical system and increase energy use. On the other hand, the heat of the summer sun can be mitigated before it hits the window, lowering the cooling load on the home’s mechanical system, and creating a more sustainable home.

In the New England climate, horizontal shading, like roof overhangs, perforated screens, or architectural louvers, are most effective in the south elevation. This is because summer is the most important time of the year for shading. In the summer, the sun is high in the sky and a projected overhang can shade the fenestration of a home during the hottest and brightest part of the day. A roof overhang to the south will allow the low winter sun into the home, providing the home with solar heat and light during those cold, short winter days. Flavin Architects works with landscape architects to plant deciduous trees to the south elevation of the home. The leaves of these trees can cut down on the hot, high summer sun. When leaves fall in the winter the sun can pass through to warm and light the home. In the rendering below, the roof extends many feet to the south, and a deciduous tree shades the two-story glass staircase.
rendering of south elevation
Rendering of new home in Newton, MA.

Vertical shading, on the other hand, is most effective in the east and west elevations of a home. When the sun is lower in the sky, it reaches deeper into the home. Overhangs are ineffective and the sun can create an uncomfortable glare. Exterior vertical slats, such as the applied wood slats as seen in the Lantern Studio image, successfully condition the light before it hits the home’s interior spaces.

Finally, climate data (weatherspark.com) is also helpful to understand the climatic conditions of a site. The data allows us to chart the direction, seasonality, and intensity of prevailing winds, observe the likely snow and rainfall, and assess the site’s potential for solar energy. Most importantly, climatic data reveals which days of the year are most likely to be comfortable and which might feel oppressive. Understanding the climate allows us to plan the operability of the home’s fenestration and respond appropriately by orientating and locating outdoor spaces with respect to that information. Climate data and sun diagrams help to optimize the homeowner’s use of outdoor spaces and creates opportunity for the home to better connect the indoors with nature.

dappled lighting through privacy wood screen
Wood screen provides shade at our Lantern Studio project.