How much overhang is needed to block summer sun?

Understanding the Sun Path

When designing a passive solar house, it’s essential to consider the sun path throughout the year. In the summer, the sun is higher in the sky, and its rays strike the building more directly. A south-facing overhang can help block these direct rays, reducing overheating and heat gain. The ideal overhang depth varies by latitude, with more extreme latitudes requiring deeper overhangs to account for the sun’s more extreme angles.

Calculating Overhang Depth

To calculate the ideal overhang depth, consider the latitude-adjusted sun path. For a latitude of 40°N, a 2-3 foot overhang is typically recommended. This overhang should be oriented 10-20° from east-west to account for the sun’s movement. For more extreme latitudes, such as 60°N, a 4-6 foot overhang may be necessary. It’s essential to note that these values are general guidelines and may need to be adjusted based on specific site conditions and building design.

Effective Overhang Techniques

In addition to depth, overhangs can be designed with specific techniques to enhance their effectiveness. A “solar overhang” with a curved or angled profile can be particularly effective at blocking summer sun while allowing winter sun to enter the building. Another technique is to use a “shadow box” overhang, which involves creating a narrow gap between the overhang and the building facade. This gap allows winter sun to enter the building while blocking summer sun. These techniques can help optimize the performance of a south-facing overhang and create a more comfortable, energy-efficient building.