Window-to-Wall Ratio

The ideal percentage of glazing to wall—often referred to as the window-to-wall ratio (WWR)—depends on several factors, including the building’s orientation, climate, and intended use. Here’s a general guideline for different orientations:

North-Facing Walls:

• Ideal WWR: 20-40%
• Reason: North-facing windows (in the Southern Hemisphere) receive the most consistent and beneficial solar gain throughout the year. A higher glazing percentage can optimize passive solar heating and daylighting, which can enhance energy efficiency and comfort.

South-Facing Walls:

• Ideal WWR: 10-20%
• Reason: South-facing windows receive less direct solar gain, especially in winter. Limiting glazing helps to reduce heat loss and prevent excessive cooling loads. However, strategic placement of high-performance windows can still contribute to daylighting without compromising energy efficiency.

East-Facing Walls:

• Ideal WWR: 10-25%
• Reason: East-facing windows benefit from morning sun, which can be useful for passive solar heating in the morning but can also cause overheating in the summer. Balancing glazing with shading devices is important to manage heat gain and glare.

West-Facing Walls:

• Ideal WWR: 10-25%
• Reason: West-facing windows receive strong afternoon sunlight, which can lead to overheating and glare issues. It’s crucial to use shading devices or limit glazing to manage these effects effectively.

General Considerations:

• Climate: In colder climates, a higher WWR can improve passive solar heating. In hotter climates, a lower WWR helps reduce cooling loads.
• Shading and Glazing Performance: The use of high-performance glazing and shading devices can allow for a higher WWR while managing solar gains and heat loss more effectively.
• Building Use: The intended use of the building (e.g., residential, commercial, or office) can influence the optimal WWR based on factors like lighting needs and privacy.

These percentages are starting points and should be adapted based on specific design requirements, local climate conditions, and performance goals. Energy modeling and consulting with building professionals can provide more tailored recommendations for achieving the best balance of daylighting, thermal performance, and energy efficiency.