Glazing: How Much is Too Much?

GLAZING: HOW MUCH IS TOO MUCH?

Glazing is a design tool that facilitates the passive heating and daylighting of interior spaces. However, you’d be hard pressed to find new builds or retrofits without expansive openings and floor to ceiling windows. This begs the question: how much glazing is too much?

• Larger areas will collect more solar energy than those shown in chart, while smaller areas will supply less solar energy (yet still a significant amount).Thermal mass and high-quality insulation must be used in conjunction with data for desired effect.
  

The above chart is based on south-facing glazing. South-facing openings receive the most direct sunlight throughout the day, and therefore should be highly considered when designing an energy efficient building. The data is categorized by 17 distinct climate regions and their reference cities.

Simply put, the optimal amount of glazing depends on the lighting and heating requirements of a design - and these requirements are greatly influenced by location. In general, the greater the latitude, the more glazing is required to effectively light and heat interior spaces.

This becomes apparent when comparing climate zones 2 and 16. At a latitude of 43°, zone 2 (reference city Madison, WI) recommends a whopping 40% ratio of glazing to floor area for optimal solar heating contribution. This means that for a home of 1000 sq. ft, there should be 400 sq. ft. of south-facing glazing. That same size home in zone 16, at a latitude of 25.7° (reference city Miami, FL), would only need a 2% ratio of glazing to floor area - making the total recommended area drop to only 20 sq. ft. This drastic contrast cannot be understated. To put these numbers in perspective, this is the difference between a 10’x40’ window in zone 2 and a 4’x5’ window in zone 16.

When designs veer far away from these recommendations, it becomes considerably less convenient and efficient to heat and light a building. To create a comfortable interior environment, compensations become a necessity in the form of mechanical air conditioning and artificial lighting usage during the daytime. Therefore, poor glazing consideration in the design phase results in high energy usage and expensive energy bills throughout the entire lifespan of a building.

In conclusion, a design has too much glazing when the cons of overheating outweigh the pros of natural daylight.

Unfortunately, this means your Florida home likely has too many windows.

Resources:

Lechner, Norbert, Patricia Andrasik, Edward Mazria, and James Marston Fitch. Heating, cooling, lighting: Sustainable design strategies towards net zero architecture. Hoboken, NJ: John Wiley & Sons, Inc., 2022.