Zone Floor Area Calculation

Maggie, the answer is yes. The daylighting zone area is determined by either 2 times the window head height or the use of the 60 degree angle for exterior or interior elements being located in areas reducing access to the sky vault.

If you have different window properties or different window areas in some floors or facades, these will need to be separated in the calculations. When documenting this, and I'm assuming that all the floors and facades are all the same, you take one floor and separate the facades in the calculator. So you would have 1st floor west, 1st floor east, etc. etc. I recommend this because the reviewer may request that you separate the facades out to demonstrate compliance since the prescriptive method is to be used for individual spaces. When you begin lumping mass areas together, the results can be askewed. If you do one floor, then you can lump all together or just copy and paste if all of the floors are the same.

Maggie,

Any glazing below 30" does not provide daylight onto the working surface, it basically just illuminates the floor. Therefore, 30" which is considered the typical sitting work plane height was used for daylighting calculations with LEED.

The prescriptive method, the glazing factor calculation, and the daylight factor calculation, are based on the premise of a uniform sky. Not a sunny clear, direct sun, or overcast. So the brightest point in the sky is the zenith, or directly above one;s head. So understanding that the light comes from directly overhead, its all about access to the skyvault. Draw lines from the zenith through a window and into a space. Anything too deep, no access, anything too close, well it just lands on the floor.

Its a little more in depth than that but that is the premise for it. When you use simulations, the program accounts for the reflection of light from these surfaces. A formula, like the prescriptive method, does not take into consideration all the complexities of daylight, such as the bounces, reflectivity, and loss of illuminance through multiple layers.

Maggie,

Rules of thumb for daylighting has always been that the a space's effectively daylit area is about 1.5 time the window head height. With a light shelf that is increased to 2H. Not sure who or why USGBC went with 2H with the prescriptive method.

My personal experience proven with actual measurements of spaces with designed with simulations, is that the effective daylit area, having about 25fc, is about 1.5H. This is for worst case scenarios of the climate that project is located in .