Solatubes (tubular skylights) and Option 2 prescriptive method

The prescriptive method is a means to provide projects some type of guidelines that will get them some daylighting scenarios that would be better if they had not even considered daylight. It is method of formulas and rules. It is not a method that can effectively or accurately provide projects teams information about the performance of their daylighting scenarios.It is not meant for anything other than punched openings in a building envelope. Your not going to get the actual performance of the solartube using the prescriptive method. You will need to use a combination of methods as Solar tube had mentioned. When simulating soar tubes you will actually simulate them as electric lights. You can get the IES file from Solar Tube to do this.

Dana, I'm working on a project which will also attempt to earn the daylighting credit with the prescriptive approach, and is also using Solatube skylights. I would be interested in what your outcome was if you have had your project reviewed- and how you chose to document the Solatubes. We have an approach we used during design - allowing us to decide how many we needed, how to space them, and we expected it to comply with the LEED requirements, but it hasn't been submitted yet. I don't want to post our idea on the forum in-case it's incorrect- (then it will just confusion), but we can compare notes if you haven't submitted yet. Here is my contact mnolan (at) BelayArchitecture (dot) com -thanks!

I have used Solatubes in projects and they have IES illumination files for different sun angles for each model. Using the modeling option it is very easy to determine the sun angle for 9 am an 3 pm place the appropriate IES file in a simple lighting program and determine your lighting fc. I believe Solatube may even do these calculations for you. If you combine it with other daylighting options you can easily do the calculations yourself it program such as 3d Studiomax which came as an add on with my version of REVIT.

For clarity, Solatubes cannot be documented with the prescriptive option. To document your use of Solatubes you must simulate them. You can either simulate all of the regularly occupied spaces turning in the entire documentation under the simulation option, or you can document the spaces that don't have Solatubes with the prescriptive option and submit the simulation and the prescriptive calculations together under the combination option.