Prescriptive Side-lighting Question

No, the prescriptive method is a formula, just like the glazing factor was. You won't find it in the Reference Guide because if your read the method by which you have to perform the method, how would you take into consideration the VLT of the interior glazing into the formula, and have it make sense. Just like you could not use shared daylighting scenarios with the glazing factor calculation, you can;t do it with the prescriptive method.

The prescriptive method was established for projects that are not using proper daylight analysis to influence there design to ensure that spaces are not over daylight, therefore creating other issues such as heat gain.

I guess I have to disagree, Todd. In fact daylight penetrating interior glazing and spaace that is not other workspace - i.e. a passageway between interior glazing and building envelope with lots of glass - has been counted in the NC 2.2 glazing factor calcs. And it is pretty harsh to characterize the prescriptive path as a tool for teams who didn't to something "properly". Many owners, including almost the entire federal government, want to see measruable daylight achieved and delivered withour regard to how it gets done.

Joslin,

I will agree to disagree.

Explain to me how, in both the glazing factor calculations and the prescriptive method, where you can take into account daylight passing through exterior glazing, then passing through interior glazing into say an office? You can;t and its not allowed. LEED interpretations for NC state that shared daylighting scenarios are not allowed and that other methods such as simulation or measurements must be used.

So if you got a project that earned the daylight credit with shared daylighting scenarios of regularly occupied spaces, then you got lucky. You state corridors and non occuppied so I;m not sure what you are saying.

Secondly, the original posters question did not mention occupied on not occupied. The question was, when using a prescriptive method, can shared daylighting scenarios, as what i described be considered. I don;t know where you are getting non-regularly occupied spaces as being allowed to be counted in shared daylightign scenarios.

Thirdly, if all you are using is the prescriptive method and or the glazing factor method as your only means to determine daylight analysis, then yes i will say that your daylight analysis was not done properly. How can say that you have provided a good daylighting scenario, refer to chapter 14 of the IESNA , for the occupants. The prescriptive method is a method that basically says that when you add x+y+z and it falls between d and g, you are ok.

Owners only wanting measurable daylight levels need educated that its more than the LEED point. Measurable is not predicted and the prescriptive path does not predict lighting levels. So how can you go to the owner and say that you'll have 25 fc throughout by only using the prescript method. How can you go to the electrical engineer and say this is how the building is performing daylight wise so he can tweek the electrical layout, you can;t.

It is our job in this profession to educate owners and others that it is more than just a bunch of checks on a scorecard.

You won;t find it specifically stating that shared daylighting is allowed with the prescriptive path anywhere. It also looks like they removed the LEED interpretation that stated that you couldn;t. I swear, every time i look at the interps page, more stuff is removed.

How can it be allowed when the method does not allow for two different surfaces of glass seperated by x distance. How are you going to justify two VLT with two different WFRs? What are your daylighting zones going to be? You cannot used a weighted average of VLTs of two different surfaces separated by a distance.

Ask yourself, how would you complete the calculator for this situation? Understand you have to submit plans, so unless you don;t include the glass interior wall in the plans and the reviewer is sleeping, it will not be allowed.

You can;t do it and be correct. Unless somebody else out there has come up with a verified methodology and formula to do such that GBCI has found acceptable, you can;t do it.

You can;t do it with the glazing factor calculations. Here is a review comment that i found on someones review which used the same scenario as you.

However, the provided drawings indicate that some of the project's interior spaces are receiving daylight using borrowed light strategies (i.e. sidelights, glazed transoms, etc.) The glazing factor calculation is designed for simple geometries and provides default data to support a simplified analysis. As described in the LEED-NC v2.2 Reference Guide, when analyzing more complex geometries, it is necessary to use daylight simulation or light measurements to demonstrate meeting the credit's requirements.

To support what Todd is saying, you cannot use the prescriptive method to account for spaces that receive daylight through more panes of glass that the ones in the exterior windows. Period. I doubt you will find this exact statement in any LEED documentation, but it is not the responsibility of any one on this forum to prove a negative. There are many, many designs that do not qualify for compliance through the prescriptive option and they can't list every reason. What they do say is that it is meant for the simplest of geometry and what they should also say is that it is meant for climates with mostly overcast skies. Even then it falls greatly short of proper daylighting analysis. Your best evidence is the lack of instruction on how to enter the second Tvis. From a mathematical perspective, interior glazing of any kind or shape provides an additional form factor that simple math cannot account for. (If it even does for the forms without it, which in my opinion, it doesn't.)