We just received our design credit responses and used method 2 - Prescriptive. We have a 3 story cafeteria space within a 30 story office building.
The lowest level butts up to the 3 story glass wall on the exterior and the 2 levels above are held back from the 3 story glass wall by 20'-0"-ish. We are getting a comment saying that these upper cafeteria levels do not count. I know that above in the explanations, it mentions borrowed light from an atrium is not allowed, but these spaces are open to the adjacent glass, just not touching the glass exterior wall.
Is there no way for us to respond to this comment with a narrative explanation that the spaces are daylit, showing a section with light hitting the surfaces of the mezzanine levels? These levels are open and only separated by a railing, not another glass wall falling under the borrowed light definition.
thanks for any comments you might have.
TODD REED
Energy Program SpecialistPA DMVA
LEEDuser Expert
890 thumbs up
February 3, 2016 - 2:42 pm
I will agree that the upper spaces do not fall under the specific definition of borrowed light but I can see why the reviewer may have used this language.
The prescriptive method is meant for simple geometries and daylighting scenarios because it is all based on formulas. Your situation is not one that would be considered simple. I think the reviewer should have provided a specific reason for saying why they cannot be included or given you a possible method to demonstrate how. Your situation is one that would require more than a narrative to show compliance with the option 2.
From a professional side, these spaces cannot technically be included in the prescriptive calculations. You would have to show how much of the 3 story curtain wall glass is allotted to each level. You would then need to establish the depth of the daylighting zone from each allotted area of glass. From the sounds of each, with each level being at 20 feet from the glazing , they might be too far away to have any sizable daylight zone. You cannot use all three floors of glazing for each level, that might actually have too much daylight. What I just described, I have never seen done or attempted with option 2. As you can see, it is complicated and does fit into the simplicity method that option 2 is meant for. You could try it and make a case and see what happens or, do a project team inquiry and ask specifically why the spaces are rejected and what must you show to demonstrate compliance.
Personally, I would have done simulations or at least do measurements. The prescriptive is too simple for the scenario you have.
Please follow up if you decide to do an inquiry and what the reviewer asks for or whatever path you choose.
Good Luck.
Elliot Young
DesignerRinkachung Architecture
1 thumbs up
February 19, 2016 - 5:37 pm
Thanks for the response - we are the LEED sub-consultant to the LEED consultant and were instructed to use method B. I agree, simulation may have saved time - and after all this, we may have to do some simulation of a few spaces to achieve our 75%. The Leed reviewer indicated that we could supplement the diagrams with a daylight model for those spaces to kick us over the 75. From the beginning though, everyone thought option B would be a slam dunk!