I just had this come up on a project. The reviewer will only allow me to count hardscape area for the LPD table if that area has over 0.2 fc.

In the past people have asked me if they can count a parking lot or sidewalk if it doesn't have any lighting. My answer has always been yes. Now, USGBC is saying no. I'm trying to find out why and where this 0.2 fc limit came from.

Rereading the language of ASHRAE 90.1 v2007 and v2010 I see the difference. v2010, section 9.4.3 states, "...for areas that are designed to be illuminated..." Back in v2007, section 9.4.5 has no mention of "illuminated areas." Letting you know that this appears to be a change that will affect v4 documentation of this credit.

So what does "illuminated area" mean? I cannot find any description in ASHRAE 90.1. Doing some Google searching I have found that in a 2010 draft of the Model Lighting Ordinance (MLO) it had a definition for "illuminated area" that stated, "An exterior area for which lighting of reasonable uniformity (20:1 or less maximum to minimum illuminance ratio) and illumination (average greater than 0.2 fc) is provided; not incidentally lighted or partially lighted."

But that was just draft language and said an average of 0.2 fc, not a minimum. The final version of the MLO does not have any definition of "illuminated area".

I can't find any other mention of 0.2 fc anywhere. This looks like an artificial limit created by the reviewers.

So, ASHRAE 90.1, v2010 does state that the LPD can only be used for areas designed to be illuminated. But they fail to explain what this means. LEED also does not define this term.

I will try to challenge this 0.2 fc requirement since I hate made up rules by LEED reviewers. I'll let everyone know my result.