Hey all,
Please bear with me, as this question is complicated and takes into account a couple different documents/rating systems. I'm sincerely hoping that I am just missing something obvious, and one of you can simply point that out, and I can stop obsessing about this. This pertains to Heat Island Effect - Roof, Option 3 (BD+C SSc7.2, and ID+C SSc1 Path 5).
On page 119 of the 2009 BD+C Reference Guide, there is an equation listed to calculate the amount of compliant roof area for a building with a combination high-albedo/vegetated roof. It is listed as follows:
[(Area Roof Meeting Minimum SRI / .75) + (Area of Vegetated Roof / .5)] >= Total Roof Area
On page 6 of the ID+C Reference Guide, there is another equation listed for the same credit, in this case SSc1, Path 5, Option 3. That equation is listed as follows:
Total Roof Area
Laurie Thorwart
Heller & Metzger PCApril 15, 2014 - 9:32 am
I understand that this was a complicated (read: terribly framed) question, but in case anyone is keeping track, I did receive a response from the USGBC and there was an error in the study guide. For the test and for project use, should it come up, the second formula listed above should be the one used:
Total Roof Area <= [(Area of SRI Roof * 1.33) + (Area of Vegetated Roof * 2)]
Just a general comment on USGBC study materials: I found a LOT of errors throughout the study material when I was looking information over for my exam. For what it's worth, I found that the redline guides on the USGBC website were probably my best resource, I just wish I had found them sooner (but don't anyone worry, I passed with flying colors).
Jake
Magda Kowalik-Gadek
Interior Architect & DesignerApril 16, 2014 - 1:35 am
Hi Jake,
I'm just studying to my AP CI+C exam and also noticed this error in study guide. Actually it is not even an error, but it is frustrating as this 'round-up' in formula (*1.33 vs /.75) is irritating. 75% should always be calculates as SRI area /.75. *1.33 is kind of 'inversion' but to be more exact it should be 1.33333(3), so why to express this formula like this..? The larger the roof area SF the difference will be 'growing' and it will always be below required 75%...
I am studying also from CI+C Ref Guide and agree - it has plenty of errors. I just wonder what are these redline guides you're referring to on USGBC website? Thanks,
Magda
Laurie Thorwart
Heller & Metzger PCApril 29, 2014 - 1:42 pm
Hi Magda,
Sorry for the delay.
With regards to your question on the formula, all I can relay is what was told to me by customer service at GBCI, and what I saw on the test. I agree that the formula can be confusing, but it is what we're supposed to use nonetheless.
As far as the redline guides are concerned, go here: http://www.usgbc.org/resources/list?keys=redline
That is the Resources tab on the USGBC website, with "redline" in the search field. Scroll down to the applicable file and you should be all set. Redline guides are nice because they show what has been changed/added/omitted over time.
Jake