Determining Occupancy: Residential Edition

My last post on determining occupancy for LEED projects did not discuss how to determine residential occupancy, an issue I've encountered recently.

Searching through the Credit Interpretation Rulings, I found a rather vague answer coughed up by the supreme court that is the CIR council (committee? emperor?) dated 2/14/2007:

Per the LEED NC v2.1 SSc4.2 ruling dated 12/9/2005, occupancy should be calculated using the number of bedrooms in the case of residential projects. Project teams should provide a narrative with calculations demonstrating how the total number of residential FTE occupants was calculated including indication of number of units, size of units (e.g. studio, one bedroom, two bedroom, etc.), and assumptions as to number of occupants per each size of unit.

So we base it on bedrooms... great! It would sure be nice to have actual guidance on how to transfer that into a hard number, but why make it that simple? Now we get into the sticky issue of what number to put to what bedroom count. Being lazy, I did not take the time to research average occupancy across the nation or anything like that. Instead I proposed the following:

Residential Occupancy Per Bedroom

• Studio/1 Bedroom - 1.5 occupants
• 2 Bedrooms - 2.5 occupants
• 3 Bedrooms - 3.5 occupants
• 4 Bedrooms - 4.5 occupants
• etc.

Being the smart guy or gal that you are, you've probably picked up on "the formula". I think it's a safe bet to assume that a one bedroom could equally be expected to be occupied by 1 or 2 people, so I split the difference and assume 1.5. For additional bedrooms, it's likely to be occupied by either kids or roommates, but doubtful it will be occupied by additional couples.

I'd like to be clear that this assumption has not gone off for review yet, and I'm not going to spend a few hundred dollars to answer the question beforehand... I think this argument is reasonable, and expect it to be accepted, but don't want you to stake a large quantity of money on the fact that I'm right. If you have used different assumptions that worked or tried this one and failed, PLEASE be sure to comment on your experience below. Thanks!

Rounding up or down?

If you're looking at preferred parking (SSc4.3) for and you determine that your project needs 4.15 LEV parking spaces, how many should you provide, 4 or 5? While this is a relatively harmless difference (one more sign probably won't break the bank), the difference between 1 or 2 showers (SSc4.2) might be more of an issue in an small office building.

I wasn't sure about this answer until I noticed that the credit templates solved the answer for me. One tenth of a shower is a full shower, and rounding up, even when the numbers would typically be rounded down is the norm.

Take the following example:

5% of 180 FTE is 9.00000 secure bicycle storage spaces require. If we add one more FTE, then 5% of 181 is 9.05, which in most minds would round down to 9. In this case however, the LEED credit calculator rounds the number up to 10 required spaces:

Determining Occupancy

So we need to know our occupancy for our nice LEED project... great. This question bothered me for a long time, especially since it affects so many credits. Then I realized you're basically supposed to make it up! Really though, the owner is supposed to supply you with the numbers, but how is he going to do that if they're not sure? If you're working a core and shell project that fits neatly into the groupings below, you can use the default occupancy numbers (in square feet/FTE) below. Most credits is defined as SSc4.2, SSc4.3, SSc4.4, EAc1, EQp1, EQc1, EQc2, EQc6, and who could forget, EQc7. See the LEED-CS reference guide (page 441) for more detail.

If you're not fitted nicely into one of those groups, you're on your own. I take the code occupancy count and break out the reasonably inferred FTE. If you have a restaurant, there are only going to be so many cooks in the kitchen, tables per waiter, a hostess, a bartender, and a manager. I would then subtract that number from the code occupancy to give me the transient loading, which would be added to the FTE number to determine peak loading. In a mixed-use project you would need to look at hours of operation - as peak loading for a movie theater is likely to be on a different schedule than peak loading for an office. See below for an example breakdown for SSc4.2, Bicycle Storage and Changing Rooms.

Am I wrong in my assumptions? TELL ME! Please use the comments to make this site more informative!