Question-and-Answer Resource for the Building Energy Modeling Community
Get started with the Help page

# 90.1 Window to Wall Ratio Calculation - Parking Garage

The Std 90.1-2013 definition of space excludes enclosed parking garages. I have a building with two floors of office space above two floors of enclosed parking garage, all above grade.

My question is: For the requirements of Section 5 for maximum allowable fenestration area (40%), would the opaque wall area for the parking garage be part of the total gross wall area?

Any references will be appreciated

edit retag close merge delete

Sort by ยป oldest newest most voted

I think it depends on if the garage is conditioned or not. See the definitions...

building envelope: the exterior plus the semi-exterior portions of a building. For the purposes of determining building envelope requirements, the classifications are defined as follows:

exterior building envelope: the elements of a building that separate conditioned spaces from the exterior.

Also, OpenStudio Standards adjusts the baseline WWR based on whether the space is conditioned.

more

1

I just wanted to follow up with the fact that since Section 5.5.4.2.1 references Tables 5.5-1 through 5.5-8, that means that the maximum of 40% vertical fenestration area is applied separately to all nonresidential and residential conditioned space exterior walls and semiheated space exterior walls. Therefore, if the enclosed parking garage is conditioned, tradeoffs are allowed between the office and parking garage fenestration ratio for an overall of 40%, but if it is semiheated or unconditioned then that is not the case, the office has to comply separately with the maximum 40% requirement.

( 2019-07-01 07:19:47 -0600 )edit
1

I looked deeper into the language from the 90.1-2013 User's Manual, and on page 5-2 it reads "The Standard distinguishes between conditioned, semiheated, unconditioned, and indirectly conditioned space classifications. The building envelope requirements do not apply to unconditioned spaces." My parking garage is unconditioned, therefore, it seems like the requirement is 40% of the conditioned wall area. However, the standard mentions 40% of "gross wall area" and Example 5-Q of page 5-62 defines it as perimeter x height.

( 2019-07-01 14:08:00 -0600 )edit
1

If you refer to Table G3.1.5.c (baseline) you'll see that it refers to gross above-grade exterior wall area. Then if you look at Figure 5.5.2, you'll notice that the wall separating an unconditioned space from the exterior (such as with the ventilated attic, ventilated crawlspace, or unconditioned space) is not labeled as either exterior or sem-exterior envelope. Therefore, the parking garage walls are not included in the "gross wall area."

( 2019-07-01 14:58:59 -0600 )edit
2

@anchapin I think that the way of phrasing this would be that the "walls" of an unconditioned space are not part of the building envelope, therefore do not fall in the ASHRAE definition of a wall and do not add to the wall area, gross.

( 2019-07-01 16:50:36 -0600 )edit

I believe that what you are saying is the same thing that I was trying to say, but maybe in a more straightforward manner.

( 2019-07-02 06:51:00 -0600 )edit

If this is for an appendix G analysis, the parking garage would typically be considered a separate "building area type" according to Table G3.1-Baseline(c) and each area type would have to comply with Table G3.1.1-1 individually, irrespective of conditioning category.

more

Could you expand on this? I have not seen this approach before.

( 2019-07-01 13:54:08 -0600 )edit

Table G3.1.5.c (baseline) indicates that if your building has a building type listed in Table G3.1.1-1, then you use the vertical fenestration area % indicated in that table, for all other building types you use either the proposed design vertical fenestration area % or 40% whichever is smaller.

( 2019-07-01 15:00:31 -0600 )edit