[BLDG-SIM] WWR definition

Larry Degelman ldegelman at cox.net
Mon Apr 24 17:07:18 PDT 2006

Possibly the interpretation of what is gross wall area depends on what
version of 90.1 you are looking at.  As for 90.1-2004, the official
interpretation on the ASHRAE web site leaves no doubt that “gross wall area”
include both above- and below-ground walls.  See the following item verbatim
from the ASHRAE web site.



Energy Standard for Buildings Except Low-Rise Residential Buildings



Date Approved June 25, 2005


Request from: Roger Chang (E-mail: roger.chang at arup.com), Associate Member,
155 Avenue of the Americas, New York, NY 10013.


Reference:  This request for interpretation refers to the requirements
presented in ANSI/ASHRAE/IESNA Standard 90.1-2004, Section 5.2.1 Compliance,
relating to gross wall area.


Background: Standard 90.1-2004 does not appear to be clear as to what gross
wall area means. International Energy Conservation Code is clear that
prescriptive requirements are based on window to above-grade wall area. This
impacts all sections of the code where the window-to- wall area ratio is
taken into consideration.



Interpretation: Gross wall area refers to above-grade wall only.



Question:  Is this interpretation correct?



Answer:  No.





Section 3.2 defines “building envelope” to include “the elements of a
that enclose...spaces through which thermal energy may be
transferred to or from the exterior”.


Section 3.2, in the definition of “wall” states “this includes above- and
below-grade walls, between floor spandrels, peripheral edges of floors, and
foundation walls”.


Section 3.2 defines “gross wall area” as “the area of the wall measured on
the exterior face from the top of the floor to the bottom of the roof”.


Therefore, for buildings with conditioned space below-grade, the gross wall
area extends from the top of the surface of the floor of the lowest
conditioned space to the bottom of the roof of the highest conditioned


(Note that the use of a similar term in a document from another organization
is irrelevant to an interpretation of Standard 90.1.)


Page 1 of 1
©2005 ASHRAE. All Rights reserved.




Larry O. Degelman, P.E.                  ldegelman at cox.net 

Prof. Emeritus of Architecture    Ph./Fax: 1-979-696-2506

Texas A&M University



-----Original Message-----
From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Jon McHugh
Sent: Sunday, April 23, 2006 8:40 PM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] WWR definition


Rene, Larry and Gerald,


I think that the the underground wall area should be included for each floor
that has windows.  These windows in partially below ground stories are
providing light and views that are no less important than similar functions
provided on upper floors.  However, if I have a skyscraper with 4 stories of
underground garage of basement areas, I don't think these fully underground
wall areas should be included.  Rene, in evaluating the energy and cost
impacts of windows in buildings, it is important to look at the potential
for daylighting or the value of view, otherwise an engineering analysis
might conclude that we don't need any windows at all.


Perhaps this should be brought up with the 90.1 envelope committee.




Jon McHugh, PE, LC
Technical Director
Heschong Mahone Group Inc.
11626 Fair Oaks Blvd #302
Fair Oaks, CA 95628 (Sacramento)
(916)962-7001 ext 38
(916)962-0101 FAX
e-mail: mchugh at h-m-g.com
URL: www.h-m-g.com 



From: BLDG-SIM at GARD.COM [mailto:BLDG-SIM at GARD.COM] On Behalf Of Renee J.
Sent: Sunday, April 23, 2006 11:11 AM
Subject: [BLDG-SIM] WWR definition

It depends on the code in use. 


I submitted an official request (CM proposal) to the ASHRAE 90.1 Envelope
committee to change the definition to only include the above grade walls but
they declined it so it is still the above and below grade walls. The reason
I sent the request is that architects tend to add more glazing to the above
grade walls because they can include the below grade walls in the
definition. I showed some modeling results of the difference between a two
story building with one above and below grade wall in a few difference
cities in the US and there was a significant energy impact.


However, I believe the IECC includes only the above grade walls. 





Renée Azerbegi, CEM, LEED-AP

President/Sustainable Design Engineer

ambient energy – solar & sustainable design solutions

t 303.278.1532 | f 303.278.8533 | c 303.885.2695

renee at ambient-e.com



From: BLDG-SIM at GARD.COM [mailto:BLDG-SIM at GARD.COM] On Behalf Of Larry
Sent: Sunday, April 23, 2006 10:26 AM
Subject: [BLDG-SIM] 


Gerald et al,


The conventional definition of window-wall-ratio is the window area divided
by the “gross” wall area, though the term “window-wall-ratio” is no longer
among the Definitions section of 90.1-2004.  For that matter, WWR is not
defined in the Abbreviations section.


Notwithstanding all that, the definition for “Gross Wall Area” is clearly
defined in the 90.1-2004 User’s Manual.


On page 5-30, example 5-G addresses “Determining Gross Wall Area”, stating
that this is very significant since the window area requirements are based
on Window-Wall-Ratio (WWR).  


Answer (as shown on the same page):  “The gross wall area includes both
above-grade walls and below-grade walls so that gross wall area is simply
the perimeter of the building 
 times the height


Larry D.


Larry O. Degelman, P.E.                  ldegelman at cox.net 

Prof. Emeritus of Architecture    Ph./Fax: 1-979-696-2506

Texas A&M University



-----Original Message-----

From: BLDG-SIM at gard.com

To: BLDG-SIM at gard.com

Sent: Fri Apr 21 09:06:56 2006

Subject: [BLDG-SIM] ASHRAE 90.1 window-wall ratio


I recently came across a paper from "Building Energy

Codes Program" called "Setting the Standard" and lists

out various new code updates. It seems that currently

we are allowed to count below-grade walls as part of

the window-wall ratio calculations.  Does anyone have

an update on this or point me to the right resource to

confirm this information?






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