3.58 Fenestration - Fenestration Geometry and Area

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What 90.1 PRM Section(s) are relevant to this issue?
-3.58 Fenestration - Fenestration Geometry and Area

Explanation of issue:

Window-wall ratio is defined as follows:

  The window wall ratio is the total fenestration area (including framing) 
  divided by the total gross exterior wall area.

Restrictions on baseline building window area indicate that window area shall 
be reduced if:

  ..the gross area of all windows in the building exceeds 40% of the gross
  *above grade* exterior wall area in the building..

Please confirm the following:
  1) The maximum window area is to be 40% of the gross above grade wall area 
     (as opposed to gross above plus below grade wall area...)

  2) Provide definition of gross above grade wall area which clarifies the
     the following:
       a) are demising walls included 
       b) are walls which enclose unconditioned space included
       c) are walls which enclose semi-conditioned space included
       d) are walls which separate semi-conditioned space from conditioned
          space included
       e) are walls located in below grade parking garages which enclose 
          conditioned spaces (i.e. stair shafts) included.

  3) Are windows enclosing unconditioned and/or semi conditioned space included
     in the total window area for this calculation

Original issue reported on code.google.com by lu...@360-analytics.com on 15 Oct 2014 at 9:30

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Luke,

1) Yes, this will be 40% of the gross above grade wall area and not above + 
below.

Mike is checking with the envelope subcommittee regarding the reply to points 
2,3. We'll get back to you soon about those

Original comment by supriya....@pnnl.gov on 17 Oct 2014 at 12:39

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We're still waiting on ESC's reply on points 2,3. For now we can go with this-

All semi-exterior walls are included in the gross-above grade wall calculation
-Walls separating conditioned/semi-conditioned from unconditioned would count 
as semi-exterior envelope and would be included in the gross above-grade walls.
-So any windows in the walls separating conditioned/semi conditioned from 
unconditioned, like the parking garage example, would be included in the WWR 
calculation.

To answer your specific questions-

2) Provide definition of gross above grade wall area which clarifies the
     the following:
       a) are demising walls included - No demising walls are not included in gross above grade wall area calculation
       b) are walls which enclose unconditioned space included - No, walls which enclose unconditioned space are not included in gross above grade wall area calculation
       c) are walls which enclose semi-conditioned space included - yes, these are included
       d) are walls which separate semi-conditioned space from conditioned
          space included - Not in gross above grade wall area calculation
       e) are walls located in below grade parking garages which enclose 
          conditioned spaces (i.e. stair shafts) included. Yes these are included since they could have windows in them.

  3) Are windows enclosing unconditioned and/or semi conditioned space included
     in the total window area for this calculation - Windows enclosing semi-conditioned spaces will be included in total window area calculations. Windows enclosing unconditioned spaces would not be included in total window area calculation.

Original comment by supriya....@pnnl.gov on 20 Oct 2014 at 11:55

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Supria - 

I was a bit confused by your response, but I just realized that the term 
'demising' partition may mean different things to different people.  For the 
purposes of the T-24 Standards, a demising wall is a wall that separates 
conditioned from unconditioned enclosed space (i.e. semi-exterior).  It seems 
that this may be different from the commonly held (internet) definition, which 
is a surface which separates tenants.

Aside from the demising wall question, I think the guidance above is clear 
enough to implement in the CBECC tool.

Original comment by lu...@360-analytics.com on 21 Oct 2014 at 9:10

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Hold off on this implementation. I expecting something back from the envelope 
subcommittee shortly (likely later today). The complication is that the WWR is 
supposed to be determined separately for each space conditioning category 
(residential conditioned, non-residential conditioned, and res and non res 
semi-heated). 

Original comment by bikerose...@gmail.com on 21 Oct 2014 at 9:17

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Copying Mike's response below-

Calculating Wall Area-
- Nonres above grade exterior wall area = the gross above grade wall  area for 
nonresidential conditioned space only includes those walls  that separate 
nonresidential conditioned spaces from the exterior, 
- Res above grade exterior wall area= the gross wall area for residential 
conditioned space only includes those wallsthat separate residential 
conditioned spaces from the exterior, and
- Semi exterior above grade wall area = the gross wall area for semiheated 
space includes (a) those walls that separate nonresidential conditioned space 
from unconditioned space and those walls that separate residential conditioned 
space from unconditioned space, and (b) all of the walls that enclose 
semiheated space (again, regardless of whether those walls are adjacent to the 
exterior, or adjacent to an unconditioned space, or adjacent to a conditioned 
space).

Hence- Semi-exterior wall area  = area of exterior walls surrounding 
semi-heated spaces + area of demising walls between semi-heated and conditioned 
space + area of demising walls between semi-heated and unconditioned + area of 
demising walls between conditioned and unconditioned.

Calculating Window Area-
WWRnon-res = window area in exterior walls enclosing non-res conditioned spaces 
/ gross area of above grade exterior walls enclosing non-res conditioned spaces 

WWRres = window area in exterior walls enclosing res conditioned spaces / gross 
area of above grade exterior walls enclosing non-res conditioned spaces 

WWRsemi-ext = window area in semi-exterior walls / gross area of above grade 
semi-exterior walls 

Each of the 3 WWR described above are calculated separately, and each must be 
40% or below in the baseline. 

Original comment by supriya....@pnnl.gov on 22 Oct 2014 at 11:52

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The same approach would also be used to calculate gross roof area and skylight 
area for each space conditioning category. The 3 skylight roof ratios will be 
calculated separately and each must be 5% or below in the baseline

Original comment by supriya....@pnnl.gov on 23 Oct 2014 at 10:06