[Equest-users] Spandrel R value

Robby Oylear robbyoylear at gmail.com
Wed Sep 3 13:00:46 PDT 2014


There is no exception for anything of the sort you speak of.  No loopholes.
 I would think the 70% WWR would be a much bigger deal than the R-value of
the spandrel opaque walls.  You're comparing 30% of your windows (likely
U=0.40 to 0.50) to walls in the base case (U=0.06 depending on climate).
 That's going to be much more of a problem than comparing an R-12.6 wall to
a R-15.6 wall.  I'm surprised the building passes Code compliance with
that, let alone any sort of LEED credits.

I'm going to offer up some advice as to spandrel wall U-factors that likely
makes your situation even worse. Please see the attached document that I
put together as a Code proposal to Washington state's energy code.  It
includes background documentation from California's Title 24 Joint
Appendices and shows that spandrel glass without any continuous insulation
behind it is unlikely to achieve a better U-factor than 0.117 (R-8.5).  I
would guess based on your description of the product (3" cavity, assuming
double pane w/ thermal break & low-e) that your U-factor is likely closer
to 0.164 or an R-value of 6.1.

I would recommend that you go back to your "facade experts" and show them
these tables, showing that they will need to provide 2-D thermal
simulations to confirm the performance is what they claim.

Robby Oylear, P.E., BEMP, LEED AP BD+C

Mechanical Engineer


On Wed, Sep 3, 2014 at 7:27 AM, Singhal, Harshul <
HSinghal at thorntontomasetti.com> wrote:

>  Hello everyone
> For one of my office building project (70% total WWR which is almost 100%
> of conditioned wall & remaining 30% are spandrel walls). For ASHRAE
> compliance 40% WWR is used with R-15.6 (U 0.064) wall. For design case,
> recommended R value for spandrel walls is 12.6 which is lesser than code
> compliance.  I know that as per 90.1 user manual spandrel walls should be
> treated as conventional walls for ASHRAE code compliance case but is there
> any exception which I am not aware of? Using R15.6 in ASHRAE & R12.6 in
> design case accounts for a chunk of penalty and I am looking for some
> “loophole” to avoid that. Please note that R value for design spandrel
> walls can’t be increased due to limited thickness available. (3 inches). R
> values are suggested by façade experts.
> Thanks
> *Harshul Singhal*
> Project Consultant
> Thornton Tomasetti
> 386 Fore Street, Suite 401
> Portland, ME  04101
> *T* 207.245.6060  *F* 207.245.6061
> *D* 207.245.6074
> HSinghal at ThorntonTomasetti.com
> www.ThorntonTomasetti.com
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