Hi All,
The roof in our 2,750 ft2 office is leaking. Since it's rainy season here
in climate zone 4, we're trying to get it repaired quickly. We've decided
to add R19 poly-iso nail base to the un-insulated roof. There is an option
to install R26 instead.
I just started digging into the commercial building tax deduction (section
1331 of HR6) to see if R26 will qualify for the $0.60 or even the $1.80/ft2
deductions. I've created a model of the existing building in eQuest 3.64.
Given my modeling experience, there is not enough time to build a ASHRAE
90.1 - 2001 compliant model in version 3.63 to compare the energy savings of
R26 v. the baseline R15. Is there an outside chance that R26, being > 50%
better, would result in a 50% reduction in energy use? Is there a chance it
would result in a 16 2/3 reduction? I realize these may be tricky
questions, any thoughts are appreciated; disclaimers are ok too.
Thanks,
Justin
Justin Tiedemann, LEED AP BD+C
Fast thoughts:
Important nuance alert: The good news is, a 50% reduction in current
energy use might actually be realistic since you have an uninsulated
roof to start... However you need to demonstrate a 50% reduction in
energy use with respect to a 90.1-2001 baseline, and that would hinge on
whether your existing HVAC/lighting/walls/floors/windows are
significantly efficient or not. It's possible.
Whether a $1.80*2,750 = $4,950 (at most) tax deduction (not credit) is
worth the time involved is perhaps a more pertinent question to explore
first...
The 16.67% reduction target, which would require to hold everything else
constant (lighting/HVAC) and isolate the envelope differences seems less
likely to me... I've only once explored various roof U-values for a
small footprint like that, and the impact was negligible.
Disclaimer: 99% of my knowledge/experience with the CBTD is using the
lighting-only approach. My hunches here are based more on my general
modeling experience - but also primarily in climate zone 4 ;).
~Nick
NICK CATON, E.I.T.
I believe that when modeling for tax deductions, the baseline envelope for
both new and existing buildings must meet the requirements of 90.1-2001.
This is spelled out in Table 7 of NREL guidelines
(http://www.nrel.gov/docs/fy07osti/40467.pdf), which lists deviations from
90.1 Appendix G protocol. I had an exchange with the document's author back
when it was first published, pointing out that this change makes it very
difficult for an existing building to qualify, but he confirmed that this
was an intended change and that the baseline envelope must be modeled as
meeting prescriptive requirements of 90.1. I am not aware of a more recent
guidance or interpretation that overrules that. Does anyone know if this has
changed?
Maria