Page 60 - Green Builder November Issue Codes Update

Building
Innovative Solutions for High-Performance Homes
Ceiling Insulation:
“Prescriptive” OptionsOption 1: “Prescriptive”
Here’s a quick primer on how to get the right R-vCaeluiliengisnwcitheAiltitnicgSspawcehsen following
the Prescriptive Path of the 2009, 2012 and 2015 IECC.
BY STEPHEN CARR
After conducting many code trainings with
local building officials, builders and insulation
companies throughout the nation, I realized
there was a common question when it
came to ceiling insulation: “What R-value
is the right R-value when following the
Prescriptive Path?” So, I broke this section
of the code down and extended the answer
to the other alternatives in the code where the
project may comply. There are two types
of ceilings in the Energy Code: ceilings
with attic spaces and ceilings without
attic spaces. Other than exceptions listed
in the code, there are no trade-offs that will
lower these R-values more.
58 GREEN BUILDER November/December 2016
InsulationFull height of insulation is
not achievable.
CREDIT: DOE’S BUILDING ENERGY CODES UNIVERSITY
Insulation
No insulation over the
top plate.
Figure 1
FCEILINGS WITH ATTIC SPACES
OR CEILINGS WITH attic spaces in climate zones requiring
a Prescriptive R-38 or higher, the insulation in the ceiling
assembly must follow the Prescriptive Method of the Code
Table R402.1.1 (2009 and 2012 IECC) or R402.1.2 (2015 IECC).
The insulation either does not cover the top plate or it is
compressed to a level less than R-30.
If your Energy Code calls for a Prescriptive R-38 in the ceiling,
then, as shown in Figure 1, that is the level to which the main part of
the attic will be insulated. The code is assuming that near the eaves
there will be less than R-38 and does not call out any requirements
for that area. This also applies for R-49 required jurisdictions as well.
Look at Figure 2. In this scenario, a raised heel truss (or energy
truss) allows for the full uncompressed R-value to be over 100 percent
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