Many states have recently increased the stringency of their
residential energy codes, forcing builders to rethink
long-established construction practices. In some areas,
contractors who have always built houses with 2x4 walls and
uninsulated basements are waking up to new regulations
requiring basement wall insulation and much higher R-values for
above-grade walls. Elsewhere, building officials have begun
checking the U-factors on window labels for the first
Energy codes vary widely from state to state. While many states
require residential builders to comply with the Inter-national
Energy Conservation Code (IECC), the successor to the old Model
Energy Code (MEC), other states — including Alabama,
Arizona, Colorado, Illinois, Mississippi, Missouri, and South
Dakota — have no statewide residential energy code.
Even when a state decides to adopt the IECC, however, plenty of
opportunities for confusion remain. At least five different
versions of the IECC are currently being enforced in the United
States. The most recent version, the 2006 IECC (adopted by
Iowa, Louisiana, Pennsylvania, and Utah), is radically
different from earlier versions of the IECC enforced in several
Moreover, a number of states have adopted the IECC with
state-specific modifications. For example, New Jersey's code
permits builders to omit basement wall insulation in any home
equipped with a 90 percent AFUE (or better) furnace; New York,
on the other hand, specifically prohibits any design with a
trade-off that eliminates basement wall insulation.
Several model residential energy codes are currently in print,
including the 1992 and 1995 MECs, and the 2000, 2003, and 2006
IECCs; code books are available at prices from $11 to $31 from
the International Code Council (www.iccsafe.org).
Forty-four states now enforce an energy code based on either
the MEC or a pre-2004 version of the IECC (see
"Residential Energy Codes by State"). These
codes allow builders to choose from three compliance options: a
prescriptive path, a component trade-off path, and a systems
The Prescriptive Path
Dubbed the "cookbook" path in Minnesota, the prescriptive path
is the simplest — though not necessarily most
cost-effective — way for builders to meet energy-code
requirements. Prescriptive-path requirements usually include
minimum R-values for insulation, with different R-values
specified for walls, ceilings, floors, basement walls, and slab
edges. Some prescriptive codes also specify a maximum U-factor
or a maximum solar heat-gain coefficient (SHGC) for
Prescriptive-code requirements are usually shown in a table
(for example, Table 602.1 in the 2000 IECC; see
below) that specifies minimum R-values, maximum
U-factors, and maximum SHGC values; these prescribed values
typically vary by climate zone or by the number of heating
degree days at the building site.
Prescriptive tables, like this one in the
2000 IECC, provide a cookbook approach to energy design but may
not result in the least expensive building.
Windows from major manufacturers are labeled with U-factor and
SHGC values calculated according to procedures established by
the National Fenestration Rating Council (NFRC). If a window
lacks an NFRC label, builders must use code-specified "default
values" when demonstrating code compliance; for example, a
vinyl window with double glazing is assigned a default U-factor
In some regions of the country, the best available default
window U-factors or SHGC values aren't low enough to satisfy
the prescriptive code, so NFRC-labeled windows are the only
option open to builders following the prescriptive path.
In pre-2004 versions of the IECC, builders following the
prescriptive path need to calculate the home's window-to-wall
ratio (WWR). Homes with a WWR of 15 percent or less should
follow the prescriptive tables in Chapter 6 of the code, and
homes with a WWR of more than 15 percent need to follow the
prescriptive tables in Chapter 5. Builders must include rim
joist areas in wall-area calculations; window areas are based
on rough-opening areas.
The idea of the WWR originated in the original 1992 MEC (see
"Making Sense of the Model Energy Code," 11/99). In pre-2004
versions of the IECC, all three compliance paths require
builders to calculate the WWR. (In Washington state, the
residential energy code requires builders to calculate a
different ratio, the window-to-floor-area ratio.)
The Component Trade-Off Path
Because the prescriptive path is inflexible, its use often
results in a house that costs more to build than a house that
follows the component trade-off path. Builders who choose the
component trade-off path are able to adjust several variables
— such as insulation thickness, window area, or furnace
efficiency — in search of the most cost-effective way to
comply with energy-code requirements. In pre-2004 versions of
the IECC, the component trade-off path is found in Chapter
In some states, the component trade-off path is called the
component performance path or — somewhat confusingly
— the performance calculation path. However, this path
does not involve a full-fledged calculation of a home's energy
performance; rather, it involves a simplified performance
calculation based on a limited number of trade-offs.
For example, many state energy codes allow a house equipped
with a high-efficiency furnace to skimp on wall or ceiling
insulation. The rationale behind such a trade-off is simple:
Although the resulting house has different specifications than
a house following the prescriptive path, the two houses cost
about the same to heat.
"The energy codes don't really require minimum levels of
insulation," says Joe Nagan, technical director for Wisconsin
Energy Star Homes. "For example, in their prescriptive
insulation tables, the codes generally assume that you have a
78 percent AFUE furnace. But as long as your trade-off gives
you a heat loss that is less than the maximum allowable heat
loss, you pass. If you don't pass, you can either beef up the
walls or you can go to a more efficient furnace."
In states with an energy code based on the 2004 IECC or earlier
model codes, adjustments in window area can be used as a
trade-off. For instance, thicker attic insulation or
better-performing windows can be used as a trade-off for a high
window-to-wall ratio; conversely, a low WWR may allow builders
to skimp on insulation.
The easiest way to follow the component trade-off path is to
use computer software — for example, a free program
called REScheck — to fine-tune a home's specifications.
Although first-time users of REScheck may be intimidated by the
software, most builders soon navigate the program with ease
(see "Using REScheck").
While the component trade-off path is popular in northern
states, southern builders often stick with the prescriptive
path. "Where the prescriptive codes most align with current
building practice, builders tend to use the prescriptive
codes," says Mike DeWein, technical director for the Building
Codes Assistance Project in Washington, D.C. "That tends to be
in the warmer climate zones. Where current practice varies from
the prescriptive requirements, builders usually want to use the
trade-off or the performance method. In a good chunk of the
northern half of the country, builders and design professionals
are very comfortable with REScheck."
Builders should remember that some trade-off strategies, though
code-compliant, may result in an uncomfortable building. For
example, many state energy codes allow builders to trade
thicker attic insulation for cheaper windows. While the
resulting house may satisfy the energy code, high U-factor
windows may lead to comfort complaints.
The Systems Analysis Path
Sophisticated energy modeling software is needed for the
systems analysis path. Depending on the state, the systems
analysis path may be called the systems performance path, the
simulated performance alternative, or whole-house performance
analysis. It's found in Chapter 4 of pre-2004 versions of the
IECC. In general, builders following this path must show that a
proposed house design has an annual energy budget less than or
equal to a similar house that complies with the code's
While REScheck is perfectly adapted to calculating the effects
of component trade-offs, it cannot be used for the systems
analysis path. Builders following the systems analysis path
need to use a program like DOE-2 or REM/Rate, the software used
by consultants who rate a home using the Home Energy Rating
System (HERS) index. Whereas the REScheck program has no way
for a builder to input a home's air infiltration rate, REM/Rate
does — so that a very tight home can obtain credit for
its superior performance compared with a typical, somewhat
If a builder follows the systems analysis path for code
compliance using an air-infiltration rate that is lower than
the code-specified default value, the code stipulates that a
blower-door test must be performed to verify that the home
meets its tightness goal. In theory, a builder who cannot
provide blower-door results under these circumstances can be
denied a certificate of occupancy.
Systems analyses are usually performed by an energy consultant,
HERS rater, architect, or engineer. A systems analysis is the
only way a builder can get full credit for certain
energy-efficiency features that are not otherwise required by
code — window orientation optimized for passive solar
heating, for example, or a sealed and tested duct system.
Following the systems analysis path makes sense for homes that
have unusual design or energy-efficiency features. Because the
systems analysis path usually requires the assistance of an
energy consultant, it is rarely used for residential
In addition to offering three compliance paths, residential
energy codes impose additional mandatory requirements. For
example, pre-2004 versions of the IECC require attics to be
equipped with permanent insulation depth markers.
Mandatory requirements also vary from state to state; for
instance, Washington state requires all homes, regardless of
which path is used for code compliance, to be equipped with a
whole-house ventilation system and equipment to provide
combustion air for solid-fuel appliances.
Getting Your Permit
In most jurisdictions, a building permit will not be issued
until the builder has submitted documentation — such as a
REScheck report — showing that the design complies with
the local energy code. Energy code documents are prepared by a
range of service providers, including builders, engineers,
architects, energy consultants, lumberyards, and heating
Although REScheck reports are routinely prepared by builders in
many areas, a few jurisdictions — including some New
Jersey municipalities — require REScheck calculations to
be submitted by a licensed engineer. California's energy code,
called Title 24, is unique. Because of the code's complexity,
California builders usually demonstrate code compliance by
hiring an energy consultant familiar with the use of Title 24
Many builders are happy to hand off responsibility for
code-compliance paperwork. "In Wisconsin, the overwhelming
number of REScheck reports are done by the lumberyard or the
heating contractor," reports Nagan.
What About Airtightness?
Since many attributes of home performance are not regulated by
code, complying with the energy code, though necessary, is not
sufficient to guarantee that a house will be energy-efficient.
For example, the prescriptive and component trade-off paths do
not directly address a home's air-leakage rate. As Nagan notes,
"REScheck can perform trade-offs between heating equipment and
insulation levels, but REScheck knows nothing about
In some countries, such as Sweden, a new home must pass a
blower-door test before it can be issued an occupancy permit.
U.S. codes, however, show no sign of following Sweden's lead.
"The 2006 IECC is better at calling out how one deals with air
leakage and duct sealing," notes DeWein. "But there is still no
performance metric for it, unless you go to the full
The 2006 IECC requires submitted plans to indicate air sealing
details (104.2); it also specifies that "the building thermal
envelope shall be durably sealed to limit infiltration"
(402.4.1). Some state codes, including the Minnesota, New York,
and Oregon residential energy codes, have similar mandatory
requirements intended to improve the airtightness of a home's
envelope. Oregon's provisions are subject to interpretation by
local building officials: "All exterior joints around windows,
around door frames, between wall cavities and window or door
frames, between wall and foundation, between wall and roof, and
other openings in the exterior envelope shall be sealed in a
manner approved by the building official."
A house that complies with the energy code does not necessarily
include all cost-effective efficiency measures.
"Most Wisconsin builders install one inch of foam on the
exterior of their basement walls," says Nagan. "When we do our
REM/Rate action reports to evaluate a house for an Energy Star
builder, overwhelmingly the reports show that the foundation is
the largest contributor to the heating cost. Even Energy Star
builders are using just one inch of foam, so these buildings
still have a very weak link. These homes could be
cost-effectively upgraded, with no more labor, just by going
from one inch of foam to two."
Code Compliance Varies
Several studies have documented the fact that in many areas of
the country, energy code provisions remain largely unenforced.
For example, a 2001 study in Fort Collins, Colo., investigated
duct tightness in new homes. In spite of a local code provision
that required ducts to be "substantially airtight," performance
testing in new homes revealed that hvac systems had duct
leakage averaging 75 percent of system airflow.
Similarly, a 2001 study of 186 new Massachusetts homes found
that only 46 percent of the homes met minimum code requirements
for UA (building envelope U-factor), and only 19 percent met
code duct-sealing requirements.
Building officials rarely bring along a home's REScheck report
during site inspections. Although all residential energy codes
except the 2006 IECC impose window-area limits, "there is not a
single jurisdiction in the country that goes out and measures
window areas on site," says Craig Conner, a former engineer at
the Pacific Northwest National Laboratory in Richland,
Some states, including Vermont, have a mandatory energy code
but no system of enforcement. "In Vermont, compliance with the
energy code requires filing a copy of the documentation report
with the local town clerk," says Richard Faesy, a senior energy
analyst for Vermont Energy Investment Corp. in Burlington. "As
far as I know, fewer than 10 percent of new houses are in
compliance with the code. There's no enforcement
Many builders see lax code enforcement as a blessing. The
trouble with uneven enforcement, however, is that a builder can
never be sure when a new building official will begin enforcing
long-ignored regulations. Builders intent on following the code
as written should be aware of the following rarely enforced
• Some codes (for example, in Massachusetts and
California) include duct-tightness requirements.
• Many codes (IECC 102.2, for instance) include a
provision requiring all materials, systems, and equipment to be
installed according to manufacturers' installation
instructions. According to this provision, fiberglass batt
insulation must be installed without voids or compression.
Moreover, housewrap must be carefully lapped at horizontal
seams, and some brands of housewrap must have taped
• Many energy codes (such as IECC 803.2.1.1) require
"right sizing" of hvac equipment; according to this
requirement, oversized furnaces, boilers, and air conditioners
violate the code.
Martin Holladayis the editor of Energy Design