This document discusses green building and sustainable design options for constructing an energy efficient custom home. It outlines several key components to consider, including building design, wall and roof materials. For design, it recommends an east-west orientation in central Texas to take advantage of breezes and shade windows appropriately. For materials, it suggests high R-value roof and wall insulation, and gives options for walls like structurally insulated panels, fiber cement blocks, or straw bales which provide insulation and moisture resistance. Metal roofs are also recommended for their heat reflection properties. Making informed choices based on budget, materials and climate can result in a healthy, efficient home.

1. 42 THE GOOD LIFE ■ WWW.GOODLIFEMAG.COM ■ OCTOBER 2007
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G
reen Building? Sustain-
able Design? Eco-Ar-
chitecture? In today’s
world, these terms are found in ever
increasing numbers.
Howdoyou—thehomeowner—
sift through the choices and make
decisions that are right for your fam-
ily and budget? This article discuss-
es the basic building components,
(design, walls and roofs) necessary
for a green, energy efficient, cost-ef-
fective custom home.
Cost-effective green building
options are dependant upon how
many years you plan to keep the
home. If you plan on staying there
for fifteen to twenty years or more,
your choices and paybacks (in terms
of lower utility bills) are much larg-
er than if you plan on selling your
What Is Green Building?
by Ben Obregon
With these incredible views also come extreme weather conditions. This home’s fiber cement block walls
will provide a very strong, moisture resistant enclosure for its owners.
Fiber cement block walls provide a well
insulated home. The textured surface
readily accepts a stucco finish and can
be installed in almost any geometric
configuration.
home in five to seven years.
The first step is the building de-
sign. Sustainable design is the most
important factor in creating an en-
ergy efficient home. Sustainable de-
sign is based on a regionally specif-
ic climatic, resource and materials
analysis. Bioregionally appropri-
ate architecture considers heating-
degree days, cooling-degree days,
wind directions and speed, topog-
raphy, sun angles and rotation.
In terms of home design this
means Green Buildings are site spe-
cific.A“green”homeinMaineisde-
signed for solar gain with minimal
overhangs and lots of south-facing
windows. In our region that same
design can be uninhabitable or very
expensive to keep at a reasonable
temperature.
In Central Texas, because of sun
angles and prevailing breezes from
the southeast, we try to put the long
axis of the home on or near an east
west orientation. Locating garag-
es, storage rooms, carports or trees
on the west or northwest side helps
block afternoon heat gain. Doors or
windows on the east or west side
should have shading devices. Cov-
ered porches on the south provide a
place to sit and capture the breezes
while allowing flow-through venti-
lation to enter the home. Wide over-
hangs help shade the doors and win-
dows. A thermal chimney is an ex-
cellent way to exhaust heat from the
home’s interior.
After basic design principles, a
number of materials choices affect
the livability and energy efficiency

2. THE GOOD LIFE ■ WWW.GOODLIFEMAG.COM ■ OCTOBER 2007 43
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of your home. We typically eval-
uate materials based on recycled
content, embodied energy analysis
and potential outgasssing. In addi-
tion, preference is given to materi-
als produced locally or regionally
to help sustain our regional econo-
my and reduce the pollution caused
by transporting materials over long
distances.
Roof insulation—This is one of
the most important aspects of build-
ing an energy efficient home in Cen-
tral Texas. It should be at least R-30.
If the insulation is installed on the
attic ceiling (as opposed to the roof
joists) a radiant barrier and flow-
through attic ventilation will great-
ly enhance the insulation’s effect by
reducingtheamountofheatthatgets
into the attic.
Wall insulation—While studies
have shown that roof insulation has
a greater effect on the home’s ener-
gy cost, wall insulation also plays
a critical factor. For a wood-frame
home, two by six studs with R-19
batts are preferred to two by fours
with R-13 batts.
Insulation options—Cotton
batts are a locally available green
option for walls and roofs. Blown
cellulose is a good ceiling insulation
option.Anotheroptionistotalfillin-
sulation. Wet blown cellulose (with
an adhesive added so the insulation
will not settle over time), Sealection
500 open-cell polyurethane foam or
Icynene spray-on cellular plastic in-
sulation is used in the wall cavity
and sprayed onto the roof joists in a
thickness equivalent to R-30 batts.
The advantage of this method is the
attic becomes conditioned space,
which eliminates the need for at-
tic ventilation, reduces the cooling
load for any air conditioning ducts
in the attic and adds to the home’s
useable space.
Wall materials—For a typical
home that is completely built by the
contractor, wood studs are typically
the most cost-effective method for
framing. However, there are a num-
ber of options such as:
Structurally insulated panels
(SIPS)—A pre-manufactured wall
and roof system made of two lay-
ers of exterior sheathing with an in-
sulated core. There are a number of
insulation options. Expanded Poly-
styrene (EPS) is preferred because
it doesn’t include ozone depleting
chemicals and is recycled. SIPS are
more expensive than wood studs,
but they have the advantage of com-
ing with all of the door and window
openings and electrical outlets pre-
cut at the factory. In addition, they
go up relatively quickly. Once they
are erected, the framing system, in-
terior and exterior sheathing and in-
sulation are completed and you are
ready to install doors, windows and
electrical boxes.
Fiber cement block systems—
These are a type of insulated con-
crete form made of a small amount
ofconcretemixedwithaninsulating
material (either expanded polysty-
rene or mineralized wood fibers—
both recycled) to form a building
block. They have open cells hori-
zontally and vertically that are filled
with rebar and concrete. The result
is a very strong, well insulated wall
system that is almost impervious to
fire and water damage. They cost
more than wood walls but have a
built-in savings factor if rendered
with an exterior stucco. (approxi-
mately two dollars and fifty cents
to two dollars seventy-five cents per
square foot, as opposed to five and a
half to six dollars per square foot on
a traditional wall system).
Straw bales or straw clay—
Both systems provide quiet, homes
with superior insulation and excel-
lent thermal characteristics. Straw
bale homes can be load bearing (the
straw holds up the roof) or used as
infill (a wood or metal frame holds
up the roof). Straw bales provide ap-
proximately R-33 insulation and re-
cently passed an ASTM (American
Society for Testing and Materials)
fire test to achieve a two-hour fire
rating.Strawclaymixtureshaveless
insulation value while having more
resistance to water damage. These
homes cost about the same as a me-
dium-range custom home. Howev-
er, homeowners can achieve signif-
icant cost savings by hosting a “wall
raising” to stack the walls. Both sys-

3. 44 THE GOOD LIFE ■ WWW.GOODLIFEMAG.COM ■ OCTOBER 2007
tems typically have a stucco exte-
rior and either stucco or plaster in-
terior.
Roofing materials—A met-
al roof with a light colored surface
works very well in our climate. It
will reflect heat back into the atmo-
sphere before it enters the attic (re-
ducing the load for both the radiant
barrier and roof insulation). In addi-
tion,itshouldlastfortytofiftyyears,
making the initial investment well
worth the extra installation cost.
There are three basic types of metal
roofing: screw down, snap lock and
standing seam.The type appropriate
for your home would be dependent
upon your budget (standing seam is
the most expensive and strongest,
followed by snap lock, then screw
down) and the amount of time you
plan to spend in the home.
There are many additional items
toconsiderfora“GreenHome.”Low
VOCpaintsandstainsthatemitneg-
ligible volatile organic compounds,
traditional versus on-demand water
heaters, properly sized heating, ven-
tilatingandairconditioningsystems
with properly sealed ductwork, low-
flow plumbing fixtures and fluores-
cent lighting fixtures, just to name
a few.
We are fortunate to live in Aus-
tin, with educated and informed
builders and architects and an inter-
nationally recognized Austin En-
ergy Green Building Program that
provides detailed descriptions of all
of these issues plus many more for
your consideration.
Ultimately, the definition of sus-
tainability varies slightly for every-
one. If you educate yourself on the
choices and make informed deci-
sions based on budget, materials
options, appropriate construction
techniques and styles, you can look
forward to a healthy, energy effi-
cient home that will work for you
and your family for many years to
come. g
Architect Ben Obregon is princi-
pal in The Sustainable Design Cen-
ter, which offices at 13429 Overland
Pass in Austin. You may contact the
firm at 512-263-0177 or www.sus-
tainabledesigncenter.com.
Straw bale homes provide excellent insulation.
This one is almost ready for it’s first coat of stucco.
This structurally insulated panel home provides an energy efficient, quite abode for it's
owner. Structurally insulated walls come with door and window openings pre-cut at the
factory and can be used with a wide variety of finish materials and architectural styles.