& Links to pages that can help understand principles of
design and application of High Thermal Mass
build with straw bales, tires, logs, or foam foundation blocks
and then expect it to be passive solar! Concrete is the
best material for many reasons, but foam foundation blocks (ICFs)
such as Rastra®, Faswall®, Tech-Block®, and Conform® were
simply not designed for passive solar homes.
The main problem with
interlocking extruded polystyrene ("EPS") foam
foundation blocks ("ICF"s) and Faswall® wood and
concrete blocks is that the insulation is on both sides of the
the exterior of your foundation wall is good thinking, but
insulating the interior of the wall simply prevents the release
of any heat which has been stored within the concrete.
Why pay for all that concrete and ICFs then never get a chance
to "use" the heat storage? The basic principle
of sustainable, passive solar heating/cooling is that the house
AND the ground around it stores heat all summer and releases it
all winter. You need to look at the home itself as a means
to store heat. The analogy of a battery is often used to
describe the way an HTM high thermal mass home functions:
storing energy (heat) when it is available, using it later, when
it's needed. Please note that we are
not talking about storing enough heat to get through a couple of
days without any sunlight; this is seasonal passive solar
misconception is that straw bale, timber frame Sip Houses and
log homes have large thermal masses. This is simply not
true. They have very low thermal masses.
Thermal mass is a relative measure of an object's ability to
store heat, "K" value. The complete
inability of straw bales and logs to store heat is what makes
them such a poor choice for a passive solar home or an attached
and plants alike are much healthier in a consistent, radiant
heat rich, naturally lighted environment. If your home is
not storing the heat brought in through the windows quickly
enough, temperatures rapidly become too high for your comfort
and will eventually kill your plants. That's why you'll
never see an attached greenhouse like this on a straw bale home.
Straw bale homes have
other problems too numerous to address here, but one to keep in
mind is the danger to your family's health. Airtight homes
are bad enough to begin with, but straw, wood, and paper are
fuels that promote black mold growth in moist, unvented
locations. Cracks in
the straw bale plaster open the wall's interior to indoor air
humidity. Meanwhile, a surface bonded block wall is
waterproof, can be further sealed with non-porous latex paint,
and provides no fuel to promote exotic growths that could affect
your indoor air quality.
Simple Design Methodology for Passive Solar Architecture
Dennis R. Holloway (the die-hard solar architect!)
following information is a precipitation of knowledge acquired
through my practice and research in the 1970's regarding the use
of solar energy to 'passively' heat and cool buildings. I
believe that continuing dissemination of this information
through the Internet is very important in a time when earth's
bio-environment is so endangered by the continued combustion of
fossil fuel into the atmosphere.
ancient discovery that the shadow of a "gnomon"--an
arrow stuck vertically into the ground--mirrored the perfectly
symmetrical path of the sun across the sky is as important to
the development of civilization as the discovery of the wheel.
By studying the movements of this shadow people first conceived
of the 90o (right) angle--the foundation of geometry, and
ultimately of architecture. A result of this "shadow
science" origin is that most architecture and city street
grids are related to the north-south east-west axes. The
ancients also gained great insights into the potential of
architecture to modify the sun's shadow and radiant heat.
Indeed, using the sun as a heat source is nothing new. In XENOPHON'S
MEMORABILIA, written 2400 years ago, Socrates observed:
"Now in houses with a south aspect, the sun's rays
penetrate into the porticos in winter, but in the summer, the
path of the sun is right over our heads and above the roof, so
that there is shade. If then this is the best arrangement, we
should build the south side loftier to get the winter sun and
the north side lower to keep out the winter winds. To put it
shortly, the house in which the owner can find a pleasant
retreat at all seasons and can store his belongings safely is
presumably at once the pleasantest and the most beautiful."
While the Greek house that Socrates described probably lost heat
as fast as it was collected, due to convective and radiation
losses, the Romans discovered that if the south-facing portico
and windows were covered with glass, the solar energy would be
trapped causing the internal temperature to stay constant into
the night. This simple phenomenon called the "greenhouse
effect" is illustrated by the experience of returning to
your car on a sunny, cool day and finding it overheated. Today
we call the house that uses the greenhouse effect for heating a
"passive solar house."
It is a common rule-of-thumb that, compared to a conventionally
designed house of the same square footage, a well-designed
passive solar house can reduce energy bills by 75% with an added
construction cost of only 5-10%. In many parts of the U.S.
passive solar houses do not require any auxiliary energy for
heating and cooling. Given current and future projected fuel
costs, the additional construction cost is recovered quickly.
Official surveys show 100,000 passive solar homes in the
U.S.(1984), but informal estimates bring to one million the
number of buildings that employ some aspects of passive solar
design, often south-facing greenhouses.
of a Passive Solar House
Passive Solar House has some distinctive design features:
1. In the northern hemisphere most of its windows are facing the
south (in the southern hemisphere its windows face north). Solar
radiation, mostly the visible light spectrum, passes through the
solar-oriented glass of windows or solar spaces, and is absorbed
by surfaces of materials inside the insulated envelope of the
building. As these heated surfaces re-radiate the energy into
the interior of the house, the air temperature rises, but the
heat is not efficiently re-radiated outside again through the
glass, nor can the heated air escape, so the result is entrapped
2. Ideally, the interior surfaces that the light strikes are
high density materials, such as concrete, brick, stone, or
adobe. These materials, because of the "flywheel"
effect (the ability to absorb energy and re-readiate it over
time), can store the energy for constant slow re-radiation,
resulting in a very smooth temperature swing curve for the
building, and reducing the possibility of overheating the air in
the house. In this way a large portion of the houses' heating
requirements can be supported by the sun.
3. In the early passive solar houses of the 70's, architects and
builders tended to reduce window areas on the east, west, and
north sides of the house in favor of southern orientation. This
is still the general rule-of-thumb, but the introduction of
energy conserving and radiation-modifying films, available in
several major window lines (see Chapter 6, p. 57f), enables
designers and builders to relax this rule. This is good news on
sites with attractive views other than to the south. West
windows are a source of high heat gain during the summer, and
should be shaded. Generally, the house plan with a long
east-west axis and optimized south-facing wall will be the best
passive solar house.
4. Passive solar homes tend to be well insulated and have
reduced air leakage rates, to keep the solar heat within the
5. Since auxiliary heat requirements are greatly reduced in a
passive solar home compared to a conventional home, smaller,
direct-vented units or a woodstove for extended cloudy periods
are often the heaters of choice.
6. Passive solar homes often have "open floor plans"
to facilitate the "thermosiphing" movement of solar
heat from the south side through the rest of the house.
Sometimes small fans are used to aid in warm air distribution in
houses with "closed floor plans".
Solar Techniques 1: Direct Gain
are two basic ways passive solar houses gain solar energy,
direct and indirect gain. Direct gain houses, considered to be
the simplest type, rely on south-facing windows, called solar
windows. These can be conventionally manufactured operable or
fixed windows on the south wall of the house or
standard-dimension insulating glass panels in the wall of the
sunspace or solarium. While some of the heat is used
immediately, walls, floors, ceilings, and furniture store the
excess heat, which radiates into the space throughout the day
and night. In all cases the performance and comfort of the
direct gain space will increase if the thermal mass (concrete,
concrete block, brick, or adobe) within the space is increased.
2: A direct gain passive solar house (Design by Dennis Holloway,
Architect, for Ellen and Matt Champion)
J. Douglas Balcomb and his research team at Los Alamos National
Laboratory recommend that the mass be spread over the largest
practical area in the direct gain space. It is preferable to
locate the thermal mass in direct sunlight (heated by radiation)
but the mass that is located out of the direct sunlight (heated
by air convection) is also important for overall performance.
Thermal mass storage is as much as four times as effective when
the mass is located so that the sun shines directly on it and it
is subject to convective heating from warmed air as compared to
only being heated by convection. The recommended mass
surface-to-glass area ratio is 6 : 1. In general, comfort and
performance increase with increase of thermal mass, and there is
no upper limit for the amount of thermal mass.
Remember, covering the mass with materials such as carpet, cork,
wallboard, or other materials with R-values greater than 0.5
will effectively insulate the mass from the solar energy you're
trying to collect. Materials such as ceramic floor tiles or
brick make better choices for covering a direct gain slab. Tiles
should be attached to the slab with a mortar adhesive and
grouted (with complete contact) to the slab.
In direct gain storage thin mass is more effective than thick
mass. The most effective thickness in masonry materials is the
first four inches--thickness beyond 6" is pointless. The
most effective thickness in wood is the first inch.
Locating thermal mass in interior partitions is more effective
than exterior partitions, assuming both have equal solar access,
because on the internal wall heat can transfer on both surfaces.
The most effective internal storage wall masses are those
located between two direct gain spaces.
3: Internal mass storage walls serve as north-south partitions
between direct -gain spaces (a) and as east-west partitions
between direct-gain sunspaces and north clerestory space (b).
Lightweight objects and surfaces of low density materials should
be light in color to reflect energy to high density materials.
If more than one-half of the walls in a direct gain space are
massive, then they should be light in color. If the mass is
concentrated in a single wall, then its color should be
dark--unless its surface is struck early in the day by sunlight,
in which case its color should be light to diffuse the the light
and heat into the rest of the space. Massive floors should be
dark in color to store the heat low. Clerestory windows should
be located so that the sunlight strikes low into the space. If
the sunlight from the clerestory first strikes high in the
space, then the wall surface should be light in color to diffuse
the light and heat downwards into the space.
In northern climates moveable insulation in the form of drapes,
panels, shutters, and quilts often are used to cover the inside
of the glass on winter nights to reduce heat loss. Because so
much high-angle summer sun is reflected off vertical
south-facing glass, heat gain is greatly reduced in the warm
season, overhanging eaves for shading may not be as crucial as
the early passive solar designers thought.
Since inhabitants will see out through the glass, this technique
is good for the site with good southerly views. Some people
object to the intense glare in direct gain rooms and fading of
furniture fabrics can be a disadvantage. Privacy can also be a
problem, since if the occupants can see out through the expanses
of glass, the rest of the world can look in.
Besides providing warmth in the winter, a well-designed passive
house should provide coolth and good ventilation in the summer.
In some quarters there is a stubbornly persistent myth, a
holdover from the news media coverage of some of the early
passive houses, that overheating in summer is common in these
Architects and builders have discovered that a two-storey solar
space or greenhouse, adjoining the main house, with operable
vent windows near the top and bottom of the space can be used to
create natural ventilation for the house during summer. When the
windows are open on a sunny day, the rising mass of warmed air
is allowed to escape through the opened top vents which in turn
draws in cooler air through the lower vents or through windows
in the adjacent house. Called the chimney effect, this
principle, employed to cool the Indian Tipi, can also keep your
passive solar house cool in any U.S. summer climate without the
use of powered fans or mechanical air-conditioning.
Shading devices used on the south side of the house can also
help. Pull-down shades or canvas awnings on the outside of the
glass of the south-facing windows, solarium, and trombe walls
can greatly reduce house heat gain. Deciduous trees and shrubs
planted to cast shadows on solar-oriented glazing can also
create a micro-climate that is several degrees cooler than
surrounding areas. When the leaves drop, winter sun can shine
into the house.
popular direct gain heating strategy is the sunspace. Many
homeowners claim this room becomes the favorite space in the
house with its spacious outdoor feeling. The sunspace/greenhouse
can, if properly designed and sited, provide as much as 50% of
the house's heating requirements. In this situation, living
spaces are better located on the south side with spaces (like
bedrooms) not requiring as much heat to the north. Clerestory
windows can be used in larger houses where it is important to
get sunlight into the north side rooms.
4a: One-story sunspaces: winter, sunspace cut off from the house
(Section A); winter, sunspave helps the lower story via open
doors (SectionB); summer, sunspace helps cool the lower story by
pulling in air from the north windows (Section C).
4b: Two-story sunspace: winter, sunspace cut off from the house
(Section A); winter, sunspace helps heat both stories of the
house (SectionB); summer, sunspace helps cool booth stories (SectionC).
If you plan to include a sunspace in your design, you'll first
need to decide on the primary function of the space. The design
considerations for a food-growing greenhouse, a living space and
a supplementary solar heater are very different, and although it
is possible to build a sunspace that will serve all three
functions, compromises will be necessary.
Sunspace / Greenhouse
greenhouse, for instance, should be a comfortable and healthy
home for plants. Plants need fresh air, water, lots of light,
and protection from extreme temperatures. Greenhouses consume
considerable amounts of energy through evapotranspiration and
the evaporation of water. One pound of evaporating water uses
about 1,000 BTU's of energy that would otherwise be available as
To stay healthy and free of insects and disease, plants need
adequate ventilation, even in winter. There are air handling
systems such as air-to-air heat exchangers that ventilate while
retaining most of the heat in the air, but these add
significantly to the cost of the project. The light requirements
of a space for growing plants call for overhead glazing which
complicates construction and maintenance, and glazed end walls,
which are net heat losers.
There will be some economic gains from reduced grocery bills if
you grow vegetables, and certainly there is much to be said for
the sense of satisfaction that comes with increased
self-reliance and the aesthetics of a roomful of healthy plants
attached to your house. The bottom line in terms of energy
efficiency, however, is that a sunspace designed as an ideal
horticultural environment is unlikely to have any energy left
for supplementary space heating.
purpose of the sunspace is to collect solar heat and distribute
it effectively to the adjacent living space, you're faced with a
different set of design criteria. Maximum gain is achieved with
sloped glazing, few plants, and insulated, unglazed end walls.
Remember that you'll get more usable heat into your living space
if there aren't plants and lots of mass soaking it up in the
sunspace. Sun-warmed air can be moved into the house through
doors or operable windows in the common wall, as well as blown
through ductwork to more remote areas.
sunspace will be a living space, you'll need to consider
comfort, convenience, and space in addition to energy
efficiency. A room you plan to live in must stay warm in the
winter, cool in the summer, have minimum glare levels, and
Vertical glazing is the choice of increasing numbers of
designers for a variety of reasons. First of all, although
sloped glazing collects more heat in the winter, it also loses
significantly more heat at night, which offsets the daytime
gains. Sloped glazing can also overheat in warmer weather,
usually the spring and fall, when you don't want the gain.
The performance of a vertical glazed south wall more closely
follows the demands of heating degree days, heating effectively
in winter when the angle of the sun is low and allowing less
solar gain as the sun rises toward its summer zenith. A
well-designed overhang may be all that's necessary to keep the
sun out when it's not needed. Vertical glazing is also cheaper
and easier to install and insulate, and is not as prone to
leaking, fogging, breakage and other glazing failures.
A sunspace designed for living requires carefully sized thermal
mass, and, as we mentioned earlier, special care must be taken
to assure that the sun can get to the mass. A masonry floor
covered with carpets and furniture is obviously not as effective
a thermal mass as masonry sitting in direct sunlight.
Once the sun goes down, the same windows that collected heat all
day begin to reradiate heat to the outdoors. To minimize
nighttime losses and maximize comfort (the human body also
radiates heat to a cool surface), you may want to include
movable window insulation in your design or investigate some of
the new high tech glazings now commercially available
of the design strategy you choose, there are some other criteria
that are important to consider. Much of the following
information is taken from The Sunspace Primer: A Guide to
Passive Solar Heating, by Robert W. Jones and Robert D.
McFarland, (Van Nostrand Reinhold Co., New York, New York,
The ideal orientation for the glazing in your sunspace is due
solar south, although an orientation within 30o east or west of
due south is acceptable. For maximum solar gain, the glass
should be tilted 50-60o from the horizon. Many designers,
depending on their design strategy, prefer vertical glazing, or
a combination of vertical and sloped glazing.
Vertical south-facing glass has advantages over angled glazing
in not having to be sealed against water leakage and in its
capacity to reflect unwanted (high angle) summer sun, but its
winter performance is 10-30% lower that tilted glass of the same
area. (Vertically glazed space, can be used like most other
rooms in the house, whereas tilted glazing results in head
height problems sometimes). The efficiency of a sunspace that
combines vertical and some angled roof glazing will be higher
than the vertically glazed sunspace, while retaining the
advantages of vertical glazing. Rain and snow will clean the
outdside of the tilted glass pretty well, whereas vertical glass
has the same maintenance problems as house windows. A
two-to-three foot wide edging of pea gravel below sunspace
glazing that is close to the ground, will prevent soil from
splashing onto the glass, which can reduce efficiency.
5: Sunspace with sloped south-wall glazing over reverse-slope
vent windows (a). Sunspace with vertical south-wall glazing
(sliding door), side venting windows, and sloped roof glazing
(b). (Design by Dennis Holloway, Architect)
sunspace is deeper than it is high, the space itself will trap
the radiation, so lighter surface colors are acceptable.
Otherwise, the surfaces of heat storage materials (thermal mass)
should be dark colors of at least 70 percent absorption. To give
you some perspective on the relative absorption of various
colors, black has an absorption of about 95 percent, a deep blue
about 90 percent, and deep red about 86 percent. Non-storage
materials should be lighter colors, so they will reflect light
to the thermal mass that isn't in the sun.
The floor, north wall, and east and west side walls are good
locations for mass walls, which should be materials with a high
thermal conductivity such as concrete, water, brick, adobe, or
rammed earth. "Light weight" concrete is not
acceptable as a thermal mass material, and concrete is most
effective in 4 to 6 inch thicknesses. If concrete blocks are
used, the cores must be grouted solid.
Figure 6: Sunspace thermal storage (a) Provide 3 square feet
of concrete (b) or 3 gallons of water (c) for each square foot
If the masonry floor and wall mass are the only thermal storage
materials in the space, three square feet of masonry surface per
square foot of south glazing is the recommended ratio. If water
in containers is the only heat storage medium used, the
recommended ratio is three gallons per square foot of glazing.
Increasing the amount of mass will stabilize the internal
temperatures, making the space more comfortable for people and
plants. A common strategy is to use an 8 to 12 inch uninsulated
masonry wall as the north wall of the sunspace. The wall is left
uninsulated so that the heat from the sunspace can be conducted
through to the interior of the house.
sunspace is to be used for growing plants or as a living space,
a minimum of double glazing is recommended. Single glazing loses
a great deal of heat at night, and will make the space
uncomfortable for plants and people. Movable insulation or a
higher-R glazing system will greatly improve the performance of
Either of these options add to the cost of the project, and the
obvious disadvantage of movable insulation is that someone has
to move it every day , and some designers refuse to use it
because of an "objectionable appearance"--something
this industry has not been creative about. On the other hand, it
is possible to have the insulation controlled automatically with
motors and thermostats, and insulation can provide privacy,
summer shading, and increased comfort on cold winter nights.
distribute the warmed air from the sunspace to the rest of the
house, openings are strategically placed in the common wall
between the sunspace and the interior living space. Heat is
transferred by the "thermo siphoning" circulation of
the air. Warm air rises in the sunspace, passes into the
adjoining space through the opening and cool air from the
adjoining space is drawn into the sunspace to be heated as the
If the openings are 6'8" doors, the minimum recommended
opening is 8 square feet of opening per 100 square feet of
glazing area. If two openings are used--one high in the
sunspace, one low--with 8 vertical feet of separation, the
recommended minimum area for each opening is 2.5 square feet per
100 square feet of glazing.
can radically overheat resulting in dead plants and unusable
living spaces if operable vents are not included in the overall
design. As we mentioned, overheating is most likely to occur in
the late summer and early fall, when the sun is lower in the sky
and the outside air temperature is still warm during the day.
Vents are placed at the top of the sunspace where the
temperature is the highest, and at the bottom of the space where
temperatures are the lowest to induce the chimney effect.
Thermostatically controlled motors can be installed to open the
vents automatically if no one will be home to operate them.
These paired vents should be sized according to the following
specified fraction of the sunspace glazing area. The required
vent area is a function of the glass slope, the vertical
distance between the top and bottom vents (stack height), and
the rise in internal temperature over outdoor temperature that
can be tolerated in the sunspace. The last column in the chart
gives fan sizes that will provide the same ventilation.
Few design strategies offer the aesthetic appeal and practical
paybacks that a carefully thought out and constructed sunspace
does. In our view, it is money well spent to take your
preliminary design to a solar engineer or architect for feedback
and a computer analysis. It is much less expensive to make
changes on paper than to alter a design once it's built.
Solar Techniques 2: Indirect Gain
second passive solar house type, indirect gain, collects and
stores energy in one part of the house and uses natural heat
movement to warm the rest of the house. One of the more
ingenious indirect gain designs employs the thermal storage
wall, or Trombe wall placed three or four inches inside an
expanse of south facing glass. Named after its French inventor,
Felix Trombe, the wall is constructed of high density
materials--masonry, stone, brick, adobe, or water-filled
containers--and is painted a dark color (like black, deep red,
brown, purple or green) to more efficiently absorb the solar
Some designers use "selective surface" materials,
chrome-anodized copper or aluminum foils with adhesive backing
that can increase the absorptive efficiency of the wall to 90%,
compared to 60% for a painted surface. These materials allow the
wall to absorb radiant heat, but drastically reduce the amount
of heat that is lost by radiation to the outdoors at night.
Some builders have had difficulty getting good adhesion between
commercially available selective surface foils and the Trombe
wall. According to the July 1, 1985 Solar Energy Intelligence
Report, Los Alamos National Laboratory is testing a selective
surface paint that may hold promise. If you would like to know
more about it, contact the National Technical Information
Service, 5285 Port Royal Road, Springfield, VA 22161,
(703)487-4600, and ask for the report on "Thickness
Insensitive Selective Surface Paint." The paint can be
brushed or sprayed on, and performs in range of 10-20 percent
better than flat black paint.
Heat collected and stored in the wall during the day, slowly
radiates into the house even up to 24 hours later. The Trombe
wall allows efficient solar heating without the elare and
ultra-violet light damage to fabrics and wood trim that is
common in direct gain solar homes. Trombe walls also afford
privacy in situations where that is an issue.
Perhaps the most useful book on passive solar design for
owner-builders is THE PASSIVE SOLAR ENERGY BOOK, by Edward
Mazria, who makes the following recommendations for sizing the
Trombe Wall: "In cold climates (average winter temperatures
20o to 30o F) use between 0.43 and 1.0 square feet of
south-facing, double-glazed, masonry thermal storage wall (0.31
and 0.65 square feet for a water wall) for each one square foot
of floor space area. In temperate climates (average winter
temperatures 35o to 45o F) use between 0.22 and 0.6 square feet
of thermal wall (0.16 and 0.43 square feet for a water wall) for
each one square foot of space floor area."
several of the earliest published Trombe wall houses, small
vents were used in the top and bottom of the wall; heated air in
the wall air space would rise and pass through the upper vent
into the high space of the room, while cooler air from low in
the room would be drawn into the wall air space through the low
wall vent to form a convective heating loop. This is
particularly effective in a building where heat is required
quickly. The convective movement of air in the wall results in a
significant decrease in efficiency over time. Vented Trombe
walls are known to be only about 5% more efficient, overall,
than non-vented Trombe walls. Therefore, for residences,
non-vented Trombe walls are recommended.
the Passive Solar House
the term, "passive solar" was introduced into the
language of professional solar researchers in the 1970's, most
people didn't have a vague notion what it meant. Later, as the
term was popularized by the media and through a large number of
public educational conferences, people probably thought that if
they wanted to build a passive solar house they would have to
hire not only an architect, but a professional solar engineer
capable of manipulating very complex mathematical equations on a
Today, thanks primarily to knowledge gained from
government-funded research and a large number of completed
"pioneer" passive solar houses that we've collected
data from, we are at the stage where even a high school student
can design a passive solar structure. Following is a composite
of recently published information to get the owner-builder on
the path to owner-designing the passive solar house.
Solar Preliminary Design Rules of Thumb
that "solar south" is different from "magnetic
south." The longest wall of the house should ideally be
facing due (solar) south to receive the maximum winter and
minimum summer heat gains. However, the south wall can be as
much as 30o east or west of solar south with only a 15% decrease
in efficiency from the optimum.
Figure 7:When designing a solar home, you must locate true
(solar) south, not magnetic south. This map shows how magnetic
south varies from true south in different parts of the United
your house so that rooms with relatively low heat and light
requirements, those that get infrequent use (storage, utility
room, garage, e.g.), and those rooms that generate high internal
heat (kitchen) are located on the north side of the house to
reduce winter heat load.
In 1983 J. Douglas Balcomb and the research team at Los Alamos
National Laboratory issued a set of direct gain and indirect
gain design guidelines for heating passive solar houses located
in the U.S. They included information on infiltration rates and
selecting R-values for the walls, ceiling, perimeter, and
basement. They also made suggestions about what kinds of
glazing's to use for east, west and north windows, as well as
about how to size the solar collection area.
The technique is not a substitute for more rigorous
computer-simulated thermal analysis by a professional engineer,
but it gives owner-builders a solid basis for the schematic
design decisions. It is an elegant if oversimplified tool for
deciding on a good mix of conservation and passive solar
strategies based on geographical location. The five-step
technique has been distilled from theoretical analysis and from
data collected at actual passive solar houses.
2: Recommended Insulation Values and Infiltration Rates
following formulas to determine insulation values and
recommended infiltration rates. (CF is the conservation factor
you selected in the first step.)
Wall R values: Multiply the CF by 14. This is the R-value for
the entire wall, includeing insulation, siding, interior
Ceiling R-values: Multiply the CF by 22. This is the R-value for
the entire ceiling, including insulation, finish surface, etc.
R-value of rigid insulation placed on the perimeter of a slab
foundation: Multiply CF by 13. Subtract 5 from this number. Use
the same value for the insulation of the floor above a crawl
space or for the perimeter insulation outside an exposed stem
R-value of rigid insulation applied to the outside of the wall
of a heated basement or bermed wall: Multiply CF by 16. Subtract
8 from this number. Use theis value for insulation extending to
4 feet below grade. Use half this R-value from 4 feet below
grade down to the footing.
Target ACH (Air Changes/Hour): Divide .42 by the CF. If the
result is lower than 0.5ACH, choose tight super insulation
techniques with controlled ventilation to maintain indoor air
Layers of glazing on east, west, and north windows: Multiply the
CF by 1.7, then choose the closest whole number. (If the number
is 2.3 , choose windows with three layers.) If the number
exceeds 3. explore insulating glass and/or movable insulation.
Based on guidance from results of these formulas, select your
conservation levels, trying to stay within 20% of the results.
Your budget will be your best guide, but remember that
conservation pays in the short and long run, so when in doubt,
opt for higher conservation levels.
3: Net Load Coefficient
compute a Net Load Coefficient (NLC). To do this, look up your
home's geometry factor (GF) in Table 1 (below). For example, if
the house will have a total floor area of nearly 3000 square
feet on three stories, the GF will be 5.7.
Now multiply the GF by your house's floor area. Thus, if the
floor area will be 2900 square feet and the GF is 5.7, you
multiply these two values to get 16,530. Finally, divide this
result by the CF. If your CF is 2.0, for example you would
divide 16,530 by 2 to get 8265. This is your NLC.
Figure 9: Use this map to find your load collector ratio (LCR).
(Source: J. Douglas Balcomb, et. al.)
5: Passive Solar Glazing Area
determine the area of the passive solar collector (Trombe wall,
sunspace, etc.) for your home, divide the NLC (the number you
got in step 3) by the LCR (the number you got in Step 4). For
example, if your NLC is 8.265 and your LCR is 20, then your
passive solar collector should have 423 square feet of
south-facing glazing. You can round this number up or down by 10
percent (so the area could be as small as 370 square feet or as
large as 450 square feet.) In hot climates, the areas should be
adjusted downward by 20 to 30 percent.
most commonly used in passive solar homes to make maximum use
of the sun's heat include direct-gain windows, direct gain
glazed solariums, and indirect-gain Trombe walls and mass
wall. Each of these elements will influence the design because
they have specific requirements.
"Direct-Gain" windows allow sunlight to enter the
home directly. Much of the heat from the sunlight should be
absorbed by some type of high-density material such as
masonry; after sunset, the heat will flow out of this
"thermal mass", helping to keep the house warm.
Direct-gain windows should be oriented due south, although the
orientation may be varied by as much as 30 degrees east or
west of south without losing much efficiency. Southerly views
from the building site become an important criterion in site
selection--you don't want huge southern windows showing you
unattrative views. Because many furniture fabrics and carpets
are susceptible to fading in sunlight, and because these
materials tend to prevent the light from reaching masonry
floors where its warmth can be stored, you should keep such
fabrics our of direct sunlight.
Figure 10: A large south-oriented glass wall and high
vents (a); A Trombe wall (b); A two-story sunspace (c).
Thermal mass is shown as solid black and speckled areas.
The direct gain solarium (otherwise known as a solar
greenhouse or sunspace) is similar in concept to teh
direct-gain window, and the same orientation rules of thumb
apply. The typical early solarium of the 1970s projected out
from the house, like na addition, and was glazed on the south,
east, and west sides as well as the roof. The south wall was
typically sloped. Today's solarium has been modified for
greater efficiency and typically is flush with the south wall
of the house, thereby eliminating the loss of energy from the
east and west walls. Surrounded by other spaces, the solarium
space can be an effective focus for the house, functioning
like a solar "hearth". To minimize the overheating
common in the early style solarium, the roof is not glazed and
the south wall is vertical rather than sloped. The
state-of-the-art solarium is sometimes a two-storey space,
with French doors opening to rooms on both levels, allowing
better circulation of solar-heated air throughout the house.
Figure 11: Orientation to true south in a passive solar
house may vary by as much as 30 degrees east or west of south
with relatively little loss of overall efficiency (top); A
direct-gain system, such as a sunspace (a), floods a space
with light, which may cause fabrics to fade. An indirect-gain
system, such as a Trombe wall (b), provides heat while
blocking the light.
Figure 12: First generation sunspaces (a) usually
protruded from the house. New sunspaces (b) are often two
story designs set into a house's south wall.
A Trombe wall is a masonry wall with glazing spaced a few
inches outside it. Solar heat is trapped between the masonry
and the glass; it enters the house by migrating through the
masonry. Whereas the direct-gain window and solarium are
virtually transparent, creating strong spatial connections
between indoors and outdoors, the Trombe wall obstructs views
to the outdoors, so it works well on a site where a southern
view is not desirable. If you do want a south view, however,
yu can place windows in a Trombe wall. Variations on the
Trombe wall include half-Trombe walls with direct-gain windows
above, and Trombe walls with integral fireplaces. A Trombe
wall can also be "bent" or shaped to fit the
internal requirements of the floor plan.
Figure 13: Trombe walls can be designed to fit virtually
any south-facing wall.
The design of a multilevel passive solar house should take
into account the fact that there will be some degree of heat
stratification, with warmer upper level spaces and cooler
lower level spaces. Thus the spaces on the upper level might
include the living, cooking, and family activity areas where
most of the waking hours are spent, and the lower level spaces
could be used for sleeping. Although this "upstairs /
downstairs" relationship seems unconventional to us, it
offers a better view from the living space and is ideal for a
hillside house with entry on the north side of the house and
the north walls of the lower level sheltered by the hill.
Future of Passive Solar Houses
emergence in the 70's of the passive solar house, in all its
variations, was a dramatic display of Yankee ingenuity applied
to the national energy crisis, and our knowledge about the
solar-thermal performance of buildings was extended by a quantum
leap. But at this writing, the political pendulum and its news
media has swung away from passive solar architecture, as the
Federal solar tax credits quietly are put to bed.
With all the current talk of an emerging energy-glutted decade,
the potential owner builder may wonder if making an energy
efficiency statement in a new home makes any sense. We surely
have to see through this cloud to know that energy shortfall in
the 70's will pale by comparison to what lies ahead in the 90's.
The growing movement of clear-sighted owner builders will
continue to show the rest of the population that our living room
comfort can, by connecting to our abundant ambient solar energy,
release us from the tyranny of tenuous foreign energy supplies.
In a recent interview, Douglas Balcomb, our foremost passive
solar researcher-spokesperson, said that the viability of
passive solar has become an established fact, and the use of
direct-gain spaces, sunspaces, and Trombe walls (in that order)
will be with us for a long time.
HABITAT FOR HUMANITY HOUSE USING
design, construction, and maintenance of buildings have a
tremendous impact on our environment and our natural resources.
There are more than 76 million residential buildings and nearly
5 million commercial buildings in the U.S. today. These
buildings together use one-third of all energy consumed in the
U.S., and two-thirds of all electricity. By the year 2010,
another 38 million buildings are expected to be constructed. The
challenge will be to build them smart, so they use a minimum of
non renewable energy, produce a minimum of pollution, and cost a
minimum of energy dollars, while increasing the comfort, health,
and safety of the people who live and work in them.
built environment is also a major source of the pollution that
causes urban air quality problems, and the pollutants that
impact climate change. They account for 49 percent of sulphur
dioxide emissions, 25 percent of nitrous oxide emissions, and 10
percent of particle emissions, all of which damage urban air
quality. 35 percent of our carbon dioxide emissions, the chief
pollutant blamed for climate change is attributed to building
building practices often overlook the interrelationships between
a building, it’s component parts, it’s surroundings, and
it’s occupants. "Typical" buildings consume more of
our resources than necessary, negatively impact the environment,
and generate a large amount of waste. According to Laurence
Doxsey, former Coordinator of the City of Austin Green Building
Program, "a standard wood-framed home consumes over one
acre of forest and the waste created during construction
averages from 3 to 7 tons." Often, these buildings are
costly to operate in terms of energy and water consumption. And
they can result in poor indoor air quality, which can lead to
are many opportunities to make buildings cleaner. For example,
if only 10 percent of homes in the U.S. used solar water-heating
systems, we would avoid 8.4 million metric tons of carbon
emissions each year.
building practices offer an opportunity to create
environmentally sound and resource-efficient buildings by using
an integrated approach to design. Sustainable buildings promote
resource conservation, including energy efficiency, renewable
energy, and water conservation features; consider environmental
impacts and waste minimization; create a healthy and comfortable
environment; reduce operation and maintenance cost; and address
issues such as historical preservation, access to public
transportation and other community infrastructure systems. The
entire life cycle of the building and its components is
considered, as well as economic and environmental impact and
ideas became important when designing and constructing Habitat
for Humanity homes. Habitat homes must be affordable to
construct, using techniques that are manageable by a largely
volunteer workforce, but more importantly, the homes must be
simple to maintain and efficient and inexpensive to operate.
Operational costs are extremely important when working
affordable housing. So it is just as important to keep future
operating costs to a minimum, as it is to keep first costs (of
construction) within an affordable range.
these sustainability, efficiency, and affordability goals, a
class was set up at the University of Illinois School of
Architecture to examine these ideas within the context of a
Habitat for Humanity home. The central ideas are to embrace
holistic, sustainable design ideas in an affordable, easy to
construct residence and participate in it’s construction.
the unique characteristics, and the focal point of this house
are the insulated concrete forms, (ICF’s). ICF’s are walls
constructed of concrete but the forms are left in place to serve
as a continuous insulation and sound barrier to reduce energy
loss and infiltration. The major advantages or this construction
the use of ICF’s, there is a 25% to 50% energy savings as
compared with that of wood or steel framed homes. The paybacks
in energy savings are estimated to be within five years.
house was designed to affordable, sustainable, and accessible.
By using a split-level design, the footprint of the building was
reduced to 900 square feet, thus allowing the plan to become
more interchangeable in it’s orientation on the lot. Depending
on the location, site orientation, and other environmental
conditions, the house can vary to become as efficient as
possible. This plan consists of a split-level, four bedroom and
one and a half bath. The total livable area is 1276 square feet.
The entry, living room and kitchen all sit above the crawl space
while the bedrooms are part of the split level. The house is
visitable, which means it has an accessible entrance, living
room, kitchen and bathroom.