"Comparative Building Shell Systems"

The following list comprises most of the building shell systems (roofs and walls) currently being used in sustainable building as it's practiced in Western Colorado. It describes each system briefly, lists it's characteristics...advantages and disadvantages..., and gives recommendations for where to use and not use that particular medium in a building for this climate. These recommendations are based on numerous case studies of structures using these systems, observations about their effectiveness, comments from owners about their satisfaction with the system, reported costs and labor intensiveness, empirical evaluation of characteristics of the medium in terms of its insulation value, massing capabilities (for absorption and storage of solar heat in passive solar design) and general suitability. Mass used in the interior of buildings helps immensly to stabilize temperature swings and make huge contributions to comfort levels, especially in extreme heat or cold. The conclusions and recommendations are those of the author...widespread differences of opinion will be found, depending on how "invested" the opinion-giver is in a particular system...especially if that person specializes in producing a particular medium. Experience with those mediums also varies from person to person. Care must be given to the fact that how something like adobe performs in southern New Mexico may or may not be relevant to its usability here (climatic differences).

Every attempt has been made here not to be biased about any particular building shell material, but to report the general performance experience of as much of the sustainable building community with that material as possible...especially owners who have lived in these structures for long periods of time. Opinions and input about these media changes daily as new techniques and more case studies are developed. Your best bet is to take what is reported here as a source of general direction in allowing you to make a good decision about your project...then go see as many homes as possible that have been built with the medium...talk to the owners...confirm your choice with "three dimensional" information and your own sense of how they feel...they are, after all, what you'll be living with for a long time.

Relative costs of these mediums is all but impossible to ascertain. It is so dependent on the equipment, experience, training and motivation of the people who use them that $/sq ft comparative prices seem illusive and useless...a lot of it is determined by your zeal and appeal for a particular medium and the time you have to play with it. They are all, to varying extents, labor intensive...but the materials are typically cheap or free.

Information about owners of homes built in particular mediums in your area is available through Smart Shelter Network. State of the art sustainable design now utilizes "hybrid" systems...which combine two or more of the following materials for different uses in different parts of the building. A treatise on Hybrid Design follows (in course material) or is available through Smart Shelter.

Strawbale

Description: Straw is a byproduct of grain harvesting and is usually burned(air pollution) or

baled and sold for minor uses...it has no feed value for livestock. Bales are either two or

three string(mostly two string here)...about 16"wide, 14"high and 30-50" long. Bales are

stacked to make a wall, then stuccoed(outside) and plastered(inside) for fire, weather and

insect protection. Most bale buildings have an independent structural support system

to carry roof and second floor loads (non-load bearing type). Some use the stuccoed bale

wall as the only means of structural support.

Characteristics: Straw is an excellent insulator (r=3/inch) a 16 inch bale wall has an r value of

48. Straw is a poor massing medium, but the plaster covering it is good...called a thin

mass. Straw walls are excellent insulators and fairly good as mass providers...vastly

superior to frame construction.

Recommendations: Stucco/plastered strawbale walls are highly recommended for north,

east and west exterior walls (in hybrid design). They are used on south walls, but perhaps

not as effectively as timber frame or adobe...because of solar exposure and ease of

glazing opening handling (bale walls are bulky and imprecise) Properly stuccoed and

plastered they have a fire rating of one to two hours (frame walls are 20 min. fire rated).

Strawbale walls are too bulky for use as interior partitions(generally)

Traditional Adobe

Description: Adobe blocks are hand made from clay soil, sand and straw...poured into a form,

then released and turned several times to dry in the sun. They are then mortar-stacked

into walls. Their sizes vary...10-20" wide..about 4" thick. and weigh 20-30# each. They

typically serve both as the wall "infill" and the structural system holding up the roof or second story floor. This is a building medium many thousands of years in use. Adobe blocks can be "stabilized" by adding tar or concrete based mixtures to the mud, increasing

their resistance to weathering.

Characteristics: Traditional adobe walls have huge mass-heat storage capabilities, but poor

insulation characteristics. Traditional walls 20-24 inches thick produced warm winter

homes, cool in the summer by storing massive amounts of heat (or coolness) and

buffering the outside weather. This form of building is very labor intensive...pouring

the bricks(or buying them) turning them six times, mortaring and stacking them...then

stucco and plaster. Reports vary between owners about how effective adobe walls

are as insulator(unless they're insulated)...especially above 6 or 7,000 ft elevation.

Recommendations: Many shell systems are more energy and labor efficient than traditional

adobe, but may not give the structural system adobe does. Thin walls (around 10"

thick ) are definitely not recommended for exterior walls without insulation, except perhaps as "trombe-type" treatments on south facing solar walls.

Pressed Earth (or Adobe) Block

Description: Blocks or bricks are made (often from the soil on site) by mixing with sand

and loading into a pneumatic press machine which compresses to 28,000psi and

produces a smooth, damp, uniform block...which is stacked onto the wetted surface

of the block coarse below. The completed wall dries as a single unit, bonded without

mortar as it's built. Blocks are usually around 10" long 6" wide 4" tall.

Characteristics: Pressed block walls are the thinnest of the earth based systems, not good

insulators, but great mass and solve lots of the labor intensity problems of traditional

adobe and rammed earth. They can be made from the soil on site with a rental machine

and crew. They are structural, typically.

Recommendations: Like other earth mediums, they shouldn't be used in exterior walls,

unless they're insulated...either with foam or rigid on the exterior...or built as a "double"

wall with an insulated air space between the two walls. Pressed block is probably the

single most desirable interior partition material, providing fast, inexpensive, sound-proof

fire-proof, flexible walls...which can be curved in any direction.

Rammed Earth

Description: Rammed earth is poured into wall forms, similar to the way concrete is formed

A mixture of clay earth, sand, water and straw (and often, steel reinforcement or bamboo)

is poured into the wall forms and "rammed" either by hand or with mechanical tampers.

The form is released and the wall stands independently...capable of bearing roof and

floor loads. Walls are 12-18" thick, typically.

Characteristics: The earth walls themselves, like thin adobe, are not good insulators, but

provide excellent mass. They must be insulated to be used as exterior walls. Insulation

is usually exterior-applied spray foam or rigid styrofoam insulation. The forming and

pouring techniques take training and are tedious, if you're not experienced with them.

Recommendations: A couple of successful projects are known in Western Colorado...it's

not real popular...it does come from the soil at hand. Definitely not recommended for

exterior walls without insulation...a good interior partition medium, but hard to do if

the ceiling or roof is already in place (pouring into the top of the form).

Poured Adobe

Description: Wall forms 10-12" tall are made and poured full of wet clay soil, straw and sand

mixture. When set, the form is moved up a course and a new layer is poured over the

last until the wall is constructed. Typically 10-16" thick.

Characteristics: (same as rammed earth)

Recommendations: (same as rammed earth)

Earth Bag

Description: Now is that a questionable name, or what...earth bag. The walls are made by

shoveling dirt into bags (like plastic woven gunnysacks) and stacking them into walls

which are plastered and stuccoed...usually about 20 " thick.

Characteristics: This is a very plastic medium...build domes and serpentine walls with it.

Like all earth forms, it's great mass and not so good insulation...although the thickness

rivals traditional adobe for temperature stability.

Recommendations: (same as trad. adobe and rammed earth)

Cob

Description: Clay soil, sand, straw and water are wadded by hand into a "bread-loaf" sized

"cob"...a British term...which is where this building form has been practiced for hundreds

of years. The cobs are stacked wet like wine bottles on top of each other to form any

shape of wall imaginable...even sculptures. Typically, they are then stuccoed and

plastered. Like pressed block, the walls cure as monolithic units.

Characteristics: (same as rammed earth,etc)

Recommendations: (same as rammed earth, etc)

Stone

Description: seen one rock, you've seen them all.

Characteristics: Stone exterior walls are invariably cold...cold in the winter, cold in the summer. They're a labor intensive, but cheap material system with excellent

structural characteristics when done right.

Recommendations: They must be insulated if used as exterior walls. They have little or

no insulation value of their own...but are incredibly good massing sources. Stone

walls and floors near south windows are a good move.

Log

Description: Cut down trees, stack up walls. The spaces between the logs must be chinked

or sealed.

Characteristics: Despite their popularity, log houses have difficulty meeting sustainability

criterion. The conventionally produced ones consume exorbitant amounts of wood

to produce a shell. One regional company gets their logs from 500 acre clear-cut tracts

in British Columbia...where the entire tract is leveled(everything) then chipped and

"napalmed"...that's right...fire bombed...ala Vietnam, to burn everything remaining to

the ground for replanting. Controversy over the warmth/insulation value of log homes

continues...generally the walls are substandard in terms of insulation and moderate

for massing.

Recommendations: There are log home owners who love their houses. The logs can be

sustainably harvested...by private small businesses or individuals who cut standing

dead trees and skid them out (usually with horses) without much forest damage. Some

of them defend the insulation value as capable of supporting passive solar design. This

seems questionable at best.

Earthship/tires

Description: Earthships were originated in Taos New Mexico by Mike Reynolds, who has

worked on the design and fabrication for 30 years. The idea is to produce a home

mostly from reused discarded materials like tires and cans to make a truly independent

"space ship" for earthlings...passive solar, water catching, greenery growing, hugely massed, nearly subterranian(bermed) and gray water-using system.

Characteristics: Earthships have a cave-like feel some don't relate to. They involve learning

a whole life-style to go along with the house. They're labor intensive...ramming earth

into tires to make the walls. Properly built, they will supply nearly if not all of their own

heat and seldom require cooling...unless they're overglazed without sunscreens(which happens).

Recommendations: Earthship fans are idiosyncratic...if you like them, you'll love them. If you

don't you won't. Call Mike and go to Taos...he has a motel setup where you can stay in

one...and see for yourself. See a lot of them and talk to the owners. They are quite

legitimate...but take a true "earthship" fan to nest contentedly.

Timber frame

Description: Large dimension wood posts and beams (not requiring a lot of milling) are

assembled into a structural frame to support roof and floors. Then the spaces between

are "infilled" with strawbale, adobe, cob, r-panels...whatever.

Characteristics: The frame isn't considered for mass or insulation value...but can support

systems like bales and earth blocks which are (see their characteristics). These

frames are pricey ($5-15/sq ft house floor area..maybe more) They appeal to lots of

people's taste for rustic and big. Used on the interior (exposed), they are difficult if not

impossible to plaster into and maintain a seal.

Recommendations: They satisfy the structural requirements(and codes) to support lots

of varying sustainable building mediums. Before you invest...if for anything other than

aesthetic reasons...do a price comparison and ease of construction investigation into

other systems...or using wall systems that don't require structural support. Be prepared

for lots of extra time plastering, if you expose the frame on the interior...and probably

plaster cracks from differential shrinkage between the cement and wood.

Salvage/reclaimed

Description: Salvaged, moved or reclaimed/remodeled structures are something we should

be using a lot more of. You can get a whole house by paying a mover to move one

that's about to be demolished...lots of times in very good condition. Tons of the

sustainable building techniques (including passive solar design) can be applied to

old structure renovations...beefing up the insulation values and increasing interior mass.

Characteristics: Remodeling can cost more than new construction if not gone about properly.

However, lots of times, you have a place to live while you work. You're saving the

salvage materials from going to the land fill... Typically an old house needs to be gutted

to the frame, rewired, insulated and plumbed...don't try to save too much of the old

plaster walls...etc.

Recommendations: Salvaged railroad cars, trailers, silos, barns, water towers...make

excellent novelty homes...for the ingenious, inventive and industrious...take your time

with them...they'll be worth it in the long run. Use them as a core to add the sustainable

systems to them...sun spaces, passive solar, green houses, super insulation.

Rastra Block

Description: These are like real long concrete building blocks, except they're made out of

recycled styrofoam coffee cups...a good insulator...they're stacked up, bonded together

with spray foam, then poured full of rebar and concrete to form a very strong wall ...

similar to "ice-block". The wall is stuccoed and plastered.

Characteristics: They provide a superior wall insulation...the mass (concrete) is isolated

by the foam and not usable...but the thin-mass plaster interior is good massing.

Recommendations: That much steel and concrete is hard to rationalize as sustainable,

but the foam is recycled. They're very owner-buildable. It's not a natural system, but

it's more recycle-based than new iceblock systems.

Iceblock/ concrete

Description: Hardly a natural building medium...same a rastra block, but made with new

styrofoam, which is a petroleum based product. (See rastra block)

Characteristics: (same as rastra block)

Recommendations: (same as rastra block)

papercrete

Description: Recycled, shredded paper is mixed with a light cement slurry and poured into

block molds, forming a fibre-based building block...fairly light weight. The medium

can also be used as a plaster and mortar.

Characteristics: Surprisingly strong...durability unknown..insulation value probably good.

Recommendations: Too new to say...play around with some of it (a lot) and find your own

uses...draw your own conclusions...and let the network know what you think.

Envelope Houses

Description: The concept comes from convection...hot air rises...and solar design...there

is an air circulation space from a sun room (gaining solar heat) through the ceiling, down

the back(north wall) and returning through the crawl space. The idea is that the hot air

rising in the sun room will convect and heat the roof and back (cold wall), returning under

the floor to be reheated in the sun room. To do this, two walls and two ceiling have to be

built to create the envelope.

Characteristics: ???

Recommendations: a handful of these structures are known by the network to exist in

Western Colorado. Most of the owners report that they don't work very well...the

convection space is too small...it would take a space 3-4 ft wide to convect well. There

are a couple of people who swear by them. Before you spring, contact the people

or the network and be sure you've seen and understand enough of them to build your

own.

Cord Houses

Description: Fire wood is chopped in 16-20" lengths and stacked up to form walls, which

are stuccoed and plastered. The walls are structural...or can be infilled in a structural

frame.

Characteristics: Unknown

Recommendations: Only one rumor of the existence of one cord house is known to the

network and it has never been found...there was an article in "Mother Jones" years

ago on them...my guess is they're a decent way for a poor man to have a home.

Cave Houses

Description: You've got it...inside the mountain. 5-6 of these exist...whole houses built

inside either a natural or a mined cave.

Characteristics: Temperature stability is a plus...claustrophobia may be a problem..though

the one I've been in, it isn't at all. Some are materials efficient...some aren't.

Recommendations: Go check them out...thoroughly.

Intrinsic Heat

Description: The one structure known to the network is basically two wall systems with

a tremendous amount of insulation in the void...depending on super-super insulation

to reduce the needed heat for the home to the amount generated by the refrigerator

motor, hot water heater, cooking and human body heat.

Characteristics: Very materials intensive...consequently labor intensive...seem to work

with no outside heat source.

Recommendations: The owner will build or consult...contact Smart Shelter

R-Panel

Description: This is a popular, energy-efficiency building technique where a home is

assembled out of "sandwich panel" of chip board glued to both sides of thick

styrofoam.

Characteristics: The energy efficiency is real...problem is the sourcing and outgassing.

The chipboard outgases MDI and the Styrofoam outgases petroleum vapors.

Neither are sustainably manufactured.

Recommendations: R-panel is outside the gamut of natural building, but recognized

as a decent "green building system". Your choice...building inspectors like it.

Stick Frame

Description: 2x4 stud walls, dimensional lumber floor joists and roof rafters,

chipboard decking...standard construction...1/2 sheet rock interiors.

Characteristics: No mass, substandard insulation(unless increased) , unsustainable

lumber harvest...this system has consumed 90% of the old-growth forests in the

pacific north west. Fiberglass insulation contains formaldehyde (outgassing)

Recommendations: It's conventional, easily financed and insured, inspectors know it.

I don't recommend it for anyone...It's how we got in the mess we're in today...both

environmentally and for indoor air quality problems..it also feeds the most

criminal corporation in US EPA history...Louisiana Pacific...and contributes directly

to regional destruction of aspen and spruce/pine forests, roading of pristine

wild areas, destruction of wildlife habitat, choking of streams and air pollution as well

as being a prime source of toxins responsible for environmental illness.