Of all the aspects of Green building, material selection
is probably the most difficult, if for no other reason there isn't good
information generally available, and when it is, its usually provided by the
manufacturer, who may or may not be reliable. To really understand the
impact of a material you need to understand Life Cycle Analysis (LCA), which
looks at all the impacts of a product from the raw materials that it is made
of, through
manufacturing, its use during its lifetime and finally its disposal.
Even if manufacturers were upfront about what went into a products, there
are so many variables involved with its use and disposal (whether recycling,
reusing or throwing it out), that generating any kind of hard numbers is
quite difficult. Of course there are always averages, or reasonable
expected outcomes, and it can certainly be argued that making some
assumptions is better than have no information at all. Until better
information is available, a good rule of thumb is "buyer beware",
because no matter what a manufacturer claims, many products just haven't
been around long enough to know how they will perform in the long term. Just
selecting a green material doesn't guarantee that overall result could be
considered green, because there is an aspect of how much you use also.
In this sense, small home advocates will argue that no matter what material
they are using, the impact is less, because they are using less of it (see
the design section for more on this).
While the square footage of a home isn't an accurate indicator of how much
material is used in it, it still is the case that using less material is
often the biggest impact you can have. Beside designing a home
to be just the right size, two other techniques have been used to reduce
material consumption: design to minimize waste and using structural
materials a finish surface. Designing to minimize waste can
involve a lot of things, some of which are fairly easy to do and others are
more difficult. The simplest thing is to plan for the use of materials up
front as much as possible: you often can make it so that if you cut a pile
of wood a certain way, many of the short pieces are also useful. In
the big picture, the motto is the same as anywhere else: "Reduce,
Reuse, Recycle". What Makes Something Green?
Determining whether a product or material is "green" has been a
challenge ever since the first time the question was asked, and continues to
be one, but various people and organizations have developed guidelines to
help sort it out. The general rule is that a product has to have a
significantly better environmental impact than whatever the commonly used
product is, and can't have any really terrible impacts. Of course
these decisions are subjective, and some find them relatively arbitrary, but
in most cases there is fairly common agreement as to what is green. The
principles used to determine whether a product is green, are generally as
follows: First, the product must be made of materials that at
least have the potential to be used sustainably. This implies that the
product is either reusable, recyclable into the same end product (not one of
lower value), or can be harvested sustainably. Products that have a
greater longevity are generally preferable, as they are generally closer to
sustainable use than shorter lifetime ones, that tend to end up in the
landfill. Second, the
manufacture, use and disposal of the product must not release significant toxic byproducts
into the environment. Third, a product which uses less
energy in creation is preferable. This energy (called the embodied energy)
is a part of the final product as much as the other raw materials that go
into it. There is a wide variety of strategies to satisfy
these principles, and any strategy that keeps materials from ending up in the
landfill is likely to be at least a very good start. The old
slogan "reduce, reuse, recycle" applies to construction as well as
anywhere else. The first question to ask is whether you need to use
the product at all ("reduce") . The next question is can you
reuse a material that have been used before. The key to reuse in most
cases is find products that can be used with minimal processing, although
some materials (e.g. an quarter-sawn solid oak door, or other finish
woodworking) have high value and are worth the time and money to
restore. Ruling those option out, using a recycled product is an
improvement over using new because you are adding another lifetime to a
material before it ends up in the landfill. Unfortunately, recycling
often results in a different product than the original, and often that
recycled product itself cannot be recycled, for example dimensional lumber
ends up as particle board and can never be dimensional lumber again.
Because recycled products are also often a conglomerate of materials, there
is an additional barrier to recycling because you typically have to separate
out the components to recycle them (in the case of particle board, you'd
have to eliminate the glue to recycle the wood particles, or alternatively
separate out the glue to use as a raw material). Until there is pressure
and/or financial incentive to do so, there is little hope of developing the
technology to recycle all products, and construction "waste" will
continue to fill landfills everywhere. Obviously any process that
works by separating components while its recycling is likely to be better
than one that requires separation as a separate step. For
a material that is renewable (wood, straw, etc), the strategy is usually to
avoid over harvesting it, reuse it however possible (even if its in a lesser
material), the let it biodegrade when it is no longer reusable. Some
inorganic materials (cement, metal) are easily recyclable provided you can
separate out the material you want from what ever it is bound up with.
In the case of cement, its most often found as concrete which is only about
15% cement. For metals, its a mater of stripping away whatever wood,
plastic or other metals to get at the one of interest. Other
inorganic materials (brick, stone, tile) could be reused as is for a few
lifetimes, if you can separate them from the cement or glue that are
set in. Polished stone slabs can also be reused, but since they
usually have holes cut in them (sinks), there is less flexibility in
subsequent uses. As a rule of thumb, the more components a
product has, the harder it will be to recycle. Since a discussion of the
thousands of building products available is far beyond the scope of this
document, we will cover just the most commonly used raw materials and just a
few common used products. For a brief comparison of the various
structural building techniques, see the construction
section. For information on the toxicity of various materials, see
the toxics section. Wood/Wood
Products Although less common in other parts
of the world, wood use in residential construction is ubiquitous in the
United States and Canada, for a number of very good reasons: In most
of the regions it is relatively plentiful, it is easy to work with, it is
durable when taken care of, and can be made to withstand earthquakes
relatively easily. On the flip side of the coin, we have consumed our
wood resources beyond their ability to grow back for so many years that we
are now a major importer of wood. Politically, environmental groups,
the government agencies, timber companies and other people affected by
logging have been battling over what is reasonable for many years, and
although it sometimes appears that both sides are coming to a reasonable
compromise, it may be a long time yet before they actually agree on anything
substantial. As environmentalists, but also as wood users, we
believe that a reasonable compromise is possible, and a key component of
that is to reduce the overall demand for wood products by using them more
carefully. We can no longer use any old growth, unless we are going to set
aside land to regenerate whatever old growth we log off, and politically
there seems to be no desire to do that: on the contrary there is pressure to
continue to log the little bit that's left and convert it to rapid rotation
forestry. As designers and builders, we have to avoid specifying and
buying it, and the problem will then fix itself. In the push
to improve the way we manage our timber resources, a couple of programs have
been created to sell wood that comes from better managed forests. The
Forest Stewardship Council (FSC) is an independent, environmentally minded
organization that acts as a third party certifier for companies that handle
wood products. Under the FSC program, a forest owner pays to have
their timber harvesting program inspected on a regular basis and receives a
certification only if they meet FSC's fairly strict rules which are tailored
to the climatic zone and specific ecology of the land in question.
When a customer purchases FSC certified wood, not only has the timber
harvest been certified sustainable, but everyone along the "chain of
custody" who processes that wood has been certified as to their ability
to accurately track certified and non-certified so that the customer knows
they are buying certified wood. To compete with FSC, the
timber industry has their own program of self monitoring, but given the
number of people in the industry with aggressive anti-environmental stances,
it is not likely that many consumers will trust a system that is akin to the
fox watching the chickens. The biggest failing of any of these
programs is that sustainability is "forever" (or at least a very
long time), and there is little to stop anyone from dropping out of the
program, which in some ways invalidates any claim they've made in the
past. Since the programs are relatively recent, and represent only a
small portion of the wood cut every year, only the future will tell what
effect these programs will have. In our view, no significant change will
result until society as a whole assumes and demands that our forests be
maintained sustainably, and rather than resorting to best case scenarios
about what sustainable means for a particular parcel, companies will take
the concept seriously and consumers will seriously punish those who don't. Wood
use in homes can be divided into three categories: framing lumber, of
which the house is built out of, exterior finish lumber such as
siding, roofing, casing, fascia, soffits and barge boards, and interior
finish lumber, which includes flooring, cabinets and trim.
There are a range of substitute products for both situations, and each has
its own set of limitations. As with any other product, the key
concepts are always "reduce, reuse, recycle". Framing
Homes use a lot of lumber: according to NAHB the average house uses 13,127 board
feet of framing lumber. One possible way to reduce wood use is to use an
alternative building method to build walls, such as straw-bale or cob, but
in each case there are complex tradeoffs, and actual wood use will depend on
many factors (for a more complete discussion, see the construction
section). Without taking any radical departures in building technique,
there are a number of ways to use wood more efficiently in building.
Build small, simple structures
While building small will generally requires less wood use, the shape and
complexity of the structure is equally important (see design
for more info). Unless you do framing layout on a computer, there is no easy way
to compare the lumber use of one design .vs. another.
Use only the minimum amount of wood necessary to make the house
structurally sound
This question has no easy answer, and certainly depends on the conditions you
want the house to be able to withstand: earthquakes, tornadoes, hurricanes, snow
loads and a room full of dancing people, being the most common. Local
building codes define a base level of structural integrity, but whether this
level is actually a good choice isn't as clear. The idea behind
"advanced" framing (circa 1980), was to give a set of framing
techniques that reduced wood use, increase energy efficiency all while
preserving structural integrity. For various reasons, its not clear if
those techniques are actually used.
Minimize waste
Although some promote the idea of designing to take advantage of standard
lumber sizes, this is much easier said than done, especially in small houses
where every space is designed to be just the right size. One alternative is to
layout wood use so that a piece cut off one place can be mostly used some place
else. Since doing this is difficult, a second best system would be to keep piles
of cutoffs, and go looking in the pile every time you need a less than whole
piece. Of course, this involves extra effort on the framer's part, although some
simple strategies can help, like always going to the cutoff pile when you need a
piece of blocking. If it were cost effective to build wall panels off site
(like is done for roof trusses), then someone could layout the each wall panel
on a computer and the factory could not only reuse many of the cut off pieces,
but could potentially use the short pieces to make finger jointed wood on site.
Use reclaimed wood
Building departments won't let you use reclaimed wood for structural uses unless
its been graded by a certified inspector, but it can still be used for
non-structural uses, and that can be a lot of lumber.
Use engineered wood products
Engineered
lumber
uses smaller diameter pieces of wood glued together to form a larger
unit. In some cases the engineered component uses less wood volume
than the comparable solid wood component (TGIs), but in other cases it
doesn't (glu-lams). Many engineered wood products are made
of small dimension trees, which more closely matches the forest management
strategies of timber companies, but is not necessarily more environmentally
friendly. Some products, like particle board and finger-jointed lumber are
made from the waste from producing other wood products, and so increase the
efficiency in which the tree is used. Many builder have converted over to using
engineered lumber for a variety of non-environmental reasons: cost, product
availability, and comparable quality. The last issue is interesting,
because as old growth lumber disappears and smaller diameter trees are used,
the general quality of dimensional lumber has gone down, and problems with
warping have gone up. Engineered lumber products are made to be very
straight and stay that way. On a performance basis, engineered lumber
compares very well with comparable solid wood products and in most
cases will not fail any faster under extreme conditions (e.g. fire, rot),
but there are clearly exceptions.
Plywood & OSB
Plywood was one of the earliest forms of
engineered lumber and was used largely to replace 1x8 board sheathing and
subflooring, and actually has far superior shear stress properties than the
wood it replaced. Unfortunately plywood was originally made from old
growth logs, and over time mills have converted to using smaller logs.
Plywood still requires somewhat larger logs than OSB, because the logs are
peeled to produce the layers that make up the plywood, while OSB is made
from small slices of wood that can come from very small trees.
Of course, just because younger trees can be used, doesn't mean that
the forest has been well managed, and in fact many have accused the industry
of doing just that. Even if OSB was a more environmental product, some
builders will not want to use it because it is more vulnerable to water damage
than plywood (apparently due to having more exposed end grain, which soaks up
water faster). The current state of affairs is that most builders use OSB
instead of plywood because it is cheaper.
Exterior Finish Lumber
Even if wood is not used for siding or roofing, there is
still often a lot of exterior wood used, especially in a house with a
"traditional" look. There are currently few or no
alternative products for most of these applications. Wood
siding - although popular in the past, in most climates
wood siding, whether the clapboard style, cedar shingles or panels like
T-111 siding, will decay rapidly if not painted or stained, and requires
frequent re-applications. For this reason, wood siding is not common
any more. Louisiana-Pacific makes and engineered siding, usually
called LP siding, which is just like OSB. In its original formula it
was prone to moisture damage, and the result was a large class action
lawsuit against the company. They now have a replacement product which
they claim eliminates the problem of moisture damage (check details). Roofing
- Cedar
shake roofs are a traditional look in some regions of the country (in
particular the pacific northwest), but due to decay have also become much
less popular. Cedar is a limited and diminishing resource and many
products are superior to it. Asphalt composition roofing is the most
common product used. Decks - While wood was always the
product of choice, many people have turned to various plastic lumber
products for decking (e.g. Trex), most of which are made out of recycled
plastic bags. Since these products are inherently not structurally
strong, the deck supports still need to be wood. Interior
Finish Lumber In many ways wood is the perfect
material for interior finish because it is easy to use and considered
beautiful by many people. Because there is no structural requirement
for finish lumber, a wider variety of wood products are suitable, including
reclaimed and finger-jointed lumber. FSC certified flooring and other
hardwood products is often available in a number of wood
species. Particle board/MDF/MDO - composed
of sawdust and glue pressed together with glue, these products make use of a
waste product (sawdust) and so have some environmental appeal.
Unfortunately most particle board uses Urea formaldehyde glue
("interior glue"), which off-gases formaldehyde for many
years. Recent innovations in Europe have found additives that force
the Urea Formaldehyde glue to off-gas quickly, which is necessary to meet
the European E1 standard for formaldehyde emissions. Medium
Density Fiberboard (MDF) is a particle board that has more glue in it, and
so is one of the worst offenders for off gassing when you buy
"interior" grade. Select a MDF that is exterior grade, or is
sold as a low VOC product (for example Medex and Medite). MDF is also a common
building product, used mostly in finish trim. Strawboard, made
out of compressed straw is available as a replacement for particle board.
Strawboard typically is made with little or no glue since the lignin in the
straw will bind together when subjected to heat and pressure. Most
strawboard is also covered in a melamine veneer, which is derived from
petrochemicals (find out where this sits in toxicity of manufacture).
A better option is to find a strawboard that is covered in a wood
veneer. Straw is a waste product from growing grains and is very
plentiful, although virtually all grains are grown using petrochemical based
fertilizers (Note: verify its really a waste product, especially in
the case of organic grains. Cement/Concrete Like
wood, cement is ubiquitous in construction, being a part of concrete, brick
mortar, and fiber cement products. The manufacture of cement accounts for
five percent of the world's total energy consumption, and the average home
requires 14 tons of concrete (about 7.5 cubic yards), which takes the
equivalent energy of 75 gallons of gasoline to manufacture (this number
seems way low, it ought to at least 25 yards if not 40, depending on whether
there is a basement). (any info
on percent in residential/commercial/roads?) Of course cement is also an
incredibly flexible product for which there is no substitute. Pure
Portland cement is an excellent glue, but is otherwise not strong at all, so
cement is always mixed with other materials and is only the glue that hold
them together. Concrete is a mixture of gravel, sand and cement;
mortar is a mixture of sand and cement, and fiber-cement products use
various fibers (wood, fiberglass) mixed with cement. In all cases,
water is added to cement and it undergoes a chemical reaction which causes
all the cement molecules to bind to each other. Not every Portland
cement is the same, and there are hundreds if not thousands of formulas
for concrete. The main identifying feature of concrete is its compressive
strength (the amount of weight it can hold up), and that is largely due to
how much Portland cement is put into it. Because concrete is not
flexible, it has little resistance to bending, and as a result almost all
applications of concrete require some kind of metal reinforcing: either
re-bar or wire mesh is typically used. Since the biggest
environmental impact of concrete is the energy used to make the Portland
cement, the focus of environmental building has been to use less of
it. There are three approaches typically used: substitute flyash, use
insulating concrete forms and substitute a completely different material. Flyash is a byproduct
of coal burning power plants or waste from blast furnaces (iron making) and has
properties similar to Portland cement, and since it is a waste product it
makes a better environmental choice. Flyash comes in two varieties,
called "class C" and "class F", with the difference
being that class C can directly replace Portland cement,
while class F can reduce the amount of Portland cement used, but not replace
it. (See EBN,V8#6 for a more complete discussion) Different kinds
of coal produce different flyash. In both cases, flyash typically makes a
stronger, more chemical resistant concrete, but achieves its strength over a
longer period (Concrete strength is usually given as the strength is gets in
28 days: flyash concrete can take twice as long to achieve that
strength. In residential construction, flyash concrete is still strong
enough in a couple of days to begin framing, and so does not impact
schedules) Flyash is often an added to concrete to make it flow better,
and in that case it does not reduce the amount of Portland cement used.
Unfortunately much of the flyash produced has too many impurities in it
(typically carbon) to make a good cement, and in addition since much of it
is the result of burning coal, it is clearly not a renewable resource. Assuming
cement quality flyash is available, is can be used to replace anywhere from
ten to fifty percent of the Portland cement needed for a particular concrete
mix. The downside is that it finishes different from normal cement,
and so the concrete installers have to be experienced with it- particularly
when using it for slabs. Flyash concrete also doesn't reach it full
strength for much longer than normal cement: the standard is that it reach
full strength in 28 days, while flyash concrete can take up to three
months. In spite of these drawbacks, many people are learning to work
with it, and some are experimenting with using greater than fifty percent.
As a rule of thumb, using 15-20% flyash as a replacement for Portland cement
is easy to do. When using a flyash mix, it is important
to make sure the flyash is replacing cement, not sand and gravel. Compare
how many sacks of cement were used to how many are normally used, rather
than the percentage of flyash. A typical mix uses five sacks of cement
(500 pounds). Insulating Concrete Forms (ICFs),
are a material that acts as both the form for a concrete
wall, but then stays in place to act as insulation. Using an ICF wall
instead of a regular poured wall can use 50% less concrete. ICFs are
typically made of polystyrene foam, and there is a product made with
recycled polystyrene and cement, as well as one made with waste wood chips
and cement. More on
ICFs is in the construction section. If
a basement isn't needed, the house can be built on a crawlspace instead,
using either a post and pier support system or a pin foundation (find out
more about these), but since there are other issues in using a crawlspace,
these must be considered also (see healthy home section).
When using any kind of post system, larger diameter pieces of wood are used
to replace the one piece foundation, so there is a tradeoff between wood and
concrete. A more radical idea to reduce concrete usage it to
construct the floor slab out of earth instead. Cob (a mixture of
straw, sand and clay) is the ideal material, because once dry it hardens
like concrete. Because Cob does not set permanently like concrete, it
must be protected from water, by a sealer of some kind (eg linseed oil).
Given it vulnerability to water, one would think it wise to raise the slab
up above the ground somewhat as an added protection against ground water
(beyond the usual sand/gravel/polyethylene sheet system). (Find out more
about this..check to see if Robert Bolman has a web site). In
any attempt to use less concrete, a creative structural engineer is almost a
must, both in getting past the building department and making sure that the
building will still last for a long time. Fiber-cement products
have recently become very popular both for siding and roofing. They have the
advantage to being relatively rot-proof (although they do wear out, and acid
rain would be a significant enemy of these products) and dimensionally
stable, which means that paint will typically last much longer on fiber
cement siding than it does on wood. Iron/Steel/Other
metals Metal is both easy to recycle and
frequently recycled. Iron & Steel products in particular often
contain a high percentage of recycled content. The other metals
commonly found in homes all have a high value in the scrap yard, and so
presumably are often recycled. Aluminum is made using large quantities
of electricity, but much less for recycled aluminum (verify this).
Copper and Brass are the other two common metals. Steel studs
have replaced 2x4s in commercial construction, but are not commonly used in
residential construction. They require a similar amount of energy to
produce (see EBN xxx), but the materials otherwise have different
environmental impacts. Steel studs are usually only used in
non-load bearing application (ie dividing walls that carry no weight from
the upper floor), but have the advantage of being perfectly straight, and
pre-drilled for electrical wiring. Since you can't nail into them
(screws are used), you can't attach trim with finishing nails, so special
consideration must be given for that situation. Steel (along
with Aluminum) is used for roofing, which comes in both "standing
seam" and a variety of shingle type patterns, where a option for the
single pattern is "stone coated". All metal roofing is very
durable, and typically will last a very long time. Standing seam roofing is
mostly used in light commercial and rural residential applications, as well
as in high snow areas because it sheds snow very well. The shingle
type roofing and its stone coated variant are more recent additions and
because they are quite expensive are often used on higher end construction. Plastics
and Petroleum derived materials The use of
synthetic material in homes has grown enormously and is responsible for most
of the thousands of VOC that can be detected in most new homes (see the
section on healthy homes). Aside from the
possible impact on the homes air quality, many plastics produce toxic
byproducts during a fire (although that could be a rare enough event to be
not relevant to most people), and their manufacture also produces toxic
byproducts, some of which seem to inevitable end up in the air and water. In
the particular case of PVC, Greenpeace has been on a long term campaign to
ban it, and the movie "Blue Vinyl" documents the effect of PVC
factories on small communities in Louisiana. Virtually all
synthetic materials are derived from petroleum, which is a non-renewable
resource, but recently there has been research into plastics based on
alternative sources. Other than vinyl siding, the total weight of
synthetics in a home is only a small percentage, and the embodied energy
isn't all that high compared to the energy used to operate the building
(verify this--get numbers). Synthetic materials are ubiquitous
in our lives for a good reason: the are cheap, easily mass produced and
often out perform all alternative materials. These materials are
commonly found in electrical components, weather stripping, gaskets,
plumbing pipe, and caulks and glues, insulation, siding, window frames and
decking. We examine only a few of these: Foam
insulation - this includes polystyrene (Styrofoam), polyurethane, and
polyisocyanurate (Polyiso) in both board and blown in varieties. In
each of these cases, a plastic is "blown" with a gas to create a
foam that has a large number of voids incorporating the gas, and hence a
high insulation value. The first versions of these were blown with
CFCs, and then later with HCFCs. The current trend is away from all of
these materials, and toward more environmentally benign ones. At the
current time, one must know not only the product, but the manufacture to
know what blowing agent was used in the product. All of these products
are derived from petroleum, which is not a renewable resource, but they
could theoretically be made from alternative sources. In
spite of these issues, foam insulation has some significant benefits.
For use under a concrete slab or other buried locations, foam board is the
only material applicable. Also in situations where there is limited
space, the greater insulation value of foam board provides more insulation
for the amount of available space. As part of an SIP, foam board is
the only insulation strong and dense enough to make a functional panel.
For more info on insulation materials, see the energy
section) Vinyl
windows - although they perform better than aluminum windows and are low
cost, their lifetime is not anticipated to be long due to the stress induced
into the glass by temperature driven expansion of the vinyl frames. In
addition vinyl is a highly toxic material to manufacture. Paint does not
stick well to vinyl. Fiberglass windows & doors -
compared to vinyl, aluminum or wood, fiberglass windows are doors are better
performing alternative, because they offer weather resistance, dimensional
stability (they don't move much with temperature or humidity), and higher
R-value when the hollow frame is filled with insulation (typically blown in
foam). Fiberglass windows are paintable. Some manufactures are
now offering a "wood clad" interior to make them look like wood
windows on the inside. PVC pipe - PVC pipe as a supply
line is banned in many locations. ABS?? for drain? PEX pipe
- PEX is short for Cross-linked Polyethylene, which is polyethylene
plastic that undergoes a chemical process that bonds the various molecules
within the plastic to each other, making it more chemically stable, and
thereby eliminating the "plastic" taste that comes with normal
polyethylene containers. Although it is vulnerable to chemical attack
and degradation due to ultraviolet light (ie sunshine), it is not normally
exposed to either. Compared to copper pipes, PEX is much easier to
install, and so significantly cheaper. The main advantage of
PEX is due energy savings by reducing the amount of wasted hot water left in
the pipes when the faucet is turned off. This is due to the fact that it is
installed like electrical wiring, with a main distribution manifold, and a
separate pipe run from the manifold to each plumbing fixture in what is
refered to as a "home run" configuration. In copper
plumbing, code requires that the shared pipes be large enough so that many
faucets can be run at once, but in reality this rarely happens, and the
large diameter pipe just leaves more hot water behind wasted. The
difference between the two strategies can easily be a half-gallon to a
gallon of hot water every time a faucet is turned on (after the hot water
from the previous use has already cooled). Of course, copper plumbing
could also be installed that way, but it would be much more expensive. Vinyl
siding - Vinyl is short for Poly Vinyl Chloride, or PVC, a plastic
that is made of toxic materials, and whose manufacture has historically been
very polluting (see www.bluevinyl.com).
While vinyl siding is very durable and long lasting, its environmental
impact is far beyond acceptable. Even if it were possible to clean up
the vinyl manufacturing plants, the risk to produce vinyl does not seem
worth the benefit, since there are undoubtedly alternatives. PVC by
itself is fairly rigid, and in order to make it soft a "softener"
is added to the plastic: typically a phthalate of some kind, many of which are
deemed to be toxic by various sources. Vinyl is unfortunately very
common in electrical components. For all these reasons, vinyl siding
should be avoided. Plastic lumber/decking - most
of these products are made from polyethylene derived from plastic bag
recycling, often combined with sawdust. Although they are mostly
limited to non-structural uses, they perform very well as both decking and
landscape timbers, since they are highly rot resistant and surprisingly not
slippery. (do they have UV stabilizers in them, or is polyethylene
fairly UV resistant?) Composition
(asphalt) roofing - traditionally made from natural fibers
impregnated with asphalt, most of the better composition roofing is now made
with fiberglass fibers (verify this!), and as a result composition roofing
is now offered in 40 and 50 year warranties. Old composition roofing
is "recyclable" but its unlikely that it is used for new roofing
(where does it go? does the asphalt degrade in the sun?
reference to EBN article?) Carpeting - most
carpeting is the synthetic variety, typically made of Nylon. Large
quantities of carpet end up in the landfill every year, although carpet
manufacturers are making great strides in recycling old carpets. Many
carpets have a significant number of additives, such as stain blockers and
can be a large source of VOCs (what is the typical "curing"
time?). An alternative synthetic carpet is made from PETE, sometime
from recycled pop bottles, and typically produces a lower amount of VOCs
(verify this). Also available are natural fiber carpets, which have
their own set of problems (NOTE: get some references and more details info..
try EBN, EPA or just google carpet. Also check Carpet and rug
institute web site). No matter what type of carpet you
choose, all carpets are havens for dust and dust mites and will absorb and
re-emit odors and other VOCs. Even if the carpet itself is benign the
backing can be a source of VOCs, and the underlayment is often the worst
offender. In general, healthy house experts recommend that you avoid
permanently installed carpet completely and use area rugs instead, sending
them out to be cleaned. (but what about the cleaning fluid? If
carpet doesn't really get clean, then why would rugs get any cleaner?) Laminate
countertops - (what are these things made out of?). They're very
low cost, but they don't last long, and aren't recyclable, so as a result
they all end up in the landfill. Because of their low cost, laminate
counters are by far the most popular choice. Paints
- paints consist of a pigment (which is typically a powder), a binder (which
is typically resinous or plastic) and a solvent which keeps the paint liquid
until it evaporates. Pigments are either an inorganic
material that is mined (typically some kind of ground up rock, or a metallic
compound), or an organic material (derived from a plant, or more typically
from coal tar or petrochemical based). Older paints were often made
with lead and other heavy metals, and so can be quite toxic. These
pigments are benign as long as they stay encased in the oil binder, but when
the flake or are scraped or sanded they can easily release heavy metal dust
into the air, with potentially serious health consequence. Until
the discovery of latex paint, the only choice was oil paint (?except what
about lime washes and milk & egg based paints?), which uses linseed oil
(from the flax plant) as the binder and solvent. These original oil
paints dried very slowly, taking two or more days to dry to the touch.
Modern oil paint contains alkyd resin as an additive, and produces a
relatively fast drying paint (dry to the touch in just a couple of
hours). Unfortunately along with the alkyds came additional VOCs, some of
which are quite toxic. It should be noted that simple oil paint is not
free of VOCs, as the linseed oil emits VOCs as part of the oxidation
reaction that causes it to harden. In latex paint the binder
is a polymer and the solvent is mostly water, so as it dries most of what
evaporates is water. Unfortunately additional solvents are often
needed to get the paint to stick better and to work with some kinds of
pigments. (more info?). clear finishes - this
category includes varnishes, waxes, shellac, lacquer, drying oils and
plastics such as polyurethane, and typically consist of a resinous material dissolved
in a solvent. Most traditional clear finishes are derived from plants
(e.g. varnish is from tree sap), and contain a fairly high level of
VOCs. Newer polyurethanes use water as a solvent, and so have lower
amount of VOCs. Unfortunately clear finishes are not interchangeable,
as they have different hardness's and water resistance. In
addition, some sit on the surface of the wood, and some are absorbed into
the wood. caulks - latex, silicone, many others. glues -
urea formaldehyde, phenol formaldehyde, MDI, woodworkers (aliphatic resin?) Other
Materials Tile/Stone/brick - Tile
is made from clay and typically glazed with a glass like mixture colored
with pigment, of which some pigments are heavy metals. All the
materials are relatively abundant, and with the exception of glazes that
contain radioactive elements, tile is environmentally benign. Old tile
all ends up in the landfill, and probably the only reason its not recycled
is that its probably much cheaper to mine new material than separate the
glazes from the tiles. Brick is also made from clay (and
sand?), but unlike tile, old bricks come loose from their mortar fairly
easily and can be reused as is (sometimes with a lot of mortar chipping!). Stone,
including granite, marble and travertine is a relatively inert material,
although some stone (particularly granites) have a relatively high level of
radioactive impurities. When mined locally stone is a good
environmental choice, but most granites and marbles come from far away. Sheetrock
- sheetrock is a sandwich of gypsum and paper, sometimes (always?)
reinforced with fiberglass fibers. The materials in it are relatively
abundant, and the gypsum is easily recycled. Gypsum is a naturally
occurring deposit that is mined in many locations, and is considered
non-toxic. The main problem with sheetrock is that it absorbs many
VOCs and so can be highly contaminated. Sheetrock is
used in virtually all houses because it is the cheapest available product
and gives a look that is generally pleasing to most people. Insulation
A comparison of insulations can be found in the energy
section. Reused/Recycled Materials
There are many uses for reused materials in construction, although most
typically they are high value finish materials. Some materials are
very easy to use, and others require a lot of effort. The biggest
difficulty is that many of them require a lot of time to gather and a lot of
space to store them. Unlike new materials, reused materials
often come in weird sizes, and often are one of a kind (or at least not in
the quantify you want), so you typically don't go looking for a specific
thing. Rather you find something you like, and try to find a place to
put it. Of course, the best reused material is one that is
left in place and just refinished. Assuming that isn't practical,
there are three classes of reused materials, each one with its own level of
difficulty.
Reclaimed & Re-manufactured These are products that someone else
has reclaimed and is selling in a form ready to use. Common products in this
category include re-milled timbers and re-milled flooring.
Another example is finger jointed wood, which comes both as 2x4's and in
moldings. In general these products are drop in replacements for the equivalent
new product.
Salvage These are products that someone else has removed, but they
are typically in the "raw" state and need some cleaning up to be
used. You find these materials at salvage yards, and sometimes
at antique stores. Example materials include flooring, doors and their
hardware, windows, cabinets and their hardware, moldings, high value wood,
lighting fixtures and plumbing fixtures. It is usually in pretty good shape,
but often tarnished in some way. These materials will need some work
to be usable: for example wood flooring might have a stray nail or staple
and probably needs to have the excess old finish scraped off its
edges. Odd size materials is the norm. Some of the materials,
like toilets and windows can't be used as replacements for new one, because
they don't perform as well. Old toilets use too much water and old
single pane windows are best used only in decorative situations.
Finally, when using any old material with paint on it, there is a high
chance it contains lead, so you need to sand/cut it with caution. Trolling These
are materials that no one has processed at all: you find them on your own
site or maybe at someone else's. You have to do all the work to remove
the material as well as the work to make it useful. This is the
hardest thing to do, but also the most fun because it encourages you to be
very creative. Finding useful material in your own scrap pile is
highly rewarding. Recycled content When you can't find anything
to re-use, there is always recycled content material. Some standard
building materials like MDF already use post-industrial waste, but not many
use post-consumer waste. Most iron and steel has some recycled
content, and fiberglass insulation is starting to use some also. One good
example is cellulose insulation, which is often 100% post-consumer. One
dilemma that often comes up with recycled content products is that they are
a composite of materials, and so many of them are difficult to recycle. Final
thoughts In the best of worlds, when the house needs
remodeling, you want your house to be easily adaptable to its new owners by
keeping it in a simple shape. You also want to make it easy to be able
to reclaim the materials that have to be removed.
For information on building
systems (SIP, ICFs, strawbale etc), and a comparison of building materials, see the construction
section. Resources Building
With Vision: Optimizing and finding Alternatives to Wood, Watershed
Media, 2001 How buildings learn, Stewart Brand Guide to Resource Efficient Building Elements,
Tracy Mumma,
Center for Resourceful Building Technology, 1997 See the material
section on buildinggreen.com "Forest
Certification Growing Fast", Environmental Building News V12#4 (Apr 2003) "Cement
and Concrete: Environmental Considerations", Environmental Building
News V2#2 (Mar/Apr 1993) "The Fly Ash Revolution: Making
Better Concrete with Less Cement",
Environmental Building News V8#6 (June 1999)
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