Materials - Plastics & Petroleum Based

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 these¹:

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.

Although most foam board is now blown with more environmentally friendly materials (in particular both CFCs and HCFCs are gone, but not for XPS), there are still brominated fire retardants in them, which are potential carcinogens etc. Someday it may be possible to buy sheets of non-fire rated foam board for below grade use, but for now its not possible.

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 readily available material (cellular glass also works).  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 (PVC) windows - although they perform better than aluminum windows and are low cost, exactly how long they will last is questionable, although clearly they will last 20-30 years.  The issue is that vinyl, like most plastics expands and contracts significantly with temperature, creating stress on the glass unit as well as to whatever is sealing it in its frame. PVC windows contain UV absorbent  molecules to reduce UV damage, but even with them, PVC exposed to the sun over long periods of time should be expected to degrade some.  Paint helps, but paint does not stick well to vinyl.  To paint vinyl windows, you need a super-sticky primer.

Vinyl is a highly toxic material to manufacture, and produces toxic chemical when it burns.

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/ABS pipe - PVC pipe as a supply line is banned in many locations, although CPVC is permitted.  The main difference is that CPVC is more flexible, so is more durable when buried.  ABS is typically used for drains.  Both materials are quite toxic to manufacture, and toxic if burned.  Given that they're not rated for exposure to sunlight, they don't include UV absorbing chemicals. For small diameter pipe indoors, PEX or other plastics are preferable.  In other applications, there are few alternatives, and they tend to be very expensive.

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.  While you would think this eliminates the "plastic" taste, in fact you often still get that taste for months.  There are 3 varieties of PEX: PEX-A, PEX-B, and PEX-C, which refer only the process used to crosslink. 

The cross link process is irreversible, making PEX not recyclable. Although it is vulnerable to  degradation due to ultraviolet light (ie sunshine), it is not normally exposed to the sun, and it's generally chemically resistant to everything except the toluene/xylene family of solvents, and hence nothing sticks to it.  Compared to copper pipes, PEX is much easier to install, and so significantly cheaper.

The main advantage of PEX is  when used in a "home run" setup, which use smaller pipe diameters to deliver hot water faster, which is done by having every plumbing fixture have its own pipe (for more see the hot water section).  Its lower heat conductivity versus copper means that even in standard plumbing configuration, there is slightly less heat loss from the pipe.  Of course, copper plumbing could also be installed that way, but it would be much more expensive.

PE--RT (Bimodal Polyethylene) - PE-RT stands for Polyethylene raised temperature and is made from bimodal polyethylene (see sidebar: kinds of polyethylene).  This specific blend of shorter and longer chain molecules and its specific set of side chains creates a strong, while still flexible plastic with a higher melting temperature than either LDPE or HDPE.  The big difference is that in PEX, the long molecules are chemically linked to each other, while in PE_RT, they remain weakly bonded. Manufacturers claim its a drop in replacement for PEX, but is more flexible and also recyclable.

Although the plastic has been available for many years and its been available in pipe form in Europe for many years, its just now (2016) becoming available in the US.

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) that provides the color, a binder (which is typically resinous or plastic) that is essentially a glue that holds the pigment and adheres to the surface, and a solvent which keeps the binder liquid until it is applied, and then evaporates producing an insoluble paint layer.

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 paint², 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?).

Paints also typically contain fungicides and biocides to keep the paint from degrading an often other chemicals to enhance it's performance.  Unless the manufacturer specifically says their paint does not contain these things, one should assume that it does.

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?)

Notes

1: toxicity, potential carcinogen, and other deleterious properties are often hotly contested.  The green building community tends toward a "guilty until proven innocent", or rather "guilty if there is any suspicion" policy much to the chagrin of manufacturers. Those who take the opposite approach will find the info here overly cautious.

2: there are other types of paint, for example lime plaster, milk and egg based paints, and their use is now having a renaissance, but they have not been in common use (in the US, and as far as I know) for many years.