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PVC or wood - the arguments

The chemical industry has brought undoubted benefits to mankind since its origin rather less than 200 years ago. However, the ever-increasing volume of toxic chemicals brings with it unseen danger to our environment. Every process has its leakage and wastage, and as the volumes of chemicals increase, so do the volumes lost in production.
PVC is undoubtedly useful, and to the casual observer the end-product appears to be clean, harmless, durable, long-lived, and low-maintenance.  However, it is a particularly unpleasant material in two ways:

Firstly, it contains a substantial volume of the highly toxic element chlorine: an element so tightly bound up in nature - quite safely - with another equally toxic element, sodium, that splitting the two apart from the sodium chloride that we know as common salt, takes a great deal of energy (usually electricity). Using it as a volume structural material in the construction industry can hardly be considered 'green'.

Secondly, free chlorine is extremely toxic and it must be used sparingly and carefully. Losses in the production of any compound - not just PVC - cannot be avoided. Worse, in practice, PVC requires the addition of a selection of other highly toxic chemicals to stabilise and retain its desired properties over its lifetime, perhaps losing them during decades of exposure to sunlight, rain, and atmospheric pollution, with consequent slow but inevitable degradation.

In 1999 the PVC window industry was devastated by a Greenpeace report on PVC that showed how permitted, known, leakages of highly damaging poisons from the industrial chemical complexes that make the " precursor" compounds from which PVC is made worldwide, far exceed the recommended levels in the environment, with observable effects on our children.

Faced with this highly critical report, it is hardly surprising that the PVC window industry fought back with its own arguments in favour of the material on which their businesses are based. Undoubtedly, over the last thirty years PVC has become the material of choice for many, but the world and our understanding of it is in constant flux, so, more than a decade on, let's take a look at the pros and cons of PVC vs wood:

Claims FOR PVC

the extruders and fabricators say it's clean and they do not pollute the environment:

    # They're missing the point: It's the PRODUCTION of PVC itself that is the big problem.
The window factories themselves may be clean, and recycling old frames will go some way to reducing the high carbon footprint of the material, (or not: See footnote***) but the damage is already done by the time the PVC crumb reaches the extruder.

Matthew says "Cheap double-glazing has brought great benefits to the environment and the population at large."

    # Of course it has, but it's the glazing that's brought the big benefit.
Frames are a relatively small part of the equation. The environmental damage wrought by the manufacture of PVC invites the question as to why it should be 'cheap'.
Bearing in mind that PVC profiles need stiffening with aluminium, galvanised steel, or more PVC, it's not easy to see why they should be cheap. All of those materials use a great deal of energy to make and shape them. The fact that smaller local fabricators have given way to large trade producers with vast investments in plant and machinery illustrate that the low cost comes from the high production volume.
This is where the fibs and misleading propaganda about wood come in. These are a few of the objections raised by a large PVC window fabricator last week:


Phil says:
"don't kill a tree fit pvc !!!"

Matthew says "A plantation of trees is no more natural than a chemical plant."

    # Can these be taken as serious comments? 
Think about it. Self-seeded trees are natural, but if I plant a seed it's like building a chemical plant? I don't think so. It certainly gave everyone a laugh at the business forum last week.
I suppose these commentators are also against planting and harvesting wheat for their bread, or barley for their pint of ale.  Farming trees is no different to any other farming. If it's managed well, it brings benefits to all of us. It gives us food and shelter, and the crops absorb the dreaded CO2 while producing the oxygen we breathe. The only difference is, we harvest wheat annually, while timber plantations are harvested at intervals of perhaps forty or eighty years.

Britain was gradually cleared of its ancient forests by slash & burn for farming over the seven or eight millennia following the last ice age. (Isn't that what's happening in the Amazon Basin right now?). The last straw for our remaining forest was the dash to build a formidable navy from Elizabethan times right up to the appearance of iron-hulled ships. The millions of hectares of oak planted by Napoleon for his fleets, but never used for that purpose, are now a wonderful managed resource for the construction and furniture industries across Europe, with no discernible adverse impact on the environment. 

The advent of modification processes such as acetylation and furfurylation mean that non-durable plantation softwoods (along with non-durable plantation hardwoods such as beech and alder) may now be made more durable than teak.  These processes themselves, while part of the chemical industry, are "closed loop". If the process heat is created from wood waste or other biomass fuel, then the overall carbon footprint remains negative, if the sequestrated carbon is taken into account.
It's not easy to think of many chemical plants producing PVC that could be described in those terms.

Matthew says ".....the suggestion was that the carbon footprint of a timber window was higher due to the less efficient manufacturing processes."

    # Could this be true? Let's look a bit closer.
PVC has approximately THIRTY times the embodied carbon of softwood, (without considering the sequestrated carbon. ie, that carbon locked up in the wood as it grows, and only released when it rots or burns).

So the argument makes all sorts of highly contentious assumptions about the production process and plant to arrive at that conclusion, without any consideration of possible design and manufacturing innovation, or the possibility that the production unit might be heated with waste wood rather than gas or oil.
I suggest that the argument is spurious at best, and still ignores the fundamental issue of uPVC production poisoning the planet.

Matthew says "Timber windows....need regular coats of paint which are made of chemicals."

     # The embodied carbon in the paint of an average window amounts to perhaps the weight of a bag of sugar (compared to almost half a tonne of embodied carbon in a uPVC window). The latest low-VOC* water-borne finishes are mostly inert pigment. One fresh coat every ten years will add around ten bags of sugar's worth of carbon to the planet in a Century. Still miniscule in comparison with the devastation wrought by uPVC over the same period.**

Matthew says "Timber windows....when buried in landfill are far more harmful than uPVC due to the methane, a far more dangerous greenhouse gas than CO2"

    # Landfill? Most people I know with scrap wood burn it in a stove.
What a ridiculous argument! Trees have been growing, maturing, dying, and rotting in forests since the dawn of time without any help from mankind.  This turns out to be a distortion of a suggestion that the calculation of sequestrated carbon (ie, that carbon locked up in the wood) should be offset by the carbon released as fallen timber rots on the forest floor.  It turns out that, while true, the decay cycle is so much longer than previously thought, that the figure represents less than 5% of the sequestrated carbon relative to the speed at which trees grow.
Read more about it here, in this article on plantation softwood in ecos magazine.

And who would want to either burn or bury modified softwood guaranteed for fifty years.  If it ever is scrapped it will be valuable, as the acetylated wood may be chipped and turned into a new class of durable, waterproof chipboard. Perfect for replacing those awful PVC fascias and soffits.   That's the chemical industry at its best.

During a recent window industry seminar at the RICOH Arena the assembled throng were advised to drum up business by selling their old customers new uPVC windows to replace the 'everlasting' windows they had been sold barely twenty years before.

    # Here's a better idea. When someone is ready to upgrade, let's persuade them to choose the latest in wood windows using farmed wood from plantations.

A final thought:
For fifty years or more we were told that lead in petrol was harmless. The all-powerful Ethyl Corporation found an army of respected chemists and other advisers to convince us, but we don't believe that any more, do we?

Likewise, Freon - a chlorofluorocarbon construct from the same chemist, with wonderful properties for refrigeration and other industrial uses, was likewise thought, for a while, to be wonderful stuff. After being implicated in the long-term destruction of the ozone layer in the top of the stratosphere, its only permitted use now is in some aircraft fire-extinguishers.

These were both wonderful inventions that turned out to have a very dark side. I suggest that future generations just might see PVC windows, doors, conservatories, fascias and soffits in the same light.

* VOC = Volatile Organic Compounds. In water-borne paints, these are mostly alcohols.  In comparison with the vast volumes of VOCs released by a winters-worth of automobile screen-wash, or everyday losses from the distilleries, those in paint are insignificant.

** Replacing  the average PVC window twice in a Century amounts to a tonne of embodied CO2, against a wood window with embodied CO
2 of less than 25kg, lasting more than a Century (and perhaps double that), for a fraction of the cost to the environment.

*** I have seen it suggested that recycling PVC is even more energy-intensive than its original manufacture. As one recycler told me that his biggest problem was carrying large volumes of air up and down the motorways (hollow profiles, of course, are more air than PVC), I can believe it.

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