Alex Wilson raises an important issue in Buildinggreen: It is not only important to insulate really well, but to also think about what insulation you are using. He makes the point that many insulations use potent greenhouse gases as blowing agents. He writes:
We rarely pay attention to the fact that insulation materials themselves contribute to greenhouse gas emissions and global warming. This happens in two ways: through the embodied energy of the insulation (the energy use and greenhouse gas emissions that result from manufacturing and transporting the material); and, with some foam insulation materials, through the leakage of blowing agents that are highly potent greenhouse gases
Alex calls out extruded polystyrene (XPS) such as Dow Styrofoam of Owens Corning Foamular, and standard closed-cell spray polyurethane foam (SPF) in particular, for using hydrofluorocarbon (HFC) blowing agents that are potent greenhouse gases.
Blowing agents create tiny bubbles of gas that are, in effect, the insulator in foam. They used to be chlorofluorocarbons (CFC) that were banned for damaging the ozone layer, and were replaced by HFCs don't cause ozone damage, but are more than a thousand times worse than CO2 as greenhouse gases.
Wilson calculates out the global warming potential of different insulations, assuming that 50% of the blowing agents will leak out of the insulation over time. This is a difficult calculation, as he doesn't really know how long this takes or how much actually leaks out.
He then calculates the "payback":
By reducing heat loss and unwanted heat gain, any insulation material reduces the use of fossil fuels or electricity required for heating and cooling buildings. In so doing, these insulation materials reduce emissions of carbon dioxide (CO2), a greenhouse gas that contributes to global climate change. We want to know how many years of energy savings it will take to pay back the lifetime GWP of the insulation to figure out whether it's a good idea to use that insulation material in our low-energy buildings. Another way to think about this is how many years of energy savings will be required to "break even" on the GWP of the insulation.
A super-insulated house made from XPS could take a hundred years for the energy savings on heating and cooling to pay back the global warming caused by the release of the blowing agents.
There are lots of insulations that do not have HFC blowing agents. There foams that use water as a blowing agent (like Icynene). There are cellulose, glass fibre and mineral wool, which have their own issues and have to be a lot thicker to get comparable levels of insulation.
But if you believe that green building means more than just saving energy, but also about reducing greenhouse gases, then you have to look at how your insulation is made.
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