Riversong

And MerrickProperties has it backwards (which is typically the case with those who buy into the spray foam industry propaganda).

First, it may be true that "green" building (in quotes) is mostly about operating energy conservation. But true green building is about creating essential shelter within the laws of the natural world, which include: using only local, natural materials; using local labor and supporting the local economy; keeping size and complexity to a minimum; creating as little disruption to the site as possible; and placing the shelter within a pattern of human settlement that minimizes transportation needs and maximizes positive social interaction.

Second, there is a linear relationship between the R-value of an envelope and its energy efficiency (there are no fictional "diminishing returns"), but there is a top end to the value of air tightening since all homes require a minimum air exchange for livability and moisture and pollution control. Once a house is tightened to limit natural leakage to the ASHRAE 62.2 minimum standard for air exchange, there is little additional advantage to a tighter house (unless mechanical pressure imbalances or poor detailing create moisture problems).

"Green building is about durability and performance more than about recycled content."

I disagree with Michael's very narrow understanding of what it means to be truly green.

Durability or longevity of a structure that is built with materials and methods which inflict a heavy burden on the earth's life-support systems is the antithesis of green. The greenest of shelters - including igloos, teepees, yurts and wigwams - are among the least durable. They return to the earth without residue, become compost for future growth, and are easily re-built with minimal environmental impact.

The reason that durability and longevity have become so important is because of the enormous ecological impact of our shelters, due in part to their excessive size and complexity. The proper definition of "durable" is a thing which outlives the earth's ability to recover from the impacts of its creation. A thing with very little impact does not have to live forever to be durable. But a thing with enormous impacts must stand for a very long time before replacement.

And "performance" is typically measured in the very narrow terms of energy consumption. But even that is heavily dependent on the size of the shelter and the number of mechanical gadgets it contains. And energy consumption almost always ignores the embodied energy and the embodied global warming contribution of our synthetic building materials. To suggest that it's OK to save petrochemical energy by consuming petrochemical plastics is analogous to waging war for the sake of peace. The means are at least as important as the ends, for the means create the ends.

To disregard what is probably the most environmentally benign and efficient insulation material on the market, borate-treated dense-pack cellulose because a major plumbing leak or a tree crashing through the roof or an ice dam (which is created by a poorly detailed roof with no ventilation, the standard with foam-insulated roofs), or a Katrina hurricane flood has created a moisture problem - is akin to blaming the victim.

In normal operation, with normal air and moisture penetration into the thermal envelope, there is no safer insulation than cellulose to prevent mold and decay problems, since its high hygroscopicity effectively redistributes moisture away from framing and sheathing and allows the insulation to safely store and release up to 30% of its weight in water without degradation. No other insulation material has such hygric benefits. Cellulose also helps moderate indoor relative humidity, much like thermal mass helps moderate temperature fluctuations.

Except for strawbales, cellulose is the most green of all insulation options currently on the market. Spray foam is anything but green and anyone who advocates such products should be drummed out of the green building movement.