Warren, VT, US

I have been designing and building super-insulated and passive solar homes for more than 30 years, and I've been teaching hygro-thermal engineering and sustainable building for five.

I built many double-wall houses and pioneered the modified Larsen Truss (Riversong Truss) wall system with dense-pack cellulose insulation and the Air-Tight Drywall Approach.

I now mostly offer design and consultation services throughout North America.

Recent comments

Re: Why I Don't Use Cellulose or Blue-Jean Insulation

I had challenged MerrickProperties when he made two incorrect claims:

"The energy savings from R-1 to R-20 is incredibly significant. However, the savings level off as you increase insulation beyond standard amounts."

"Energy savings from air sealing does not have a leveling-point."

And then he returned by simply repeating the error (which is generally found in the advertising claims of the foam insulation industry which often tries to sell less than code minimum R-values as acceptable). He also ignored that "standard amounts" according to the current International Residential Code has been climbing, with R-38 to 49 ceilings required in the majority of the United States (including for renovation work in some areas).

I teach Hygro-Thermal Engineering and this issue needs to be better understood.

MerrickProperties re-stated: "The heat loss/R-value relationship is not linear, there is a strong curve with drastically decreasing slope after R-20."

R-value is mathematically the inverse of heat flow. Double the R-value of an envelope and the heat loss through that envelope is cut in half. That's a perfectly linear relationship.

What is also true is that, when the heat loss has been halved initially, halving it again reduces it by only one-quarter of the initial amount but by half of the new baseline amount. And energy savings, which is a linear relationship, may not be the same as lifetime dollar savings when payback on investment is considered.

Where there is, however, a point of strongly diminishing returns on insulation beyond about R-20 is with closed-cell spray foam or XPS foam board, both of which at present use blowing agents that are much more powerful greenhouse gasses than CO2. The lifetime global warming savings of such foams becomes negative after a few inches of application, which means you may not be able to achieve code minimums without doing planetary damage.

As for the alleged "no diminishing returns" on air sealing, most case studies dispute this. It's relatively easy to air seal new construction to the 2-3 ACH50 level (that meets or exceeds all current US codes and energy programs) without additional expense beyond being attentive to details. Decreasing it beyond that requires both a level of attention and a dollar cost that are either nearly impossible in the trades or not justifiable in the market. And there is little advantage in terms of building durability, indoor air quality or energy savings since ASHRAE sets a minimum required mechanical ventilation rate which assumes a natural leakage rate of 0.15 ACHnat, which is the equivalent of about 3 ACH50.

Re: Why I Don't Use Cellulose or Blue-Jean Insulation

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).

Re: Why I Don't Use Cellulose or Blue-Jean Insulation

"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.