No dilemma more clearly demonstrates the compromises that cannot be avoided when trying to think about building green than the decisions involved in choosing insulation. A quick assessment shows the trade-off may lie between materials that require huge amounts of energy to produce as opposed to the energy they save in their lifetimes.

Examples are found in rockwool and fiberglass—each requires a great degree of heat to produce, even though they may become inert and environmentally safe. However, is the tiny amount of risky chemicals in polyiso and its petrochemical source more than offset by the highest R-value of any material? What is the return on investment (for the user and for the planet) if we use more costly materials, such as Thermablok and recycled denim?

One way to examine these difficult questions is to look at the history and manufacture of insulation itself along several strata, beginning with raw-material acquisition for insulation, which involves wide variance in benefits and costs, ranging, from say, sand in fiberglass to petrochemicals in foam plastic and newspapers in cellulose. The depletion of limited resources and pollution resulting from mining are problematic here, whereas the recycled content of many materials is a boon.

With specific reference to foam plastic, as component parts, including Polystyrene, benzene, Polyisocyanurate and polyurethane ultimately are sourced from in fossil fuels (petroleum), the resource is, as we know, finite. So, too, with the boron used in fiberglass insulation (often used as a fire retardant), which has roughly a five-decade supply in this country. This is problematic in the long run.

The impact from raw-material acquisition in an environmental sense is also palpable. Air and water pollution and erosion often present many-faceted problems (tailings waste from mining, with its attendant runoff of high levels of suspended solids, ultimately the cause of deoxygenation of the water, potentially killing fish). Then there is pollution from oil spills and leaks during extraction/transporting the fossil fuels to make plastic foam, which is not insignificant.

However, buildings employing recycled content require less natural resources, use less energy in manufacturing and actually divert materials from the solid waste stream. Each has its merits:

  • cellulose—usually 80% post-consumer recycled newspaper (and the remainder fire retardant chemicals and/or acrylic binders). New technologies take this process further and to greener effect.
  • mineral wool—formerly the most common insulation type, slag wool and rock wool account for roughly 80%/20% split of the mineral wool industry, with 75% post-industrial recycled content.
  • fiberglass—each major manufacturer of fiberglass uses at least 20% recycled glass cullet in their insulation products to comply with the EPA recycled-content; the potential, it is said, is for 90% recycled glass cullet, which is being produced in one overseas plant.
  • polystrene—recycled plastic resin is used in some polystyrene, as in Amoco Foam Products (50% recycled resin), though expanded polystyrene (EPS) can also be made out of recycled polystyrene—but because of fire retardants, non-building applications are limited.
  • polyisocyanurate—according to the industry associations, all products today meet the EPA procurement guidelines for federally funded buildings (a minimum 9% recycled content). In addition to the raw chemicals having recycled content, the foil facings used on polyiso are typically 70-80% recycled aluminum.
  • radiant Barriers—aluminum used in radiant barriers is also mostly recycled. At least one radiant barrier insulation material also uses recycled plastic in the foam core (its recycled content is certified by SCS)
  • cotton Insulation—fire safety with cotton insulation is an issue, but Greenwood Cotton insulation, the present product, is approximately 95% post-industrial recycled fiber, with 25% polyester fiber. The polyester improves tear strength and recoil characteristics.

Of the above, the proposed choices for Viridian Future is the lightweight, easily cut Johns Manville AP polyiso. It is a preferred product to provide a major part of all our insulation needs, as it can be left exposed for up to 60 days and has no HFRs or noxious chemicals. Its only downside is that, if it burns, it produces thick black smoke. As it is always encased it in fire resistant drywall in a building with full sprinklers, however, this issue isn’t a full concern.

Cellulose will be our blown-in insulation (Rockwool has chemicals that don’t meet Red List standards), and both it and fiberglass use large amounts of energy in their production. This means that the cellulose must be protected from moisture, but everything should be protected from moisture in either case. For installation, ease of installation is better with cellulose, and air flow is better prevented as well. In terms of the cold, cellulose performs better for our purposes and uses less embodied energy.

Our SIPs have EPS in them, which also must be buffered from fire, which we also do. Thermoblok will be deployed as a high-R value insulation—used in thin strips where needed, along with Foamglas where a structural insulating material is required. Foamglas becomes a more cost-effective insulation when you factor across levels: greater durability and the reduced thickness of other elements.


The complexion of the insulation debate is multi-tiered and difficult to understand at times. At base, potential courses of action involve the following:

  1. Adequate insulation levels—the reduction of energy use in a building is the single most important thing you can do to reduce the building’s overall environmental impact. Substituting a “green” insulation material for a non-green material, if the change severely impairs energy performance, is not workable.
  2. With lower R-value materials, insulation thickness is crucial—if using a green insulation material as opposed to a higher-R-value less green insulation material, building design requires greater insulation thickness to make up for any loss in energy performance.
  3. Do not use HCFC-foamed insulation materials—HCFC cause damage, and substitutions (as above) are available.
  4. Avoid thermal bridging—provided you install a layer of insulating sheathing, minimizing the cavity-fill insulation allows your budget to employ insulative sheathing over the framing.
  5. High-recycled-content insulation—cellulose and mineral wool, instead of fiberglass, are preferable. If not use Schuller International’s (with the highest post-consumer recycled content; or Amofoam, with recycled content).
  6. In built-up roofing, install a layer of sheathing between insulation and roofing surface (allowing for reroofing without destroying insulation).
  7. Consider boardstock insulation (as it is self-supporting—cavityfill fiber insulation materials call for a framed cavity). Even though the fiber insulation material might be environmentally superior, when you factor in additional framing resource required, the advantages may not be as great.
  8. Install a continuous air barrier between insulation and living space to keep fibers out of the indoors.
  9. Specify a non-offgassing insulation material, such as Miraflex, or Air Krete. Down the road, consider Icynene and Greenwood Cotton as well, provided testing holds out.
  10. Your insulation contractor should recycle scrap insulation—Batt insulation scraps and Icynene trimmings can be chopped into loose-fill insulation with a Big Green Machine.