Insulation Alternatives: Blown or Foamed Through a Membrane Loose insulation that is installed by blowing it into a cavity like mineral wool and cellulose. Four entries in the PATH Technology Inventory describe alternatives to conventional fiberglass batts or rolls: - Non-fiberglass batts
- Sprayed foam insulation
- Sprayed fiber insulation
- Blown or Foamed through a membrane.
This document deals with insulation Blown or Foamed through a membrane. Fibrous insulation material is commonly "blown-in" to fill fully enclosed wall, floor and roof cavities in existing homes. The same technique can be used in new construction if the "interior plane" of the cavity can be covered by a membrane fastened to the framing to close the cavity. A fabric similar to that used on the underside of furniture, nylon netting, or polyethylene is used as the membrane in various systems. Fiberglass, cellulose and mineral blowing wool, can be used. Cementitious foam is blown with air, resulting in a continuous network of mineral surrounding bubbles of air. It is inert, non-toxic, fireproof, and vermin proof, being made entirely of magnesium oxide and air. At its minimum density, about 2.0 pcf, it is rated at R-3.9 per inch, but it is fragile. To create a more durable product, the density can be doubled, reducing the R value to R-3.6 per inch. The material also acts as fireproofing; it can be held safely in the hand while a torch is applied to the surface. 
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Cellulose Insulation is covered by the following government and industry standards: - 16 CFR Part 1209 (Consumer Products Safety Commission, or CPSC) - covers settled density, corrosiveness, critical radiant flux, and smoldering combustion.
- ASTM Standard C-739 - loose-fill cellulose insulation - covers all factors of the CPSC regulation and five additional characteristics, R-value, starch content, moisture absorption, odor, and resistance to fungus growth.
- ASTM Standard C-1149 - Industry standard for self-supported spray-applied cellulose insulation for exposed or wall cavity application - covers density, R-value, surface burning, adhesive strength, smoldering combustion, fungi resistance, corrosion, moisture vapor absorption, odor, flame resistance permanency (no test exists for this characteristic), substrate deflection (for exposed application products), and air erosion (for exposed application products).
- 16 CFR Part 460 - (Federal Trade Commission regulation) commonly known as the "R-Value Rule," intended to eliminate misleading insulation marketing claims and ensure publication of accurate R-Value and coverage data.
The States of California and Minnesota have their own standards, based on ASTM standards.
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If the membrane is an open netting, air pressure created when the insulation is forced into the cavity is relieved through the netting. Using a plastic membrane either requires openings to allow air to escape, or arranging the membrane so that air escapes into the adjacent cavity. One challenge for a system using fibers is to prevent the insulation from piling up between the framing and the netting. If this happens, the interior surface may be too irregular to apply drywall. Various schemes are used to resolve this problem: stretching the netting very tight, applying a coat of glue through the netting to secure it continuously to studs, or in the case of polyethylene, stretching it hand tight and applying frequent inset stapling. In the case of cementitious foam, the wet foam can be squeezed out from between a plastic membrane and the studs, or wiped off the face of the stud. A taut membrane is required to keep fiber insulation from bulging too far out when installed at a density sufficient to prevent settling. Otherwise, the insulation would cause a bulge in the interior finish. Another challenge is to determine the proper density to prevent settling. For cellulose, this is typically 3 pcf.; for fiberglass, approximately 2 pcf. Cementitious foam is thick enough when installed to be retained by almost any netting, screening, or chicken wire; or it can be foamed in behind housewrap or polyethylene.
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These systems share the advantage of any blown-in or sprayed-on insulation: they completely fill cavities with insulation. This inhibits air circulation within the cavities, eliminating an important cause of condensation and moisture problems. It also contributes to creating a tighter house by inhibiting air movement through the envelope. Unlike wet-spray systems, blowing through a membrane can use dry material, although water and water-activated adhesive can be added to fiberglass insulation if desired. Insulation can be packed around wiring and plumbing, because any voids or "shadows" can be seen through the membrane and immediately corrected. Higher density insulation also improves acoustic performance. Installation under some pressure eliminates settling, and raises the R-value to ranges of 3.7 per inch for fiberglass to 4.0 per inch for cellulose. Scientists at the National Research Council of Canada report that "cellulose in the wall cavity provided an increase in fire resistance performance of 22% to 55%," relative to fiberglass batts, provided the cellulose is treated with fire retardants. A similar effect may occur when using blown-in fiberglass without a binder. When a highly impermeable vapor retarder is specified, using polyethylene as a membrane automatically provides the barrier. Otherwise, netting may be used, with or without an added vapor retarder. The insulation itself creates an excellent air barrier, so the vapor retarder should be evaluated solely with regard to vapor transmission, and not with regard to its secondary function as an air barrier. The cost of fiber insulation is dependent upon the method used to close the cavity; typically about double the cost of fiberglass batts. Cementitious foam ranges from $.30 to $.50 per square foot. |
