ToolBase.org logo
The Home Building Industry's Technical Information Resource

Back to Standard View
Building SystemsHome Building TopicsDesign & Construction GuidesBest PracticesConstruction Methods

Symbol Legend
Adobe Acrobat Reader required for PDF documents

PDF documents require the free Adobe Reader.


All PDF documents open in a new browser window. Close the browser window to return to the site.

Insulation Alternatives: Blown or Foamed Through a Membrane

Loose insulation that is installed by blowing it into a cavity like mineral wool and cellulose.

View the ToolBase TechSpecs- Alternative Insulation Materials PDF file for an overview of this technology.

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 that is blown or foamed through a membrane.

To add insulation to existing homes, it is common practice to blow fibrous insulation material into enclosed wall, floor, and roof cavities. The same technique can be used in new construction by covering an open wall cavity tightly with a membrane fastened to the framing. 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 through a membrane 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, 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 insulating 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.

More information about insulation blown or foamed through a membrane is available in a ToolBase TechSpecs PDF file summary.

More about Blown Cellulose Insulation is available in this online video.


Energy Efficiency

Insulation improves the thermal resistance of exterior walls.


Easy


For an R-19 wall, fiberglass blown through a membrane costs about $1.40 per s.f.; Cementitious foam costs about $1.45 to $2.45 per s.f. for the same R-value.


Not Applicable


ll insulation products must meet ASTM standards for fire and thermal resistance. Section R316 of the 2003 International Residential Code covers insulation products (other than foam plastic).


Not Applicable


To prepare walls for blown-in insulation, areas that should not receive insulation are taped off. Next, membrane is installed per manufacturer’s instructions. Typically, the membrane is installed tightly against the wall studs to avoid “pillowing” which can create an uneven surface and complicate drywall attachment. Various schemes are used to resolve this problem: stretching the netting very tightly, 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.

If the membrane is 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.

It is important to follow manufacturer guidelines on blowing density and number of bags required for a given area to ensure proper installation. For cellulose, this is typically 3 pounds per cubic foot; for fiberglass, approximately 2 pounds per cubic foot.

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.

A separate vapor barrier may be required. Check with the local building department to determine if it is required in your area.


Warranties vary by manufacturer, up to a lifetime limited warranty from manufacturing defects. Typical installer warranties normally apply.


Insulation that is blown or foamed through a membrane share the advantage of any blown-in or sprayed-on insulation: they completely fill cavities with insulation. The process inhibits air circulation within the cavities, thereby eliminating an important cause of condensation and moisture problems. It can also help create 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.

The cost of fiber insulation depends on the method used to close the cavity; typical costs are about double the cost of fiberglass batts or about $1.40 per s.f. for an R-19 wall. Cementitious foam costs between about $1.45 to $2.45 per s.f. for an R-19 wall.

Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the NAHB Research Center. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.