Table of building insulation costs   (C) Daniel Friedman Light-Weight Concrete Wall Insulation for buildings

  • Use of light-weight concrete insulation such as Thermal Krete™ as a wall cavity insulation material
    • Does use of light weight concrete insulation eliminate the need for wall vapor barriers?
    • Is there a problem using Thermal Krete™ in thick double-framed walls in superinsulated houses?
    • Does use of AirKrete cementious foam insulation affect structural integrity of a building?
    • Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices
  • POST a QUESTION or READ FAQs about how light weight concrete insulation

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This article discusses the use of light-weight concrete building insulation (such as Thermal Krete™ in building wall-stud cavities. Table at page top and accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

For a complete listing of types of building insulation, their properties, and how to identify or use them, see INSULATION INSPECTION & IMPROVEMENT. Readers should see INSULATION R-VALUES & PROPERTIES for a more extensive table describing the properties of different insulating materials.

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Properties of Light-Weight Concrete Building Insulation

The link to the original Q&A article in PDF form immediately below is followed by an expanded/updated online version of this article.

The question-and-answer article below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

Topic: What do you think of using light-weight concrete insulation such as Thermal Krete™ in Walls?

Question: What is the Effectiveness of using Cementious Foam Insulation in a Super-Insulated Building Using Double-Wall Construction

What do you think of using light-weight concrete insulation such as Thermal Krete™ as an insulating filler for double 2x4 walls?

Would use of lightweight concrete insulation eliminate the need for a moisture and/or air barrier? - Lane Felker, Jefferson MD


Thermal Krete™ (discussed at "Product Update," Solar Age 11/83) is a special magnesite concrete that is pumped into wall cavities in a way that traps air bubbles. It insulates to about R-4 per inch.

Can I install light-weight concrete insulation in a super-insulated double-framed building wall?

According to Thermal Krete™ company president Fred Moer, the thickest cavity in which Thermal Krete™ has been installed is a 2x8 framed (rafter depth nominal size 2" x 8" is actually about 1.5" x 7.5") cathedral ceiling. The company should be consulted regarding lightweight concrete installations in cavities beyond 8-inches thick.

The weight of the material (4-5 pounds per cubic foot) could bow out drywall in a double-framed super-insulated building wall design, or the water from the larger volume of concrete could damage building materials.

See our discussion of super-insulated buildings and double-framed wall studs at INSULATION CHOICES & PROPERTIES.

Do I need a moisture barrier on a light-weight concrete-insulated wall?

Thermal Krete is fairly permeable to water vapor, so a vapor retarder is recommended.

Do I need an air barrier on a light-weight concrete-insulated wall?

As for air leakage, you should be primarily concerned about places where the concrete does not penetrate, e.g. under soleplates (sill plates), through ceiling penetrations, and out through interior partitions. Thermal Krete's manufacturer, Omni Tech Energy Products, welcomes inquiries.

Structural Properties of Air-Entrained or "Foamed in Place" Concrete Insulation such as AirKrete® Insulation

The link to the original Q&A article in PDF form immediately below is followed by an expanded/updated online version of this article.

The question-and-answer article below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

Question: Will insulation retrofit using AirKrete Cause Problems with the Structure of the Building?

I am renovating a 100-year-old house that is a mix of timber frame and stick frame construction, with massive diagonals at the corners. At some point a second story was added, and later a balloon-framed addition.

I had planned to cut fiberglass batts to fit the stud spaces but I'm beginning to think that foam-in-place insulation might save enough on labor to offset the higher material cost.

Would a foam such as Air Krete® cause any problems with the structural integrity of the house due to pressure during application, or will it actually strengthen the framework? - Stephen Ortado, contractor, White Stone, VA.


AirKrete® is a cementious foam with the consistency of shaving cream and an R-value of about 4 per inch. (See our table just below, and see INSULATION R-VALUES & PROPERTIES to compare various insulation products.).

When foamed in place, AirKrete® (and similar products such as discussed above), has finished expanding and flows around obstacles. So it places little stress on the structure of a building. After it sets, the foam is dimensionally stable, and there is no shrinkage problem.

Because it has no structural strength, AirKrete or other cementious foam insulating products will not make the building frame any stiffer.

A vapor barrier is recommended according to the product specifications and also according to Jay Savery, an East Coast manufacturer of the material, because the foam is very porous to moisture flow.

The table below summarizes the properties of various types of cementious building insulation and was excerpted from the more extensive table of insulation properties found at INSULATION R-VALUES & PROPERTIES.

Material 9
R-Value1 Density2 Perm3 Absorption4 Flame
Smoke6 Toxicity7 Aging
Concrete, uninsulated 0.0818 - 0.312517             Typical residential weight concrete 8" wall = R 2.5
Concrete-insulated 0.85 - 1.2 12-88 Varies Varies 0 0 0 Insulated forms available
Concrete, air entrained 3.9021              

Air Krete®26


3.9026 2.07 lbs/cuFt26 0.1457 in/sec coefficient, or 0.3407 in/sec flow rate at 68 degF H2O27   026 026 no Cementious foam insulation, fireproof, non-toxic, non-shrinking, also used for acoustical sound proofing; MgO cement (Magnesium Oxide); 6 mil poly vapor barrier required

Notes to the Table of Building Insulation Properties

  1. R-Value is expressed as rate of heat loss per hour per square foot per inch of thickness of material per deg. F - see "R" value definition at Definitions of R K U values
  2. Insulation density is expressed in pounds per cubic foot of material
  3. Permeability is expressed as the water vapor permeability of the material per inch of thickness. These numbers are most useful to compare one insulating material to another.
  4. Absorption is the tendency of the insulation to absorb water in percent by weight. This is important for assessing the risk of mold in some materials
  5. Flame Spread is a measure of fire resistance of the material. Use these numbers to compare one insulating material to another.
  6. Smoke is a measure of fire safety - that is, the relative amount of smoke produced if the insulation is exposed to flame or combustion
  7. Toxicity is a measure of fire safety - that is, toxins given off if the insulation is exposed to flame or combustion.
  8. Polystyrene may be in molded or extruded forms and like some other plastic or foam insulations may be in open or closed cell form. (Closed cell foams are more moisture resistant). Polystyrene also is referred to as molded expanded polystyrene (MEPS), expanded polystyrene (EPS), and extruded polystyrene (XPS) - the most common foam board insulation product. MEPS & XPS are used in insulated structural panels and in insulating concrete forms (ICFs).
  9. Links to details: Insulation product names in the first table column include links to articles that help identify and provide the properties of each insulating material listed.
  10. Open vs. closed cell: Foam insulation densities vary among closed-cell vs open cell forms. Open cell foams are typically about 1/2 lb/cubic foot; Closed cell foams are more dense and rigid, typically about 2 lb/cu. ft.
  11. C or Thermal conductance of these materials is the reciprocal of the R-value. C is known only when the k, the thermal conductivity of a material is known. k is the heat transmitted through a 1-inch thickness of homogenous material per square foot per hour when there is 1 degree of temperature change. k= (BTU * inch) / sq.ft. * hour * degF.
  12. Air film: This table of R-values does not consider the insulating characteristic of the air film on each side of a surface nor the effects of wind on the air film or on the material itself. Some of these materials are more resistant to wind-caused heat transmission than others.
  13. Moisture: Closed cell foams resist moisture uptake (good) but if construction is improper they can trap moisture (bad) leading to rot or mold problems in other building materials.
  14. Insects: Exterior foam board on foundations can ease attack by wood destroying insects.
  15. Fire & smoke: Foam insulation products present fire-smoke hazards and usually they must be protected with a fire barrier (usually 1/2" drywall).
  16. R-Values for wooden log walls given by the U.S. DOE are in error except for square log walls. D-logs and round logs that are given a nominal log thickness, say 6" logs are calculated by DOE as having an R-value of just over 8. This is incorrect for non-square logs because the cross section of the log is 6" only at the log's widest point. A correct assessment of the R-value of a wooden log wall needs to be calculated based on the average wall thickness, considering the variation in thicknesses over the curvature of the logs. Therefore the DOE's value is on the "high" end of the R-value of a log wall.
  17. R-Values of uninsulated concrete: Concrete Homes Magazine web search 5/18/2010
  18. R-Value for concrete, glass, other materials, Wikipedia web search 5/18/2010 citing Ristinen, Robert A., and Jack J. Kraushaar. Energy and the Environment. 2nd ed. Hoboken, NJ: John Wiley & Sons, Inc., 2006.
  19. E-Star Colorado. Energy Saving Calculations. Energy Living Alliance, 2008. Web 05/18/2010
  20. U.S. Department of Energy, DOE Handbook, see 18 May 2010. The DOE in turn cited these sources
    • ASHRAE, 1997 ASHRAE Handbook: Fundamentals, p. 24-4, 22-5
    • DOE, Insulation Fact Sheet, Jan. 1988, p. 6
    • Journal of Thermal Insulation, 1987, p. 81-95
    • ORNL, ORNL/SUB/88-SA835/1, 1990
    • ORNL, Science and Technology for a Sustainable Energy Future, Mar. 1995, p. 17
    • ORNL for vacuum insulation panel
  21. Wikipedia, web search 5/18/2010 R-Values per Inch
  22. EcoHaus UltraTouch cotton insulation batts batts Web search 5/18/2010
  23. Icynene product information see - Web search 5/18/2010
  24. ICC Legacy Report ER-2833 - Cocoon Thermal and Sound Insulation Products, ICC Evaluation Services, Inc., - Web search 5/18/2010
  25. HomeFoam®, Home Insulation Corp. - see - Web search 5/18/2010
    Home Foam® does not contain formaldehyde, fibrous particulate, HFCs1, CFCs2 or HCFCs3 and is a zero-ODP4 product. The Saskatchewan Research Council (SRC) advises that even sensitive individuals may take occupancy just 24 hours after application is complete.
  26. Air Krete®, Air Krete Inc., P.O. Box 380, Weedsport NY 13166-0380 –Keene Christopher, Principal Telephone: (315) 834- 6609, Retrieved 05 Dec 2010, AirKrete® Green Insulation Specifications, original source: Specifications for AirKrete® can be found at
  27. AirKrete® Water Permeability Coefficient, 03/02/2005, letter provided by AirKrete, retrieved 05 Dec 2010, original source:

Specifications for Wall Insulation for Superinsulated Homes

Foam insulation sprayed in a crawl space - this is not mold - Daniel Friedman 04-11-01

As we discuss at INSULATION CHOICES & PROPERTIES , for superinsulated buildings the article concludes that a double-stud wall with fiberglass batts provided the greatest insulating value per dollar. However other insulating products may be a better choice depending on other construction details and space limitations.

Our photograph (left) shows an insulation retrofit in a crawl space where icynene foam spray was applied to the crawl space wall and between the floor joists overhead.

The article also discusses the question of air permeability of fiberglass insulation and its impact on the actual insulating value of the material compared with impermeable (to air) foam insulation products. The impact of moisture on the R-value of fiberglass insulation is also discussed (it's low). Fiberglass both gains and loses moisture more rapidly than some other insulating products.

Foil-faced polyisocyanurate insulation such as the Thermax® and Hi-R® brands are discussed - these products give the highest R-value per inch among insulating materials. Also, as we tested in the 1970's, the use of these products combined with a 3/4" air space permits achieving an additional R 2.7 provided that the foil is clean and the gap or air space is uniform.


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