Spray Foam Insulation

spray foam insulationWhen building an energy efficient, net-zero home in Texas, it is vital to eliminate or greatly reduce energy loss with a high performance thermal envelope. Spray foam insulation, an alternative to traditional building insulation such as fiberglass, saves on energy costs and greatly lowers utility bills.

Studies by the US Department of Energy show that 40% of a home’s energy is lost as the result of air infiltration through walls, windows and doorways. Buildings treated with spray foam insulation typically insulate as much as 50% better than traditional insulation products.

Here in central Texas, we live in a Hot-Humid climate zone, which requires mechanical ventilation to remove humidity and maintain temperature for comfort. 80-90% of heat gain occurs at the roof. Spray foam insulation prevents heat from entering the thermal envelope.

Thermal Resistance (R-value)

Spray Foam insulationR-value is the term given to thermal resistance to heat flow. The higher the R-value of an insulation product, the more effective the insulation properties. R-value increases with thickness of insulating material, but *note that air sealing capabilities and air in/exfiltration is not considered when measuring thermal resistance. Polyurethane is a closed-cell foam insulation material that contains a low-conductivity gas in its cells. As a result of the high thermal resistance of the gas, spray polyurethane insulation typically has an R-value around R-5 to R-6 per inch. In comparison, blown fiberglass typically has an R-Value of only R-2 to R-4 per inch.

Spray foam insulation’s most important attribute is the ability to air seal creating a custom airtight envelope within the building structure. The added benefit to air sealing is the ability to block convective heat transfer from interior to exterior during heating months and vice versa during cooling months, as the heat cannot escape through gaps in the buildings envelope without the aid of air movement from infiltration as a means of transport.

Spray Foam insulation blocks all three forms of heat transfer:

  • Conductive heat transfer – The flow of thermal energy through a substance from a higher to a lower temperature region.
  • Radiant heat transfer – The process by which heat energy in the form of light (usually IR unless the substrate is hot enough to glow in the visible range) is emitted more strongly by warm surfaces and absorbed by other materials especially those of low IR reflectivity (think matte black finish).
  • Convective heat transfer – Heat which is created elsewhere that is transported by means of a fluid, such as water or in our case air.


How it Works

Spray Foam insulationSpray foam insulation has a two part spray process, starting with two 55 gallon drums – one with urethane material, and water based blowing agent in the other.

Two chemicals mix at the spray nozzle and instantly expands to 100X applied thickness, adhering to the sprayed surface, and filling all gaps and voids to make a great air barrier.

Open Cell Foam – R-3.7/inch

  • Air barrier, but water vapor permeable
  • Primarily used on interior applications against wood to prevent vapor from being trapped against framing.


Closed Cell Foam – R-6/inch

  • Air and water vapor barrier
  • Primarily used on exterior applications where vapor barrier is needed, ie: crawlspaces
  • Approximately 2X cost of open cell foam


Example of Application

Spray Foam Insulation Pros & Cons

The Good

  • Excellent air sealing
  • Easy retrofit in attic
  • Places insulation at roof deck
    • puts mechanicals inside conditioned space
  • Keeps attic within 8-10° of living space
  • Reduces mechanical sizing requirements
  • Approximately 25% energy reduction

The Bad

  • Contains polyurethane
  • Off-gasses VOCs for a couple of days
  • When applied to full-fill walls, can result in lots of landfill waste
  • More expensive than batt insulation


  1. Neal Foley October 15, 2015 at 12:35 pm - Reply

    How combustible is this foam? The New York Times had an article last week describing new building materials as increasing the flammable risks of these structures.

    • Native October 22, 2015 at 1:56 pm - Reply

      If installed incorrectly, it could be an issue. The spray foam we use contains flame retardant, because untreated foam would actually be a fire accelerant. We are very experienced and install it correctly. There is off-gassing for a couple of days, so it’s best to not be around during that time.

  2. Alan Basinger October 15, 2015 at 3:57 pm - Reply

    interested in having a quote for this in my hill country home can you recommend someone?

  3. Nash Rich March 9, 2016 at 3:22 pm - Reply

    I’ve never even heard of spray foam insulation. I’m mostly just familiar with fiberglass, so hearing about other kinds is interesting. I always thought fiberglass was the most efficient, but I guess not. I was surprised to see that spray foam was way better. Cool stuff, thanks for the info.

    • Native March 10, 2016 at 10:24 am - Reply

      You’re welcome Nash! Yes, spray foam is a lot more efficient, especially when you completely fill the cavities.

  4. Chris Mann October 13, 2016 at 8:49 am - Reply

    Great information you have shared in this post, spray foam is one of the most versatile forms of insulation available and it can seal home from air and moisture intrusion, strengthen building structure and provide thermal, air and vapor barriers capable of ably performing in all U.S. climates.

  5. TJ December 9, 2016 at 12:34 am - Reply

    Very informative post for people looking to learn more about spray foam insulation. This is becoming very popular in Iowa, as we get a lot of wind and it doubles as an air barrier and insulation! Great article.

  6. Braden Bills March 1, 2017 at 2:09 pm - Reply

    I don’t know what kind of insulation to use. I didn’t realize that foam insulation was so perfect! It makes sense that it would be, considering it’s thermal resistance.

  7. Sandra Hexner June 13, 2017 at 7:21 pm - Reply

    Thank you for all this great information about spray foam installation! I really like your explanation of how spray foam works. I remember watching our house get it done and it was very cool to watch. I also really appreciate you point out that it’s great for air sealing because that was a huge selling point for us.

  8. Lynn Schuman February 19, 2018 at 9:50 pm - Reply

    In the long term, how healthy is the closed envelope spray foam to use in an attic? I am finding different information about how it doesn’t work well in Texas because of our humidity. And, it can get into our living space and trigger respitory problems. Is this material safe to use?

    • admin February 21, 2018 at 1:26 pm - Reply

      Lynn, while there is an off gassing that occurs upon application, the spray foam is inert once it cures. The spray foam that we utilize is an open cell variety that allows for water vapor to pass through it. This does work well in our Texas climate and is completely safe.

  9. Susan Wright July 5, 2018 at 10:25 pm - Reply

    Is this soy based? And I would like all the old insulation removed. Do you do that?

  10. Nick Ryza July 10, 2018 at 1:16 pm - Reply


    The “soy based” spray foams contain very similar chemicals to other spray foams. This is largely a marketing strategy for these manufacturers.

    For homes that we have retrofit with foam, we have gone both ways with the existing insulation, sometimes we remove it, sometimes we leave it. Its up to the homeowner.

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