One of our primary goals for the new 1004 Central was to build a very energy-efficient home. In addition to installing insulation on the exterior of the home, we beefed up the interior with insulation well beyond code requirements using closed-cell spray foam.

Open Cell vs. Closed Cell Foam

Spray foam in residential building is generally categorized into two groups – open and closed cell (or cellular structure):

• Open-cell – Less dense (0.4 – 0.5 lbs per cubic foot). The tiny cells of foam are not completely closed and air fills all of the “open” space inside the material. This results in a foam that is weaker or softer than closed-cell foam. Open-cell generally has a much higher rate of expansion (100-1) versus closed cell (closer to 30-1) so when a wall is sprayed with open-cell material the overflow must be trimmed and disposed of – a significant amount of material is often sent to landfill as part of a open-cell insulation job.
• Closed-cell – More dense (1.7 – 2.0 lbs per cubic foot). The tiny foam cells are closed and packed tightly together. They are filled with a gas that helps the foam rise and expand and become a better insulator. Since closed cell is quite rigid it can actually contribute to a home’s strength – some expects claim it can as much as 40% sheer strength to a wall assembly.

Closed-cell foam offers a stronger material, higher insulation factor (R-value) and an increased resistance to air or water vapor leakage. It is denser, requires more material for coverage and is more expensive. Both open and closed-cell foam are commonly used in many building applications and the choice for which to use can be based on several factors including the need for additional strength, vapor control and the space available for insulation.

What We Did

We choose a closed-cell foam made by Corbond (installed by Barry’s Insulation). Based on our research we felt the closed-cell spray foam was a superior product for our application.

The R-value of foam degrades over time – it cures, essentially, and stabilize at a final value. The Corbond product’s final R-value is 6.7. We installed 4.5″ in the walls and 6″ in the roof, for a total spray foam R value of 30.15 and 40.2, respectively. The final value for the walls is R 37.2 because the exterior insulation adds an addition R 7.2. Additionally, we plan to add loose fill insulation in the roof to achieve a higher R-value. Code requires R 19 walls and R 38 ceilings (or roof, in our case, as the attic is part of the conditioned envelope).

Spray foam insulation in the walls – 4″ thick

In addition to our belief that the closed-cell spray foam was a superior insulation product in general, using spray foam was important because of our roof assembly. Traditionally, homes are built with a vented roof assembly, meaning that they have soffet and ridge venting. These vents allow air to pass back and forth underneath the roof sheathing, preventing condensation which can cause both mold and rot. We chose to do an unvented roof assembly in part because it allowed us to put the heat recovery ventilator (HRV) in the attic and have less concern about possible leakage from the HRV as well as a simpler installation of the duct work associated with it. Minimal insulation was required on the fresh air intake for the HRV to prevent condensation on the the outside of the duct within the attic. Had we used a vented roof assembly (i.e. the attic had not been part of the conditioned space) we would have had to insulate all of the ductwork as well as the HRV itself.

Spray foam insulation in the roof structure – 6″ thick.

Insulation truck staged outside front door.