Basic Comparison: Open vs Closed Cell Spray Foam
This basic comparison of Open cell and Closed cell spray foam insulation is intended for the reader with little construction, or building science background.
In reality the differences are just what they appear to be one version of the spray foam, open cell, has cells or bubbles that are intentionally cracked open to allow for a lighter product and one that breathes more freely. It is referred to as "half-pound" foam. Open cell spray foam insulation provides a significant reduction in sound transmittance through it and allows the moisture vapors to more freely pass through. Different manufacturers of open cell foam material have different claims of R-value performance ranging between 3.5 and 4.5 per inch of material. Open cell should always be used on the interior of the building shell/envelope and typically offer very little additional "racking strength" (term used to describe additional structural support from twisting, bending, etc) and is classified as a "semi-rigid" insulation material. Open cell foam insulation is commonly used in new construction exterior walls when applied to the stud wall cavities and then shaved even with the studs for applying the sheetrock. Open cell applied to a 2x4 exterior wall will most typically provide an R-value between R-12 and R-13. Some specific formulations of open cell materials can go a little higher, however these levels of insulation meet the current standards for exterior walls. When applied to the roof rafters at 6-inches of depth, the R-values reach R-21 to R-27, again depending on the specific material (chemical formulas) used. Open cell installed prices range typically about one-half of closed cell foam. However when compared to the fiberglass products, open cell spray foam is superior in reduction of air infiltration and preventing convection loop heating in the wall cavities.
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The other version of spray foam insulation, closed cell provides significantly better reduction in moisture and air infiltration and typically has better than twice the R-value ratings. Closed cell foam is intentionally formulated for the cells to remain closed during the expansion process and is heavier in weight, being referred to as "two-pound" foam.Closed cell foam does not reduce sound transmittance as well since it is a more "rigid" material. This rigidness does provide tremendous "racking strength" properties, up to 250%. This greatly impacts a building's ability to withstand the wind forces applied during severe weather. Different manufacturers of closed cell foam material have different claims of R-value performance ranging between 6.5 and 7.1 per inch of material. Closed cell foam is approved for use on both external and interior walls and is approved for use as a drainage plain since water is she'd off the product. The applications of closed cell foam are determined by general building requirements (or existing conditions when used in retro-fit applications). An example would be climate conditions being warm and humid or mostly arid. Condensation dew points in winter months would be another factor. Because very little vapor can pass through closed cell foam, consideration of climate and air infiltration or building tightness need to be factored into using closed cell foam.Given the higher material cost of closed cell foam and potentially not needing maximum R-values, many times open cell foam makes more sense. When deciding between using open cell or closed cell foam, many contractors will have differing opinions. In later blogs we will discuss more of the building science and technical data that should be considered when making this decision. [For now most applications in central Texas can use either one. Let the specific requirements of the job and the budget make the final decision.]
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Posted in Home Improvement Post Date 01/29/2015