re: SC Flood area__Insulation from underneath home

Closed cell has been known to trap moisture and not allow it to wick away or dry up which can cause rot and mold.

Closed cell does offer a better R value but you can google about the lawsuits people have over it due to it causing rot and issues.

Think of it like this, if you have a leak in a roof, and have closed cell underneath it, where is that water going to go?

ETA: There is some speculation that open cell foam can cause moisture issues too because it is permeable and can allow humidity from inside an attic to stay against roof sheathing but if that were true then every attic with cellulose and batting would have issues as well.

I think both have a lot to do with how well it is installed and how well the house is vented but just thinking logically about leaks, it makes sense that open cell will allow water and moisture to dry.

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So which foam is best?

The best foam to use should be determined by the application. Some spray foam contractors recommend closed cell foam in some applications since their open cell foam tends to absorb moisture. All foams are not created equal. In some applications, open cell foam with a vapor retarding paint is the best application.

Closed cell foam should never be used on wooden roof decks. Moisture will be trapped in the roof's wood decking if you were to apply closed cell foam to the underside of the roof of a home and the roof develops a leak. This can lead to rotting of the roof deck before the roof leak is ever discovered. Open cell foam is not a vapor barrier, so it allows the water from the roof leak to weep through the foam to the space below so it is the better choice for most residential applications.

In most applications, the buildings energy performance will be the same regardless whether you used open or closed cell foam. Open cell foam is more flexible than closed cell foam. When the framing members expand and contract with the weather, or are impacted by high winds, open cell foam will flex with the structure. Closed cell foam however, will not flex, a will get hairline cracks where it was connected to the studs and walls and lose some of its benefits.

Open cell foam is usually more suitable for residential applications because of its moisture permeability, or the ability for moisture to pass through the insulation. (See above) Most homes are constructed out of wood, and it is this reason, moisture permeability, that is the main reason why open cell foam is best suited for your home.

Closed cell foam is best used in refrigeration, marine, industrial, and roofing or, when we are trying to solve a moisture problem and the problem can't be solved with a vapor retardant paint. Closed cell foam is commonly found outdoors.

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