Will A Roof Leak Travel With Open Or Closed Foam

A sealed and insulated roof deck can t dry inward to the attic if the roofing happens to let water.

Will a roof leak travel with open or closed foam.

Chemical manufacturer s claim if a roof leaks water will migrate through the foam structure therefore not trapping the water. Applying closed cell spray insulation to the underside of a roof deck at the sheathing to truss connection can double or triple the strength of the assembly boosting the roof sheathing s resistance to wind uplift in a hurricane. That s an important consideration because if there s a leak in the roofing or the ridge cap moisture could get trapped between the roof and the insulation. But foam also traps moisture in the roof in case of a leak.

This can be especially helpful in attic encapsulation where high temperatures can force hot air through gaps around joints air ducts and light fixtures. Note that not all open cell spray foam insulations have the exact same physical properties as some are able to absorb a significant amount of water which could aggravate moisture conditions in an attic. So if you re considering spraying foam to the roof deck of your new or existing home you want open cell. Closed cell spray foam insulation has a tendency to fill voids and gaps because it doesn t expand as much as open cell insulation.

Closed celled foams will perform better in terms of deflecting water away from interior elements but may allow leaks to go undetected longer. Open cell foam is just that open cell. I have taken apart existing leaking roofs all over the place open cell closed cell sips compact etc. Open cell foams will tend to leak closer to the point of entry making leaks easier to identify and locate.

Common sense tell s me if this is valid marketing then what stops water vapor from moving through the foam under pressure. Moisture barrier open cell spray foam is not a moisture vapor barrier and will allow moisture to pass. Open cell foams will tend to leak closer to the point of water entry making leaks easier to identify and locate. With the mock ups and the field experience i have not noticed any difference between open cell and closed cell in terms of detectability and damage with respect to roof leaks.

Let s not confuse open cell vs closed cell foam.