Spray foam insulation applied on the underside of the roof deck in cold climate commercial buildings allows for a significant reduction in condensation potential particularly compared to interior air permeable batt systems.
Roof deck foam insulation.
Insulate an attic in an existing home by installing spray foam open cell or closed cell on the underside of the roof deck.
When the choice is made to insulate along the underside of the roof deck spray foams have advantages over other insulation types because of the ability of spray foams to effectively air seal complex assemblies.
The installation steps are as follows.
Moisture generated indoors or that infiltrates into the home is responsible for the bulk of the moisture in an attic insulated with spray foam on the underside of the roof sheathing.
It s not coming from above the roof and it s not some new moisture source resulting from the spray foam.
The ratio of insulation above the roof deck or air permeable insulation below the roof deck is a matter of climate and interior conditions.
As air impermeable insulation spray foam insulation can be used in such applications.
This construction approach was first used in the 1970s and it has been implemented much more widely since it was first included in the international code council s icc model building code in 2007 irc section 806 4.
Also the higher the indoor humidity the more insulation is needed to avoid condensation.
Generally more insulation is needed for condensation control in colder climates.
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Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls.