The unvented roof deck with spray foam insulation is growing in popularity in existing homes. Spray foam is installed under the roof deck and on the gable end walls. This house “cap” saves energy by placing HVAC equipment in a friendly environment, sealing the attic against heat loss, and reducing radiant heat that raises attic temperatures. When a homeowner chooses this system, they often ask if the existing flat attic insulation need be removed- the simple answer is yes!
Once an existing attic is unvented, there is no escape for the dust and fibers that accompany cellulose or fiberglass insulation. The existing insulation’s fibrous nature also has the potential to trap the odors that are sometimes associated with spray foam insulation. If the insulation is left in the attic floor, air migration that semi-conditions this space is impeded. This can cause attic temperatures to remain high or low, depending on the season. Without the floor insulation, attic temperatures will remain with in 12 degrees of the rest of the home. This creates a friendly environment for your HVAC equipment and a wonderfully clean, conditioned storage area.
Many spray foam contractors will give the homeowner the choice to leave the exsiting insulation in place. Experience tells us that the home performs better and indoor air quality improves once existing insulation is removed. Although it is an additional cost, remove that attic insulation. You will be glad you did.