Closed Envelope Attic

Too often mechanical ventilation ducts from bathrooms kitchens or laundry rooms deposit warm moist air into the attic instead of outside the building envelope.

Closed envelope attic.

Reason 1 to move the building envelope upward and encapsulate the attic is to get hvac equipment and ductwork out of the blast furnace. By air sealing all wiring penetrations in your attic and sealing and encapsulating your crawlspace more on that in a moment you can further tighten your home envelope and maintain greater control over indoor temperatures all year round. The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling. When hvac equipment is in the attic insulation and an air barrier at the roof line brings that equipment within the conditioned enclosure envelope thereby allowing it to operate in more favorable temperature and humidity conditions without air leakage and heat loss gain directly to the exterior.

A combination of air sealing and insulating the attic floor while providing ventilation considerably reduces the potential for condensation as warm moist air is less likely to enter the space and condense on cold surfaces. Increasing the thickness and r value will improve the hers index. Poor workmanship during attic and roof installation will result in expensive callbacks and repairs as insulation will have to be replaced. Insulation gets blown placed or stuffed between the ceiling joists at the base of the attic but the space above those joists is left unconditioned and intentionally vented to the outside.

Spray foam insulation is more expensive than batt insulation and needs to be expertly installed to prevent missed areas or pockets that can reduce the efficacy of the building envelope. The only time most people bring the attic inside the envelope is when they want to convert it to a living space. Intake vents located at the lowest part of the roof under the eaves allow cool. Minimize the entry of dirty unhealthy air.

A fundamental requirement of an unvented attic assembly is the use of air impermeable insulation on the underside of the unvented roof to prevent air infiltration and exclude airborne moisture from the attic. Attic ventilation works on the principle that heated air naturally rises primarily utilizing two types of vents.