You re used to thinking of your car as a closed envelope which is why you weren t worried about the dust.
Closed envelope attic.
When determining how to insulate this attic space various assemblies were taken into consideration and a hybrid combination of vented and unvented attic space was planned.
The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling.
The dormers and the attic space over the outside porch were sealed off from the rest of the attic by making a wall of plywood then insulating the wall with closed cell spf.
But when there s a hole in the envelope pollution can get inside not to mention lots of hot or cold air wind and precipitation.
Reason 1 to move the building envelope upward and encapsulate the attic is to get hvac equipment and ductwork out of the blast furnace.
An attic which can get up to 130 f or so on a hot summer day is not a good environment for your heating and cooling system.
Pretty soon you re coughing and sneezing and trying to rub the dirt out of your eyes.
Bringing the attic inside the envelope doesn t mean you can stop addressing the water vapor.
To truly be a fully conditioned attic it should be included in the hvac or ventilation system.
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.
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.
Intake vents located at the lowest part of the roof under the eaves allow cool.