What is a conditioned attic? Why haven't I heard this term before now?

Eliminate all attic ventilation and condition the space- the photo above is of a mini-split heat pump inside a conditioned attic. Notice the closed cell spray foam is applied to the underside of the roof sheathing.

In modern residences, the challenge of achieving a continuous air infiltration barrier and thermal insulation barrier at the interior ceiling level is especially difficult. The air barrier, used to isolate the living space from the attic, is usually the taped drywall, while the thermal barrier is the insulation placed on top of the drywall. Typically, the ceiling is not a single horizontal plane, but a series of horizontal planes, vertical planes (knee walls), and sloped planes, all intersecting to create the ceiling. Field inspections repeatedly show how the continuity of the air barrier and thermal barrier is compromised at knee walls, coffered ceilings, dropped ceilings, framed soffits or mechanical chases, recessed canister lights, fireplace flues or chimneys, and penetrations for plumbing, electrical, and space conditioning, etc. In reality, it is often impractical to try to maintain air and thermal barrier continuity at all of these locations. Air-tight recessed cannister lights rated for insulation contact, foam sealing of penetrations, and full-depth blown insulation to cover the variations in ceiling plane can help to alleviate the problems, but at significant added cost.

The most cost-effective location to both air seal and insulate the attic may be at the roof plane rather than the interior ceiling plane. Where attic insulation is placed along the underside of the roof sheathing, this has been referred to as "cathedralized" residential attic construction (Rose 1995). In "cathedralized" construction, there may still be roof plane changes that create knee wall areas, such as build-over roofs where girder trusses are used, but these are usually few and relatively easy to access. In many cases, the roof layer (sheathing, roofing paper, flashing) which provides rain-proofing can also provide air leakage control. Some additional air sealing may be necessary at roof penetrations for vents and exhaust ducts. If stucco is used for the exterior wall finish, the fascia, soffit, and rake areas can be finished with stucco as well to provide an attic that is restricted from outdoor air exchange.

Another outcome of using the roof plane to create the air and thermal barrier is that the enclosed attic space is essentially inside the conditioned space. This space can be used to locate the space conditioning equipment and the air distribution system, and possibilities for additional storage are available. Also, the mechanical systems (electrical, plumbing, HVAC) placed in the attic are left exposed and accessible in the event of the need for repair or remodeling.

More latter -I always say trying to absorb all this information is like trying to eat an elephant, just take one small bite at a time and pretty soon..........