Attic Conditioned Space

Attic hvac systems save space.

Attic conditioned space.

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. Well mainly it s a way to save space. The loss of energy efficiency means some designers choose to move the ductwork into the conditioned areas of the home and leave the attics unvented. Compact assembly or hot roof ventilated roof assembly.

The intended purpose was to allow warm air and moisture to escape. Making the attic a conditioned space taking the building envelope to the roof is a good approach and will save energy another approach is to use radiant coated deck sheathing seal all ceiling attic penetrations and blow in r 60 insulation as it will cost less than spray foam and should give at least the same energy efficiency to the home. The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling. So why put an hvac system up in the attic at all.

In a roof attic assembly the builder has two choices. Traditionally building codes have required attic ventilation. The thermal boundary can be at the ceiling plane leaving the attic space above uninsulated and vented or the thermal boundary can be located at the roof line creating a sealed insulated conditioned or semi conditioned attic space. An outdoor unit which houses the fan condenser and compressor and an indoor unit which holds the evaporator and fan.

You can insulate the rafter space provided that you leave a ventilation space between the top of the insulation typically fiberglass batts or blown cellulose and the underside of the roof sheathing section r806 1 ventilation required. Building america research has demonstrated unvented conditioned attics can substantially improve energy performance while allowing home builders to continue locating hvac systems in the attic space. Most updated central air conditioned homes have a new air conditioner split system meaning the ac is broken up into parts. In warmer climates unvented attics can prevent the condensation that occurs on ductwork in some vented attic spaces.

You can use rigid foam. In the winter any small air leaks in the attic probably not through the foam but elsewhere leak air out and the warm humid air from the conditioned space refills the attic providing a fresh supply of humidity that can replenish the reservoir of humidity in the roof deck.