Attic Conditioned Space

The intended purpose was to allow warm air and moisture to escape.

Attic conditioned space.

Though it s against building code to vent any kind of exhaust to an attic space many home builders have gotten away with this shortcut. 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. The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling.

In a roof attic assembly the builder has two choices. In warmer climates unvented attics can prevent the condensation that occurs on ductwork in some vented attic spaces. Most updated central air conditioned homes have a new air conditioner split system meaning the ac is broken up into parts. Well mainly it s a way to save space.

Attic hvac systems save space. Traditionally building codes have required attic ventilation. 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. Compact assembly or hot roof ventilated roof assembly.

So why put an hvac system up in the attic at all. 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. An unvented attic assembly a k a. 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.

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. You can use rigid foam.