Attic Conditioned Space

Well mainly it s a way to save space.

Attic conditioned space.

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. An outdoor unit which houses the fan condenser and compressor and an indoor unit which holds the evaporator and fan. However you do not describe the potential uses for that space and that gives me pause as to how to properly evaluate the risks of your options.

If you re considering turning your attic into conditioned storage or living space it s worth changing tactics to insulate between the rafters and wall joists instead of the floor. Most updated central air conditioned homes have a new air conditioner split system meaning the ac is broken up into parts. If you planned to leave the open cell foam exposed to the attic it would certainly dry to the inside much more easily. The intended purpose was to allow warm air and moisture to escape.

Your stated goal is to turn your attic into a non vented conditioned space. Compact assembly or hot roof ventilated roof assembly. Traditionally building codes have required attic ventilation. In warmer climates unvented attics can prevent the condensation that occurs on ductwork in some vented attic spaces.

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. You can use rigid foam panels or do as tom silva does with nearly all houses these days. In a roof attic assembly the builder has two choices. The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling.

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. 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. 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.