The advantages of the unvented, conditioned attic construction are increasingly being recognized within the industry to help with the following:
- Energy conservation
- Moisture management
- Enhanced home comfort
In an unvented attic assembly, air-impermeable insulation is applied directly to the underside of the structural roof deck and is tied into the insulation located in the walls so that the roof system becomes part of the insulated building enclosure.
The attic space becomes indirectly conditioned as a result of the air leakage, heat transfer and vapor diffusion through the ceiling.
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. This reduces latent air-conditioning loads and provides further reductions in energy consumption.
In hot climates, unvented attics are ideal where HVAC equipment and ductwork are located in the attic. Modifying the attic to create an indirectly conditioned attic space with a spray foam product, in many cases Icynene, can significantly reduce energy consumption.
In cold climates, attic ventilation is a common method to remove humid air. In some cases, a conditioned attic assembly may be desired where scissor trusses make it difficult to insulate the floor, or in cathedral ceilings where the intent is to turn the attic into living space. A vapor retarder is recommended in cold climates.
With any roof system, there should always be a contingency plan to address the possibility of roof leaks, especially with wood roof decks. The open cell structure easily allows any moisture or water vapor intrusion to quickly drain and dry out.