Unvented Attic Insulation

The quest for greater energy efficiency in buildings has led to increasing interest and need for insulation improvements in hvac equipment more airtight construction new materials and assemblies.

Unvented attic insulation. Unvented roof systems where the insulation and air barrier are applied directly to the underside of the roof deck are common in applications where designers are seeking cost effective and energy efficient roof assemblies. Fibrous insulation e g batt or blown in can be installed under the roof deck in the hot dry climate zone but this will cause moisture problems in all other climates straube and grin 2010. Unvented attic assemblies code notes 2009 irc 2012 irc adequate attic ventilation is a long standing requirement in building codes for moisture control. Senior engineer manager at icynene john broniek makes the case for the unvented attic assembly and why insulating the underside of the roof makes sense.

An unvented assembly can perform well but it s important to get the details right to avoid sheathing rot. The insulation extends down the roofline to the rim joists and soffit areas as well as on gable wall ends. Insulation approaches for unvented attics vary by climate. The trusses do cost more but this added expense can be mitigated by a.

However designers of compact roof assemblies must consider vapor permeance and arrangement of the roofing materials to produce acceptable hygrothermal performance and low. Humid or cold climates require either rigid. Unvented attic system pros and cons. The unvented attic system or conditioned attic is the new way to make your attic energy efficient.

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. Adding unvented attic insulation like spray foam seals the building envelope and stops airflow. To provide an unvented conditioned space for locating hvac equipment in the attic and or to provide a continuous thermal barrier for designs that have complex coffered ceiling planes and or numerous penetrations for lights speakers vents. This air seal will help to make your home more energy efficient.

Install insulation along the underside of the roof deck of an unvented attic rather than on the ceiling deck of a vented attic for either of two reasons. This allows you to install your bulkheads above the ceiling plane without the need for spray foam insulation. The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling. Air permeable insulation such as fiberglass batts dense packed cellulose or blown in fiberglass can t be used alone for an unvented assembly since these types of insulation can allow moist indoor air to reach the cold roof sheathing leading to condensation or moisture accumulation.