Vented Attic Detailed Cross Section

An individual vent for a single appliance shall have a cross sectional area equal to or greater than the area of the connector to the appliance but not less than 7 square inches 4515 mm 2 except where the vent is an integral part of a listed and labeled appliance.

Vented attic detailed cross section.

2015 iecc irc section r402 1 3 n1102 1 3 or 2012 iecc irc. This section indicates that the prescriptive requirement for r 38 ceiling insulations is deemed to be met by r 30 insulation when the r 30 insulation extends over the wall top plate at eaves and when the insulation is at full loft and uncompressed over the wall top plate at eaves. Blocking and bridging shall be arranged so as not to interfere with the movement of air. Theinternational building code 2012 edition ibc 2012 requires enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof framing to have cross ventilation for each separate space.

The net free vent area nfva shall not be less than 1 150 of the area of the space being vented. Section r806 4 of the 2009 international residential code irc and section r806 5 of the 2012 irc have requirements for unvented conditioned attic assemblies. The building codes and building science for. 2015 iecc irc section r402 1 2 n1102 1 2 insulation criteria.

However spurred by recent claims of energy savings and moisture control unvented attics have become popular in both residential and commercial applications. If there is no vapor barrier double it to one square foot of nfa for every 150 square feet of attic floor space half for intake half for exhaust. Attic ventilation works on the principle that heated air naturally rises primarily utilizing two types of vents. Intake vents located at the lowest part of the roof under the eaves allow cool.

The idea of roof vents existed for hundreds of years with natural vents employed in chinese buildings during the tang dynasty natural ventilation ducts in the buddhist monks caves and wind catchers incorporated in arabian architecture. Vent roofs with steeples towers or cupolas can be found in different buildings from barns to cathedrals. The overall insulation level in the roof assembly must meet the baseline requirements for energy efficiency as given in the irc section n1102 or iecc section 402. For decades designers of attics and crawl spaces have used cross ventilation to minimize the potential for moisture accumulation and condensation.

If your attic floor has a vapor barrier you will need one square foot of nfa per every 300 square feet of attic floor area half of that will be intake half for exhaust.