Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction.
Iecc unvented roof.
The model building codes allow both vented and unvented roof assemblies.
The building codes have included requirements for ventilating attics for some time.
Additionally there are requirements related to the arrangement of the insulation so as to prevent moisture condensation in the roof assembly.
While the vast majority of roof designs are vented a growing number of homes are being constructed with unvented attics or unvented cathedral ceilings.
Attics or roofs can be designed and constructed to be either vented or unvented in any hygro thermal zone map 1.
Although not expressly defined the authors interpretations are that this provision applies to both steep slope and low slope roof assemblies.
This construction approach was first used in the 1970s and it has been implemented much more widely since it was first included in the international code council s icc model building code in 2007 irc section 806 4.
Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls.
In ceiling assemblies with attic spaces r 402 2 1 states that r 38 is satisfactory wherever the full height of uncompressed r 38 insulation extends over the top plate at the eaves.
These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck.
Ibc section 1203 3 outlines the only circumstances when a roof may have an unvented attic or enclosed rafter truss assembly.
The choice of venting or not venting is a design and construction choice not a requirement determined by the physics or by the building code.
Exterior roof complies with table c402 2 11 commercial cool roof or insulation of r 15 if present attics above insulation are vented and attics below insulation unvented roof surface slope of not less than unit vertical in 12 units horizontal i e 1 48 or 2 1 code says 21 tropical zone.
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.
Code establishing a baseline for energy efficiency by setting performance standards for the building envelope defined as the boundary that separates heated cooled air from unconditioned outside air mechanical systems lighting systems and service water heating systems in homes and commercial businesses.
Unvented attics and unvented enclosed roof framing assemblies created by ceilings that are applied directly to the underside of the roof framing members and structural roof sheathing applied directly to the top of the roof framing members rafters shall be permitted where all the following conditions are met.
