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.
Iecc unvented roof.
While the vast majority of roof designs are vented a growing number of homes are being constructed with unvented attics or unvented cathedral ceilings.
Although not expressly defined the authors interpretations are that this provision applies to both steep slope and low slope roof assemblies.
Ibc section 1203 3 outlines the only circumstances when a roof may have an unvented attic or enclosed rafter truss assembly.
Unvented roof construction let s review the basic code requirement for roofs.
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.
These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck.
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.
The building codes have included requirements for ventilating attics for some time.
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.
The 2012 international energy conservation code iecc requires r 49 for ceilings.
The model building codes allow both vented and unvented roof assemblies.
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.
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.
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.
Attics or roofs can be designed and constructed to be either vented or unvented in any hygro thermal zone map 1.
