Unvented Roof Air Gap

An unvented roof assembly is possible only if you keep the roof sheathing warm enough to prevent conditioned air from condensing against it.

Unvented roof air gap. Insufficient fill below the impermeable insulation layer. The map at right which is based on table r806 4 of the irc lists the minimum r values required to prevent condensation in unvented assemblies in various climate zones. This is typical practice when an old fashioned black sarking felt is in place and commonly found in existing buildings. This can be accomplished by the installation of an air barrier system or by the control of the air pressure difference across the assembly depressurizing a building enclosure reduces the exfiltration of interior air pressurizing a roof assembly with exterior air also reduces the exfiltration of interior air.

When you re using only air permeable insulation in the framing cavity option 2 top right you must install the right amount of rigid insulation above the roof deck. Two potential unvented roof assemblies. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. Monolithic continuous exterior insulation ci above structural sheathing.

For complex roof designs the international residential code irc now allows unvented cathedral ceilings. Next i ll be screwing down 5 1 2 raycore sips panels over heated space and framing. Vented cathedral ceilings can be difficult to insulate well ventilation channels maintain an air gap between the insulation and the roof sheathing. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck.

In climate zones 1 2 and 3 air permeable insulation installed in unvented attics shall meet the following requirements. Beams on 5 centers. Insulation options for unvented roofs. If you don t want to use sips or nailbase there are four basic approaches.

Unvented roof assemblies should be insulated either with air impermeable insulation rigid foam or spray polyurethane foam or with a combination of foam and air permeable insulation. This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction. 1 1 2 t g decking. When you re using only air impermeable insulation option 1 top left it must be installed directly below the roof deck.

If air gaps are present between insulation layers convection currents can significantly reduce the performance of the assembly and compromise durability. The roof slope shall be greater than or equal to 3 12 vertical horizontal so it is not a sweeping limitation on roof pitch for unvented attics it is specific to air permeable insulation. 3 8 plywood diaphragm seams taped. Hi everyone need to make a final decision on which underlayment to use under a metal roof on an unvented roof system.

If the roof covering or roof membrane is a material of high moisture resistance or impermeable then the building regulations require a 50mm wide ventilation gap beneath the roofing felt and tiles.