Unvented Roof Assembly Impermeable Insulation

If you don t want to use sips or nailbase there are four basic approaches.

Unvented roof assembly impermeable insulation. Some roof assemblies use very impermeable materials such as peel and stick membranes on the exterior. As we note in our blog post yes unvented roof assemblies can be insulated with fiberglass a wufi post the building code written for the foam industry does ask for air impermeable insulation or foam. They are designed without ventilation openings and the attic is conditioned like the rest of the living space. Zones 5 6 7 and 8 in that the manufacturers of these materials assume that roof deck may require ventilation to assist drying.

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 soffits etc which make it difficult to achieve an airtight ceiling plane. R 19 air impermeable insulation is proposed to be placed on the underside and in direct contact with the roof sheathing. Unvented roofs operate by the principle that venting is not necessary to control moisture accumulation. An unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation.

Alternatively insulation entirely under the roof deck can be composed of a combination of air impermeable and air permeable insulation in order to meet the requirements of 5 1 3. Yes unvented roof assemblies can be insulated with fiberglass a wufi post and not just in climate zones 2b 3b. 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. Based on table r806 4 r 20 rigid board insulation will be required to be placed on top of the roof deck to keep the condensing surface temperature at or above 45 f.

Closed cell medium density spray polyurethane foam ccspf insulation can be used to create an unvented roof assembly for any climate zone. Four options for building an unvented roof assembly. 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. Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof.