Unvented Flat Roof Insulation

An unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation.

Unvented flat roof insulation.

Minimum of felt paper should be installed as the primary water barrier under the roofing. Two potential unvented roof assemblies. If you don t want to use sips or nailbase there are four basic approaches. Insulation and air barrier are applied directly to the underside of the roof deck are common in applications where designers are seeking cost effective and energy efficient roof assemblies.

Insufficient fill below the impermeable insulation layer. Unvented flat roofs a technical discussion flat roofs have often been built with the insulation all on top of the vapor closed drainage plane as this avoids dew point condensation issues inboard of the roofing. Closed cell medium density spray polyurethane foam ccspf insulation can be used to create an unvented roof assembly for any climate zone. Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls.

Layers of rigid insulation have staggered joints to facilitate airtightness. Two layers are preferable to one layer due to increase in air flow resistance. Four options for building an unvented roof assembly. Low slope and steep slope unvented roof systems i e.

R 46 unvented roof assembly two layers of r 6 5 inch rigid insulation yielding a total combined thickness of 2 5 inches. In this post we will show that while the propink unvented insulation system may provide a safe roof in zones 2b 3b if we instead combine dense fiberglass insulation batts or densepacked with intello smart vapor retarder and airtight membrane we can make safe and robust unvented roofs in climate zone 6. If air gaps are present between insulation layers convection currents can significantly reduce the performance of the assembly and compromise durability. However architects of these compact roof assemblies must consider vapor permeance and arrangement of the materials to produce acceptable hygrothermal performance and low risk of condensation in the resulting conditioned attic space.

Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof. Monolithic continuous exterior insulation ci above structural sheathing.