Unvented Flat Roof Insulation

Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof.

Unvented flat roof insulation.

When hvac equipment and ducts with significant air leakage inhabit the attic much greater energy savings are possible as that leakage is now contained. Layers of rigid insulation have staggered joints to facilitate airtightness. If air gaps are present between insulation layers convection currents can significantly reduce the performance of the assembly and compromise durability. 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.

Two potential unvented roof assemblies. Closed cell medium density spray polyurethane foam ccspf insulation can be used to create an unvented roof assembly for any climate zone. Monolithic continuous exterior insulation ci above structural sheathing. Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls.

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. Insufficient fill below the impermeable insulation layer. An unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation. Low slope and steep slope unvented roof systems i e.

Control rain in any roof assembly an underlayment e g. Four options for building an unvented roof assembly. If you don t want to use sips or nailbase there are four basic approaches. 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.

Two layers are preferable to one layer due to increase in air flow resistance. R 46 unvented roof assembly two layers of r 6 5 inch rigid insulation yielding a total combined thickness of 2 5 inches.