Unvented Flat Roof Insulation

Two layers are preferable to one layer due to increase in air flow resistance.

Unvented flat roof insulation.

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. An unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation. Layers of rigid insulation have staggered joints to facilitate airtightness.

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. If you don t want to use sips or nailbase there are four basic approaches. Four options for building an unvented roof assembly. Insufficient fill below the impermeable insulation layer.

Monolithic continuous exterior insulation ci above structural sheathing. Low slope and steep slope unvented roof systems i e. Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof. When hvac equipment and ducts with significant air leakage inhabit the attic much greater energy savings are possible as that leakage is now contained.

R 46 unvented roof assembly two layers of r 6 5 inch rigid insulation yielding a total combined thickness of 2 5 inches. Control rain in any roof assembly an underlayment e g. 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. 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.

Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls. 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.