Unvented Flat Roof Assembly

Four options for building an unvented roof assembly.

Unvented flat roof assembly.

Yes unvented roof assemblies can be insulated with fiberglass a wufi post and not just in climate zones 2b amp. In unvented flat or low slope roofs with parapets perform a full flood test to ensure leak free installation of roofing membrane. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. If you don t want to use sips or nailbase there are four basic approaches.

The higher the interior moisture level the thicker the rigid insulation required. In some climates it requires a vapor barrier. The colder the climate the thicker the rigid insulation required. It s not and so code doesn t require r value ratios.

Unvented flat roof assembly. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction. 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. Martin s post focuses on the marketing of owens corning 039 s propink unvented attic insulation system. Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof. Before constructing a flat roof assembly please refer to the unvented roof assembly comments under 6 2 vented and unvented roof assemblies and if applicable 6 3 parapet walls.

This is a mis interpretation of the code. 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. Recent building codes only allow unvented roof assemblies for pitches 3 12 and greater irc 2015 section r806 5 2 7. 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.

Read all of r806 5 carefully. 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. Drying of unvented roofing assemblies is by definition only provided to the interior. There is absolutely no room for error in the detailing and installation of roofing and air sealing in these assemblies.