Unvented Flat Roof Assembly

Four options for building an unvented roof assembly.

Unvented flat roof assembly. Condensing surface temperature controlled the thickness of the rigid insulation at both the roof deck and perimeter is determined by a calculation procedure similar to figure 5. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. 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.

Low slope and steep slope unvented roof systems i e. 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 should be insulated either with air impermeable insulation rigid foam or spray polyurethane foam or with a combination of foam and air permeable insulation. 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.

Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. There is absolutely no room for error in the detailing and installation of roofing and air sealing in these assemblies. It s not and so code doesn t require r value ratios. Unvented flat roof assembly.

By installing spf insulation spray in place insulation in lieu of mineral fiber insulation in the joist cavity of a flat roof or between rafters of a cathedral ceiling the assembly may perform the same as or better than that of a typical one and venting can be shown to be unnecessary. In some climates it requires a vapor barrier. Yes unvented roof assemblies can be insulated with fiberglass a wufi post and not just in climate zones 2b amp. If you don t want to use sips or nailbase there are four basic approaches.

This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction. Drying of unvented roofing assemblies is by definition only provided to the interior. Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof. This is a mis interpretation of the code.

Recent building codes only allow unvented roof assemblies for pitches 3 12 and greater irc 2015 section r806 5 2 7. The colder the climate the thicker the rigid insulation required. The higher the interior moisture level the thicker the rigid insulation required. Martin s post focuses on the marketing of owens corning 039 s propink unvented attic insulation system.