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.

Unvented flat roof assembly.

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. 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. Recent building codes only allow unvented roof assemblies for pitches 3 12 and greater irc 2015 section r806 5 2 7.

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. This is a mis interpretation of the code. 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. The higher the interior moisture level the thicker the rigid insulation required. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. Four options for building an unvented roof assembly.

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. There is absolutely no room for error in the detailing and installation of roofing and air sealing in these assemblies. In some climates it requires a vapor barrier.

It s not and so code doesn t require r value ratios. 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. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. Read all of r806 5 carefully.

An unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation. Martin s post focuses on the marketing of owens corning 039 s propink unvented attic insulation system. This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction. 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.