Unvented Flat Roof

However designers of compact roof assemblies must consider vapor permeance and arrangement of the roofing materials to produce acceptable hygrothermal performance and low.

Unvented flat roof.

2012 irc section r806 5 unvented attic assemblies unvented attic assemblies spaces between the ceiling joists of the top story of the roof rafters shall be permitted if all of the following conditions are met. In this case you can learn a lot from foam tech s article vented vs. 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. Controlling ice damming by keeping the roof cold.

Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. Removing moisture from roof cavities structural members sheathing and insulation. Unvented roofs which provides a detailed explanation of each. There are traditionally four main reasons for venting a roof.

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. The unvented attic space is completely contained within the building thermal envelope. 2009 irc section r806 4. Unvented roofs vented roof.

Air permeable insulation such as fiberglass batts dense packed cellulose or blown in fiberglass can t be used alone for an unvented assembly since these types of insulation can allow moist indoor air to reach the cold roof sheathing leading to condensation or moisture accumulation. The higher the interior moisture level the thicker the. However in many situations the insulation may need to be primarily or entirely below the flat roof membrane and between the roof joists if so what are the best options. Basically the term cold roof refers to a traditional roof or vented roof while hot roof refers to a roof that is not ventilated and which has foam insulation attached directly to the roof.

An unvented assembly can perform well but it s important to get the details right to avoid sheathing rot. Enhancing roofing material life span by reducing sheathing temperature. This brings us full circle back to flat or low slope roofs being difficult to ventilate particularly if they re used as occupiable space such as a rooftop patio. Unvented flat roof assembly.

Unvented roof systems where the 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.