Unvented flat roof assembly.
Unvented flat roof.
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.
In some of the above areas where vented attics can be a challenge an alternative solution is an unvented roof assembly.
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.
2009 irc section r806 4.
Unvented roofs which provides a detailed explanation of each.
Removing moisture from roof cavities structural members sheathing and insulation.
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.
An unvented assembly can perform well but it s important to get the details right to avoid sheathing rot.
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.
However designers of compact roof assemblies must consider vapor permeance and arrangement of the roofing materials to produce acceptable hygrothermal performance and low.
The unvented attic space is completely contained within the building thermal envelope.
In this case you can learn a lot from foam tech s article vented vs.
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.
Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction.
These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck.
Unvented roofs vented roof.
Controlling ice damming by keeping the roof cold.
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.
The colder the climate the thicker the rigid insulation required.
There are traditionally four main reasons for venting a roof.
