Unvented Flat Roof Green Building

Flat roofs for residential homes is a low desert southwest style of building because there are no snow loads and rain is far and few between.

Unvented flat roof green building. A local engineer thinks i can stuff the cavities with fiberglass insulation paint the drywall with vapor barrier sealer and call it good. Removing moisture from roof cavities structural members sheathing and insulation. R 46 unvented roof assembly two layers of r 6 5 inch rigid insulation yielding a total combined thickness of 2 5 inches. However designers of compact roof assemblies must consider vapor permeance and arrangement of the roofing materials to produce acceptable hygrothermal performance and low.

Layers of rigid insulation have staggered joints to facilitate airtightness. 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. Enhancing roofing material life span by reducing sheathing temperature.

There is no potential for condensation until interior moisture levels exceed 45 rh at 70 f during the coldest month. Even then i have observed many flat roofs that are 5 years old that leak during the rainy monsoon season. There are traditionally four main reasons for venting a roof. 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.

Roof assemblies must control for exterior moisture in a monolithic and complete fashion. Test roofing membranes for integrity prior to covering from below. The insulation can go below the roof deck above the roof deck or both. Controlling ice damming by keeping the roof cold.

With flat roofs all roof penetrations must be detailed with a belt suspender approach. Unvented roofs vented roof. Unvented attics are not allowed by the building code yet in canada but are allowed in the international residential code in the us in section r806 which describes three different insulation strategies for unvented roofs. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck.

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.