Unvented Flat Roof Green Building

Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction.

Unvented flat roof green building.

Removing moisture from roof cavities structural members sheathing and insulation. 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. There is no potential for condensation until interior moisture levels exceed 45 rh at 70 f during the coldest month. A local engineer thinks i can stuff the cavities with fiberglass insulation paint the drywall with vapor barrier sealer and call it good.

Two layers are preferable to one layer due to increase in air flow resistance. 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 roofs vented roof.

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

R 46 unvented roof assembly two layers of r 6 5 inch rigid insulation yielding a total combined thickness of 2 5 inches. Enhancing roofing material life span by reducing sheathing temperature. Walla walla se washington state 99362 i m planning for an icf residence with a flat unvented roof built with 14 i joists epdm on top. 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.

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. Even then i have observed many flat roofs that are 5 years old that leak during the rainy monsoon season. An unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation. There are traditionally four main reasons for venting a roof.