Unvented Attic Metal Roof

Should you vent a metal roof.

Unvented attic metal roof.

In the process of construction currently have a standing seam metal room installed over synthetic felt over osb. This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof 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. This is because the top floor ceiling is no longer the air barrier for the house the spray foam at the roof deck underside in the attic is the air barrier.

I ve read elsewhere on this forum venting of attics is required for metal roofs. He says by detailing the air barrier correctly especially the connection between the roof air barrier and the wall air barrier designers can ensure an unvented metal roof design is airtight vapor tight and functional. Unvented roof assemblies are becoming an increasingly common construction alternative to traditional vented roofs. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction.

The other option of course is a vented attic which requires an equal balance of intake and exhaust vents. Unvented roofs operate by the principle that venting is not necessary to control moisture accumulation. The unvented attic space is completely within the building thermal envelope. Ted storm posted in energy efficiency and durability on april 27 2011 09 53am.

I ll soon be building in texas a 2000 sq ft. As unvented attics are now code approved through the icc is the mra planning on adopting new guidelines. The energy savings touted by unvented attics can be as high as 20. There will be ducting and other hvac equipment in the attic.

However if moisture is able to enter the unvented attic space it may lead to roofing panel issues. Metal roofing works well with this because the metal is unaffected by heat not being able to pass through it and enter the attic. In an unvented attic penetrations through the ceiling directly below the attic do not need to be air sealed. Home with an unvented attic and am thinking about using a metal roof.

Should you opt to run ductwork or place mechanical systems in the attic an unvented roof is best for avoiding thermal penalties as the ductwork will be located in a conditioned space allowing the system to recover thermal losses through the ducts. Lstiburek says common failures in unvented metal roof designs include seams in insulated metal panels not being sealed correctly and missing air barriers in metal roof panel systems. No insulation installed yet. Unventilated attics can help to mitigate energy loss through leaky ducts or ceiling fittings.