Converting Vented Attic To Unvented

An unvented attic system relies on an air seal and no vents to make the attic a conditioned space.

Converting vented attic to unvented.

Asked by gary lichtenstein. By using an air impermeable insulation like spray foam on the roof deck will stop any air movement. 5 dumb ways to build in the south. I m considering converting my vented attic into a non vented conditioned space.

Convert a vented attic to an unvented attic and insulate using one of the methods described in the description tab or similar. 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. This allows you to install your bulkheads above the ceiling plane without the need for spray foam insulation. An alternate to spray foam insulation in an unvented attic is plenum trusses which allow you create a reverse bulkhead above the ceiling plane that is insulated.

I live in maryland and own a house that has the hvac system in the attic. Should i use open cell or closed cell foam to insulate. I ve been warned that closed cell foam can lead to sheathing rot from either roof leak or vapors from the house. From my research it looks like the best option is to make the attic a conditioned nonvented space.

I ve been researching several methods to insulate my attic. Currently the attic is vented and has zero insulation anywhere. Close and seal all attic vents including roof deck and soffit vents. If you convert your vented unconditioned attic to an unvented conditioned attic by installing open cell spray foam on the underside of your roof sheathing you may be surprised to discover that your attic is now the most humid room in your house.

Converting an attic from vented to unvented can reduce utility costs while improving comfort indoor air quality and durability. If the insulation is only placed on the bottom of the roof deck between the rafters it must be air impermeable. I m converting my attic into a non vented conditioned space.