Converting Vented Attic To Unvented

I ve been researching several methods to insulate my attic.

Converting vented attic to unvented. I ve been warned that closed cell foam can lead to sheathing rot from either roof leak or vapors from the house. 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. Currently the attic is vented and has zero insulation anywhere. Close and seal all attic vents including roof deck and soffit vents.

By using an air impermeable insulation like spray foam on the roof deck will stop any air movement. I live in maryland and own a house that has the hvac system in the attic. Watch this if you ve not seen it. If the insulation is only placed on the bottom of the roof deck between the rafters it must be air impermeable.

If installing insulation above the decking remove existing roof tiles or shingles and replace weather resistant barrier if needed. An unvented attic system relies on an air seal and no vents to make the attic a conditioned space. I m considering converting my vented attic into a non vented conditioned space. Converting an attic from vented to unvented can reduce utility costs while improving comfort indoor air quality and durability.

From my research it looks like the best option is to make the attic a conditioned nonvented space. I m converting my attic into a non vented conditioned space. 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.

Should i use open cell or closed cell foam to insulate. 5 dumb ways to build in the south. Asked by gary lichtenstein.