Spray Foam Under Roof Deck

The biggest weak point in my opinion is that if there is a roof leak you won t find out until the wood is rotted.

Spray foam under roof deck.

Your indoor air quality may get worse. The spray foam definitely has its merits. By encapsulating the attic and leaving the old insulation up there that filth is in your conditioned space. I ve done a lot of work in energy efficient building and design.

Closed cell foam has been applied underside of roof decks since the late 60s early 70s and to my knowledge i have not seen or heard of a rotted substrate under and conditions closed cell foam was applied. But spray foam insulation used at the underside of the roof deck would need to be covered by a thermal barrier and intumescent coatings are commonly used. Where wood shingles or shakes. The roof currently has 4 of medium density open cell spray under the deck giving us an r value of just under 22.

The movement of air into indirect conditioning of an unvented attic is a slow gradual process that will not be noticeable by occupants and typically will not put any strain on the hvac system. Spray foam under roof decks. No interior class i vapor retarders e g plastic sheeting are installed on the ceiling side attic floor of the. If spray foam is used in these climates zones vapor retarder requirements apply drying to the interior is limited and a vented space may still be needed directly under the roof deck.

It would come with 3 1 2 or 4 of polyiso adhered to a 7 16 deck. Going back to the moisture which develops under the underlayment if this moisture has nothing to dry it out air movement under the roof deck you have a problem and having an insulation directly under it exacerbates the problem because any moisture will expand in high heat conditions. How spray foam should be installed on the underside of the roof decking the unvented attic space is completely within the building s thermal envelope. With enough closed cell spray foam under the deck or enough rigid above the deck interior moist air can t condense if the there is no condensation you don t need drying thus no need to vent.

If you use open cell spray foam on your roof rafters you should cover the finished application with a paint or sealant that retards water vapor. Yeah you probably still breathed some of it but not as much as you will now with spray foam on the roof deck. You may have odor problems. Instead of installing a couple layers of polyiso with staggered joints and then decking he is proposing using a product like the gaf thermacal insulated nailing base.