Insulation At Underside Of Roof Deck

Fiberglass insulation is installed between the rafters as shown schematically below.

Insulation at underside of roof deck.

It s not coming from above the roof and it s not some new moisture source resulting from the spray foam. When installing rigid insulation in an attic to be finished as a living space you must provide a route by which hot air. Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls. Moisture generated indoors or that infiltrates into the home is responsible for the bulk of the moisture in an attic insulated with spray foam on the underside of the roof sheathing.

Closed cell foam has been applied underside of roof decks since the late 60s early. Lstiburek takes blame for bad language. The problem arises with moisture. The attic will be a conditioned space and i m planning to apply spray foam insulation to the underside of the roof sheathing.

For some building uses the ceiling might be absent. T he problem with the insulation against the sheathing expands. If there is a roof leak the insulation will be damaged by the water leaving you with less insulating value. In addition to the air permeable insulation installed directly below the structural sheathing rigid board or sheet insulation shall be installed directly above the structural roof sheathing as specified in table r806 5 for condensation control.

Air impermeable and air permeable insulation. In addition to installing the foam board on the underside of the roof deck you can attach it to the bottom edges of the. When installing a foil faced foam board insulation. Insulation shall be applied in direct contact with the underside of the structural roof sheathing.

This construction approach was first used in the 1970s and it has been implemented much more widely since it was first included in the international code council s icc model building code in 2007 irc section 806 4. This type of system can also be found in low slope residential buildings in inner city areas. Applying closed cell spray insulation to the underside of a roof deck at the sheathing to truss connection can double or triple the strength of the assembly boosting the roof sheathing s resistance to wind uplift in a hurricane.