Is venting required when insulation is installed between roof rafters?
In Massachusetts there are two ways that this can be accomplished. You can insulate the rafter space provided that you leave a ventilation space between the top of the insulation (typically fiberglass batts or blown cellulose) and the underside of the roof sheathing (Section 5806.1 Ventilation required). The minimum net free area of the ventilation space is described inSection 5806.2 Minimum area andSection 5806.3 Vent clearance. Alternately, ventilation can be omitted from the assembly if one of the two methods described in the Exceptions of Section 5801.6 Ventilation required are used. These alternate methods install an air impermeable insulation to the underside of the roof sheathing (as with the use of expanding spray foam insulation) or to the top of the roof sheathing (as with the use of board foam plastic insulation). Both of these are types of closed-cell foam insulation.In both cases, additional cavity insulation can be installed (typically fiberglass batts or blown cellulose)