The lengthier that you simply wait to set up rigid foam over your roof sheathing after your rafter bays are full of fluffy insulation, the bigger the chance that the roof sheathing will accumulate humidity. 1 or 2 decades really should be no issue, but I would not extend the figure out Considerably farther than that.for an unvented building without

In order to install a mix of closed-mobile spray-foam within the underside with the roof sheathing and air-permeable insulation involving your rafters — an strategy in some cases named “flash and batt” — the setting up code demands that spray foam (or, arguably, rigid foam insulation) be “applied in direct connection