Insulation Replacement in a Re-Roof C503

[Hyrax4978]

C503.1 is fairly self explanatory. As is exemption 4 for not exposing the cavity.
My question is in regards to exemption 3. If you expose a cavity, and there is "some" insulation. Not completely filled. Do you need to upgrade.
Its a generic question, but my specific instance is a butler roof assembly that has the draped insulation. so once you take the roof off you run into the insulation draped over the purlins. But it does not meet the current thermal requirements. to reinsulate that space is an extreme undertaking as you would now need a full liner system and filled cavity. going over the roof with EPDM and polyiso is very expensive in lieu of just replacing the metal panels. Would be nice to take the roof panel off, and just put a new on on, without touching the draped insulation.

Any thoughts....

 

[Paul Sweet]

Could this be considered a roof recover so exception 5 could apply?

C503.3.1 only applies to roof replacements where insulation is entirely above the roof deck.

The building manufacturer might make a system with thicker insulation and styrofoam blocks above the purlins to preevent thermal bridging.

Most metal buildings aren't engineered to take more than 1 or 2 PSF added roof load.

 

[steveray]

You need to fill the cavity.....you do not need to hit todays R value, but you do need to fill the cavity...