Designing a Class A unvented roof assembly with metal covering in WUI area

[flightcrazed]

Hi all, working on a project that was originally designed to be an unvented attic with asphalt shingles.  Plan is to change to metal, however the underlayment (Titanium UDL50) has already been laid and is only Class A under asphalt.  I've found that Versashield can bring metal to Class A but not intended for unvented assembly. 

 

Anyone know of another product that could be laid on top of UDL50 to reach Class A for metal?  I've found Atlas FR10 but all the documentation seem to support a commercial roofing system.  

 

Much appreciated!