Polyisocyanurate coverboards with improved fire resistance

A construction board comprising:

• (i) a foam body having first and second planar surfaces, said foam body including a polyisocyanurate foam matrix defining a plurality of closed cells, said closed cells including carbon dioxide, air, or a partial vacuum and less than 0.5 percent by volume of hydrocarbon blowing agents, said foam body being characterized by a density, pursuant to ASTM C303, of at least 2.5 lbs/ft3, and said foam being characterized by an ISO Index of from at least 220 to less than 360;
• and
• (ii) a facer disposed on one of the first and second planar surfaces of said foam body, said facer including
• (iii) a glass substrate having an internal planar surface proximate to said foam body and an external planar surface opposite said foam body,
• (iv) a first coating disposed on said external planar surface, and
• (v) a second coating disposed on or proximate to said internal planar surface,
• where said first coating disposed on said external planar surface includes filler, the filler consisting of inert filler, where the inert filler is present in an amount of from 3 to 30 weight percent with respect to the entire weight of the first coating, and
• where said second coating disposed on or proximate to said internal planar surface includes intumescent material, where said second coating includes a polymeric binder in which said intumescent material is dispersed.